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Sample records for satellite attitude determination

  1. Micro-Satellite Attitude Determination Using GPS Carrier Phases

    Institute of Scientific and Technical Information of China (English)

    He Xiu-feng; Ling Keck-voon

    2003-01-01

    GPS is an attractive attitude sensor for micro-satellites due to small package and advantage for cost savings. However, the major difficulty in attitude determination for a micro-satellite is that baseline lengths are short (less than a meter) . Thus , to obtain precise accuracy of attitudes for a micro-satellite, the algorithm selection and error source calibration are important. In this paper, a technique based on the attitude cost function is proposed. To verify the method proposed, the experiments have been conducted. The results indicate that attitude errors are less than 1 deg.

  2. DOA estimation for attitude determination on communication satellites

    Directory of Open Access Journals (Sweden)

    Yang Bin

    2014-06-01

    Full Text Available In order to determine an appropriate attitude of three-axis stabilized communication satellites, this paper describes a novel attitude determination method using direction of arrival (DOA estimation of a ground signal source. It differs from optical measurement, magnetic field measurement, inertial measurement, and global positioning system (GPS attitude determination. The proposed method is characterized by taking the ground signal source as the attitude reference and acquiring attitude information from DOA estimation. Firstly, an attitude measurement equation with DOA estimation is derived in detail. Then, the error of the measurement equation is analyzed. Finally, an attitude determination algorithm is presented using a dynamic model, the attitude measurement equation, and measurement errors. A developing low Earth orbit (LEO satellite which tests mobile communication technology with smart antennas can be stabilized in three axes by corporately using a magnetometer, reaction wheels, and three-axis magnetorquer rods. Based on the communication satellite, simulation results demonstrate the effectiveness of the method. The method could be a backup of attitude determination to prevent a system failure on the satellite. Its precision depends on the number of snapshots and the input signal-to-noise ratio (SNR with DOA estimation.

  3. DOA estimation for attitude determination on communication satellites

    Institute of Scientific and Technical Information of China (English)

    Yang Bin; He Feng; Jin Jin; Xiong Huagang; Xu Guanghan

    2014-01-01

    In order to determine an appropriate attitude of three-axis stabilized communication satellites, this paper describes a novel attitude determination method using direction of arrival (DOA) estimation of a ground signal source. It differs from optical measurement, magnetic field measurement, inertial measurement, and global positioning system (GPS) attitude determination. The proposed method is characterized by taking the ground signal source as the attitude reference and acquiring attitude information from DOA estimation. Firstly, an attitude measurement equation with DOA estimation is derived in detail. Then, the error of the measurement equation is analyzed. Finally, an attitude determination algorithm is presented using a dynamic model, the attitude measurement equation, and measurement errors. A developing low Earth orbit (LEO) satellite which tests mobile communication technology with smart antennas can be stabilized in three axes by corporately using a magnetometer, reaction wheels, and three-axis magnetorquer rods. Based on the communication satellite, simulation results demonstrate the effectiveness of the method. The method could be a backup of attitude determination to prevent a system failure on the satellite. Its precision depends on the number of snapshots and the input signal-to-noise ratio (SNR) with DOA estimation.

  4. Review on gyroless attitude determination methods for small satellites

    Science.gov (United States)

    Hajiyev, Chingiz; Cilden Guler, Demet

    2017-04-01

    This study surveys the developments in the gyroless attitude determination system, especially for small satellites. Two kinds of gyroless satellite attitude determination algorithms were reviewed namely, vector measurements and Kalman filter based methods. Traditional and nontraditional Kalman filters were considered in the Kalman filter based methods including Unscented Kalman Filter (UKF) and Extended Kalman Filter (EKF). Also, robust versions of those Kalman filters, which were incorporated with single, and multiple measurement noise scale factors (SMNSF, MMNSF respectively) are investigated and compared in the presence of measurement faults.

  5. GPS/Magnetometer Based Satellite Navigation and Attitude Determination

    Science.gov (United States)

    Deutschmann, Julie; Bar-Itzhack, Itzhack; Harman, Rick; Bauer, Frank H. (Technical Monitor)

    2001-01-01

    In recent years algorithms were developed for orbit, attitude and angular-rate determination of Low Earth Orbiting (LEO) satellites. Those algorithms rely on measurements of magnetometers, which are standard, relatively inexpensive, sensors that are normally installed on every LEO satellite. Although magnetometers alone are sufficient for obtaining the desired information, the convergence of the algorithms to the correct values of the satellite orbital parameters, position, attitude and angular velocity is very slow. The addition of sun sensors reduces the convergence time considerably. However, for many LEO satellites the sun data is not available during portions of the orbit when the spacecraft (SC) is in the earth shadow. It is here where the GPS space vehicles (SV) can provide valuable support. This is clearly demonstrated in the present paper. Although GPS measurements alone can be used to obtain SC position, velocity, attitude and angular-rate, the use of magnetometers improve the results due to the synergistic effect of sensor fusion. Moreover, it is possible to obtain these results with less than three SVs. In this paper we introduce an estimation algorithm, which is a combination of an Extended Kalman Filter (EKF) and a Pseudo Linear Kalman Filter (PSELIKA).

  6. UKF-based attitude determination method for gyroless satellite

    Institute of Scientific and Technical Information of China (English)

    张红梅; 邓正隆

    2004-01-01

    UKF (unscented Kalman filtering) is a new filtering method suitable to nonlinear systems. The method need not linearize nonlinear systems at the prediction stage of filtering, which is indispensable in EKF (extended Kalman filtering). As a result, the linearization error is avoided, and the filtering accuracy is greatly improved. UKF is applied to the attitude determination for gyroless satellite. Simulations are made to compare the new filter with the traditional EKF.The results indicate that under same conditions, compared with EKF, UKF has faster convergence speed, higher filtering accuracy and more stable estimation performance.

  7. Satellite Attitude Determination with Low-Cost Sensors

    Science.gov (United States)

    Springmann, John C.

    This dissertation contributes design and data processing techniques to maximize the accuracy of low-cost attitude determination systems while removing pre-flight calibration requirements. This enables rapid development of small spacecraft to perform increasingly complex missions. The focus of this work is magnetometers and sun sensors, which are the two most common types of attitude sensors. Magnetometer measurements are degraded by the magnetic fields of nearby electronics, which traditionally limit their utility on satellites unless a boom is used to provide physical separation between the magnetometer and the satellite. This dissertation presents an on-orbit, attitude-independent method for magnetometer calibration that mitigates the effect of nearby electronics. With this method, magnetometers can be placed anywhere within the spacecraft, and as demonstrated through application to flight data, the accuracy of the integrated magnetometer is reduced to nearly that of the stand-alone magnetometer. Photodiodes are light sensors that can be used for sun sensing. An individual photodiode provides a measurement of a single sun vector component, and since orthogonal photodiodes do not provide sufficient coverage due to photodiode field-of-view limitations, there is a tradeoff between photodiode orientation and sun sensing angular accuracy. This dissertation presents a design method to optimize the photodiode configuration for sun sensing, which is also generally applicable to directional sensors. Additionally, an on-orbit calibration method is developed to estimate the photodiode scale factors and orientation, which are critical for accurate sun sensing. Combined, these methods allow a magnetometer to be placed anywhere within a spacecraft and provide an optimal design technique for photodiode placement. On-orbit calibration methods are formulated for both types of sensors that correct the sensor errors on-orbit without requiring pre-flight calibration. The calibration

  8. Small satellite attitude determination during plasma brake deorbiting experiment

    Science.gov (United States)

    Khurshid, Osama; Selkäinaho, Jorma; Soken, Halil Ersin; Kallio, Esa; Visala, Arto

    2016-12-01

    This paper presents a study on attitude estimation during the Plasma Brake Experiment (PBE) onboard a small satellite. The PBE demands that the satellite be spun at a very high angular velocity, up to 200 deg/s, to deploy the tether using centrifugal force. The spin controller, based on purely magnetic actuation, and the PBE demands accurate attitude estimation for the successful execution of the experiment. The biases are important to be estimated onboard small satellites due to the closely integrated systems and relatively higher interference experienced by the sensors. However, bias estimation is even more important for PBE due to the presence of a high voltage unit, onboard the satellite, that is used to charge the tether and can be the source of interference. The attitude and the biases, when estimated simultaneously, results in an augmented state vector that poses a challenge to the proper tuning of process noise. The adaptation of process noise covariance has, therefore, been studied and analysed for the challenging PBE. It has been observed that adapting the process noise covariance improves the estimation accuracy during the spin-up phase. Therefore, it is very important to use adaptive process noise covariance estimation.

  9. Earth's thermal radiation sensors for attitude determination systems of small satellites

    Science.gov (United States)

    Vertat, I.; Linhart, R.; Masopust, J.; Vobornik, A.; Dudacek, L.

    2017-07-01

    Satellite attitude determination is a complex process with expensive hardware and software and it could consume the most of resources (volume, mass, electric power), especially of small satellites as CubeSats. Thermal radiation infrared detectors could be one of useful sensors for attitude determination systems in such small satellites. Nowadays, these sensors are widely used in contact-less thermometers and thermo-cameras resulting in a low-cost technology. On low Earth orbits the infrared thermal sensors can be utilized for coarse attitude determination against a relative warm and close Earth's globe.

  10. BeiDou Inter-Satellite-Type Bias Evaluation and Calibration for Mixed Receiver Attitude Determination

    Directory of Open Access Journals (Sweden)

    Noor Raziq

    2013-07-01

    Full Text Available The Chinese BeiDou system (BDS, having different types of satellites, is an important addition to the ever growing system of Global Navigation Satellite Systems (GNSS. It consists of Geostationary Earth Orbit (GEO satellites, Inclined Geosynchronous Satellite Orbit (IGSO satellites and Medium Earth Orbit (MEO satellites. This paper investigates the receiver-dependent bias between these satellite types, for which we coined the name “inter-satellite-type bias” (ISTB, and its impact on mixed receiver attitude determination. Assuming different receiver types may have different delays/biases for different satellite types, we model the differential ISTBs among three BeiDou satellite types and investigate their existence and their impact on mixed receiver attitude determination. Our analyses using the real data sets from Curtin’s GNSS array consisting of different types of BeiDou enabled receivers and series of zero-baseline experiments with BeiDou-enabled receivers reveal the existence of non-zero ISTBs between different BeiDou satellite types. We then analyse the impact of these biases on BeiDou-only attitude determination using the constrained (C-LAMBDA method, which exploits the knowledge of baseline length. Results demonstrate that these biases could seriously affect the integer ambiguity resolution for attitude determination using mixed receiver types and that a priori correction of these biases will dramatically improve the success rate.

  11. Semi-active Attitude Control and Off-line Attitude Determination for the SEETI-Express Student Micro-satellite

    DEFF Research Database (Denmark)

    Alminde, Lars

    This paper concerns the development of the Attitude Determination and Control System (ADCS) for the SSETI-Express micro-satellite mission. The mission is an educational project involving 14 universities and the European Space Agency (ESA). The satellite has been designed and built, by students...

  12. Semi-active Attitude Control and Off-line Attitude Determination for the SSETI-Express Student Micro-satellite

    DEFF Research Database (Denmark)

    Alminde, Lars

    2005-01-01

    This paper concerns the development of the Attitude Determination and Control System (ADCS) for the SSETI-Express micro-satellite mission. The mission is an educational project involving 14 universities and the European Space Agency (ESA). The satellite has been designed and built, by students...

  13. Small satellite attitude determination based on GPS/IMU data fusion

    Energy Technology Data Exchange (ETDEWEB)

    Golovan, Andrey [Navigation and Control Laboratory, M.V. Lomonosov Moscow State University, GSP-1, Leninskie Gory, Moscow (Russian Federation); Cepe, Ali [Department of Applied Mechanics and Control, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

    2014-12-10

    In this paper, we present the mathematical models and algorithms that describe the problem of attitude determination for a small satellite using measurements from three angular rate sensors (ARS) and aiding measurements from multiple GPS receivers/antennas rigidly attached to the platform of the satellite.

  14. Attitude determination for three-axis stabilized geostationary meteorological satellite image navigation

    Science.gov (United States)

    Wu, Yaguang; Wang, Zhigang

    2005-11-01

    To achieve the high accuracy of attitude determination for three-axis stabilized geostationary meteorological satellite image navigation, a new approach combined gyro with star trackers is proposed, and a real-time algorithm for attitude estimation is designed. This algorithm begins with a prediction for angular rate model errors induced by gyro drifting error, and ends with the extended Kalman filtering (EKF) for attitude estimation of three-axis. A Matlab-based time domain simulation model is developed to evaluate the attitude determination performance. Simulation results demonstrate that the proposed algorithm has characteristics of high accuracy, rapid convergence and strong robustness.

  15. Attitude Determination with Magnetometers and Accelerometers to Use in Satellite Simulator

    Directory of Open Access Journals (Sweden)

    Helio Koiti Kuga

    2013-01-01

    Full Text Available Attitude control of artificial satellites is dependent on information provided by its attitude determination process. This paper presents the implementation and tests of a fully self-contained algorithm for the attitude determination using magnetometers and accelerometers, for application on a satellite simulator based on frictionless air bearing tables. However, it is known that magnetometers and accelerometers need to be calibrated so as to allow that measurements are used to their ultimate accuracy. A calibration method is implemented which proves to be essential for improving attitude determination accuracy. For the stepwise real-time attitude determination, it was used the well-known QUEST algorithm which yields quick response with reduced computer resources. The algorithms are tested and qualified with actual data collected on the streets under controlled situations. For such street runaways, the experiment employs a solid-state magnetoresistive magnetometer and an IMU navigation block consisting of triads of accelerometers and gyros, with MEMS technology. A GPS receiver is used to record positional information. The collected measurements are processed through the developed algorithms, and comparisons are made for attitude determination using calibrated and noncalibrated data. The results show that the attitude accuracy reaches the requirements for real-time operation for satellite simulator platforms.

  16. Semi-active Attitude Control and Off-line Attitude Determination for the SSETI-Express Student Micro-satellite

    OpenAIRE

    Alminde, Lars

    2005-01-01

    This paper concerns the development of the Attitude Determination and Control System (ADCS) for the SSETI-Express micro-satellite mission. The mission is an educational project involving 14 universities and the European Space Agency (ESA). The satellite has been designed and built, by students, over a period of only 18 months. This paper emphasises on the trade-offs required to build an operational ADCS system within such a rapidly developing project.

  17. Micro-Satellite Attitude Determination with Only a Single Horizon Sensor

    Directory of Open Access Journals (Sweden)

    Ouyang Gaoxiang

    2016-01-01

    Full Text Available Through using measurement from only a single horizon sensor, this paper presented a quaternion-based 3-axis attitude determination method, which can be implemented on board micro-satellites and applied over a whole orbital period. Firstly, a description of attitude representation on the quaternion is given. Secondly, a detailed modeling formulation with nadir vector and measurement equations on attitude estimation system is demonstrated. Afterwards, a correction is made to eliminate the estimation error resulted from Earth’s oblateness, and able to further improve the accuracy of the attitude determination algorithm. Finally, a six degree-of-freedom closed-loop simulation is used to validate the accuracy of the attitude determination method given in this paper.

  18. Autonomous Attitude Determination and Control System for the Ørsted Satellite

    DEFF Research Database (Denmark)

    Bak, Thomas; Wisniewski, Rafal; Blanke, M.

    1996-01-01

    The Ørsted Satellite mission imposes comparatively high requirements on autonomy of the attitude control system.......The Ørsted Satellite mission imposes comparatively high requirements on autonomy of the attitude control system....

  19. Determination of Foton M-2 satellite attitude motion by the data of microacceleration measurements

    Science.gov (United States)

    Beuselinck, T.; van Bavinchove, C.; Sazonov, V. V.; Chebukov, S. Yu.

    2009-12-01

    The results of reconstruction of uncontrolled attitude motion of the Foton M-2 satellite using measurements with the accelerometer TAS-3 are presented. The attitude motion of this satellite has been previously determined by the measurement data of the Earth’s magnetic field and the angular velocity. The TAS-3 data for this purpose are used for the first time. These data contain a well-pronounced additional component which made impossible their direct employment for the reconstruction of the attitude motion and whose origin was unknown several years ago. Later it has become known that the additional component is caused by the influence of the Earth’s magnetic field. The disclosure of this fact allowed us to take into account a necessary correction in processing of TAS-3 data and to use them for the reconstruction of the attitude motion of Foton M-2. Here, a modified method of processing TAS-3 data is described, as well as results of its testing and employing. The testing consisted in the direct comparison of the motion reconstructed by the new method with the motion constructed by the magnetic measurements. The new method allowed us to find the actual motion of Foton M-2 in the period June 9, 2005-June 14, 2005, when no magnetic measurements were carried out.

  20. Satellite single-axis attitude determination based on Automatic Dependent Surveillance - Broadcast signals

    Science.gov (United States)

    Zhou, Kaixing; Sun, Xiucong; Huang, Hai; Wang, Xinsheng; Ren, Guangwei

    2017-10-01

    The space-based Automatic Dependent Surveillance - Broadcast (ADS-B) is a new technology for air traffic management. The satellite equipped with spaceborne ADS-B system receives the broadcast signals from aircraft and transfers the message to ground stations, so as to extend the coverage area of terrestrial-based ADS-B. In this work, a novel satellite single-axis attitude determination solution based on the ADS-B receiving system is proposed. This solution utilizes the signal-to-noise ratio (SNR) measurement of the broadcast signals from aircraft to determine the boresight orientation of the ADS-B receiving antenna fixed on the satellite. The basic principle of this solution is described. The feasibility study of this new attitude determination solution is implemented, including the link budget and the access analysis. On this basis, the nonlinear least squares estimation based on the Levenberg-Marquardt method is applied to estimate the single-axis orientation. A full digital simulation has been carried out to verify the effectiveness and performance of this solution. Finally, the corresponding results are processed and presented minutely.

  1. Engineering parameter determination from the radio astronomy explorer /RAE I/ satellite attitude data

    Science.gov (United States)

    Lawlor, E. A.; Davis, R. M.; Blanchard, D. L.

    1974-01-01

    An RAE-I satellite description is given, taking into account a dynamics experiment and the attitude sensing system. A computer program for analyzing flexible spacecraft attitude motions is considered, giving attention to the geometry of rod deformation. The characteristics of observed attitude data are discussed along with an analysis of the main boom root angle, the bending rigidity, and the damper plane angle.

  2. Performance improvement of GPS single frequency, single epoch attitude determination with poor satellite visibility

    Science.gov (United States)

    Chen, Wantong; Sun, Xingli

    2016-07-01

    Similar to global positioning system (GPS) positioning in urban canyons, a fast and successful attitude determination with limited satellite visibility is very significant. For land vehicles, the possible attitude candidates can be treated as a spherical zone with the center at the reference antenna and the baseline as the radius. This provides an important constraint, which can be exploited to improve the reliability of GPS single frequency and single epoch attitude determination in the case of poor satellite reception. First, we fully integrate the spherical zone constraint into the estimation procedure of ambiguity resolution, but not in the validation procedure. Combining both the coordinate domain search and the ambiguity domain search, allows development of a global minimizer of the fixed ambiguity objective function. This scheme also improves the precision of the float ambiguity solution, thus avoiding the problem of search halting. The performance of the new ambiguity resolution method was analyzed by means of several experimental tests, using simulated as well as actual GPS data in urban environments. The experimental results showed that this new, proposed method can utilize a priori spherical zone knowledge to improve the reliability of ambiguity resolution in difficult environments.

  3. Attitude measurements and determination

    Science.gov (United States)

    Foliard, J.

    Satellite attitude determination using an inertial reference system is explained. The utility of being able to determine attitude is outlined. Construction of an attitude matrix from the Euler and Cardan angles of the satellite-Earth system is illustrated. Static and dynamic analysis methods are shown. The sensors employed when using the Sun, Earth's magnetic field, the Earth, and the stars as reference direction are described.

  4. On-orbit real-time magnetometer bias determination for micro-satellites without attitude information

    Institute of Scientific and Technical Information of China (English)

    Zhang Zhen; Xiong Jianping; Jin Jin

    2015-01-01

    Due to the disadvantages such as complex calculation, low accuracy of estimation, and being non real time in present methods, a new real-time algorithm is developed for on-orbit mag-netometer bias determination of micro-satellites without attitude knowledge in this paper. This method uses the differential value approach. It avoids the impact of quartic nature and uses the iter-ative method to satisfy real-time applications. Simulation results indicate that the new real-time algorithm is more accurate compared with other methods, which are also tested by an experiment system using real noise data. With the new real-time algorithm, a magnetometer calibration can be taken on-orbit and will reduce the demand for computing power effectively.

  5. On-orbit real-time magnetometer bias determination for micro-satellites without attitude information

    Directory of Open Access Journals (Sweden)

    Zhang Zhen

    2015-10-01

    Full Text Available Due to the disadvantages such as complex calculation, low accuracy of estimation, and being non real time in present methods, a new real-time algorithm is developed for on-orbit magnetometer bias determination of micro-satellites without attitude knowledge in this paper. This method uses the differential value approach. It avoids the impact of quartic nature and uses the iterative method to satisfy real-time applications. Simulation results indicate that the new real-time algorithm is more accurate compared with other methods, which are also tested by an experiment system using real noise data. With the new real-time algorithm, a magnetometer calibration can be taken on-orbit and will reduce the demand for computing power effectively.

  6. Mechatronic Design, Dynamic Modeling and Results of a Satellite Flight Simulator for Experimental Validation of Satellite Attitude Determination and Control Schemes in 3-Axis

    Directory of Open Access Journals (Sweden)

    M.A. Mendoza-Bárcenas

    2014-06-01

    Full Text Available This paper describes the integration and implementation of a satellite flight simulator based on an air bearing system, which was designed and instrumented in our laboratory to evaluate and to perform research in the field of Attitude Determination and Control Systems for satellites, using the hardware-in-the-loop technique. The satellite flight simulator considers two main blocks: an instrumented mobile platform and an external computer executing costume-made Matlab® software. The first block is an air bearing system containing an FPGA based on-board computer with capabilities to integrate digital architectures for data acquisition from inertial navigation sensors, control of actuators and communications data handling. The second block is an external personal computer, which runs in parallel Matlab® based algorithms for attitude determination and control. Both blocks are linked by means of radio modems. The paper also presents the analysis of the satellite flight simulator dynamics in order to obtain its movement equation which allows a better understanding of the satellite flight simulator behavior. In addition, the paper shows experimental results about the automated tracking of the satellite flight simulator based a virtual reality model developed in Matlab®. It also depicts two different versions of FPGA based on-board computers developed in-house to integrate embedded and polymorphic digital architectures for spacecrafts applications. Finally, the paper shows successful experimental results for an attitude control test using the satellite flight simulator based on a linear control law.

  7. Evaluation and modeling of autonomous attitude thrust control for the Geostation Operational Environmental Satellite (GOES)-8 orbit determination

    Science.gov (United States)

    Forcey, W.; Minnie, C. R.; Defazio, R. L.

    1995-01-01

    The Geostationary Operational Environmental Satellite (GOES)-8 experienced a series of orbital perturbations from autonomous attitude control thrusting before perigee raising maneuvers. These perturbations influenced differential correction orbital state solutions determined by the Goddard Space Flight Center (GSFC) Goddard Trajectory Determination System (GTDS). The maneuvers induced significant variations in the converged state vector for solutions using increasingly longer tracking data spans. These solutions were used for planning perigee maneuvers as well as initial estimates for orbit solutions used to evaluate the effectiveness of the perigee raising maneuvers. This paper discusses models for the incorporation of attitude thrust effects into the orbit determination process. Results from definitive attitude solutions are modeled as impulsive thrusts in orbit determination solutions created for GOES-8 mission support. Due to the attitude orientation of GOES-8, analysis results are presented that attempt to absorb the effects of attitude thrusting by including a solution for the coefficient of reflectivity, C(R). Models to represent the attitude maneuvers are tested against orbit determination solutions generated during real-time support of the GOES-8 mission. The modeling techniques discussed in this investigation offer benefits to the remaining missions in the GOES NEXT series. Similar missions with large autonomous attitude control thrusting, such as the Solar and Heliospheric Observatory (SOHO) spacecraft and the INTELSAT series, may also benefit from these results.

  8. Spacecraft Attitude Determination

    DEFF Research Database (Denmark)

    Bak, Thomas

    This thesis describes the development of an attitude determination system for spacecraft based only on magnetic field measurements. The need for such system is motivated by the increased demands for inexpensive, lightweight solutions for small spacecraft. These spacecraft demands full attitude...... determination based on simple, reliable sensors. Meeting these objectives with a single vector magnetometer is difficult and requires temporal fusion of data in order to avoid local observability problems. In order to guaranteed globally nonsingular solutions, quaternions are generally the preferred attitude...... is a detailed study of the influence of approximations in the modeling of the system. The quantitative effects of errors in the process and noise statistics are discussed in detail. The third contribution is the introduction of these methods to the attitude determination on-board the Ørsted satellite...

  9. BeiDou inter-satellite-type bias evaluation and calibration for mixed receiver attitude determination

    NARCIS (Netherlands)

    Nadarajah, N.; Teunissen, P.J.G.; Raziq, N.

    2013-01-01

    The Chinese BeiDou system (BDS), having different types of satellites, is an important addition to the ever growing system of Global Navigation Satellite Systems (GNSS). It consists of Geostationary Earth Orbit (GEO) satellites, Inclined Geosynchronous Satellite Orbit (IGSO) satellites and Medium

  10. BeiDou inter-satellite-type bias evaluation and calibration for mixed receiver attitude determination

    NARCIS (Netherlands)

    Nadarajah, N.; Teunissen, P.J.G.; Raziq, N.

    2013-01-01

    The Chinese BeiDou system (BDS), having different types of satellites, is an important addition to the ever growing system of Global Navigation Satellite Systems (GNSS). It consists of Geostationary Earth Orbit (GEO) satellites, Inclined Geosynchronous Satellite Orbit (IGSO) satellites and Medium Ea

  11. Visual attitude propagation for small satellites

    Science.gov (United States)

    Rawashdeh, Samir A.

    As electronics become smaller and more capable, it has become possible to conduct meaningful and sophisticated satellite missions in a small form factor. However, the capability of small satellites and the range of possible applications are limited by the capabilities of several technologies, including attitude determination and control systems. This dissertation evaluates the use of image-based visual attitude propagation as a compliment or alternative to other attitude determination technologies that are suitable for miniature satellites. The concept lies in using miniature cameras to track image features across frames and extracting the underlying rotation. The problem of visual attitude propagation as a small satellite attitude determination system is addressed from several aspects: related work, algorithm design, hardware and performance evaluation, possible applications, and on-orbit experimentation. These areas of consideration reflect the organization of this dissertation. A "stellar gyroscope" is developed, which is a visual star-based attitude propagator that uses relative motion of stars in an imager's field of view to infer the attitude changes. The device generates spacecraft relative attitude estimates in three degrees of freedom. Algorithms to perform the star detection, correspondence, and attitude propagation are presented. The Random Sample Consensus (RANSAC) approach is applied to the correspondence problem to successfully pair stars across frames while mitigating falsepositive and false-negative star detections. This approach provides tolerance to the noise levels expected in using miniature optics and no baffling, and the noise caused by radiation dose on orbit. The hardware design and algorithms are validated using test images of the night sky. The application of the stellar gyroscope as part of a CubeSat attitude determination and control system is described. The stellar gyroscope is used to augment a MEMS gyroscope attitude propagation

  12. Innovative power management, attitude determination and control tile for CubeSat standard NanoSatellites

    Science.gov (United States)

    Ali, Anwar; Mughal, M. Rizwan; Ali, Haider; Reyneri, Leonardo

    2014-03-01

    Electric power supply (EPS) and attitude determination and control subsystem (ADCS) are the most essential elements of any aerospace mission. Efficient EPS and precise ADCS are the core of any spacecraft mission. So keeping in mind their importance, they have been integrated and developed on a single tile called CubePMT module. Modular power management tiles (PMTs) are already available in the market but they are less efficient, heavier in weight, consume more power and contain less number of subsystems. Commercial of the shelf (COTS) components have been used for CubePMT implementation which are low cost and easily available from the market. CubePMT is developed on the design approach of AraMiS architecture: a project developed at Politecnico di Torino that provides low cost and higher performance space missions with dimensions larger than CubeSats. The feature of AraMiS design approach is its modularity. These modules can be reused for multiple missions which helps in significant reduction of the overall budget, development and testing time. One has just to reassemble the required subsystems to achieve the targeted specific mission.

  13. Incorporation of star measurements for the determination of orbit and attitude parameters of a geosynchronous satellite: An iterative application of linear regression

    Science.gov (United States)

    Phillips, D.

    1980-01-01

    Currently on NOAA/NESS's VIRGS system at the World Weather Building star images are being ingested on a daily basis. The image coordinates of the star locations are measured and stored. Subsequently, the information is used to determine the attitude, the misalignment angles between the spin axis and the principal axis of the satellite, and the precession rate and direction. This is done for both the 'East' and 'West' operational geosynchronous satellites. This orientation information is then combined with image measurements of earth based landmarks to determine the orbit of each satellite. The method for determining the orbit is simple. For each landmark measurement one determines a nominal position vector for the satellite by extending a ray from the landmark's position towards the satellite and intersecting the ray with a sphere with center coinciding with the Earth's center and with radius equal to the nominal height for a geosynchronous satellite. The apparent motion of the satellite around the Earth's center is then approximated with a Keplerian model. In turn the variations of the satellite's height, as a function of time found by using this model, are used to redetermine the successive satellite positions by again using the Earth based landmark measurements and intersecting rays from these landmarks with the newly determined spheres. This process is performed iteratively until convergence is achieved. Only three iterations are required.

  14. Satellite Attitude Control System Simulator

    Directory of Open Access Journals (Sweden)

    G.T. Conti

    2008-01-01

    Full Text Available Future space missions will involve satellites with great autonomy and stringent pointing precision, requiring of the Attitude Control Systems (ACS with better performance than before, which is function of the control algorithms implemented on board computers. The difficulties for developing experimental ACS test is to obtain zero gravity and torque free conditions similar to the SCA operate in space. However, prototypes for control algorithms experimental verification are fundamental for space mission success. This paper presents the parameters estimation such as inertia matrix and position of mass centre of a Satellite Attitude Control System Simulator (SACSS, using algorithms based on least square regression and least square recursive methods. Simulations have shown that both methods have estimated the system parameters with small error. However, the least square recursive methods have performance more adequate for the SACSS objectives. The SACSS platform model will be used to do experimental verification of fundamental aspects of the satellite attitude dynamics and design of different attitude control algorithm.

  15. Small Satellite Passive Magnetic Attitude Control

    Science.gov (United States)

    Gerhardt, David T.

    Passive Magnetic Attitude Control (PMAC) is capable of aligning a satellite within 5 degrees of the local magnetic field at low resource cost, making it ideal for a small satellite. However, simulation attempts to date have not been able to predict the attitude dynamics at a level sufficient for mission design. Also, some satellites have suffered from degraded performance due to an incomplete understanding of PMAC system design. This dissertation alleviates these issues by discussing the design, inputs, and validation of PMAC systems for small satellites. Design rules for a PMAC system are defined using the Colorado Student Space Weather Experiment (CSSWE) CubeSat as an example. A Multiplicative Extended Kalman Filter (MEKF) is defined for the attitude determination of a PMAC satellite without a rate gyro. After on-orbit calibration of the off-the-shelf magnetometer and photodiodes and an on-orbit fit to the satellite magnetic moment, the MEKF regularly achieves a three sigma attitude uncertainty of 4 degrees or less. CSSWE is found to settle to the magnetic field in seven days, verifying its attitude design requirement. A Helmholtz cage is constructed and used to characterize the CSSWE bar magnet and hysteresis rods both individually and in the flight configuration. Fitted parameters which govern the magnetic material behavior are used as input to a PMAC dynamics simulation. All components of this simulation are described and defined. Simulation-based dynamics analysis shows that certain initial conditions result in abnormally decreased settling times; these cases may be identified by their dynamic response. The simulation output is compared to the MEKF output; the true dynamics are well modeled and the predicted settling time is found to possess a 20 percent error, a significant improvement over prior simulation.

  16. Satellite Laser Ranging Photon-Budget Calculations for a Single Satellite Cornercube Retroreflector: Attitude Control Tolerance

    Science.gov (United States)

    2015-11-01

    UNCLASSIFIED Satellite Laser Ranging Photon-Budget Calculations for a Single Satellite Cornercube Retroreflector: Attitude Control Tolerance Philip C...the SLR station, and the direction of the satellite from the SLR station. The required attitude control tolerance is to within 17◦ of the optimal... attitude control strategy determined in the present work. A pre-launch measurement of the re- flectance (diffraction) pattern of each retroreflector is

  17. QMRPF-UKF Master-Slave Filtering for the Attitude Determination of Micro-Nano Satellites Using Gyro and Magnetometer

    Directory of Open Access Journals (Sweden)

    Huijuan Zhang

    2010-11-01

    Full Text Available In this paper, the problem of estimating the attitude of a micro-nano satellite, obtaining geomagnetic field measurements via a three-axis magnetometer and obtaining angle rate via gyro, is considered. For this application, a QMRPF-UKF master-slave filtering method is proposed, which uses the QMRPF and UKF algorithms to estimate the rotation quaternion and the gyro bias parameters, respectively. The computational complexicity related to the particle filtering technique is eliminated by introducing a multiresolution approach that permits a significant reduction in the number of particles. This renders QMRPF-UKF master-slave filter computationally efficient and enables its implementation with a remarkably small number of particles. Simulation results by using QMRPF-UKF are given, which demonstrate the validity of the QMRPF-UKF nonlinear filter.

  18. Attitude Control Subsystem for the Advanced Communications Technology Satellite

    Science.gov (United States)

    Hewston, Alan W.; Mitchell, Kent A.; Sawicki, Jerzy T.

    1996-01-01

    This paper provides an overview of the on-orbit operation of the Attitude Control Subsystem (ACS) for the Advanced Communications Technology Satellite (ACTS). The three ACTS control axes are defined, including the means for sensing attitude and determining the pointing errors. The desired pointing requirements for various modes of control as well as the disturbance torques that oppose the control are identified. Finally, the hardware actuators and control loops utilized to reduce the attitude error are described.

  19. Satellite Attitude from a Raven Class Telescope

    Science.gov (United States)

    2010-09-01

    Cache MATLAB was used as an interface to the jSim libraries, including orbit propagation, Earth Track determination, and satellite orientation methods...collection opportunities of the satellite. The combined software tool calculates the satellite orientation required to image the asset location... satellite orientation estimations, with only the photometric signatures with strong features being correctly estimated. The strong features that

  20. Adaptive Fuzzy Attitude Control of Flexible Satellite

    Institute of Scientific and Technical Information of China (English)

    GUAN Ping; LIU Xiang-dong; CHEN Jia-bin

    2005-01-01

    The adaptive fuzzy control is applied in the attitude stabilization of flexible satellite. The detailed design procedure of the adaptive fuzzy control system is presented. Two T-S models are used as both controller and identifier. The parameters of the controller could be modified according to the information of the identifier. Simulation results show that the method can effectively cope with the uncertainty of flexible satellite by on-line learning and thus posses the good robustness. With the proposed method, the precise attitude control is accomplished.

  1. Lorentz Force Based Satellite Attitude Control

    Science.gov (United States)

    Giri, Dipak Kumar; Sinha, Manoranjan

    2016-07-01

    Since the inception of attitude control of a satellite, various active and passive control strategies have been developed. These include using thrusters, momentum wheels, control moment gyros and magnetic torquers. In this present work, a new technique named Lorentz force based Coulombic actuators for the active control is proposed. This method uses electrostatic charged shells, which interact with the time varying earth's magnetic field to establish a full three axes control of the satellite. It is shown that the proposed actuation mechanism is similar to a satellite actuated by magnetic coils except that the resultant magnetic moment vanishes under two different conditions. The equation for the required charges on the the Coulomb shells attached to the satellite body axes is derived, which is in turn used to find the available control torque for actuating the satellite along the orbit. Stability of the proposed system for very high initial angular velocity and exponential stability about the origin are proved for a proportional-differential control input. Simulations are carried out to show the efficacy of the proposed system for the attitude control of the earth-pointing satellite.

  2. ALGORITHM OF SAR SATELLITE ATTITUDE MEASUREMENT USING GPS AIDED BY KINEMATIC VECTOR

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this paper, in order to improve the accuracy of the Synthetic Aperture Radar (SAR)satellite attitude using Global Positioning System (GPS) wide-band carrier phase, the SAR satellite attitude kinematic vector and Kalman filter are introduced. Introducing the state variable function of GPS attitude determination algorithm in SAR satellite by means of kinematic vector and describing the observation function by the GPS wide-band carrier phase, the paper uses the Kalman filter algorithm to obtian the attitude variables of SAR satellite. Compared the simulation results of Kalman filter algorithm with the least square algorithm and explicit solution, it is indicated that the Kalman filter algorithm is the best.

  3. GNSS Carrier Phase-based Attitude Determination: Estimation and Applications

    NARCIS (Netherlands)

    Giorgi, G.

    2011-01-01

    Attitude determination through the use of Global Navigation Satellite System (GNSS) signals is one of the many applications of satellite-based navigation. Multiple GNSS antennas installed on a given platform are used to provide orientation estimates, thus adding attitude information to the standard

  4. GNSS Carrier Phase-based Attitude Determination: Estimation and Applications

    NARCIS (Netherlands)

    Giorgi, G.

    2011-01-01

    Attitude determination through the use of Global Navigation Satellite System (GNSS) signals is one of the many applications of satellite-based navigation. Multiple GNSS antennas installed on a given platform are used to provide orientation estimates, thus adding attitude information to the standard

  5. Star trackers for attitude determination

    DEFF Research Database (Denmark)

    Liebe, Carl Christian

    1995-01-01

    One problem comes to all spacecrafts using vector information. That is the problem of determining the attitude. This paper describes how the area of attitude determination instruments has evolved from simple pointing devices into the latest technology, which determines the attitude by utilizing...... a CCD camera and a powerful microcomputer. The instruments are called star trackers and they are capable of determining the attitude with an accuracy better than 1 arcsecond. The concept of the star tracker is explained. The obtainable accuracy is calculated, the numbers of stars to be included...

  6. Chaotic satellite attitude control by adaptive approach

    Science.gov (United States)

    Wei, Wei; Wang, Jing; Zuo, Min; Liu, Zaiwen; Du, Junping

    2014-06-01

    In this article, chaos control of satellite attitude motion is considered. Adaptive control based on dynamic compensation is utilised to suppress the chaotic behaviour. Control approaches with three control inputs and with only one control input are proposed. Since the adaptive control employed is based on dynamic compensation, faithful model of the system is of no necessity. Sinusoidal disturbance and parameter uncertainties are considered to evaluate the robustness of the closed-loop system. Both of the approaches are confirmed by theoretical and numerical results.

  7. Estimating the yaw-attitude of BDS IGSO and MEO satellites

    Science.gov (United States)

    Dai, Xiaolei; Ge, Maorong; Lou, Yidong; Shi, Chuang; Wickert, Jens; Schuh, Harald

    2015-10-01

    Precise knowledge and consistent modeling of the yaw-attitude of GNSS satellites are essential for high-precision data processing and applications. As the exact attitude control mechanism for the satellites of the BeiDou Satellite Navigation System (BDS) is not yet released, the reverse kinematic precise point positioning (PPP) method was applied in our study. However, we confirm that the recent precise orbit determination (POD) processing for GPS satellites could not provide suitable products for estimating BDS attitude using the reverse PPP because of the special attitude control switching between the nominal and the orbit-normal mode. In our study, we propose a modified processing schema for studying the attitude behavior of the BDS satellites. In this approach, the observations of the satellites during and after attitude switch are excluded in the POD processing, so that the estimates, which are needed in the reverse PPP, are not contaminated by the inaccurate initial attitude mode. The modified process is validated by experimental data sets and the attitude yaw-angles of the BDS IGSO and MEO satellites are estimated with an accuracy of better than . Furthermore, the results confirm that the switch is executed when the Sun elevation is about and the actual orientation is very close to its target one. Based on the estimated yaw-angles, a preliminary attitude switch model was established and reintroduced into the POD, yielding to a substantial improvement in the orbit overlap RMS.

  8. Satellite Photometric Error Determination

    Science.gov (United States)

    2015-10-18

    of nearly specular reflections from most solar panels. Our primary purpose in presenting these two plots is to demonstrate the usefulness of...than a transformation for stars because the spectral energy distribution of satellites can change with phase angle and is subject to specular

  9. Online attitude determination of a passively magnetically stabilized spacecraft

    Science.gov (United States)

    Burton, R.; Rock, S.; Springmann, J.; Cutler, J.

    2017-04-01

    An online attitude determination filter is developed for a nano satellite that has no onboard attitude sensors or gyros. Specifically, the attitude of NASA Ames Research Center's O/OREOS, a passively magnetically stabilized 3U CubeSat, is determined using only an estimate of the solar vector obtained from solar panel currents. The filter is based upon the existing multiplicative extended Kalman filter (MEKF) but instead of relying on gyros to drive the motion model, the filter instead incorporates a model of the spacecraft's attitude dynamics in the motion model. An attitude determination accuracy of five degrees is demonstrated, a performance verified using flight data from the University of Michigan's RAX-1. Although the filter was designed for the specific problem of a satellite without gyros or attitude determination it could also be used to provide smoothing of noisy gyro signals or to provide a backup in the event of gyro failures.

  10. Attitude Control of a Satellite by using Digital Signal Processing

    Directory of Open Access Journals (Sweden)

    Adirelle C. Santana

    2012-03-01

    Full Text Available This article has discussed the development of a three-axis attitude digital controller for an artificial satellite using a digital signal processor. The main motivation of this study is the attitude control system of the satellite Multi-Mission Platform, developed by the Brazilian National Institute for Space Research for application in different sort of missions. The controller design was based on the theory of the Linear Quadratic Gaussian Regulator, synthesized from the linearized model of the motion of the satellite, i.e., the kinematics and dynamics of attitude. The attitude actuators considered in this study are pairs of cold gas jets powered by a pulse width/pulse frequency modulator. In the first stage of the project development, a system controller for continuous time was studied with the aim of testing the adequacy of the adopted control. The next steps had included an analysis of discretization techniques, the setting time of sampling rate, and the testing of the digital version of the Linear Quadratic Gaussian Regulator controller in the MATLAB/SIMULINK. To fulfill the study, the controller was implemented in a digital signal processor, specifically the Blackfin BF537 from Analog Devices, along with the pulse width/pulse frequency modulator. The validation tests used a scheme of co-simulation, where the model of the satellite was simulated in MATLAB/SIMULINK, while the controller and modulator were processed in the digital signal processor with a tool called Processor-In-the-Loop, which acted as a data communication link between both environments.function and required time to achieve a given mission accuracy are determined, and results are provided as illustration.

  11. Observer-based Satellite Attitude Control and Simulation Researches

    Institute of Scientific and Technical Information of China (English)

    王子才; 马克茂

    2002-01-01

    Observer design method is applied to the realization of satellite attitude control law baaed on simplified control model. Exact mathematical model of the satellite attitude control system is also constructed, together with the observer-based control law, to conduct simulation research. The simulation results justify the effectiveness andfeasibility of the observer-based control method.

  12. An active attitude control system for a drag sail satellite

    Science.gov (United States)

    Steyn, Willem Herman; Jordaan, Hendrik Willem

    2016-11-01

    The paper describes the development and simulation results of a full ADCS subsystem for the deOrbitSail drag sail mission. The deOrbitSail satellite was developed as part of an European FP7 collaboration research project. The satellite was launched and commissioning started on 10th July 2015. Various new actuators and sensors designed for this mission will be presented. The deOrbitSail satellite is a 3U CubeSat to deploy a 4 by 4 m drag sail from an initial 650 km circular polar low earth orbit. With an active attitude control system it will be shown that by maximising the drag force, the expected de-orbiting period from the initial altitude will be less than 50 days. A future application of this technology will be the use of small drag sails as low-cost devices to de-orbit LEO satellites, when they have reached their end of life, without having to use expensive propulsion systems. Simulation and Hardware-in-Loop experiments proved the feasibility of the proposed attitude control system. A magnetic-only control approach using a Y-Thomson spin, is used to detumble the 3U Cubesat with stowed sail and subsequently to 3-axis stabilise the satellite to be ready for the final deployment phase. Minituarised torquer rods, a nano-sized momentum wheel, attitude sensor hardware (magnetometer, sun, earth) developed for this phase will be presented. The final phase will be to deploy and 3-axis stabilise the drag sail normal to the satellite's velocity vector, using a combined Y-momentum wheel and magnetic controller. The design and performance improvements when using a 2-axis translation stage to adjust the sail centre-of-pressure to satellite centre-of-mass offset, will also be discussed, although for launch risk reasons this stage was not included in the final flight configuration. To accurately determine the drag sail's attitude during the sunlit part of the orbit, an accurate wide field of view dual sensor to measure both the sun and nadir vector direction was developed for

  13. Flexible Satellite Attitude Control via Adaptive Fuzzy Linearization

    Institute of Scientific and Technical Information of China (English)

    GUAN Ping; LIU Xiang-dong; CHEN Jia-bin; LIU Xiao-he

    2005-01-01

    The adaptive fuzzy control is combined with input-output linearization control to constitute the hybrid controller. The control method is then applied to the attitude maneuver control of the flexible satellite.The basic control structure is given. The rules of the controller parameter selection, which guarantee the attitude stabilization of the satellite with parameter uncertainties, have been analyzed. Simulation results show that the precise attitude control is accomplished in spite of the uncertainty in the system.

  14. An Attitude Modelling Method Based on the Inherent Frequency of a Satellite Platform

    Science.gov (United States)

    Mo, F.; Tang, X.; Xie, J.; Yan, C.

    2017-05-01

    The accuracy of attitude determination plays a key role in the improvement of surveying and mapping accuracy for high-resolution remote-sensing satellites, and it is a bottleneck in large-scale satellite topographical mapping. As the on-board energy is constrained and the performance of an attitude-measurement device is limited, the attitude acquired is discretely sampled with a settled time interval. The larger the interval, the easier the data transmission, and the more deviation the attitude data will have. Meanwhile, several kinds of jitter frequencies have been detected in satellite platforms. This paper presents a novel attitude modelling (AttModel) method that sufficiently considers the discrete and periodic characteristics, and the attitude model built is continuous and consists of several inherent waves of different frequencies. The process of modelling includes two steps: (a) frequency detection, which uses raw gyroscope data within a period of time to detect the attitude frequencies (as the gyroscope data can actually reflect continuous, very small changes of the satellite platform), and (b) attitude modelling , which processes the attitude data that was filtered by extended Kalman filtering based on general polynomial and trigonometric polynomials, and these trigonometric polynomials are rebuilt by those frequencies detected in the first part of the modelling process. Finally, one experiment designed for verifying the effectiveness of the presented method shows that the AttModel method can reach a slightly better pointing accuracy without ground-control points than traditional attitude-interpolation methods.

  15. Satellite attitude prediction by multiple time scales method

    Science.gov (United States)

    Tao, Y. C.; Ramnath, R.

    1975-01-01

    An investigation is made of the problem of predicting the attitude of satellites under the influence of external disturbing torques. The attitude dynamics are first expressed in a perturbation formulation which is then solved by the multiple scales approach. The independent variable, time, is extended into new scales, fast, slow, etc., and the integration is carried out separately in the new variables. The theory is applied to two different satellite configurations, rigid body and dual spin, each of which may have an asymmetric mass distribution. The disturbing torques considered are gravity gradient and geomagnetic. Finally, as multiple time scales approach separates slow and fast behaviors of satellite attitude motion, this property is used for the design of an attitude control device. A nutation damping control loop, using the geomagnetic torque for an earth pointing dual spin satellite, is designed in terms of the slow equation.

  16. Touchless attitude correction for satellite with constant magnetic moment

    Science.gov (United States)

    Ao, Hou-jun; Yang, Le-ping; Zhu, Yan-wei; Zhang, Yuan-wen; Huang, Huan

    2017-09-01

    Rescue of satellite with attitude fault is of great value. Satellite with improper injection attitude may lose contact with ground as the antenna points to the wrong direction, or encounter energy problems as solar arrays are not facing the sun. Improper uploaded command may set the attitude out of control, exemplified by Japanese Hitomi spacecraft. In engineering practice, traditional physical contact approaches have been applied, yet with a potential risk of collision and a lack of versatility since the mechanical systems are mission-specific. This paper puts forward a touchless attitude correction approach, in which three satellites are considered, one having constant dipole and two having magnetic coils to control attitude of the first. Particular correction configurations are designed and analyzed to maintain the target's orbit during the attitude correction process. A reference coordinate system is introduced to simplify the control process and avoid the singular value problem of Euler angles. Based on the spherical triangle basic relations, the accurate varying geomagnetic field is considered in the attitude dynamic mode. Sliding mode control method is utilized to design the correction law. Finally, numerical simulation is conducted to verify the theoretical derivation. It can be safely concluded that the no-contact attitude correction approach for the satellite with uniaxial constant magnetic moment is feasible and potentially applicable to on-orbit operations.

  17. Performance comparison of attitude determination, attitude estimation, and nonlinear observers algorithms

    Science.gov (United States)

    MOHAMMED, M. A. SI; BOUSSADIA, H.; BELLAR, A.; ADNANE, A.

    2017-01-01

    This paper presents a brief synthesis and useful performance analysis of different attitude filtering algorithms (attitude determination algorithms, attitude estimation algorithms, and nonlinear observers) applied to Low Earth Orbit Satellite in terms of accuracy, convergence time, amount of memory, and computation time. This latter is calculated in two ways, using a personal computer and also using On-board computer 750 (OBC 750) that is being used in many SSTL Earth observation missions. The use of this comparative study could be an aided design tool to the designer to choose from an attitude determination or attitude estimation or attitude observer algorithms. The simulation results clearly indicate that the nonlinear Observer is the more logical choice.

  18. Low-power attitude determination for magnetometry planetary missions

    DEFF Research Database (Denmark)

    Christensen, Thorbjørn Helvig

    This work covers the subject of orientation or attitude in space and on the surface of a planet. Different attitude sensor technologies have been investigated with emphasis on very low power consumption and mass. In addition robust methods for attitude determination have been covered again...... with emphasis on the limited budget onboard very small satellites. A true low-power attitude sensor using the Anisotropic Magneto Resistor effect have been designed to late prototype state. Two prototypes of the AMR magnetometer have been built. One of the prototypes has an analog output and the second...... calibration has been performed on both of the prototypes of the AMR magnetometer with very good overall result. Different attitude representations such as orthogonal matrices, Euler angles and quaternions are presented. Also methods for attitude determination of a sensor platform with more than one vector...

  19. Satellite Aerodynamics and Density Determination from Satellite Dynamic Response

    Science.gov (United States)

    Karr, G. R.

    1972-01-01

    The aerodynamic drag and lift properties of a satellite are first expressed as a function of two parameters associated with gas-surface interaction at the satellite surface. The dynamic response of the satellite as it passes through the atmosphere is then expressed as a function of the two gas-surface interaction parameters, the atmospheric density, the satellite velocity, and the satellite orientation to the high speed flow. By proper correlation of the observed dynamic response with the changing angle of attack of the satellite, it is found that the two unknown gas-surface interaction parameters can be determined. Once the gas-surface interaction parameters are known, the aerodynamic properties of the satellite at all angles of attack are also determined.

  20. Satellite Attitude Control Using Only Electromagnetic Actuation

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    The primary purpose of this work was to develop control laws for three axis stabilization of a magnetic actuated satellite. This was achieved by a combination of linear and nonlinear system theory. In order to reach this goal new theoretical results were produced in both fields. The focus...... was that interaction between the Earth's magnetic field and a magnetic field generated by a set of coils in the satellite can be used for actuation. Magnetic torquing was found attractive for generation of control torques on small satellites, since magnetic control systems are relatively lightweight, require low power...... was stated as a continuous function of the state. A control law for magnetic actuated satellite was proposed. Complete comprehension of the nature of the satellite control problem required a new approach merging the nonlinear control theory with physics of the rigid body motion and an extension of earlier...

  1. Satellite Attitude Control System Design considering the Fuel Slosh Dynamics

    Directory of Open Access Journals (Sweden)

    Luiz Carlos Gadelha de Souza

    2014-01-01

    Full Text Available The design of the satellite attitude control system (ACS becomes more complex when the satellite structure has different type of components like, flexible solar panels, antennas, mechanical manipulators, and tanks with fuel. A crucial interaction can occur between the fuel slosh motion and the satellite rigid motion during translational and/or rotational manoeuvre since these interactions can change the satellite centre of mass position damaging the ACS pointing accuracy. Although, a well-designed controller can suppress such disturbances quickly, the controller error pointing may be limited by the minimum time necessary to suppress such disturbances thus affecting the satellite attitude acquisition. As a result, the design of the satellite controller needs to explore the limits between the conflicting requirements of performance and robustness. This paper investigates the effects of the interaction between the liquid motion (slosh and the satellite dynamics in order to predict what the damage to the controller performance and robustness is. The fuel slosh dynamics is modelled by a pendulum which parameters are identified using the Kalman filter technique. This information is used to design the satellite controller by the linear quadratic regulator (LQR and linear quadratic Gaussian (LQG methods to perform a planar manoeuvre assuming thrusters are actuators.

  2. Attitude Determination and Control Systems

    Science.gov (United States)

    Starin, Scott R.; Eterno, John

    2011-01-01

    In the year 1900, Galveston, Texas, was a bustling community of approximately 40,000 people. The former capital of the Republic of Texas remained a trade center for the state and was one of the largest cotton ports in the United States. On September 8 of that year, however, a powerful hurricane struck Galveston island, tearing the Weather Bureau wind gauge away as the winds exceeded 100 mph and bringing a storm surge that flooded the entire city. The worst natural disaster in United States history even today the hurricane caused the deaths of between 6000 and 8000 people. Critical in the events that led to such a terrible loss of life was the lack of precise knowledge of the strength of the storm before it hit. In 2008, Hurricane Ike, the third costliest hurricane ever to hit the United States coast, traveled through the Gulf of Mexico. Ike was gigantic, and the devastation in its path included the Turk and Caicos Islands, Haiti, and huge swaths of the coast of the Gulf of Mexico. Once again, Galveston, now a city of nearly 60,000, took the direct hit as Ike came ashore. Almost 200 people in the Caribbean and the United States lost their lives; a tragedy to be sure, but far less deadly than the 1900 storm. This time, people were prepared, having received excellent warning from the GOES satellite network. The Geostationary Operational Environmental Satellites have been a continuous monitor of the world's weather since 1975, and they have since been joined by other Earth-observing satellites. This weather surveillance to which so many now owe their lives is possible in part because of the ability to point accurately and steadily at the Earth below. The importance of accurately pointing spacecraft to our daily lives is pervasive, yet somehow escapes the notice of most people. But the example of the lives saved from Hurricane Ike as compared to the 1900 storm is something no one should ignore. In this section, we will summarize the processes and technologies used in

  3. Satellite orbit determination and gravity field recovery from satellite-to-satellite tracking

    Science.gov (United States)

    Wakker, K. F.; Ambrosius, B. A. C.; Leenman, H.

    1989-07-01

    Studies on satellite-to-satellite tracking (SST) with POPSAT (a geodetic satellite concept) and a ERS-class (Earth observation) satellite, a Satellite-to-Satellite Tracking (SST) gravity mission, and precise gravity field determination methods and mission requirements are reported. The first two studies primarily address the application of SST between the high altitude POPSAT and an ERS-class or GRM (Geopotential Research Mission) satellite to the orbit determination of the latter two satellites. Activities focussed on the determination of the tracking coverage of the lower altitude satellite by ground based tracking systems and by POPSAT, orbit determination error analysis and the determination of the surface forces acting on GRM. The third study surveys principles of SST, uncertainties of existing drag models, effects of direct luni-solar attraction and tides on orbit and the gravity gradient observable. Detailed ARISTOTELES (which replaced POPSAT) orbit determination error analyses were performed for various ground based tracking networks.

  4. Advanced Attitude Control af Pico Sized Satellites

    DEFF Research Database (Denmark)

    Larsen, Jesper A.; Amini, Rouzbeh; Izadi-Zamanabadi, Roozbeh

    2005-01-01

    accuracy of better than 5 degrees. Cost, size, weight and power requirements, on the other hand, impose selecting relative simple sensors and actuators which leads to an attitude control requirement of less than 1 degree. This precision is obtained by a combination of magnetorquers and momentum wheels...

  5. The inertial attitude augmentation for ambiguity resolution in SF/SE-GNSS attitude determination.

    Science.gov (United States)

    Zhu, Jiancheng; Hu, Xiaoping; Zhang, Jingyu; Li, Tao; Wang, Jinling; Wu, Meiping

    2014-06-26

    The Unaided Single Frequency/Single Epoch Global Navigation Satellite System (SF/SE GNSS) model is the most challenging scenario for ambiguity resolution in the GNSS attitude determination application. To improve the performance of SF/SE-GNSS ambiguity resolution without excessive cost, the Micro-Electro-Mechanical System Inertial Measurement Unit (MEMS-IMU) is a proper choice for the auxiliary sensor that carries out the inertial attitude augmentation. Firstly, based on the SF/SE-GNSS compass model, the Inertial Derived Baseline Vector (IDBV) is defined to connect the MEMS-IMU attitude measurement with the SF/SE-GNSS ambiguity search space, and the mechanism of inertial attitude augmentation is revealed from the perspective of geometry. Then, through the quantitative description of model strength by Ambiguity Dilution of Precision (ADOP), two ADOPs are specified for the unaided SF/SE-GNSS compass model and its inertial attitude augmentation counterparts, respectively, and a sufficient condition is proposed for augmenting the SF/SE-GNSS model strength with inertial attitude measurement. Finally, in the framework of an integer aperture estimator with fixed failure rate, the performance of SF/SE-GNSS ambiguity resolution with inertial attitude augmentation is analyzed when the model strength is varying from strong to weak. The simulation results show that, in the SF/SE-GNSS attitude determination application, MEMS-IMU can satisfy the requirements of ambiguity resolution with inertial attitude augmentation.

  6. Quaternion normalization in additive EKF for spacecraft attitude determination

    Science.gov (United States)

    Bar-Itzhack, I. Y.; Deutschmann, J.; Markley, F. L.

    1991-01-01

    This work introduces, examines, and compares several quaternion normalization algorithms, which are shown to be an effective stage in the application of the additive extended Kalman filter (EKF) to spacecraft attitude determination, which is based on vector measurements. Two new normalization schemes are introduced. They are compared with one another and with the known brute force normalization scheme, and their efficiency is examined. Simulated satellite data are used to demonstrate the performance of all three schemes. A fourth scheme is suggested for future research. Although the schemes were tested for spacecraft attitude determination, the conclusions are general and hold for attitude determination of any three dimensional body when based on vector measurements, and use an additive EKF for estimation, and the quaternion for specifying the attitude.

  7. Comparison of ENVISAT's Attitude Simulation and Real Optical and SLR Observations in order to Refine the Satellite Attitude Model

    Science.gov (United States)

    Silha, J.; Schildknecht, T.; Pittet, J.; Bodenmann, D.; Kanzler, R.; Karrang, P.; Krag, H.

    2016-09-01

    The Astronomic Institute of the University of Bern (AIUB) in cooperation with other three partners is involved in an ESA study dedicated to the attitude determination of large spacecraft and upper stages. Two major goals are defined. First is the long term prediction of tumbling rates (e.g. 10 years) for selected targets for the future Active Debris Removal (ADR) missions. Second goal is the attitude state determination in case of contingencies, when a short response time is required between the observations themselves and the attitude determination. One of the project consortium partners, Hypersonic Technology Goettingen (HTG), is developing a highly modular software tool ιOTA to perform short- (days) to long-term (years) propagations of the orbit and the attitude motion of spacecraft in space. Furthermore, ιOTA's post-processing modules will generate synthetic measurements, e.g. light curves, SLR residuals and Inverse Synthetic Aperture Radar (ISAR) images that can be compared with the real measurements. In our work we will present the first attempt to compare real measurements with synthetic measurements in order to estimate the attitude state of tumbling satellite ENVISAT from observations performed by AIUB. We will shortly discuss the ESA project and ιOTA software tool. We will present AIUB's ENVISAT attitude state determined from the SLR ranges acquired by the Zimmerwald SLR station. This state was used as the initial conditions within the ιOTA software. Consequently the attitude of satellite was predicted by using ιOTA and compared with the real SLR residuals, as well with the high frame-rate light curves acquired by the Zimmerwald 1-m telescope.

  8. Sliding Mode Attitude Control for Magnetic Actuated Satellite

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    1998-01-01

    Magnetic torquing is attractive as a control principle on small satellites. The actuation principle is to use the interaction between the earth's magnetic field and magnetic field generated by a coil set in the satellite. This control principle is inherently nonlinear, and difficult to use becaus...... the spacecraft attitude using only magnetic torquing is realized in the form of the sliding mode control. A three dimensional sliding manifold is proposed, and it is shown that the satellite motion on the sliding manifold is asymptotically stable......Magnetic torquing is attractive as a control principle on small satellites. The actuation principle is to use the interaction between the earth's magnetic field and magnetic field generated by a coil set in the satellite. This control principle is inherently nonlinear, and difficult to use because...... control torques can only be generated perpendicular to the local geomagnetic field vector. This has been a serious obstacle for using magnetorquer based control for three-axis attitude control. This paper deals with three-axis stabilization of a low earth orbit satellite. The problem of controlling...

  9. Satellite Attitude Control Using Atmospheric Drag

    Science.gov (United States)

    2007-03-01

    Astronautics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In...yaw axes and provide magnetic damping on both the pitch and yaw axes. The satellite resem- bles a shuttlecock used in badminton (see Figure 2.2). The...Control Using Atmospheric Drag Guettler, David B., Captain, USAF Air Force Institute of Technology Graduate School of Engineering and Management (AFIT

  10. Determination of attitude motion of the Foton M-3 satellite according to the data of onboard measurements of the Earth's magnetic field

    Science.gov (United States)

    Beuselinck, T.; van Bavinchove, C.; Abrashkin, V. I.; Kazakova, A. E.; Sazonov, V. V.

    2010-06-01

    The results of reconstruction of rotational motion of the Foton M-3 satellite during its uncontrolled flight in September 2007 are presented. The reconstruction was performed by processing the data of onboard measurements of the Earth’s magnetic field obtained by the DIMAC instruments. The measurements were carried out continuously throughout the flight, but the processing technique dealt with the data portions covering time intervals of a few orbital revolutions. The data obtained on each such interval were processed jointly by the least squares method with using integration of the equations of satellite motion relative to its center of mass. When processing, the initial conditions of motion and the used mathematical model’s parameters were estimated. The results of processing 16 data sets gave us complete information about the satellite motion. This motion, which began at a low angular velocity, had gradually accelerated and in five days became close to the regular Euler precession of an axisymmetric solid body. At the end of uncontrolled flight the angular velocity of the satellite relative to its lengthwise axis was 0.5 deg/s; the angular velocity projection onto the plane perpendicular to this axis had a magnitude of about 0.18 deg/s.

  11. Analysis of Characteristics of QZSS Satellite Orbit and Clock Products during Yaw Attitude Model Switching

    Directory of Open Access Journals (Sweden)

    ZHOU Peiyuan

    2016-03-01

    Full Text Available Yaw attitude model switching of navigation satellites have great impact on its orbit and clock products derived from precise orbit determination. Firstly, the yaw attitude and solar radiation model of QZSS is given briefly. Then, using QZSS precise orbit and clock products provided by IGS MGEX analysis center, precision of orbit and clock is analyzed by satellite laser ranging residuals and polynomial fit residuals respectively. Finally, spectral analysis and modified Allan variance is carried out on clock products to reveal its periodic variations. Research on QZSS satellite orbit and clock products of 2014 shows that there are two eclipse seasons of 20 days and the beta angle is fluctuating with a period of half-year. And there is significant correlation between the precision of orbit and clock products and beta angle. Moreover, the satellite clock offset has periodic variations similar to orbit periods and its amplitude is changing with the beta angle which indicates problems of current orbit determination strategies. In view of similarities between QZSS and BeiDou IGSO and MEO satellites in yaw attitude model, the conclusion is beneficial to improve BeiDou precise orbit determination.

  12. Orbit Determination Using Satellite-to-Satellite Tracking Data

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Satellite-to-Satellite Tracking (SST) data can be used to determine the orbits of spacecraft in two ways. One is combined orbit determination, which combines SST data with ground-based tracking data and exploits the enhanced tracking geometry. The other is the autonomous orbit determination, which uses only SST. The latter only fits some particular circumstances since it suffers the rank defect problem in other circumstances. The proof of this statement is presented. The na ture of the problem is also investigated in order to find an effective solution. Several methods of solution are discussed. The feasibility of the methods is demonstrated by their apphcation to a simulation.

  13. Attitude control of a small satellite using magnetic bearing momentum wheel

    OpenAIRE

    Terui, Fuyuto; Nakajima, Atsushi; 照井 冬人; 中島 厚

    1996-01-01

    An attitude controller for a 50 kg-class micro satellite which could be launched by H-2 rocket as a piggyback payload of a main satellite is considered. The survey of the proposals of the mission using a micro satellite from national institutes, universities and private companies shows that the development of a small, light and inexpensive three axis attitude controller is widely expected. One of the candidate configurations for such an attitude controller is bias momentum control using a mag...

  14. Advanced numerical study of the three-axis magnetic attitude control and determination with uncertainties

    Science.gov (United States)

    Ivanov, D. S.; Ovchinnikov, M. Yu.; Penkov, V. I.; Roldugin, D. S.; Doronin, D. M.; Ovchinnikov, A. V.

    2017-03-01

    Attitude motion of a satellite equipped with magnetic control system is considered. System comprises of three magnetorquers and one three-axis magnetometer. Satellite is stabilized in orbital reference frame using PD controller and extended Kalman filter. Three-axis attitude is analyzed numerically with advanced assumptions: inertia tensor uncertainty, disturbances of unknown nature, magnetometer errors are taken into account. Stabilization and determination accuracy dependence on orbit inclination is studied.

  15. Determination of Vessel Attitudes Using GPS

    Institute of Scientific and Technical Information of China (English)

    王书寅; 周丰年; 金建霞; 吴敬文

    2002-01-01

    With the development of GPS carrier wave phase technology, it becomes possible that the height accuracy of centimeter level is got by GPS RTK technology. Vessel attitudes are very important parameters in marine survey. In this paper, they were determined by 4 GPS receivers. At the same time, the arithmetic and procedure of vessel attitude determining were given. Based on an experiment, some useful conclusions were obtained and the corresponding methods were put forward to improve the accuracy.

  16. High Precision Orbit Determination of CHAMP Satellite

    Institute of Scientific and Technical Information of China (English)

    ZHAO Qile; LIU Jingnan; GE Maorong

    2006-01-01

    The precision orbit determination of challenging minisatellite payload(CHAMP) satellite was done based on position and navigation data analyst(PANDA) software which is developed in Wuhan University, using the onboard GPS data of year 2002 from day 126 to 131. The orbit accuracy was assessed by analyzing the difference from GFZ post-processed science orbits (PSO), the GPS carrier and pseudo-range data residuals and the satellite laser ranging (SLR) residuals.

  17. Fundamentals of spacecraft attitude determination and control

    CERN Document Server

    Markley, F Landis

    2014-01-01

    This book explores topics that are central to the field of spacecraft attitude determination and control. The authors provide rigorous theoretical derivations of significant algorithms accompanied by a generous amount of qualitative discussions of the subject matter. The book documents the development of the important concepts and methods in a manner accessible to practicing engineers, graduate-level engineering students and applied mathematicians. It includes detailed examples from actual mission designs to help ease the transition from theory to practice, and also provides prototype algorithms that are readily available on the author’s website. Subject matter includes both theoretical derivations and practical implementation of spacecraft attitude determination and control systems. It provides detailed derivations for attitude kinematics and dynamics, and provides detailed description of the most widely used attitude parameterization, the quaternion. This title also provides a thorough treatise of attitu...

  18. Attitude determination for balloon-borne experiments

    CERN Document Server

    Gandilo, N N; Amiri, M; Angile, F E; Benton, S J; Bock, J J; Bond, J R; Bryan, S A; Chiang, H C; Contaldi, C R; Crill, B P; Devlin, M J; Dober, B; Dore, O P; Farhang, M; Filippini, J P; Fissel, L M; Fraisse, A A; Fukui, Y; Galitzki, N; Gambrel, A E; Golwala, S; Gudmundsson, J E; Halpern, M; Hasselfield, M; Hilton, G C; Holmes, W A; Hristov, V V; Irwin, K D; Jones, W C; Kermish, Z D; Klein, J; Korotkov, A L; Kuo, C L; MacTavish, C J; Mason, P V; Matthews, T G; Megerian, K G; Moncelsi, L; Morford, T A; Mroczkowski, T K; Nagy, J M; Netterfield, C B; Novak, G; Nutter, D; O'Brient, R; Pascale, E; Poidevin, F; Rahlin, A S; Reintsema, C D; Ruhl, J E; Runyan, M C; Savini, G; Scott, D; Shariff, J A; Soler, J D; Thomas, N E; Trangsrud, A; Truch, M D; Tucker, C E; Tucker, G S; Tucker, R S; Turner, A D; Ward-Thompson, D; Weber, A C; Wiebe, D V; Young, E Y

    2014-01-01

    An attitude determination system for balloon-borne experiments is presented. The system provides pointing information in azimuth and elevation for instruments flying on stratospheric balloons over Antarctica. In-flight attitude is given by the real-time combination of readings from star cameras, a magnetometer, sun sensors, GPS, gyroscopes, tilt sensors and an elevation encoder. Post-flight attitude reconstruction is determined from star camera solutions, interpolated by the gyroscopes using an extended Kalman Filter. The multi-sensor system was employed by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol), an experiment that measures polarized thermal emission from interstellar dust clouds. A similar system was designed for the upcoming flight of SPIDER, a Cosmic Microwave Background polarization experiment. The pointing requirements for these experiments are discussed, as well as the challenges in designing attitude reconstruction systems for high altitude balloon flights. ...

  19. Attitude guidance and simulation with animation of a land-survey satellite motion

    Science.gov (United States)

    Somova, Tatyana

    2017-01-01

    We consider problems of synthesis of the vector spline attitude guidance laws for a land-survey satellite and an in-flight support of the satellite attitude control system with the use of computer animation of its motion. We have presented the results on the efficiency of the developed algorithms.

  20. Flight results of a low-cost attitude determination system

    Science.gov (United States)

    Springmann, John C.; Cutler, James W.

    2014-06-01

    This paper presents flight results of the attitude determination system (ADS) flown on the Radio Aurora Explorer (RAX) satellites, RAX-1 and RAX-2, which are CubeSats developed to study space weather. The ADS sensors include commercial-off-the-shelf magnetometers, coarse sun sensors (photodiodes), and a MEMs rate gyroscope. A multiplicative extended Kalman filter is used for attitude estimation. On-orbit calibration was developed and applied to compensate for sensor and alignment errors, and attitude determination accuracies of 0.5° 1-σ have been demonstrated on-orbit. The approach of using low-cost sensors in conjunction with on-orbit calibration, which mitigates the need for pre-flight calibration and high-tolerance alignment during spacecraft assembly, reduces the time and cost associated with the subsystem development, and provides a low-cost solution for modest attitude determination requirements. Although the flight results presented in this paper are from a specific mission, the methods used and lessons learned can be used to maximize the performance of the ADS of any vehicle while minimizing the pre-flight calibration and alignment requirements.

  1. Passivity Based Nonlinear Attitude Control of the Rømer Satellite

    DEFF Research Database (Denmark)

    Quottrup, Michael Melholt; Krogh-Sørensen, J.; Wisniewski, Rafal

    2001-01-01

    This paper suggests nonlinear attitude control of the Danish satellite Rømer. This satellite will be designed to fulfil two scientific objectives: The observation of stellar oscillations and the detection and localisation of gamma-ray bursts. The satellite will be equipped with a tetrahedron...

  2. Passivity based nonlinear attitude control of the Rømer satellite

    DEFF Research Database (Denmark)

    Quottrup, Michael Melholt; Krogh-Sørensen, J.; Wisniewski, Rafal

    This paper suggests nonlinear attitude control of the Danish satellite Rømer. This satellite will be designed to fulfil two scientific objectives: The observation of stellar oscillations and the detection and localisation of gamma-ray bursts. The satellite will be equipped with a tetrahedron...

  3. Spacecraft Attitude Determination with Earth Albedo Corrected Sun Sensor Measurements

    DEFF Research Database (Denmark)

    Bhanderi, Dan

    This thesis focuses on advanced modeling of the Earth albedo experienced by satellites in Earth orbit. The model of the Earth albedo maintains directional information of the Earth albedo irradiance from each partition on the Earth surface. This allows enhanced modeling of Sun sensor current outputs......-Method, Extended Kalman Filter, and Unscented Kalman Filter algorithms are presented and the results are compared. Combining the Unscented Kalman Filter with Earth albedo and enhanced Sun sensor modeling allows for three-axis attitude determination from Sun sensor only, which previously has been perceived...

  4. A method of autonomous orbit determination for satellite using star sensor

    Institute of Scientific and Technical Information of China (English)

    MA; Jianbo; XU; Jin

    2005-01-01

    In this paper a method of autonomous orbit determination using star sensor is studied. By building relatively consummate dynamical models which simulate attitude motion of satellite and observation from satellite to background stars, the simulant computation of this method is executed, and it is shown that the method of autonomous orbit determination is feasible. Academic and calculation analyses have been done for the relation between the direction of star sensor with respect to satellite-body coordinate system and the accuracy of autonomous orbit determination.

  5. A comparing design of satellite attitude control system based on reaction wheel

    Institute of Scientific and Technical Information of China (English)

    CHENG Hao; GE Sheng-min; SHEN Yi

    2008-01-01

    The disturbance caused by the reaction wheel with a current controller greatly influences the accuracy and stability of the satellite attitude control system.To solve this problem,the idea of speed feedback compensation control reaction wheel is put forward.This paper introduces the comparison on design and performance of two satellite attitude control systems,which are separately based on the current control reaction wheel and the speed feedback compensation control reaction wheel.Analysis shows that the speed feedback compensation control flywheel system may effectively suppress the torque fluctuation.Simulation results indicate that the satellite attitude control system with the speed feedback compensation control flywheel has improved performance.

  6. An adaptive Multiplicative Extened Kalman Filter for Attitude Estimation of Marine Satellite Tracking Antenna

    DEFF Research Database (Denmark)

    Wang, Yunlong; Soltani, Mohsen; Hussain, Dil muhammed Akbar

    2016-01-01

    Satellite tracking is a challenging task for marine applications due to the disturbance from ocean waves. An Attitude Heading and Reference System (AHRS) for measuring ship attitude, based on Microelectromechanical Systems (MEMS) sensors, is a key part for satellite tracking. In this paper......, an adaptive Multiplicative Extended Kalman Filter (MEKF) for attitude estimation of Marine Satellite Tracking Antenna (MSTA) is presented with the measurement noise covariance matrix adjusted according to the norm of accelerometer measurements, which can significantly reduce the slamming influence from waves...

  7. Microsatellite Attitude Determination and Control Subsystem Design and Implementation: Software-in-the-Loop Approach

    Directory of Open Access Journals (Sweden)

    Ho-Nien Shou

    2014-01-01

    Full Text Available The paper describes the development of a microsatellite attitude determination and control subsystem (ADCS and verification of its functionality by software-in-the-loop (SIL method. The role of ADCS is to provide attitude control functions, including the de-tumbling and stabilizing the satellite angular velocity, and as well as estimating the orbit and attitude information during the satellite operation. In Taiwan, Air Force Institute of Technology (AFIT, dedicating for students to design experimental low earth orbit micro-satellite, called AFITsat. For AFITsat, the operation of the ADCS consists of three modes which are initialization mode, detumbling mode, and normal mode, respectively. During the initialization mode, ADCS collects the early orbit measurement data from various sensors so that the data can be downlinked to the ground station for further analysis. As particularly emphasized in this paper, during the detumbling mode, ADCS implements the thrusters in plus-wide modulation control method to decrease the satellite angular velocity. ADCS provides the attitude determination function for the estimation of the satellite state, during normal mode. The three modes of microsatellite adopted Kalman filter algorithm estimate microsatellite attitude. This paper will discuss using the SIL validation ADCS function and verify its feasibility.

  8. Optimality of incompletely measurable active and passive attitude control systems. [for satellites

    Science.gov (United States)

    Schiehlen, W.; Popp, K.

    1973-01-01

    Passive attitude control systems and active systems with incomplete state measurements are only suboptimal systems in the sense of optimal control theory, since optimal systems require complete state measurements or state estimations. An optimal system, then, requires additional hardware (especially in the case of flexible spacecraft) which results in higher costs. Therefore, it is a real engineering problem to determine how much an optimal system exceeds the suboptimal system, or in other words, what is the suboptimal system's degree of optimality. The problem will be treated in three steps: (1) definition of the degree of optimality for linear, time-invariant systems; (2) a computation method using the quadratic cost functional; (3) application to a gravity-gradient stabilized three-body satellite and a spinning flexible satellite.

  9. Flight Mechanics/Estimation Theory Symposium. [with application to autonomous navigation and attitude/orbit determination

    Science.gov (United States)

    Fuchs, A. J. (Editor)

    1979-01-01

    Onboard and real time image processing to enhance geometric correction of the data is discussed with application to autonomous navigation and attitude and orbit determination. Specific topics covered include: (1) LANDSAT landmark data; (2) star sensing and pattern recognition; (3) filtering algorithms for Global Positioning System; and (4) determining orbital elements for geostationary satellites.

  10. Sun-synchronous satellite orbit determination

    Science.gov (United States)

    Ma, Der-Ming; Zhai, Shen-You

    2004-02-01

    The linearized dynamic equations used for on-board orbit determination of Sun-synchronous satellite are derived. Sun-synchronous orbits are orbits with the secular rate of the right ascension of the ascending node equal to the right ascension rate of the mean sun. Therefore the orbit is no more a closed circle but a tight helix about the Earth. In the paper, instead of treating the orbit as a closed circle, the actual helix orbit is taken as nominal trajectory. The details of the linearized equations of motion for the satellite in the Sun-synchronous orbit are derived. The linearized equations are obtained by perturbing the Keplerian motion with the J2 correction and the effect of sun's attraction being neglected. Combined with the GPS navigation equations, the Kalman filter formulation is given. The particular application considered is the circular Sun-synchronous orbit with the altitude of 800 km and inclination of 98.6°. The numerical example simulated by MATLAB® shows that only the pseudo-range data used in the algorithm still gives acceptable results. Based on the simulation results, we can use the on-board GPS receivers' signal only as an alternative to determine the orbit of Sun-Synchronous satellite and therefore circumvents the need for extensive ground support.

  11. Attitude stabilization of a pico-satellite by momentum wheel and magnetic coils

    Institute of Scientific and Technical Information of China (English)

    Tao MENG; Hao WANG; Zhong-he JIN; Ke HAN

    2009-01-01

    The three-axis active attitude control method with a momentum wheel and magnetic coils for a pico-satellite is considered. The designed satellite is a 2.5 kg class satellite stabilized to nadir pointing. The momentum wheel performs a pitch-axis momentum bias, nominally spinning at a particular rate. Three magnetic coils are mounted perpendicularly along the body axis for precise attitude control through the switch control mechanism. Momentum wheel start up control, damping control and attitude acquisition control are considered. Simulation results show that the proposed combined control laws for the pico-satellite is reliable and has an appropriate accuracy under different separation conditions. The proposed strategy to start up the wheel after separation from the launch vehicle shows that its pitch momentum wheel can start up successfully to its nominal speed from rest,and the attitude convergence can be completed within several orbits, depending on separation conditions.

  12. Correction of ZY-3 image distortion caused by satellite jitter via virtual steady reimaging using attitude data

    Science.gov (United States)

    Wang, Mi; Zhu, Ying; Jin, Shuying; Pan, Jun; Zhu, Quansheng

    2016-09-01

    ZiYuan-3 (ZY-3), the first Chinese civilian stereo mapping satellite, suffers from 0.67 Hz satellite jitter that deteriorates its geometric performance in mapping, resource monitoring and other applications. This paper proposes a distortion correction method based on virtual steady reimaging (VSRI) using attitude data to eliminate the negative influence caused by satellite jitter in satellite data preprocessing. VSRI helps linear array pushbroom cameras rescan the ground with a uniform integral time and smooth attitude. In this method, a VSRI model is proposed, and the geometric relationship between the original and corrected image is determined in terms of geolocation consistency based on a rigorous geometric model. Thus, the corrected image is obtained by resampling from the original one. Three areas of ZY-3 three-line images suffering from satellite jitter were used to validate the accuracy and efficiency of the proposed method. First, different attitude interpolation methods were compared. It is found that the Lagrange polynomial model and the cubic piecewise polynomial model have higher interpolation accuracy for original imagery. Then, the replacement accuracy of the rational function model (RFM) for ZY-3 was analyzed with 0.67 Hz satellite jitter. The results indicate that attitude oscillation reduces the fitting precision of the RFM for the rigorous imaging model. Finally, the relative orientation accuracy of the three-line images and the geo-positioning accuracy with ground control points (GCPs) before and after distortion correction were compared. The results show that the distortion caused by satellite jitter is corrected efficiently, and the accuracy of the three experimental datasets is improved in both the image space and the ground space.

  13. Multi-platform Integrated Positioning and Attitude Determination using GNSS

    NARCIS (Netherlands)

    Buist, P.J.

    2013-01-01

    There is trend in spacecraft engineering toward distributed systems where a number of smaller spacecraft work as a larger satellite. However, in order to make the small satellites work together as a single large platform, the precise relative positions (baseline) and orientations (attitude) of the e

  14. Quaternion normalization in spacecraft attitude determination

    Science.gov (United States)

    Deutschmann, J.; Markley, F. L.; Bar-Itzhack, Itzhack Y.

    1993-01-01

    Attitude determination of spacecraft usually utilizes vector measurements such as Sun, center of Earth, star, and magnetic field direction to update the quaternion which determines the spacecraft orientation with respect to some reference coordinates in the three dimensional space. These measurements are usually processed by an extended Kalman filter (EKF) which yields an estimate of the attitude quaternion. Two EKF versions for quaternion estimation were presented in the literature; namely, the multiplicative EKF (MEKF) and the additive EKF (AEKF). In the multiplicative EKF, it is assumed that the error between the correct quaternion and its a-priori estimate is, by itself, a quaternion that represents the rotation necessary to bring the attitude which corresponds to the a-priori estimate of the quaternion into coincidence with the correct attitude. The EKF basically estimates this quotient quaternion and then the updated quaternion estimate is obtained by the product of the a-priori quaternion estimate and the estimate of the difference quaternion. In the additive EKF, it is assumed that the error between the a-priori quaternion estimate and the correct one is an algebraic difference between two four-tuple elements and thus the EKF is set to estimate this difference. The updated quaternion is then computed by adding the estimate of the difference to the a-priori quaternion estimate. If the quaternion estimate converges to the correct quaternion, then, naturally, the quaternion estimate has unity norm. This fact was utilized in the past to obtain superior filter performance by applying normalization to the filter measurement update of the quaternion. It was observed for the AEKF that when the attitude changed very slowly between measurements, normalization merely resulted in a faster convergence; however, when the attitude changed considerably between measurements, without filter tuning or normalization, the quaternion estimate diverged. However, when the

  15. Deploying process modeling and attitude control of a satellite with a large deployable antenna

    OpenAIRE

    Zhigang Xing; Gangtie Zheng

    2014-01-01

    Modeling and attitude control methods for a satellite with a large deployable antenna are studied in the present paper. Firstly, for reducing the model dimension, three dynamic models for the deploying process are developed, which are built with the methods of multi-rigid-body dynamics, hybrid coordinate and substructure. Then an attitude control method suitable for the deploying process is proposed, which can keep stability under any dynamical parameter variation. Subsequently, this attitude...

  16. Attitude Model of a Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data

    Science.gov (United States)

    2005-03-01

    with an in-depth discussion on the model that provides satellite orientation from received telemetry data. 3.1 Hardware This first section talks about... satellite orientation from 5-1 attitude controllers, but a lot of work remains to be done in improving the fidelity of the model in order to achieve more

  17. Guidance and adaptive-robust attitude & orbit control of a small information satellite

    Science.gov (United States)

    Somov, Ye.; Butyrin, S.; Somov, S.; Somova, T.; Testoyedov, N.; Rayevsky, V.; Titov, G.; Yakimov, Ye.; Ovchinnikov, A.; Mathylenko, M.

    2017-01-01

    We consider a small information satellite which may be placed on an orbit with altitude from 600 up to 1000 km. The satellite attitude and orbit control system contains a strap-down inertial navigation system, cluster of four reaction wheels, magnetic driver and a correcting engine unit with eight electro-reaction engines. We study problems on design of algorithms for spatial guidance, in-flight identification and adaptive-robust control of the satellite motion on sun-synchronous orbit.

  18. The study of gravity gradient effect on attitude of low earth orbit satellite

    Science.gov (United States)

    Hamzah, Nor Hazadura; Yaacob, Sazali; Muthusamy, Hariharan; Hamzah, Norhizam; Ghazali, Najah

    2013-04-01

    Simulations and mathematical models are increasingly used to assist the process of decision making in engineering design. The objective of this paper is to simulate the linear attitude dynamics of small satellites under gravity gradient torque which is inherent in low earth orbit. The equations were first derived in their nonlinear form, and then manipulated and simulated in their linear form. Simulation results demonstrate the importance of choosing the appropriate values of satellite's moment of inertia in designing phase of a satellite.

  19. Model predictive control of attitude maneuver of a geostationary flexible satellite based on genetic algorithm

    Science.gov (United States)

    TayyebTaher, M.; Esmaeilzadeh, S. Majid

    2017-07-01

    This article presents an application of Model Predictive Controller (MPC) to the attitude control of a geostationary flexible satellite. SIMO model has been used for the geostationary satellite, using the Lagrange equations. Flexibility is also included in the modelling equations. The state space equations are expressed in order to simplify the controller. Naturally there is no specific tuning rule to find the best parameters of an MPC controller which fits the desired controller. Being an intelligence method for optimizing problem, Genetic Algorithm has been used for optimizing the performance of MPC controller by tuning the controller parameter due to minimum rise time, settling time, overshoot of the target point of the flexible structure and its mode shape amplitudes to make large attitude maneuvers possible. The model included geosynchronous orbit environment and geostationary satellite parameters. The simulation results of the flexible satellite with attitude maneuver shows the efficiency of proposed optimization method in comparison with LQR optimal controller.

  20. Design and simulation of satellite attitude control system based on Simulink and VR

    Science.gov (United States)

    Zhang, Yang; Gan, Qingbo; Kang, Jingshu

    2016-01-01

    In order to research satellite attitude control system design and visual simulation, the simulation framework of satellite dynamics and attitude control using Simulink were established. The design of satellite earth-oriented control system based on quaternion feedback was completed. The 3D scene based on VR was created and models in the scene were driven by simulation data of Simulink. By coordinate transformation. successful observing the scene in inertial coordinate system, orbit coordinate system and body coordinate system. The result shows that application of simulation method of Simulink combined with VR in the design of satellite attitude control system field, has the advantages of high confidence level, hard real-time property, multi-perspective and multi-coordinate system observing the scene, and improves the comprehensibility and accuracy of the design.

  1. The determination of the attitude and attitude dynamics of TeamSat

    DEFF Research Database (Denmark)

    Betto, Maurizio; Jørgensen, John Leif; Riis, Troels

    1999-01-01

    , in space, multiple autonomous processes intended for spacecraft applications such as autonomous star identification, attitude determination and identification and tracking of non-stellar objects, imaging and real-time compression of image and science data for further ground analysis. AVS successfully...... determined the attitude and attitude dynamics of TeamSat....

  2. Vision-Based Attitude and Formation Determination System Project

    Data.gov (United States)

    National Aeronautics and Space Administration — To determine pointing and position vectors in both local and inertial coordinate frames, multi-spacecraft missions typically utilize separate attitude determination...

  3. Satellite cascade attitude control via fuzzy PD controller with active force control under momentum dumping

    Science.gov (United States)

    Ismail, Z.; Varatharajoo, R.

    2016-10-01

    In this paper, fuzzy proportional-derivative (PD) controller with active force control (AFC) scheme is studied and employed in the satellite attitude control system equipped with reaction wheels. The momentum dumping is enabled via proportional integral (PI) controller as the system is impractical without momentum dumping control. The attitude controllers are developed together with their governing equations and evaluated through numerical treatment with respect to a reference satellite mission. From the results, it is evident that the three axis attitudes accuracies can be improved up to ±0.001 degree through the fuzzy PD controller with AFC scheme for the attitude control. In addition, the three-axis wheel angular momentums are well maintained during the attitude control tasks.

  4. GPS Attitude Determination for Launch Vehicles Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Toyon Research Corporation proposes to develop a family of compact, low-cost GPS-based attitude (GPS/A) sensors for launch vehicles. In order to obtain 3-D attitude...

  5. Access to Attitude-Relevant Information in Memory as a Determinant of Attitude-Behavior Consistency.

    Science.gov (United States)

    Kallgren, Carl A.; Wood, Wendy

    Recent reserach has attempted to determine systematically how attitudes influence behavior. This research examined whether access to attitude-relevant beliefs and prior experiences would mediate the relation between attitudes and behavior. Subjects were 49 college students with a mean age of 27 who did not live with their parents or in…

  6. Three-Axis Satellite Attitude Control Based on Magnetic Torquing

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    1995-01-01

    Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics.......Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics....

  7. Three-Axis Satellite Attitude Control Based on Magnetic Torquing

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    1995-01-01

    Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics.......Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics....

  8. Integrated power and attitude control of a rigid satellite with onboard magnetic bearing suspended rigid flywheels

    Science.gov (United States)

    Kim, Yeonkyu

    2003-10-01

    A system of differential equations governing the translational and rotational motion of a system model consisting of a rigid satellite and multiple MB suspended rigid flywheels in general configuration is developed. Flywheel modules are contained in a housing rigidly mounted on the satellite and floated by an active MB suspension system, therefore each flywheel module has six degrees of freedom (DOF) as well as the satellite module. Equations of motion for the satellite and flywheels are naturally coupled and the satellite rotational motion and translational motion are coupled. A nonlinear state feedback tracking control law, which is globally asymptotically stable, is developed following a Lyapunov stability theory for integrated power and attitude control using the MB suspended flywheels. The stability, robustness, and tracking and disturbance rejection performance of the present control law with respect to initial attitude error, system modeling error, an imbalance disturbance, is demonstrated by case studies. The satellite departure motion equation derived from the definition of the angular velocity error and the system dynamics equations is presented. Application study of existing power tracking algorithm with this control law shows perfect power tracking for both power charging from and power delivery to the satellite operations and the power tracking can be performed simultaneously with and independent of the attitude control function.

  9. A new method for determination of satellite orbits by transfer

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The original idea of a new method for determination of satellite orbits by transfer is from Two-Way Satellite Time and Frequency Transfer (TWSTFT). The original method is called "determination of satellite orbit by transfer". The method is not only for determination of satellite orbit but also for the time transfer with high accuracy and precision. The advantage is that the accuracy and the precision for determination of satellite orbit are very high and the new method is favorable for various applications. The combination of various signals disseminated and received forms various modes of satellite orbit determinations. If receivers at stations receive the own station-disseminated signals via a satellite transponder, it forms an orbit determination mode called "receiving the own station-disseminated signals mode". If receivers at all stations receive the signals disseminated from the master station via satellite transponders, it forms an orbit determination mode called "receiving the master station-disseminated signals mode". If all of receivers at stations receive all stations-disseminated signals via satellite transponders, it forms an orbit determination mode called "receiving all stations-disseminated signals mode". Also there are other combinations of signals for satellite orbit determination. For dif- ferent orbit determination modes with different signal combinations, their rigorous formulae of proc- essing are hereby presented in this paper. The accurate and the precise satellite orbit determination for both of the modes, "receiving the own station-disseminated signals mode" and "receiving the master station-disseminated signals mode" is attempted. It shows that the accuracy and precision for both of modes are nearly the same, the ranging accuracy is better than 1 cm, and the observation residuals of satellite orbit determination are better than 9 cm in the observation duration of 1 day.

  10. A new method for determination of satellite orbits by transfer

    Institute of Scientific and Technical Information of China (English)

    LI ZhiGang; YANG XuHai; AI GuoXiang; SI HuLi; QIAO RongChuan; FENG ChuGang

    2009-01-01

    The original idea of a new method for determination of satellite orbits by transfer is from Two-Way Satellite Time and Frequency Transfer (TWSTFT).The original method is called "determination of satellite orbit by transfer".The method is not only for determination of satellite orbit but also for the time transfer with high accuracy and precision.The advantage is that the accuracy and the precision for determination of satellite orbit are very high and the new method is favorable for various applications.The combination of various signals disseminated and received forms various modes of satellite orbit determinations.If receivers at stations receive the own station-disseminated signals via a satellite transponder,it forms an orbit determination mode called "receiving the own station-disseminated signals mode".If receivers at all stations receive the signals disseminated from the master station via satellite transponders,it forms an orbit determination mode called "receiving the master station-disseminated signals mode".If all of receivers at stations receive all stations-disseminated signals via satellite transponders,it forms an orbit determination mode called "receiving all stations-disseminated signals mode".Also there are other combinations of signals for satellite orbit determination.For different orbit determination modes with different signal combinations,their rigorous formulae of processing are hereby presented in this paper.The accurate and the precise satellite orbit determination for both of the modes,"receiving the own station-disseminated signals mode" and "receiving the master station-disseminated signals mode" is attempted.It shows that the accuracy and precision for both of modes are nearly the same,the ranging accuracy is better than 1 cm,and the observation residuals of satellite orbit determination are better than 9 cm in the observation duration of 1 day.

  11. Performance analysis of a GPS Interferometric attitude determination system for a gravity gradient stabilized spacecraft. M.S. Thesis

    Science.gov (United States)

    Stoll, John C.

    1995-01-01

    The performance of an unaided attitude determination system based on GPS interferometry is examined using linear covariance analysis. The modelled system includes four GPS antennae onboard a gravity gradient stabilized spacecraft, specifically the Air Force's RADCAL satellite. The principal error sources are identified and modelled. The optimal system's sensitivities to these error sources are examined through an error budget and by varying system parameters. The effects of two satellite selection algorithms, Geometric and Attitude Dilution of Precision (GDOP and ADOP, respectively) are examined. The attitude performance of two optimal-suboptimal filters is also presented. Based on this analysis, the limiting factors in attitude accuracy are the knowledge of the relative antenna locations, the electrical path lengths from the antennae to the receiver, and the multipath environment. The performance of the system is found to be fairly insensitive to torque errors, orbital inclination, and the two satellite geometry figures-of-merit tested.

  12. Attitude Determination Error Analysis System (ADEAS) mathematical specifications document

    Science.gov (United States)

    Nicholson, Mark; Markley, F.; Seidewitz, E.

    1988-01-01

    The mathematical specifications of Release 4.0 of the Attitude Determination Error Analysis System (ADEAS), which provides a general-purpose linear error analysis capability for various spacecraft attitude geometries and determination processes, are presented. The analytical basis of the system is presented. The analytical basis of the system is presented, and detailed equations are provided for both three-axis-stabilized and spin-stabilized attitude sensor models.

  13. Attitude dynamics of gyrostat-satellites under control by magnetic actuators at small perturbations

    Science.gov (United States)

    Doroshin, Anton V.

    2017-08-01

    The angular motion of gyrostat-satellites with one axial rotor is considered under control by magnetic actuators and at the action of small polyharmonic perturbations of the own dipole magnetic moment's components which are created proportionally to components of the angular velocity of the satellite. The attitude dynamics is investigated in conditions of the coincidence of the vector of magnetic induction of the external magnetic field and the initial angular momentum vector of the satellite. General and heteroclinic analytical solutions are obtained for dynamical parameters at the relative smallness of the magnetic torques. The chaotic regimes are examined on the base of the Melnikov method and Poincaré sections.

  14. Rotation Matrix Method Based on Ambiguity Function for GNSS Attitude Determination.

    Science.gov (United States)

    Yang, Yingdong; Mao, Xuchu; Tian, Weifeng

    2016-06-08

    Global navigation satellite systems (GNSS) are well suited for attitude determination. In this study, we use the rotation matrix method to resolve the attitude angle. This method achieves better performance in reducing computational complexity and selecting satellites. The condition of the baseline length is combined with the ambiguity function method (AFM) to search for integer ambiguity, and it is validated in reducing the span of candidates. The noise error is always the key factor to the success rate. It is closely related to the satellite geometry model. In contrast to the AFM, the LAMBDA (Least-squares AMBiguity Decorrelation Adjustment) method gets better results in solving the relationship of the geometric model and the noise error. Although the AFM is more flexible, it is lack of analysis on this aspect. In this study, the influence of the satellite geometry model on the success rate is analyzed in detail. The computation error and the noise error are effectively treated. Not only is the flexibility of the AFM inherited, but the success rate is also increased. An experiment is conducted in a selected campus, and the performance is proved to be effective. Our results are based on simulated and real-time GNSS data and are applied on single-frequency processing, which is known as one of the challenging case of GNSS attitude determination.

  15. Attitude motion compensation for imager on Fengyun-4 geostationary meteorological satellite

    Science.gov (United States)

    Lyu, Wang; Dai, Shoulun; Dong, Yaohai; Shen, Yili; Song, Xiaozheng; Wang, Tianshu

    2017-09-01

    A compensation method is used in Chinese Fengyun-4 satellite to counteracting the line-of-sight influence by attitude motion during imaging. The method is acted on-board by adding the compensation amount to the instrument scanning control circuit. The mathematics simulation and the three-axis air-bearing test results show that the method works effectively.

  16. An adaptive Multiplicative Extened Kalman Filter for Attitude Estimation of Marine Satellite Tracking Antenna

    DEFF Research Database (Denmark)

    Wang, Yunlong; Soltani, Mohsen; Hussain, Dil muhammed Akbar

    2016-01-01

    , an adaptive Multiplicative Extended Kalman Filter (MEKF) for attitude estimation of Marine Satellite Tracking Antenna (MSTA) is presented with the measurement noise covariance matrix adjusted according to the norm of accelerometer measurements, which can significantly reduce the slamming influence from waves...

  17. Solar attitude control including active nutation damping in a fixed-momentum wheel satellite

    Science.gov (United States)

    Azor, Ruth

    1992-08-01

    In geostationary cruise of a momentum biased satellite, it is necessary to stabilize the roll/yaw attitude due to disturbances, caused mainly by solar pressure. This work presents a roll/yaw control, which is obtained by the use of solar arrays and fixed flaps as actuators, with a horizon sensor for roll measurement. The design also includes an active nutation damping.

  18. Orbit and Attitude Control of Asymmetric Satellites in Polar Near-Circular Orbit

    Directory of Open Access Journals (Sweden)

    Wei Zhao

    2009-10-01

    Full Text Available In this paper, the general problem about the orbit and attitude dynamic model is discussed. A feedback linearization control method is introduced for this model. Due to the asymmetric structure, the orbital properties of such satellites are the same as traditional symmetric ones, but the attitude properties are greatly different from the symmetric counterparts. With perturbations accumulate with time, the attitude angles increase periodically with time, but the orbital elements change much slower than the attitude angles. In the attitude dynamic model, chaos could appear. Traditional linear controllers can not compensate enough for asymmetric satellite when the mission is complex, especially in maneuver missions. Thus nonlinear control method is required to solve such problem in large scale. A feedback linearization method, one robust nonlinear control method, is introduced and applied to the asymmetric satellite in this paper. Some simulations are also given and the results show that feedback linearization controller not only stabilizes the system, but also exempt the chaos in the system.

  19. Autonomous satellite constellation orbit determination using the star sensor and inter-satellite links data

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A method of autonomous orbit determination for a satellite constellation using a star sensor combined with inter satellite links(ISLs) is studied.Two types of simulated observation data,Three-Satellite Constellation ISLs and background stellar observations by a CCD star sensor,are first produced.Based on these data,an observation equation is built for the constellation joint autonomous orbit determination,in which the simulations are run.The accuracy of this method with different orbital determination models are analyzed and compared with regard to the effect of potential measurement errors.The results show that autonomous satellite constellation orbit determination using star sensor measurement and ISLs data is feasible.Finally,this paper arrives at several conclusions which contribute to extending this method to a more general satellite constellation.

  20. Robust double gain unscented Kalman filter for small satellite attitude estimation

    Science.gov (United States)

    Cao, Lu; Yang, Weiwei; Li, Hengnian; Zhang, Zhidong; Shi, Jianjun

    2017-08-01

    Limited by the low precision of small satellite sensors, the estimation theories with high performance remains the most popular research topic for the attitude estimation. The Kalman filter (KF) and its extensions have been widely applied in the satellite attitude estimation and achieved plenty of achievements. However, most of the existing methods just take use of the current time-step's priori measurement residuals to complete the measurement update and state estimation, which always ignores the extraction and utilization of the previous time-step's posteriori measurement residuals. In addition, the uncertainty model errors always exist in the attitude dynamic system, which also put forward the higher performance requirements for the classical KF in attitude estimation problem. Therefore, the novel robust double gain unscented Kalman filter (RDG-UKF) is presented in this paper to satisfy the above requirements for the small satellite attitude estimation with the low precision sensors. It is assumed that the system state estimation errors can be exhibited in the measurement residual; therefore, the new method is to derive the second Kalman gain Kk2 for making full use of the previous time-step's measurement residual to improve the utilization efficiency of the measurement data. Moreover, the sequence orthogonal principle and unscented transform (UT) strategy are introduced to robust and enhance the performance of the novel Kalman Filter in order to reduce the influence of existing uncertainty model errors. Numerical simulations show that the proposed RDG-UKF is more effective and robustness in dealing with the model errors and low precision sensors for the attitude estimation of small satellite by comparing with the classical unscented Kalman Filter (UKF).

  1. Unscented Kalman Filter for Autonomous Warship Attitude Determination

    Institute of Scientific and Technical Information of China (English)

    FU Jian-guo; WANG Xiao-tong; JIN Lian-gan; MA Ye

    2005-01-01

    To address a problem of autonomous attitude determination algorithm using gravitational field and geomagnetic field observation, a new recursive optimization autonomous attitude estimation algorithm is proposed. The algorithm is based on unscented Kalman filter(UKF), and can synchronously provide the attitude rate information. The simulated results show that the measurement precision of the method could be increased by 2 times compared to that of the common methods.

  2. Performance analysis of an integrated GPS/inertial attitude determination system. M.S. Thesis - MIT

    Science.gov (United States)

    Sullivan, Wendy I.

    1994-01-01

    The performance of an integrated GPS/inertial attitude determination system is investigated using a linear covariance analysis. The principles of GPS interferometry are reviewed, and the major error sources of both interferometers and gyroscopes are discussed and modeled. A new figure of merit, attitude dilution of precision (ADOP), is defined for two possible GPS attitude determination methods, namely single difference and double difference interferometry. Based on this figure of merit, a satellite selection scheme is proposed. The performance of the integrated GPS/inertial attitude determination system is determined using a linear covariance analysis. Based on this analysis, it is concluded that the baseline errors (i.e., knowledge of the GPS interferometer baseline relative to the vehicle coordinate system) are the limiting factor in system performance. By reducing baseline errors, it should be possible to use lower quality gyroscopes without significantly reducing performance. For the cases considered, single difference interferometry is only marginally better than double difference interferometry. Finally, the performance of the system is found to be relatively insensitive to the satellite selection technique.

  3. Quaternion normalization in additive EKF for spacecraft attitude determination. [Extended Kalman Filters

    Science.gov (United States)

    Bar-Itzhack, I. Y.; Deutschmann, J.; Markley, F. L.

    1991-01-01

    This work introduces, examines and compares several quaternion normalization algorithms, which are shown to be an effective stage in the application of the additive extended Kalman filter to spacecraft attitude determination, which is based on vector measurements. Three new normalization schemes are introduced. They are compared with one another and with the known brute force normalization scheme, and their efficiency is examined. Simulated satellite data are used to demonstate the performance of all four schemes.

  4. High Accuracy Attitude Control System Design for Satellite with Flexible Appendages

    Directory of Open Access Journals (Sweden)

    Wenya Zhou

    2014-01-01

    Full Text Available In order to realize the high accuracy attitude control of satellite with flexible appendages, attitude control system consisting of the controller and structural filter was designed. When the low order vibration frequency of flexible appendages is approximating the bandwidth of attitude control system, the vibration signal will enter the control system through measurement device to bring impact on the accuracy or even the stability. In order to reduce the impact of vibration of appendages on the attitude control system, the structural filter is designed in terms of rejecting the vibration of flexible appendages. Considering the potential problem of in-orbit frequency variation of the flexible appendages, the design method for the adaptive notch filter is proposed based on the in-orbit identification technology. Finally, the simulation results are given to demonstrate the feasibility and effectiveness of the proposed design techniques.

  5. Federated nonlinear predictive filtering for the gyroless attitude determination system

    Science.gov (United States)

    Zhang, Lijun; Qian, Shan; Zhang, Shifeng; Cai, Hong

    2016-11-01

    This paper presents a federated nonlinear predictive filter (NPF) for the gyroless attitude determination system with star sensor and Global Positioning System (GPS) sensor. This approach combines the good qualities of both the NPF and federated filter. In order to combine them, the equivalence relationship between the NPF and classical Kalman filter (KF) is demonstrated from algorithm structure and estimation criterion. The main features of this approach include a nonlinear predictive filtering algorithm to estimate uncertain model errors and determine the spacecraft attitude by using attitude kinematics and dynamics, and a federated filtering algorithm to process measurement data from multiple attitude sensors. Moreover, a fault detection and isolation algorithm is applied to the proposed federated NPF to improve the estimation accuracy even when one sensor fails. Numerical examples are given to verify the navigation performance and fault-tolerant performance of the proposed federated nonlinear predictive attitude determination algorithm.

  6. A Performance Improvement Method for Low-Cost Land Vehicle GPS/MEMS-INS Attitude Determination

    Directory of Open Access Journals (Sweden)

    Li Cong

    2015-03-01

    Full Text Available Global positioning system (GPS technology is well suited for attitude determination. However, in land vehicle application, low-cost single frequency GPS receivers which have low measurement quality are often used, and external factors such as multipath and low satellite visibility in the densely built-up urban environment further degrade the quality of the GPS measurements. Due to the low-quality receivers used and the challenging urban environment, the success rate of the single epoch ambiguity resolution for dynamic attitude determination is usually quite low. In this paper, a micro-electro-mechanical system (MEMS—inertial navigation system (INS-aided ambiguity resolution method is proposed to improve the GPS attitude determination performance, which is particularly suitable for land vehicle attitude determination. First, the INS calculated baseline vector is augmented with the GPS carrier phase and code measurements. This improves the ambiguity dilution of precision (ADOP, resulting in better quality of the unconstrained float solution. Second, the undesirable float solutions caused by large measurement errors are further filtered and replaced using the INS-aided ambiguity function method (AFM. The fixed solutions are then obtained by the constrained least squares ambiguity decorrelation (CLAMBDA algorithm. Finally, the GPS/MEMS-INS integration is realized by the use of a Kalman filter. Theoretical analysis of the ADOP is given and experimental results demonstrate that our proposed method can significantly improve the quality of the float ambiguity solution, leading to high success rate and better accuracy of attitude determination.

  7. A performance improvement method for low-cost land vehicle GPS/MEMS-INS attitude determination.

    Science.gov (United States)

    Cong, Li; Li, Ercui; Qin, Honglei; Ling, Keck Voon; Xue, Rui

    2015-03-09

    Global positioning system (GPS) technology is well suited for attitude determination. However, in land vehicle application, low-cost single frequency GPS receivers which have low measurement quality are often used, and external factors such as multipath and low satellite visibility in the densely built-up urban environment further degrade the quality of the GPS measurements. Due to the low-quality receivers used and the challenging urban environment, the success rate of the single epoch ambiguity resolution for dynamic attitude determination is usually quite low. In this paper, a micro-electro-mechanical system (MEMS)-inertial navigation system (INS)-aided ambiguity resolution method is proposed to improve the GPS attitude determination performance, which is particularly suitable for land vehicle attitude determination. First, the INS calculated baseline vector is augmented with the GPS carrier phase and code measurements. This improves the ambiguity dilution of precision (ADOP), resulting in better quality of the unconstrained float solution. Second, the undesirable float solutions caused by large measurement errors are further filtered and replaced using the INS-aided ambiguity function method (AFM). The fixed solutions are then obtained by the constrained least squares ambiguity decorrelation (CLAMBDA) algorithm. Finally, the GPS/MEMS-INS integration is realized by the use of a Kalman filter. Theoretical analysis of the ADOP is given and experimental results demonstrate that our proposed method can significantly improve the quality of the float ambiguity solution, leading to high success rate and better accuracy of attitude determination.

  8. Unscented predictive variable structure filter for satellite attitude estimation with model errors when using low precision sensors

    Science.gov (United States)

    Cao, Lu; Li, Hengnian

    2016-10-01

    For the satellite attitude estimation problem, the serious model errors always exist and hider the estimation performance of the Attitude Determination and Control System (ACDS), especially for a small satellite with low precision sensors. To deal with this problem, a new algorithm for the attitude estimation, referred to as the unscented predictive variable structure filter (UPVSF) is presented. This strategy is proposed based on the variable structure control concept and unscented transform (UT) sampling method. It can be implemented in real time with an ability to estimate the model errors on-line, in order to improve the state estimation precision. In addition, the model errors in this filter are not restricted only to the Gaussian noises; therefore, it has the advantages to deal with the various kinds of model errors or noises. It is anticipated that the UT sampling strategy can further enhance the robustness and accuracy of the novel UPVSF. Numerical simulations show that the proposed UPVSF is more effective and robustness in dealing with the model errors and low precision sensors compared with the traditional unscented Kalman filter (UKF).

  9. Linear Time Varying Approach to Satellite Attitude Control Using only Electromagnetic Actuation

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    1997-01-01

    Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technological improvement of micro-electronics. Required pointing accuracy of small, inexpensive satellites is often relatively loose, within a couple of degrees. Application of cheap......, lightweight, and power efficient actuators is therefore crucial and viable. This paper discusses linear attitude control strategies for a low earth orbit satellite actuated by a set of mutually perpendicular electromagnetic coils. The principle is to use the interaction between the Earth's magnetic field...... and the magnetic field generated by the coils. A key challenge is the fact that the mechanical torque can only be produced in a plane perpendicular to the local geomagnetic field vector, therefore the satellite is not controllable when considered at fixed time. Availability of design methods for time varying...

  10. Linear Time Varying Approach to Satellite Attitude Control Using only Electromagnetic Actuation

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    2000-01-01

    Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technological improvemant of micro-electronics. Required pointing accuracy of small, inexpensive satellites is often relatively loose, within a couple of degrees. Application of cheap......, lightweight, and power efficient actuators is therefore crucial and viable. This paper discusser linear attitude control strategies for a low earth orbit satellite actuated by a set of mutually perpendicular electromagnetic coils. The principle is to use the interaction between the Earth's magnetic field...... and the magnetic field generated by the coils. A key challenge is the fact that the mechanical torque can only be produced in a plane perpendicular to the local geomagnetic field vector, therefore the satellite is not controllable at fixed time. Avaliability of design methods for time varying systems is limited...

  11. A Comparative Study of Actuator Configurations for Satellite Attitude Control

    Directory of Open Access Journals (Sweden)

    Raymond Kristiansen

    2005-10-01

    Full Text Available In this paper a controllability study of different actuator configurations consisting of magnetic torquers, reaction wheels and a gravity boom is presented. The theoretical analysis is performed with use of controllability gramians, and simulation results with the different configurations are presented and compared regarding settling time and power consumption to substantiate the theoretical analysis. A reference model is also introduced to show how the power consumption can he lowered to the same magnitude as when magnetic torquers are used, without degrading the satellite response significantly.

  12. Attitude Control Synthesis for Small Satellites Using Gradient Method. Part I - Nonlinear Equations

    Directory of Open Access Journals (Sweden)

    Teodor-Viorel CHELARU

    2012-12-01

    Full Text Available The paper presents some aspects for synthesis of small satellites attitude control. Thesatellite nonlinear model presented here will be with six degrees of freedom. After movement equationlinearization the stability and command matrixes will be established and the controller will beobtained using gradient and gradient method. Two attitude control cases will be analysed: thereaction wheels and the micro thrusters. The results will be used in the project European Space MoonOrbit - ESMO founded by European Space Agency in which the University POLITEHNICA ofBucharest is involved.

  13. Attitude Control Synthesis for Small Satellites Using Gradient Method. Part II Linear Equations, Synthesis

    Directory of Open Access Journals (Sweden)

    Adrian CHELARU

    2013-03-01

    Full Text Available In order to continue paper [5] which presented the nonlinear equations of the movement for small satellite, this paper presents some aspects regarding the synthesis of the attitude control. Afterthe movement equation linearization, the stability and command matrixes will be established and by using the gradient methods controller we will obtain them. Two attitude control cases will beanalysed: the reaction wheels and the micro thrusters. The results will be used in the project European Space Moon Orbit - ESMO, founded by the European Space Agency in which the POLITEHNICA University of Bucharest is involved.

  14. Personality and Attitude Determinants of Voting Behavior

    Science.gov (United States)

    Brigham, John C.; Severy, Lawrence J.

    1976-01-01

    Measures of racial attitude, conceptual style, commitment to candidate and electoral process, social-political evaluation, and voting intentions, were administered to white college students (N=320) before the 1972 Presidential election. Prediction of behavioral intentions becomes more powerful as attitudinal measures are made more directly…

  15. Determinants of Student Attitudes toward Team Exams

    Science.gov (United States)

    Reinig, Bruce A.; Horowitz, Ira; Whittenburg, Gene

    2014-01-01

    We examine how student attitudes toward their group, learning method, and perceived development of professional skills are initially shaped and subsequently evolve through multiple uses of team exams. Using a Tobit regression model to analyse a sequence of 10 team quizzes given in a graduate-level tax accounting course, we show that there is an…

  16. DETERMINATION OF THE EARTH’S GEOID BY SATELLITE OBSERVATIONS

    Science.gov (United States)

    Determinations of the geoid made by different authors have differed by more than forty meters in some geographic locations. The authors differed in...conducted with Doppler observations on satellites have shown moderate variations (rarely as much as 30 meters) in the geoid determined if the number of...satellite orbital inclinations employed is reduced by one. Reduction of the number of gravity parameters used to represent the geoid also resulted in

  17. Orbit Propagation and Determination of Low Earth Orbit Satellites

    OpenAIRE

    Ho-Nien Shou

    2014-01-01

    This paper represents orbit propagation and determination of low Earth orbit (LEO) satellites. Satellite global positioning system (GPS) configured receiver provides position and velocity measures by navigating filter to get the coordinates of the orbit propagation (OP). The main contradictions in real-time orbit which is determined by the problem are orbit positioning accuracy and the amount of calculating two indicators. This paper is dedicated to solving the problem of tradeoffs. To plan t...

  18. Attitude control for part actuator failure of agile small satellite

    Institute of Scientific and Technical Information of China (English)

    J. R. Zhang; A. Rachid; Y. Zhang

    2008-01-01

    The stability and singularity problem of agile small satellite (ASS) with actuator failure is discussed in this paper. Firstly, the three-axis stabilized controller of an ASS is designed, where micro control moment gyros (MCMG's) in pyramid configuration (PC) is used as the actuator. By using the same controller and steering law, the control results before and after one gyro fails are compared by simulation. The variation of singular momentum envelope before and after one gyro fails is also compared. The simulation results show that the failure intensively decreases the capacity of output torque, which leads to the emergence of more singular points and the rapid saturation of MCMG's. Finally, the parameters of system controller are changed to compare the control effect.

  19. Synthetically adaptive robust filtering for satellite orbit determination

    Institute of Scientific and Technical Information of China (English)

    YANG; Yuanxi

    2004-01-01

    The quality of the satellite orbit determination is rested on the knowledge of perturbing forces acting on the satellite and stochastic properties of the observations, and the ability of controlling various kinds of errors. After a brief discussion on the dynamic and geometric orbit determinations, Sage adaptive filtering and robust filtering are reviewed. A new synthetically adaptive robust filtering based on a combination of robust filtering and Sage filtering is developed. It is shown, by derivations and calculations, that the synthetically adaptive robust filtering for orbit determination is not only robust but also simple in calculation. It controls the effects of the outliers of tracking observations and the satellite dynamical disturbance on the parameter estimates of the satellite orbit.

  20. Multiagent Attitude Control System for Satellites Based in Momentum Wheels and Event-Driven Synchronization

    Science.gov (United States)

    Garcia, Juan L.; Moreno, Jose Sanchez

    2012-12-01

    Attitude control is a requirement always present in spacecraft design. Several kinds of actuators exist to accomplish this control, being momentum wheels one of the most employed. Usually satellites carry redundant momentum wheels to handle any possible single failure, but the controller remains as a single centralized element, posing problems in case of failures. In this work a decentralized agent-based event-driven algorithm for attitude control is presented as a possible solution. Several agents based in momentum wheels will interact among them to accomplish the satellite control. A simulation environment has been developed to analyze the behavior of this architecture. This environment has been made available through the web page http://www.dia.uned.es.

  1. Solar sail attitude control including active nutation damping in a fixed-momentum wheel satellite

    Science.gov (United States)

    Azor, Ruth

    1992-02-01

    In the geostationary cruise of a momentum biased satellite, it is necessary to stabilize the roll/yaw attitude due to disturbances caused by solar radiation pressure. This work presents a roll/yaw control system with a horizon sensor for roll measurement. Roll/yaw control is obtained by the use of solar arrays and fixed flaps as actuators. The design also includes an active nutation damping method.

  2. Rate-gyro-integral constraint for ambiguity resolution in GNSS attitude determination applications.

    Science.gov (United States)

    Zhu, Jiancheng; Li, Tao; Wang, Jinling; Hu, Xiaoping; Wu, Meiping

    2013-06-21

    In the field of Global Navigation Satellite System (GNSS) attitude determination, the constraints usually play a critical role in resolving the unknown ambiguities quickly and correctly. Many constraints such as the baseline length, the geometry of multi-baselines and the horizontal attitude angles have been used extensively to improve the performance of ambiguity resolution. In the GNSS/Inertial Navigation System (INS) integrated attitude determination systems using low grade Inertial Measurement Unit (IMU), the initial heading parameters of the vehicle are usually worked out by the GNSS subsystem instead of by the IMU sensors independently. However, when a rotation occurs, the angle at which vehicle has turned within a short time span can be measured accurately by the IMU. This measurement will be treated as a constraint, namely the rate-gyro-integral constraint, which can aid the GNSS ambiguity resolution. We will use this constraint to filter the candidates in the ambiguity search stage. The ambiguity search space shrinks significantly with this constraint imposed during the rotation, thus it is helpful to speeding up the initialization of attitude parameters under dynamic circumstances. This paper will only study the applications of this new constraint to land vehicles. The impacts of measurement errors on the effect of this new constraint will be assessed for different grades of IMU and current average precision level of GNSS receivers. Simulations and experiments in urban areas have demonstrated the validity and efficacy of the new constraint in aiding GNSS attitude determinations.

  3. Determination of the key parameters affecting historic communications satellite trends

    Science.gov (United States)

    Namkoong, D.

    1984-01-01

    Data representing 13 series of commercial communications satellites procured between 1968 and 1982 were analyzed to determine the factors that have contributed to the general reduction over time of the per circuit cost of communications satellites. The model by which the data were analyzed was derived from a general telecommunications application and modified to be more directly applicable for communications satellites. In this model satellite mass, bandwidth-years, and technological change were the variable parameters. A linear, least squares, multiple regression routine was used to obtain the measure of significance of the model. Correlation was measured by coefficient of determination (R super 2) and t-statistic. The results showed that no correlation could be established with satellite mass. Bandwidth-year however, did show a significant correlation. Technological change in the bandwidth-year case was a significant factor in the model. This analysis and the conclusions derived are based on mature technologies, i.e., satellite designs that are evolutions of earlier designs rather than the first of a new generation. The findings, therefore, are appropriate to future satellites only if they are a continuation of design evolution.

  4. Algorithm of orbit determination using one or two GPS satellites

    Institute of Scientific and Technical Information of China (English)

    刘艳芳; 洪炳荣; 郭建宁; 巨涛

    1999-01-01

    The problem of orbit determination using one or two GPS satellites is discussed. Methods of getting initial values based on linear translation is presented; the Secant method and the descend Newton iterative procedure and the continuation algorithm are used synthetically to solve the nonlinear equations. Computer simulation shows that this algorithm can give preliminary state of satellite orbit with a certain precision in short time.

  5. Advancements of in-flight mass moment of inertia and structural deflection algorithms for satellite attitude simulators

    Science.gov (United States)

    Wright, Jonathan W.

    Experimental satellite attitude simulators have long been used to test and analyze control algorithms in order to drive down risk before implementation on an operational satellite. Ideally, the dynamic response of a terrestrial-based experimental satellite attitude simulator would be similar to that of an on-orbit satellite. Unfortunately, gravitational disturbance torques and poorly characterized moments of inertia introduce uncertainty into the system dynamics leading to questionable attitude control algorithm experimental results. This research consists of three distinct, but related contributions to the field of developing robust satellite attitude simulators. In the first part of this research, existing approaches to estimate mass moments and products of inertia are evaluated followed by a proposition and evaluation of a new approach that increases both the accuracy and precision of these estimates using typical on-board satellite sensors. Next, in order to better simulate the micro-torque environment of space, a new approach to mass balancing satellite attitude simulator is presented, experimentally evaluated, and verified. Finally, in the third area of research, we capitalize on the platform improvements to analyze a control moment gyroscope (CMG) singularity avoidance steering law. Several successful experiments were conducted with the CMG array at near-singular configurations. An evaluation process was implemented to verify that the platform remained near the desired test momentum, showing that the first two components of this research were effective in allowing us to conduct singularity avoidance experiments in a representative space-like test environment.

  6. Instantaneous GNSS attitude determination: A Monte Carlo sampling approach

    Science.gov (United States)

    Sun, Xiucong; Han, Chao; Chen, Pei

    2017-04-01

    A novel instantaneous GNSS ambiguity resolution approach which makes use of only single-frequency carrier phase measurements for ultra-short baseline attitude determination is proposed. The Monte Carlo sampling method is employed to obtain the probability density function of ambiguities from a quaternion-based GNSS-attitude model and the LAMBDA method strengthened with a screening mechanism is then utilized to fix the integer values. Experimental results show that 100% success rate could be achieved for ultra-short baselines.

  7. Optimizing the Attitude Control of Small Satellite Constellations for Rapid Response Imaging

    Science.gov (United States)

    Nag, S.; Li, A.

    2016-12-01

    Distributed Space Missions (DSMs) such as formation flight and constellations, are being recognized as important solutions to increase measurement samples over space and time. Given the increasingly accurate attitude control systems emerging in the commercial market, small spacecraft now have the ability to slew and point within few minutes of notice. In spite of hardware development in CubeSats at the payload (e.g. NASA InVEST) and subsystems (e.g. Blue Canyon Technologies), software development for tradespace analysis in constellation design (e.g. Goddard's TAT-C), planning and scheduling development in single spacecraft (e.g. GEO-CAPE) and aerial flight path optimizations for UAVs (e.g. NASA Sensor Web), there is a gap in open-source, open-access software tools for planning and scheduling distributed satellite operations in terms of pointing and observing targets. This paper will demonstrate results from a tool being developed for scheduling pointing operations of narrow field-of-view (FOV) sensors over mission lifetime to maximize metrics such as global coverage and revisit statistics. Past research has shown the need for at least fourteen satellites to cover the Earth globally everyday using a LandSat-like sensor. Increasing the FOV three times reduces the need to four satellites, however adds image distortion and BRDF complexities to the observed reflectance. If narrow FOV sensors on a small satellite constellation were commanded using robust algorithms to slew their sensor dynamically, they would be able to coordinately cover the global landmass much faster without compensating for spatial resolution or BRDF effects. Our algorithm to optimize constellation satellite pointing is based on a dynamic programming approach under the constraints of orbital mechanics and existing attitude control systems for small satellites. As a case study for our algorithm, we minimize the time required to cover the 17000 Landsat images with maximum signal to noise ratio fall

  8. A vectorial bootstrapping approach for integrated GNSS-based relative positioning and attitude determination of spacecraft

    Science.gov (United States)

    Buist, Peter J.; Teunissen, Peter J. G.; Verhagen, Sandra; Giorgi, Gabriele

    2011-04-01

    Traditionally in multi-spacecraft missions (e.g. formation flying, rendezvous) the GNSS-based relative positioning and attitude determination problem are treated as independent. In this contribution we will investigate the possibility to use multi-antenna data from each spacecraft, not only for attitude determination, but also to improve the relative positioning between spacecraft. Both for ambiguity resolution and accuracy of the baseline solution, we will show the theoretical improvement achievable as a function of the number of antennas on each platform. We concentrate on ambiguity resolution as the key to precise relative positioning and attitude determination and will show the theoretical limit of this kind of approach. We will use mission parameters of the European Proba-3 satellites in a software-based algorithm verification and a hardware-in-the-loop simulation. The software simulations indicated that this approach can improve single epoch ambiguity resolution up to 50% for relative positioning applying the typical antenna configurations for attitude determination. The hardware-in-the-loop simulations show that for the same antenna configurations, the accuracy of the relative positioning solution can improve up to 40%.

  9. Testing a new multivariate GNSS carrier phase attitude determination method for remote sensing platforms

    Science.gov (United States)

    Giorgi, Gabriele; Teunissen, Peter J. G.; Verhagen, Sandra; Buist, Peter J.

    2010-07-01

    GNSS (Global Navigation Satellite Systems)-based attitude determination is an important field of study, since it is a valuable technique for the orientation estimation of remote sensing platforms. To achieve highly accurate angular estimates, the precise GNSS carrier phase observables must be employed. However, in order to take full advantage of the high precision, the unknown integer ambiguities of the carrier phase observables need to be resolved. This contribution presents a GNSS carrier phase-based attitude determination method that determines the integer ambiguities and attitude in an integral manner, thereby fully exploiting the known body geometry of the multi-antennae configuration. It is shown that this integral approach aids the ambiguity resolution process tremendously and strongly improves the capacity of fixing the correct set of integer ambiguities. In this contribution, the challenging scenario of single-epoch, single-frequency attitude determination is addressed. This guarantees a total independence from carrier phase slips and losses of lock, and it also does not require any a priori motion model for the platform. The method presented is a multivariate constrained version of the popular LAMBDA method and it is tested on data collected during an airborne remote sensing campaign.

  10. On-the Fly Merging of Attitude Solutions

    DEFF Research Database (Denmark)

    Jørgensen, Peter Siegbjørn; Jørgensen, John Leif; Denver, Troelz

    2008-01-01

    Recent advances in autonomous attitude determination instrumentation enable even small satellites flying fully autonomous multi head star trackers providing full accurate and robust attitude information. Each sensor provides the full attitude information but for robustness and optimal usage...

  11. A novel method for low-cost MIMU aiding GNSS attitude determination

    Science.gov (United States)

    Yang, Yingdong; Mao, Xuchu; Tian, Weifeng

    2016-07-01

    Global navigation satellite systems (GNSS) are well suited for attitude determination. In most cases, the success rate of the initialization is always a difficult problem, especially the single-frequency measurement model of the double-difference carrier phase. The main reason for this is excessively large noise error that arises in the measurement of the double-difference carrier phase. When the geometric relations of the equations are not good, the difference between the residual error of the optimal solution and that of the suboptimal solution is not very obvious. In this study, we design a smoothing model based on MEMS. The noise error of the measurement of the double-difference carrier phase is suppressed and smoothed via this model. It is designed to reduce the initialization time and improve the success rate of the solution. In addition, we propose a new method based on the rotation matrix to resolve the attitude angle. This method produces a better performance in reducing computation time and selecting satellites. The condition of the baseline length is combined with the ambiguity function method (AFM) to search for integer ambiguity, and this method is validated in reducing the span of candidates. The experiment is conducted in a selected campus, and the performance is proved to be effective. Our results are based on simulated and real-time GNSS data and are applied on single-frequency processing, which is known as one of the challenging cases of GNSS attitude determination.

  12. Low-cost attitude determination system using an extended Kalman filter (EKF) algorithm

    Science.gov (United States)

    Esteves, Fernando M.; Nehmetallah, Georges; Abot, Jandro L.

    2016-05-01

    Attitude determination is one of the most important subsystems in spacecraft, satellite, or scientific balloon mission s, since it can be combined with actuators to provide rate stabilization and pointing accuracy for payloads. In this paper, a low-cost attitude determination system with a precision in the order of arc-seconds that uses low-cost commercial sensors is presented including a set of uncorrelated MEMS gyroscopes, two clinometers, and a magnetometer in a hierarchical manner. The faster and less precise sensors are updated by the slower, but more precise ones through an Extended Kalman Filter (EKF)-based data fusion algorithm. A revision of the EKF algorithm fundamentals and its implementation to the current application, are presented along with an analysis of sensors noise. Finally, the results from the data fusion algorithm implementation are discussed in detail.

  13. Advances in precision orbit determination of GRACE satellites

    Science.gov (United States)

    Bettadpur, Srinivas; Save, Himanshu; Kang, Zhigui

    The twin Gravity Recovery And Climate Experiment (GRACE) satellites carry a complete suite of instrumentation essential for precision orbit determination (POD). Dense, continuous and global tracking is provided by the Global Positioning System receivers. The satellite orientation is measured using two star cameras. High precision measurements of non-gravitational accel-erations are provided by accelerometers. Satellite laser ranging (SLR) retroreflectors are used for collecting data for POD validation. Additional validation is provided by the highly precise K-Band ranging system measuring distance changes between the twin GRACE satellites. This paper presents the status of POD for GRACE satellites. The POD quality will be vali-dated using the SLR and K-Band ranging data. The POD quality improvement from upgraded modeling of the GPS observations, including the transition to the new IGS05 standards, will be discussed. In addition, the contributions from improvements in the gravity field modeling -partly arising out of GRACE science results -will be discussed. The aspects of these improve-ments that are applicable for the POD of other low-Earth orbiting satellites will be discussed as well.

  14. Spacecraft attitude determination using the earth's magnetic field

    Science.gov (United States)

    Simpson, David G.

    1989-01-01

    A method is presented by which the attitude of a low-Earth orbiting spacecraft may be determined using a vector magnetometer, a digital Sun sensor, and a mathematical model of the Earth's magnetic field. The method is currently being implemented for the Solar Maximum Mission spacecraft (as a backup for the failing star trackers) as a way to determine roll gyro drift.

  15. Attitude control system design and on-orbit performance analysis of nano-satellite--‘‘Tian Tuo 1’’

    Institute of Scientific and Technical Information of China (English)

    Ran Dechao; Sheng Tao; Cao Lu; Chen Xiaoqian; Zhao Yong

    2014-01-01

    ‘‘Tian Tuo 1’’ (TT-1) nano-satellite is the first single-board nano-satellite that was suc-cessfully launched in China. The main objective of TT-1 is technology demonstration and scientific measurements. The satellite carries out the significant exploration of single-board architecture fea-sibility validation, and it is tailored to the low-cost philosophy by adopting numerous commercial-off-the-shelf (COTS) components. The satellite is featured with three-axis stabilization control capability. A pitch bias momentum wheel and three magnetic coils are adopted as control actuators. The sun sensors, magnetometers and a three-axis gyro are employed as the measurement sensors. The quaternion estimator (QUEST) and unscented Kalman filter (UKF) method are adopted for the nano-satellite attitude determination. On-orbit data received by ground station is conducted to analysis the performance of attitude determination and control system (ADCS). The results show that the design of ADCS for TT-1 is suitable, robust and feasible.

  16. Spin period and attitude of satellites and space debris measured by using photometry

    Science.gov (United States)

    Shakun, Leonid; Koshkin, Nikolay; Korobeynikova, Elena; Strakhova, Svetlana; Melikyants, Seda; Ryabov, Andrey

    2016-07-01

    Photometry is an essential method for studying of the properties of the proper rotation of satellites and space debris. The observation method with high time resolution is used in the Odessa astronomical observatory for observations of artificial satellites. This method provides the measuring of the orbital motion and the proper rotation of satellites. Worth note, that the time resolution of the light curve and the accuracy of positioning in time of the details in the light curve are more important for the interpretation of the brightness variations than the precise measuring of the brightness. The rapid photometry allows not only registering of the flashes caused by mirror surfaces of structure satellite elements but also determining the indicatrix of the corresponding structure satellite element. This principal change of the photometric quality allows significant improving the interpretation of the satellites' light curves. We obtained a large amount of the photometric observations sequences of the satellites with time resolution 0.02 sec on the 50 cm telescope during last 11 years. We used this data for determination of the rotational parameters of several space objects. We present the method and results of the data analysis for the inactive satellites such as Envisat, Cbers-2B, Topex and other. Each of them changes its rotational parameters in its own way. For some satellites, the rotation period increases, for other it decreases. The rotation axis also change their orientation in space. The obtained information about rotation characteristics can be used for the precise numerical models of the satellite orbital motion and for the future Active Debris Removal missions.

  17. Design of Satellite Attitude Control Algorithm Based on the SDRE Method Using Gas Jets and Reaction Wheels

    Directory of Open Access Journals (Sweden)

    Luiz C. G. de Souza

    2013-01-01

    Full Text Available An experimental attitude control algorithm design using prototypes can minimize space mission costs by reducing the number of errors transmitted to the next phase of the project. The Space Mechanics and Control Division (DMC of INPE is constructing a 3D simulator to supply the conditions for implementing and testing satellite control hardware and software. Satellite large angle maneuver makes the plant highly nonlinear and if the parameters of the system are not well determined, the plant can also present some level of uncertainty. As a result, controller designed by a linear control technique can have its performance and robustness degraded. In this paper the standard LQR linear controller and the SDRE controller associated with an SDRE filter are applied to design a controller for a nonlinear plant. The plant is similar to the DMC 3D satellite simulator where the unstructured uncertainties of the system are represented by process and measurements noise. In the sequel the State-Dependent Riccati Equation (SDRE method is used to design and test an attitude control algorithm based on gas jets and reaction wheel torques to perform large angle maneuver in three axes. The SDRE controller design takes into account the effects of the plant nonlinearities and system noise which represents uncertainty. The SDRE controller performance and robustness are tested during the transition phase from angular velocity reductions to normal mode of operation with stringent pointing accuracy using a switching control algorithm based on minimum system energy. This work serves to validate the numerical simulator model and to verify the functionality of the control algorithm designed by the SDRE method.

  18. Determination of atmospheric aerosol properties over land using satellite measurements

    NARCIS (Netherlands)

    Kokhanovsky, A.A.; Leeuw, G. de

    2009-01-01

    Mostly, aerosol properties are poorly understood because the aerosol properties are very sparse. The first workshop on the determination of atmospheric aerosol properties over land using satellite measurements is convened in Bremen, Germany. In this workshop, the topics of discussions included a var

  19. Pico satellite attitude estimation via Robust Unscented Kalman Filter in the presence of measurement faults.

    Science.gov (United States)

    Soken, Halil Ersin; Hajiyev, Chingiz

    2010-07-01

    In the normal operation conditions of a pico satellite, a conventional Unscented Kalman Filter (UKF) gives sufficiently good estimation results. However, if the measurements are not reliable because of any kind of malfunction in the estimation system, UKF gives inaccurate results and diverges by time. This study introduces Robust Unscented Kalman Filter (RUKF) algorithms with the filter gain correction for the case of measurement malfunctions. By the use of defined variables named as measurement noise scale factor, the faulty measurements are taken into consideration with a small weight, and the estimations are corrected without affecting the characteristics of the accurate ones. Two different RUKF algorithms, one with single scale factor and one with multiple scale factors, are proposed and applied for the attitude estimation process of a pico satellite. The results of these algorithms are compared for different types of measurement faults in different estimation scenarios and recommendations about their applications are given.

  20. Precise Relative Orbit Determination of Twin GRACE Satellites

    Institute of Scientific and Technical Information of China (English)

    ZHAO Qile; HU Zhigang; GUO Jing; LI Min; GE Maorong

    2010-01-01

    When formation flying spacecrafts are used as platform to gain earth oriented observation, precise baselines between these spacecrafts are always essential. Gravity recovery and climate experiment (GRACE) mission is aimed at mapping the global gravity field and its variation. Accurate baseline of GRACE satellites is necessary for the gravity field modeling. The determination of kinematic and reduced dynamic relative orbits of twin satellites has been studied in this paper, and an accuracy of 2 mm for dynamic relative orbits and 5 mm for kinematic ones can be obtained, whereby most of the double difference onboard GPS ambiguities are resolved.

  1. Precision Attitude Determination for an Infrared Space Telescope

    Science.gov (United States)

    Benford, Dominic J.

    2008-01-01

    We have developed performance simulations for a precision attitude determination system using a focal plane star tracker on an infrared space telescope. The telescope is being designed for the Destiny mission to measure cosmologically distant supernovae as one of the candidate implementations for the Joint Dark Energy Mission. Repeat observations of the supernovae require attitude control at the level of 0.010 arcseconds (0.05 microradians) during integrations and at repeat intervals up to and over a year. While absolute accuracy is not required, the repoint precision is challenging. We have simulated the performance of a focal plane star tracker in a multidimensional parameter space, including pixel size, read noise, and readout rate. Systematic errors such as proper motion, velocity aberration, and parallax can be measured and compensated out. Our prediction is that a relative attitude determination accuracy of 0.001 to 0.002 arcseconds (0.005 to 0.010 microradians) will be achievable.

  2. Precise Orbit Determination of Earth's Satellites for Climate Change Investigation

    Science.gov (United States)

    Vespe, Francesco

    The tremendous improvement of the gravity field models which we are achieving with the last Earth's satellite missions like, CHAMP, GRACE and GOCE devoted to its recovery could make feasibile the use of precise orbit determination (POD) of Earth satellites as a tool for sensing global changes of some key atmosphere parameters like refractivity and extinction. Such improvements indeed, coupled with the huge number of running Earth's satellites and combinations of their orbital parameters (namely the nodes) in a gravity field free fashion (hereafter GFF) can magnify the solar radiation pressure acting on medium earth orbit satellites :GPS, Etalon and, in near real future GALILEO and its smooth modulation through the Earth's atmosphere (penumbra). We would remind that The GFF technique is able to cancel out with "n" satellite orbital parameters the first n-1 even zonal harmonics of the gravity field. Previously it was demonstrated that the signal we want to detect could in principle emerge from the noise threshold but, more refined models of the atmosphere would be needed to perform a more subtle analysis. So we will re-compute the signal features of penumbra by applying more refined atmospheric models. The analysis will be performed by including in GFF Earth's satellites equipped with DORIS systems (Jason, Spot 2-3-4-5, ENVISAT etc.) other than those ranged with SLR and GPS. The introduction of DORIS tracked satellites indeed will allow to cancel higher and higher order of even zonal harmonics and will make still more favourable the signal to noise budget. The analysis will be performed over a time span of at least few tens of years just to enhance probable climate signatures.

  3. Adaptive Hierarchical Sliding Mode Control with Input Saturation for Attitude Regulation of Multi-satellite Tethered System

    Science.gov (United States)

    Ma, Zhiqiang; Sun, Guanghui

    2017-06-01

    This paper proposes a novel adaptive hierarchical sliding mode control for the attitude regulation of the multi-satellite inline tethered system, where the input saturation is taken into account. The governing equations for the attitude dynamics of the three-satellite inline tethered system are derived firstly by utilizing Lagrangian mechanics theory. Considering the fact that the attitude of the central satellite can be adjusted by using the simple exponential stabilization scheme, the decoupling of the central satellite and the terminal ones is presented, and in addition, the new adaptive sliding mode control law is applied to stabilize the attitude dynamics of the two terminal satellites based on the synchronization and partial contraction theory. In the adaptive hierarchical sliding mode control design, the input is modeled as saturated input due to the fact that the flywheel torque is bounded, and meanwhile, an adaptive update rate is introduced to eliminate the effect of the saturated input and the external perturbation. The proposed control scheme can be applied on the two-satellite system to achieve fixed-point rotation. Numerical results validate the effectiveness of the proposed method.

  4. Adaptive Hierarchical Sliding Mode Control with Input Saturation for Attitude Regulation of Multi-satellite Tethered System

    Science.gov (United States)

    Ma, Zhiqiang; Sun, Guanghui

    2016-11-01

    This paper proposes a novel adaptive hierarchical sliding mode control for the attitude regulation of the multi-satellite inline tethered system, where the input saturation is taken into account. The governing equations for the attitude dynamics of the three-satellite inline tethered system are derived firstly by utilizing Lagrangian mechanics theory. Considering the fact that the attitude of the central satellite can be adjusted by using the simple exponential stabilization scheme, the decoupling of the central satellite and the terminal ones is presented, and in addition, the new adaptive sliding mode control law is applied to stabilize the attitude dynamics of the two terminal satellites based on the synchronization and partial contraction theory. In the adaptive hierarchical sliding mode control design, the input is modeled as saturated input due to the fact that the flywheel torque is bounded, and meanwhile, an adaptive update rate is introduced to eliminate the effect of the saturated input and the external perturbation. The proposed control scheme can be applied on the two-satellite system to achieve fixed-point rotation. Numerical results validate the effectiveness of the proposed method.

  5. Improvement of orbit determination accuracy for Beidou Navigation Satellite System with Two-way Satellite Time Frequency Transfer

    Science.gov (United States)

    Tang, Chengpan; Hu, Xiaogong; Zhou, Shanshi; Guo, Rui; He, Feng; Liu, Li; Zhu, Lingfeng; Li, Xiaojie; Wu, Shan; Zhao, Gang; Yu, Yang; Cao, Yueling

    2016-10-01

    The Beidou Navigation Satellite System (BDS) manages to estimate simultaneously the orbits and clock offsets of navigation satellites, using code and carrier phase measurements of a regional network within China. The satellite clock offsets are also directly measured with Two-way Satellite Time Frequency Transfer (TWSTFT). Satellite laser ranging (SLR) residuals and comparisons with the precise ephemeris indicate that the radial error of GEO satellites is much larger than that of IGSO and MEO satellites and that the BDS orbit accuracy is worse than GPS. In order to improve the orbit determination accuracy for BDS, a new orbit determination strategy is proposed, in which the satellite clock measurements from TWSTFT are fixed as known values, and only the orbits of the satellites are solved. However, a constant systematic error at the nanosecond level can be found in the clock measurements, which is obtained and then corrected by differencing the clock measurements and the clock estimates from orbit determination. The effectiveness of the new strategy is verified by a GPS regional network orbit determination experiment. With the IGS final clock products fixed, the orbit determination and prediction accuracy for GPS satellites improve by more than 50% and the 12-h prediction User Range Error (URE) is better than 0.12 m. By processing a 25-day of measurement from the BDS regional network, an optimal strategy for the satellite-clock-fixed orbit determination is identified. User Equivalent Ranging Error is reduced by 27.6% for GEO satellites, but no apparent reduction is found for IGSO/MEO satellites. The SLR residuals exhibit reductions by 59% and 32% for IGSO satellites but no reductions for GEO and MEO satellites.

  6. Simultaneous state and actuator fault estimation for satellite attitude control systems

    Institute of Scientific and Technical Information of China (English)

    Cheng Yao; Wang Rixin; Xu Minqiang; Li Yuqing

    2016-01-01

    In this paper, a new nonlinear augmented observer is proposed and applied to satellite attitude control systems. The observer can estimate system state and actuator fault simultaneously. It can enhance the performances of rapidly-varying faults estimation. Only original system matrices are adopted in the parameter design. The considered faults can be unbounded, and the proposed augmented observer can estimate a large class of faults. Systems without disturbances and the fault whose finite times derivatives are zero piecewise are initially considered, followed by a discussion of a general situation where the system is subject to disturbances and the finite times derivatives of the faults are not null but bounded. For the considered nonlinear system, convergence conditions of the observer are provided and the stability analysis is performed using Lyapunov direct method. Then a feasible algorithm is explored to compute the observer parameters using linear matrix inequalities (LMIs). Finally, the effectiveness of the proposed approach is illustrated by considering an example of a closed-loop satellite attitude control system. The simulation results show satisfactory perfor-mance in estimating states and actuator faults. It also shows that multiple faults can be estimated successfully.

  7. An autonomous orbit determination method for MEO and LEO satellite

    Science.gov (United States)

    Zhang, Hui; Wang, Jin; Yu, Guobin; Zhong, Jie; Lin, Ling

    2014-09-01

    A reliable and secure navigation system and assured autonomous capability of satellite are in high demand in case of emergencies in space. This paper introduces a novel autonomous orbit determination method for Middle-Earth-Orbit and Low-Earth-Orbit (MEO and LEO) satellite by observing space objects whose orbits are known. Generally, the geodetic satellites, such as LAGEOS and ETALONS, can be selected as the space objects here. The precision CCD camera on tracking gimbal can make a series of photos of the objects and surrounding stars when MEO and LEO satellite encounters the space objects. Then the information processor processes images and attains sightings and angular observations of space objects. Several clusters of such angular observations are incorporated into a batch least squares filter to obtain an orbit determination solution. This paper describes basic principle and builds integrated mathematical model. The accuracy of this method is analyzed by means of computer simulation. Then a simulant experiment system is built, and the experimental results demonstrate the feasibility and effectiveness of this method. The experimental results show that this method can attain the accuracy of 150 meters with angular observations of 1 arcsecond system error.

  8. Astrometric positioning and orbit determination of geostationary satellites

    Science.gov (United States)

    Montojo, F. J.; López Moratalla, T.; Abad, C.

    2011-03-01

    In the project titled “Astrometric Positioning of Geostationary Satellite” (PASAGE), carried out by the Real Instituto y Observatorio de la Armada (ROA), optical observation techniques were developed to allow satellites to be located in the geostationary ring with angular accuracies of up to a few tenths of an arcsec. These techniques do not necessarily require the use of large telescopes or especially dark areas, and furthermore, because optical observation is a passive method, they could be directly applicable to the detection and monitoring of passive objects such as space debris in the geostationary ring.By using single-station angular observations, geostationary satellite orbits with positional uncertainties below 350 m (2 sigma) were reconstructed using the Orbit Determination Tool Kit software, by Analytical Graphics, Inc. This software is used in collaboration with the Spanish Instituto Nacional de Técnica Aeroespacial.Orbit determination can be improved by taking into consideration the data from other stations, such as angular observations alone or together with ranging measurements to the satellite. Tests were carried out combining angular observations with the ranging measurements obtained from the Two-Way Satellite Time and Frequency Transfer technique that is used by ROA’s Time Section to carry out time transfer with other laboratories. Results show a reduction of the 2 sigma uncertainty to less than 100 m.

  9. Confirmation of gravitationally induced attitude drift of spinning satellite Ajisai with Graz high repetition rate SLR data

    Science.gov (United States)

    Kucharski, Daniel; Kirchner, Georg; Otsubo, Toshimichi; Lim, Hyung-Chul; Bennett, James; Koidl, Franz; Kim, Young-Rok; Hwang, Joo-Yeon

    2016-02-01

    The high repetition rate Satellite Laser Ranging system Graz delivers the millimeter precision range measurements to the corner cube reflector panels of Ajisai. The analysis of 4599 passes measured from October 2003 until November 2014 reveals the secular precession and nutation of Ajisai spin axis due to the gravitational forces as predicted by Kubo (1987) with the periods of 35.6 years and 116.5 days respectively. The observed precession cone is oriented at RA = 88.9°, Dec = -88.85° (J2000) and has a radius of 1.08°. The radius of the nutation cone increases from 1.32° to 1.57° over the 11 years of the measurements. We also detect a draconitic wobbling of Ajisai orientation due to the 'motion' of the Sun about the satellite's orbit. The observed spin period of Ajisai increases exponentially over the investigated time span according to the trend function: T = 1.492277·exp(0.0148388·Y) [s], where Y is in years since launch (1986.6133), RMS = 0.412 ms. The physical simulation model fitted to the observed spin parameters proves a very low interaction between Ajisai and the Earth's magnetic field, what assures that the satellite's angular momentum vector will remain in the vicinity of the south celestial pole for the coming decades. The developed empirical model of the spin axis orientation can improve the accuracy of the range determination between the ground SLR systems and the satellite's center-of-mass (Kucharski et al., 2015) and enable the accurate attitude prediction of Ajisai for the laser time-transfer experiments (Kunimori et al., 1992).

  10. Two Axis Pointing System (TAPS) attitude acquisition, determination, and control

    Science.gov (United States)

    Azzolini, John D.; McGlew, David E.

    1990-12-01

    The Two Axis Pointing System (TAPS) is a 2 axis gimbal system designed to provide fine pointing of Space Transportation System (STS) borne instruments. It features center-of-mass instrument mounting and will accommodate instruments of up to 1134 kg (2500 pounds) which fit within a 1.0 by 1.0 by 4.2 meter (40 by 40 by 166 inch) envelope. The TAPS system is controlled by a microcomputer based Control Electronics Assembly (CEA), a Power Distribution Unit (PDU), and a Servo Control Unit (SCU). A DRIRU-II inertial reference unit is used to provide incremental angles for attitude propagation. A Ball Brothers STRAP star tracker is used for attitude acquisition and update. The theory of the TAPS attitude determination and error computation for the Broad Band X-ray Telescope (BBXRT) are described. The attitude acquisition is based upon a 2 star geometric solution. The acquisition theory and quaternion algebra are presented. The attitude control combines classical position, integral and derivative (PID) control with techniques to compensate for coulomb friction (bias torque) and the cable harness crossing the gimbals (spring torque). Also presented is a technique for an adaptive bias torque compensation which adjusts to an ever changing frictional torque environment. The control stability margins are detailed, with the predicted pointing performance, based upon simulation studies. The TAPS user interface, which provides high level operations commands to facilitate science observations, is outlined.

  11. Stellar Gyroscope for Determining Attitude of a Spacecraft

    Science.gov (United States)

    Pain, Bedabrata; Hancock, Bruce; Liebe, Carl; Mellstrom, Jeffrey

    2005-01-01

    A paper introduces the concept of a stellar gyroscope, currently at an early stage of development, for determining the attitude or spin axis, and spin rate of a spacecraft. Like star trackers, which are commercially available, a stellar gyroscope would capture and process images of stars to determine the orientation of a spacecraft in celestial coordinates. Star trackers utilize chargecoupled devices as image detectors and are capable of tracking attitudes at spin rates of no more than a few degrees per second and update rates typically gyroscope would utilize an activepixel sensor as an image detector and would be capable of tracking attitude at a slew rate as high as 50 deg/s, with an update rate as high as 200 Hz. Moreover, a stellar gyroscope would be capable of measuring a slew rate up to 420 deg/s. Whereas a Sun sensor and a three-axis mechanical gyroscope are typically needed to complement a star tracker, a stellar gyroscope would function without them; consequently, the mass, power consumption, and mechanical complexity of an attitude-determination system could be reduced considerably.

  12. The Inertial Stellar Compass (ISC): A Multifunction, Low Power, Attitude Determination Technology Breakthrough

    Science.gov (United States)

    Bauer, Frank H. (Technical Monitor); Dennehy, Neil; Gambino, Joel; Maynard, Andrew; Brady, T.; Buckley, S.; Zinchuk, J.

    2003-01-01

    The Inertial Stellar Compass (ISC) is a miniature, low power, stellar inertial attitude determination system with an accuracy of better than 0.1 degree (1 sigma) in three axes. The ISC consumes only 3.5 Watts of power and is contained in a 2.5 kg package. With its embedded on-board processor, the ISC provides attitude quaternion information and has Lost-in-Space (LIS) initialization capability. The attitude accuracy and LIS capability are provided by combining a wide field of view Active Pixel Sensor (APS) star camera and Micro- ElectroMechanical System (MEMS) inertial sensor information in an integrated sensor system. The performance and small form factor make the ISC a useful sensor for a wide range of missions. In particular, the ISC represents an enabling, fully integrated, micro-satellite attitude determination system. Other applications include using the ISC as a single sensor solution for attitude determination on medium performance spacecraft and as a bolt on independent safe-hold sensor or coarse acquisition sensor for many other spacecraft. NASA's New Millennium Program (NMP) has selected the ISC technology for a Space Technology 6 (ST6) flight validation experiment scheduled for 2004. NMP missions, such a s ST6, are intended to validate advanced technologies that have not flown in space in order to reduce the risk associated with their infusion into future NASA missions. This paper describes the design, operation, and performance of the ISC and outlines the technology validation plan. A number of mission applications for the ISC technology are highlighted, both for the baseline ST6 ISC configuration and more ambitious applications where ISC hardware and software modifications would be required. These applications demonstrate the wide range of Space and Earth Science missions that would benefit from infusion of the ISC technology.

  13. Attitude-Tracking Control with Path Planning for Agile Satellite Using Double-Gimbal Control Moment Gyros

    Directory of Open Access Journals (Sweden)

    Peiling Cui

    2012-01-01

    Full Text Available In view of the issue of rapid attitude maneuver control of agile satellite, this paper presents an attitude-tracking control algorithm with path planning based on the improved genetic algorithm, adaptive backstepping control as well as sliding mode control. The satellite applies double gimbal control moment gyro as actuator and is subjected to the external disturbance and uncertain inertia properties. Firstly, considering the comprehensive mathematical model of the agile satellite and the double gimbal control moment gyro, an improved genetic algorithm is proposed to solve the attitude path-planning problem. The goal is to find an energy optimal path which satisfies certain maneuverability under the constraints of the input saturation, actuator saturation, slew rate limit and singularity measurement limit. Then, the adaptive backstepping control and sliding mode control are adopted in the design of the attitude-tracking controller to track accurately the desired path comprised of the satellite attitude quaternion and velocity. Finally, simulation results indicate the robustness and good tracking performance of the derived controller as well as its ability to avert the singularity of double gimbal control moment gyro.

  14. Precise orbit determination for the GOCE satellite using GPS

    Science.gov (United States)

    Bock, H.; Jäggi, A.; Švehla, D.; Beutler, G.; Hugentobler, U.; Visser, P.

    Apart from the gradiometer as the core instrument, the first ESA Earth Explorer Core Mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) will carry a 12-channel GPS receiver dedicated for precise orbit determination (POD) of the satellite. The EGG-C (European GOCE Gravity-Consortium), led by the Technical University in Munich, is building the GOCE HPF (High-level Processing Facility) dedicated to the Level 1b to Level 2 data processing. One of the tasks of this facility is the computation of the Precise Science Orbit (PSO) for GOCE. The PSO includes a reduced-dynamic and a kinematic orbit solution. The baseline for the PSO is a zero-difference procedure using GPS satellite orbits, clocks, and Earth Rotation Parameters (ERPs) from CODE (Center for Orbit Determination in Europe), one of the IGS (International GNSS Service) Analysis Centers. The scheme for reduced-dynamic and kinematic orbit determination is based on experiences gained from CHAMP and GRACE POD and is realized in one processing flow. Particular emphasis is put on maximum consistency in the analysis of day boundary overlapping orbital arcs, as well as on the higher data sampling rate with respect to CHAMP and GRACE and on differences originating from different GPS antenna configurations. We focus on the description of the procedure used for the two different orbit determinations and on the validation of the procedure using real data from the two GRACE satellites as well as simulated GOCE data.

  15. Signal Conditioning for the Kalman Filter: Application to Satellite Attitude Estimation with Magnetometer and Sun Sensors.

    Science.gov (United States)

    Esteban, Segundo; Girón-Sierra, Jose M; Polo, Óscar R; Angulo, Manuel

    2016-10-31

    Most satellites use an on-board attitude estimation system, based on available sensors. In the case of low-cost satellites, which are of increasing interest, it is usual to use magnetometers and Sun sensors. A Kalman filter is commonly recommended for the estimation, to simultaneously exploit the information from sensors and from a mathematical model of the satellite motion. It would be also convenient to adhere to a quaternion representation. This article focuses on some problems linked to this context. The state of the system should be represented in observable form. Singularities due to alignment of measured vectors cause estimation problems. Accommodation of the Kalman filter originates convergence difficulties. The article includes a new proposal that solves these problems, not needing changes in the Kalman filter algorithm. In addition, the article includes assessment of different errors, initialization values for the Kalman filter; and considers the influence of the magnetic dipole moment perturbation, showing how to handle it as part of the Kalman filter framework.

  16. Analysis of stability boundaries of satellite's equilibrium attitude in a circular orbit

    Science.gov (United States)

    Novikov, M. A.

    2016-03-01

    An asymmetric satellite equipped with control momentum gyroscopes (CMGs) with the center of mass of the system moving uniformly in a circular orbit was considered. The stability of a relative equilibrium attitude of the satellite was analyzed using Lyapunov's direct method. The Lyapunov function V is a positive definite integral of the total energy of the perturbed motion of the system. The asymptotic stability analysis of the stationary motion of the conservative system was based on the Barbashin-Krasovskii theorem on the nonexistence of integer trajectories of the set dot V, which was obtained using the differential equations of motion of the satellite with CMGs. By analyzing the sign definiteness of the quadratic part of V, it was found earlier by V.V. Sazonov that the stability region is described by four strict inequalities. The asymptotic stability at the stability boundary was analyzed by sequentially turning these inequalities into equalities with terms of orders higher than the second taken into account in V. The sign definiteness analysis of the inhomogeneous function V at the stability boundary involved a huge amount of computations related to the multiplication, expansion, substitution, and factorization of symbolic expressions. The computations were performed by applying a computer algebra system on a personal computer.

  17. Signal Conditioning for the Kalman Filter: Application to Satellite Attitude Estimation with Magnetometer and Sun Sensors

    Directory of Open Access Journals (Sweden)

    Segundo Esteban

    2016-10-01

    Full Text Available Most satellites use an on-board attitude estimation system, based on available sensors. In the case of low-cost satellites, which are of increasing interest, it is usual to use magnetometers and Sun sensors. A Kalman filter is commonly recommended for the estimation, to simultaneously exploit the information from sensors and from a mathematical model of the satellite motion. It would be also convenient to adhere to a quaternion representation. This article focuses on some problems linked to this context. The state of the system should be represented in observable form. Singularities due to alignment of measured vectors cause estimation problems. Accommodation of the Kalman filter originates convergence difficulties. The article includes a new proposal that solves these problems, not needing changes in the Kalman filter algorithm. In addition, the article includes assessment of different errors, initialization values for the Kalman filter; and considers the influence of the magnetic dipole moment perturbation, showing how to handle it as part of the Kalman filter framework.

  18. Attitude Determination for MAVs Using a Kalman Filter

    Institute of Scientific and Technical Information of China (English)

    LIU Cheng; ZHOU Zhaoying; FU Xu

    2008-01-01

    This paper presents a Kalman filter to effectively and economically determine the Euler angles for micro aerial vehicles(MAVs),whose size and payload are severely limited.The filter uses data from a series of micro-electro mechanical system sensors to determine the selected 3 vanables of the direction cosine matrix and the bias of the rata gyro sensors as state elements in a dynamic model,with the gravitational acceleration to build a measurement model.For high speed maneuvers,rigid motion equations are used to correct the measurements of the gravitational acceleration.The filter is designed to automatically tune its gain based on the dynamic system state.Simulations indicate that the Euler angles can be determined with standard deviations less than 3.The algorithm was successfully implemented in a miniature attitude measurement system suitable for MAVs.Aerobatic flights show that the attitude determination algorithm works effectively.The attitude determination algorithm is effective and economical,and can also be applied to bionic rebofishs and land vehicles,whose size and payload are also greatly limited.

  19. Orbit Propagation and Determination of Low Earth Orbit Satellites

    Directory of Open Access Journals (Sweden)

    Ho-Nien Shou

    2014-01-01

    Full Text Available This paper represents orbit propagation and determination of low Earth orbit (LEO satellites. Satellite global positioning system (GPS configured receiver provides position and velocity measures by navigating filter to get the coordinates of the orbit propagation (OP. The main contradictions in real-time orbit which is determined by the problem are orbit positioning accuracy and the amount of calculating two indicators. This paper is dedicated to solving the problem of tradeoffs. To plan to use a nonlinear filtering method for immediate orbit tasks requires more precise satellite orbit state parameters in a short time. Although the traditional extended Kalman filter (EKF method is widely used, its linear approximation of the drawbacks in dealing with nonlinear problems was especially evident, without compromising Kalman filter (unscented Kalman Filter, UKF. As a new nonlinear estimation method, it is measured at the estimated measurements on more and more applications. This paper will be the first study on UKF microsatellites in LEO orbit in real time, trying to explore the real-time precision orbit determination techniques. Through the preliminary simulation results, they show that, based on orbit mission requirements and conditions using UKF, they can satisfy the positioning accuracy and compute two indicators.

  20. Atmospheric Drag Perturbation in an Autonomous Orbit Determination for Satellite

    Institute of Scientific and Technical Information of China (English)

    XUE shen-fang; JIN Sheng-zhen; NING Shu-nian; SUN Cai-hong

    2005-01-01

    In this paper, an autonomous orbit determination method for satellite using a large field of view star sensor is presented. The simulation of orbit under atmospheric drag perturbation are given with expanded Kalman filtering.The large field of view star sensor has the same precision as star sensor and a sufficient filed of view. Therefore ,the refraction stars can be observed more accurately in real time. The geometric relation between the refracted starlight and the earth can be determined by tangent altitude of the refraction starlight. And then the earth enter can be determined in satellite body frame. The simulation shows that the precision of the mean square deviation of satellite's position and velocity is 5m and 0.01m/s respectively. The calculated decrement of the semi-major axis in one day is close to the theoretical result, and the absolute error is in the range of decimeter when the altitude of orbit is 750 km. The simulateion of orbit of different initial semi-major axis shows that the higher the altitude of orbit is, the smaller the decrement of the semi-major axis is, and when the altitude of orbit is 1700 km the decimeter of the semi-major axis is 10-7km.

  1. Determining Fire Dates and Locating Ignition Points With Satellite Data

    Directory of Open Access Journals (Sweden)

    Akli Benali

    2016-04-01

    Full Text Available Each wildfire has its own “history”, burns under specific conditions and leads to unique environmental impacts. Information on where and when it has started and its duration is important to improve understanding on the dynamics of individual wildfires. This information is typically included in fire databases that are known to have: (i multiple error sources; (ii limited spatial coverage and/or time span, and; (iii often unknown accuracy and uncertainty. Satellite data have a large potential to reduce such limitations. We used active fire data from the MODerate Resolution Imaging Spectroradiometer (MODIS to estimate fire start/end dates and ignition location(s for large wildfires that occurred in Alaska, Portugal, Greece, California and southeastern Australia. We assessed the agreement between satellite-derived estimates and data from fire databases, and determined the associated uncertainty. Fire dates and ignition location(s were estimated for circa 76% of the total burnt area extent for the five study regions. The ability to estimate fire dates and ignitions from satellite data increased with fire size. The agreement between reported and estimated fire dates was very good for start dates (Model efficiency index, MEF = 0.91 and reasonable for end dates (MEF = 0.73. The spatio-temporal agreement between reported and satellite-derived wildfire ignitions showed temporal lags and distances within 12 h and 2 km, respectively. Uncertainties associated with ignition estimates were generally larger than the disagreements with data reported in fire databases. Our results show how satellite data can contribute to improve information regarding dates and ignitions of large wildfires. This contribution can be particularly relevant in regions with scarce fire information, while in well-documented areas it can be used to complement, potentially detect, and correct inconsistencies in existing fire databases. Using data from other existing and/or upcoming

  2. Precise orbit determination for quad-constellation satellites at Wuhan University: strategy, result validation, and comparison

    Science.gov (United States)

    Guo, Jing; Xu, Xiaolong; Zhao, Qile; Liu, Jingnan

    2016-02-01

    This contribution summarizes the strategy used by Wuhan University (WHU) to determine precise orbit and clock products for Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). In particular, the satellite attitude, phase center corrections, solar radiation pressure model developed and used for BDS satellites are addressed. In addition, this contribution analyzes the orbit and clock quality of the quad-constellation products from MGEX Analysis Centers (ACs) for a common time period of 1 year (2014). With IGS final GPS and GLONASS products as the reference, Multi-GNSS products of WHU (indicated by WUM) show the best agreement among these products from all MGEX ACs in both accuracy and stability. 3D Day Boundary Discontinuities (DBDs) range from 8 to 27 cm for Galileo-IOV satellites among all ACs' products, whereas WUM ones are the largest (about 26.2 cm). Among three types of BDS satellites, MEOs show the smallest DBDs from 10 to 27 cm, whereas the DBDs for all ACs products are at decimeter to meter level for GEOs and one to three decimeter for IGSOs, respectively. As to the satellite laser ranging (SLR) validation for Galileo-IOV satellites, the accuracy evaluated by SLR residuals is at the one decimeter level with the well-known systematic bias of about -5 cm for all ACs. For BDS satellites, the accuracy could reach decimeter level, one decimeter level, and centimeter level for GEOs, IGSOs, and MEOs, respectively. However, there is a noticeable bias in GEO SLR residuals. In addition, systematic errors dependent on orbit angle related to mismodeled solar radiation pressure (SRP) are present for BDS GEOs and IGSOs. The results of Multi-GNSS combined kinematic PPP demonstrate that the best accuracy of position and fastest convergence speed have been achieved using WUM products, particularly in the Up direction. Furthermore, the accuracy of static BDS only PPP degrades when the BDS IGSO and MEO satellites switches to orbit-normal orientation

  3. Navigation using local position determination from a mobile satellite terminal

    Science.gov (United States)

    Kee, Steven M.; Marquart, Robert C.

    The authors describe the implementation and performance evaluation of a location-determination system which uses a mobile satellite transmitter for one-way communications of position data for vehicle tracking. Field results have demonstrated that a mobile satellite terminal can provide reliable messaging and position reporting for many over-the-road applications. With installation techniques suitable for nontechnical personnel using a minimum of test equipment, the mobile terminal can provide proximity reporting adequate for most fleet dispatch requirements. Position data with one-way or two-way communications can improve the logistics and management of service fleets by eliminating deadhead mileage, maximizing route efficiencies, and heading off problems with up-to-date status information of transported loads.

  4. Satellite techniques for determining the geopotential of sea surface elevations

    Science.gov (United States)

    Pisacane, V. L.

    1986-01-01

    Spaceborne altimetry with measurement accuracies of a few centimeters which has the potential to determine sea surface elevations necessary to compute accurate three-dimensional geostrophic currents from traditional hydrographic observation is discussed. The limitation in this approach is the uncertainties in knowledge of the global and ocean geopotentials which produce satellite and height uncertainties about an order of magnitude larger than the goal of about 10 cm. The quantitative effects of geopotential uncertainties on processing altimetry data are described. Potential near term improvements, not requiring additional spacecraft, are discussed. Even though there is substantial improvements at the longer wavelengths, the oceanographic goal will be achieved. The geopotential research mission (GRM) is described which should produce geopotential models that are capable of defining the ocean geoid to 10 cm and near-earth satellite position. The state of the art and the potential of spaceborne gravimetry is described as an alternative approach to improve our knowledge of the geopotential.

  5. REKF and RUKF for pico satellite attitude estimation in the presence of measurement faults

    Institute of Scientific and Technical Information of China (English)

    Halil Ersin Söken; Chingiz Hajiyev

    2014-01-01

    When a pico satel ite is under normal operational condi-tions, whether it is extended or unscented, a conventional Kalman filter gives sufficiently good estimation results. However, if the measurements are not reliable because of any kind of malfunc-tions in the estimation system, the Kalman filter gives inaccurate results and diverges by time. This study compares two different robust Kalman filtering algorithms, robust extended Kalman filter (REKF) and robust unscented Kalman filter (RUKF), for the case of measurement malfunctions. In both filters, by the use of de-fined variables named as the measurement noise scale factor, the faulty measurements are taken into the consideration with a smal weight, and the estimations are corrected without affecting the characteristic of the accurate ones. The proposed robust Kalman filters are applied for the attitude estimation process of a pico satel-lite, and the results are compared.

  6. On-Ground Processing of Yaogan-24 Remote Sensing Satellite Attitude Data and Verification Using Geometric Field Calibration.

    Science.gov (United States)

    Wang, Mi; Fan, Chengcheng; Yang, Bo; Jin, Shuying; Pan, Jun

    2016-07-30

    Satellite attitude accuracy is an important factor affecting the geometric processing accuracy of high-resolution optical satellite imagery. To address the problem whereby the accuracy of the Yaogan-24 remote sensing satellite's on-board attitude data processing is not high enough and thus cannot meet its image geometry processing requirements, we developed an approach involving on-ground attitude data processing and digital orthophoto (DOM) and the digital elevation model (DEM) verification of a geometric calibration field. The approach focuses on three modules: on-ground processing based on bidirectional filter, overall weighted smoothing and fitting, and evaluation in the geometric calibration field. Our experimental results demonstrate that the proposed on-ground processing method is both robust and feasible, which ensures the reliability of the observation data quality, convergence and stability of the parameter estimation model. In addition, both the Euler angle and quaternion could be used to build a mathematical fitting model, while the orthogonal polynomial fitting model is more suitable for modeling the attitude parameter. Furthermore, compared to the image geometric processing results based on on-board attitude data, the image uncontrolled and relative geometric positioning result accuracy can be increased by about 50%.

  7. Reusable Reentry Satellite (RRS) system design study. Phase B, appendix E: Attitude control system study

    Science.gov (United States)

    1991-01-01

    A study which consisted of a series of design analyses for an Attitude Control System (ACS) to be incorporated into the Re-usable Re-entry Satellite (RRS) was performed. The main thrust of the study was associated with defining the control laws and estimating the mass and power requirements of the ACS needed to meet the specified performance goals. The analyses concentrated on the different on-orbit control modes which start immediately after the separation of the RRS from the launch vehicle. The three distinct on-orbit modes considered for these analyses are as follows: (1) Mode 1 - A Gravity Gradient (GG) three-axis stabilized spacecraft with active magnetic control; (2) Mode 2 - A GG stabilized mode with a controlled yaw rotation rate ('rotisserie') using three-axis magnetic control and also incorporating a 10 N-m-s momentum wheel along the (Z) yaw axis; and (3) Mode 3 - A spin stabilized mode of operation with the spin about the pitch (Y) axis, incorporating a 20 N-m-s momentum wheel along the pitch (Y) axis and attitude control via thrusters. To investigate the capabilities of the different controllers in these various operational modes, a series of computer simulations and trade-off analyses have been made to evaluate the achievable performance levels, and the necessary mass and power requirements.

  8. Copernicus POD Service: Orbit Determination of the Sentinel Satellites

    Science.gov (United States)

    Peter, Heike; Fernández, Jaime; Ayuga, Francisco; Féménias, Pierre

    2016-04-01

    The Copernicus POD (Precise Orbit Determination) Service is part of the Copernicus Processing Data Ground Segment (PDGS) of the Sentinel-1, -2 and -3 missions. A GMV-led consortium is operating the Copernicus POD Service being in charge of generating precise orbital products and auxiliary data files for their use as part of the processing chains of the respective Sentinel PDGS. Sentinel-1A was launched in April 2014 while Sentinel-2A was on June 2015 and both are routinely operated since then. Sentinel-3A is expected to be launched in February 2016 and Sentinel-1B is planned for spring 2016. Thus the CPOD Service will be operating three to four satellites simultaneously in spring 2016. The satellites of the Sentinel-1, -2, and -3 missions are all equipped with dual frequency high precision GPS receivers delivering the main observables for POD. Sentinel-3 satellites will additionally be equipped with a laser retro reflector for Satellite Laser Ranging and a receiver for DORIS tracking. All three types of observables (GPS, SLR and DORIS) will be used routinely for POD. The POD core of the CPOD Service is NAPEOS (Navigation Package for Earth Orbiting Satellites) the leading ESA/ESOC software for precise orbit determination. The careful selection of models and inputs is important to achieve the different but very demanding requirements in terms of orbital accuracy and timeliness for the Sentinel -1, -2 & -3 missions. The three missions require orbital products with various latencies from 30 minutes up to 20-30 days. The accuracy requirements are also different and partly very challenging, targeting 5 cm in 3D for Sentinel-1 and 2-3 cm in radial direction for Sentinel-3. Although the characteristics and the requirements are different for the three missions the same core POD setup is used to the largest extent possible. This strategy facilitates maintenance of the complex system of the CPOD Service. Updates in the dynamical modelling of the satellite orbits, e

  9. Flight Vehicle Attitude Determination Using the Modified Rodrigues Parameters

    Institute of Scientific and Technical Information of China (English)

    Chen Jizheng; Yuan Jianping; Fang Qun

    2008-01-01

    There are two attitude estimation algorithms based on the different representations of attitude errors when modified Rodrigues parameters are applied to attitude estimation. The first is multiplicative error attitude estimator (MEAE), whose attitude error is expressed by the modified Rodrigues parameters representing the rotation from the estimated to the true attitude. The second is subtractive error attitude estimator (SEAE), whose attitude error is expressed by the arithmetic difference between the true and the estimated attitudes. It is proved that the two algorithms are equivalent in the case of small attitude errors. It is possible to describe rotation without encountering singularity by switching between the modified Rodrigues parameters and their shadow parameters. The attitude parameter switching does not bring disturbance to MEAE, but it does to SEAE. This article introduces a modification to eliminate the disturbance on SEAE,and simulation results demonstrate the efficacy of the presented algorithm.

  10. Determination of crustal motions using satellite laser ranging

    Science.gov (United States)

    1991-01-01

    Satellite laser ranging has matured over the last decade into one of the essential space geodesy techniques. It has demonstrated centimeter site positioning and millimeter per year velocity determinations in a frame tied dynamically to the mass center of the solid Earth hydrosphere atmosphere system. Such a coordinate system is a requirement for studying long term eustatic sea level rise and other global change phenomena. Earth orientation parameters determined with the coordinate system have been produced in near real time operationally since 1983, at a relatively modest cost. The SLR ranging to Lageos has also provided a rich spectrum of results based upon the analysis of Lageos orbital dynamics. These include significant improvements in the knowledge of the mean and variable components of the Earth's gravity field and the Earth's gravitational parameter. The ability to measure the time variations of the Earth's gravity field has opened as exciting area of study in relating global processes, including meteorologically derived mass transport through changes in the satellite dynamics. New confirmation of general relativity was obtained using the Lageos SLR data.

  11. The Detection of Structural Deformation Errors in Attitude Determination

    Institute of Scientific and Technical Information of China (English)

    M. J. Moore; C. Rizos; J. Wang

    2003-01-01

    In the determination of the attitude parameters from a multi-antenna GPS array, one of the major assumptions is that the body frame is rigid at all times. If this assumption is not true then the derived attitude parameters will be in error. It is well known that in airborne platforms the wings often experience some displacement during flight, especially during periods of initializing maneouvres, such as taking off, landing,and banking. Often it is at these points in time that it is most critical to have the most precise attitude parameters.There are a number of techniques available for the detection of modeling errors.The CUSUM algorithm has successfully been implemented in the past to detect small persistent changes. In this paper the authors investigate different methods of generating the residuals, to be tested by the CUSUM algorithm, in an effort to determine which technique is best suited for the detection of structural deformation of an airborne platform. The methods investigated include monitoring the mean of the residuals generated from the difference between the known body frame coordinates, and those calculated from the derived attitude parameters. The generated residuals are then passed to a CUSUM algorithm to detect any small persistent changes. An alternative method involves transforming the generated residuals into the frequency domain through the use of the Fast Fourier Transform. The CUSUM algorithm is then used to detect any frequency changes. The final technique investigated involves transforming the generated residuals using the Haar wavelet. The wavelet coefficients are then monitored by the CUSUM algorithm in order to detect any significant change to the rigidity of the body frame.Detecting structural deformation, and quantifying the degree of deformation, during flight will ensure that these effects can be removed from the system, thus ensuring the most precise and reliable attitude parameter solutions. This paper, through a series

  12. Integrated GNSS attitude determination and positioning for direct geo-referencing.

    Science.gov (United States)

    Nadarajah, Nandakumaran; Paffenholz, Jens-André; Teunissen, Peter J G

    2014-07-17

    Direct geo-referencing is an efficient methodology for the fast acquisition of 3D spatial data. It requires the fusion of spatial data acquisition sensors with navigation sensors, such as Global Navigation Satellite System (GNSS) receivers. In this contribution, we consider an integrated GNSS navigation system to provide estimates of the position and attitude (orientation) of a 3D laser scanner. The proposed multi-sensor system (MSS) consists of multiple GNSS antennas rigidly mounted on the frame of a rotating laser scanner and a reference GNSS station with known coordinates. Precise GNSS navigation requires the resolution of the carrier phase ambiguities. The proposed method uses the multivariate constrained integer least-squares (MC-LAMBDA) method for the estimation of rotating frame ambiguities and attitude angles. MC-LAMBDA makes use of the known antenna geometry to strengthen the underlying attitude model and, hence, to enhance the reliability of rotating frame ambiguity resolution and attitude determination. The reliable estimation of rotating frame ambiguities is consequently utilized to enhance the relative positioning of the rotating frame with respect to the reference station. This integrated (array-aided) method improves ambiguity resolution, as well as positioning accuracy between the rotating frame and the reference station. Numerical analyses of GNSS data from a real-data campaign confirm the improved performance of the proposed method over the existing method. In particular, the integrated method yields reliable ambiguity resolution and reduces position standard deviation by a factor of about 0:8, matching the theoretical gain of √ 3/4 for two antennas on the rotating frame and a single antenna at the reference station.

  13. Integrated GNSS Attitude Determination and Positioning for Direct Geo-Referencing

    Directory of Open Access Journals (Sweden)

    Nandakumaran Nadarajah

    2014-07-01

    Full Text Available Direct geo-referencing is an efficient methodology for the fast acquisition of 3D spatial data. It requires the fusion of spatial data acquisition sensors with navigation sensors, such as Global Navigation Satellite System (GNSS receivers. In this contribution, we consider an integrated GNSS navigation system to provide estimates of the position and attitude (orientation of a 3D laser scanner. The proposed multi-sensor system (MSS consists of multiple GNSS antennas rigidly mounted on the frame of a rotating laser scanner and a reference GNSS station with known coordinates. Precise GNSS navigation requires the resolution of the carrier phase ambiguities. The proposed method uses the multivariate constrained integer least-squares (MC-LAMBDA method for the estimation of rotating frame ambiguities and attitude angles. MC-LAMBDA makes use of the known antenna geometry to strengthen the underlying attitude model and, hence, to enhance the reliability of rotating frame ambiguity resolution and attitude determination. The reliable estimation of rotating frame ambiguities is consequently utilized to enhance the relative positioning of the rotating frame with respect to the reference station. This integrated (array-aided method improves ambiguity resolution, as well as positioning accuracy between the rotating frame and the reference station. Numerical analyses of GNSS data from a real-data campaign confirm the improved performance of the proposed method over the existing method. In particular, the integrated method yields reliable ambiguity resolution and reduces position standard deviation by a factor of about 0.8, matching the theoretical gain of 3/4 for two antennas on the rotating frame and a single antenna at the reference station.

  14. Horizon Acquisition for Attitude Determination Using Image Processing Algorithms- Results of HORACE on REXUS 16

    Science.gov (United States)

    Barf, J.; Rapp, T.; Bergmann, M.; Geiger, S.; Scharf, A.; Wolz, F.

    2015-09-01

    The aim of the Horizon Acquisition Experiment (HORACE) was to prove a new concept for a two-axis horizon sensor using algorithms processing ordinary images, which is also operable at high spinning rates occurring during emergencies. The difficulty to cope with image distortions, which is avoided by conventional horizon sensors, was introduced on purpose as we envision a system being capable of using any optical data. During the flight on REXUS1 16, which provided a suitable platform similar to the future application scenario, a malfunction of the payload cameras caused severe degradation of the collected scientific data. Nevertheless, with the aid of simulations we could show that the concept is accurate (±0.6°), fast (~ lOOms/frame) and robust enough for coarse attitude determination during emergencies and also applicable for small satellites. Besides, technical knowledge regarding the design of REXUS-experiments, including the detection of interferences between SATA and GPS, was gained.

  15. Direct determination of surface albedos from satellite imagery

    Science.gov (United States)

    Mekler, Y.; Joseph, J. H.

    1983-01-01

    An empirical method to measure the spectral surface albedo of surfaces from Landsat imagery is presented and analyzed. The empiricism in the method is due only to the fact that three parameters of the solution must be determined for each spectral photograph of an image on the basis of independently known albedos at three points. The approach is otherwise based on exact solutions of the radiative transfer equation for upwelling intensity. Application of the method allows the routine construction of spectral albedo maps from satelite imagery, without requiring detailed knowledge of the atmospheric aerosol content, as long as the optical depth is less than 0.75, and of the calibration of the satellite sensor.

  16. Robust Fault-Tolerant Control for Satellite Attitude Stabilization Based on Active Disturbance Rejection Approach with Artificial Bee Colony Algorithm

    OpenAIRE

    Fei Song; Shiyin Qin

    2014-01-01

    This paper proposed a robust fault-tolerant control algorithm for satellite stabilization based on active disturbance rejection approach with artificial bee colony algorithm. The actuating mechanism of attitude control system consists of three working reaction flywheels and one spare reaction flywheel. The speed measurement of reaction flywheel is adopted for fault detection. If any reaction flywheel fault is detected, the corresponding fault flywheel is isolated and the spare reaction flywhe...

  17. Integrated Orbit, Attitude, and Structural Control Systems Design for Space Solar Power Satellites

    Science.gov (United States)

    Wie, Bong; Roithmayr, Carlos M.

    2001-01-01

    The major objective of this study is to develop an integrated orbit, attitude, and structural control systems architecture for very large Space Solar Power Satellites (SSPS) in geosynchronous orbit. This study focuses on the 1.2-GW Abacus SSPS concept characterized by a 3.2 x 3.2 km solar-array platform, a 500-m diameter microwave beam transmitting antenna, and a 500 x 700 m earth-tracking reflector. For this baseline Abacus SSPS configuration, we derive and analyze a complete set of mathematical models, including external disturbances such as solar radiation pressure, microwave radiation, gravity-gradient torque, and other orbit perturbation effects. The proposed control systems architecture utilizes a minimum of 500 1-N electric thrusters to counter, simultaneously, the cyclic pitch gravity-gradient torque, the secular roll torque caused by an offset of the center-of-mass and center-of-pressure, the cyclic roll/yaw microwave radiation torque, and the solar radiation pressure force whose average value is about 60 N.

  18. Determination of Factors Affecting Preschool Teacher Candidates' Attitudes towards Science Teaching

    Science.gov (United States)

    Timur, Betul

    2012-01-01

    The purpose of this study was to determine preschool teacher candidates' attitudes towards science teaching and to examine the reasons behind their attitudes in depth. In this study, mixed methods were used including quantitative and qualitative data. Quantitative data gained by attitudes towards science teaching scale, qualitative data gained by…

  19. Determinants of attitude and buying intention of organic milk

    Directory of Open Access Journals (Sweden)

    Ivica Faletar

    2016-01-01

    Full Text Available The consumption of organic milk is increasing rapidly. However, the behaviour of organic milk consumers is still not enough investigated. The purpose of this study was to determine variables which influence the attitude towards organic milk consumption, as well as variables which influence the buying intention of organic milk. Thereat, factors such as positive opinion toward organic milk and food related lifestyle, as well as level of trust in home as in EU organic food label, objective knowledge and gender of respondents showed to have a significant influence on organic milk buying intention. More precisely, a significant and positive influence on buying intention of organic milk was observed considering the belief in positive aspects of organic milk, subjective knowledge, objective knowledge, and attitude towards buying organic milk. According to the results of this study recommendations for marketing practice and especially for communication policy might be created. Communication directed to female population should use classic advertising based on functional information, while the one directed to male population should use more emotional advertising. By using classic advertising education of consumers should be performed in order to promote benefits of organic milk in regards to conventional milk.

  20. Determining optimal parameters in magnetic spacecraft stabilization via attitude feedback

    Science.gov (United States)

    Bruni, Renato; Celani, Fabio

    2016-10-01

    The attitude control of a spacecraft using magnetorquers can be achieved by a feedback control law which has four design parameters. However, the practical determination of appropriate values for these parameters is a critical open issue. We propose here an innovative systematic approach for finding these values: they should be those that minimize the convergence time to the desired attitude. This a particularly diffcult optimization problem, for several reasons: 1) such time cannot be expressed in analytical form as a function of parameters and initial conditions; 2) design parameters may range over very wide intervals; 3) convergence time depends also on the initial conditions of the spacecraft, which are not known in advance. To overcome these diffculties, we present a solution approach based on derivative-free optimization. These algorithms do not need to write analytically the objective function: they only need to compute it in a number of points. We also propose a fast probing technique to identify which regions of the search space have to be explored densely. Finally, we formulate a min-max model to find robust parameters, namely design parameters that minimize convergence time under the worst initial conditions. Results are very promising.

  1. Interlaced optimal-REQUEST and unscented Kalman filtering for attitude determination

    Institute of Scientific and Technical Information of China (English)

    Quan Wei; Xu Liang; Zhang Huijuan; Fang Jiancheng

    2013-01-01

    Aimed at low accuracy of attitude determination because of using low-cost components which may result in non-linearity in integrated attitude determination systems,a novel attitude determination algorithm using vector observations and gyro measurements is presented.The various features of the unscented Kalman filter (UKF) and optimal-REQUEST (quaternion estimator) algorithms are introduced for attitude determination.An interlaced filtering method is presented for the attitude determination of nano-spacecraft by setting the quaternion as the attitude representation,using the UKF and optimal-REQUEST to estimate the gyro drifts and the quaternion,respectively.The optimal-REQUEST and UKF are not isolated from each other.When the optimal-REQUEST algorithm estimates the attitude quaternion,the gyro drifts are estimated by the UKF algorithm synchronously by using the estimated attitude quaternion.Furthermore,the speed of attitude determination is improved by setting the state dimension to three.Experimental results show that the presented method has higher performance in attitude determination compared to the UKF algorithm and the traditional interlaced filtering method and can estimate the gyro drifts quickly.

  2. A close examination of under-actuated attitude control subsystem design for future satellite missions' life extension

    Science.gov (United States)

    Lam, Quang M.; Barkana, Itzhak

    2014-12-01

    Satellite mission life, maintained and prolonged beyond its typical norm of their expectancy, are primarily dictated by the state of health of its Reaction Wheel Assembly (RWA), especially for commercial GEO satellites since torquer bars are no longer applicable while thruster assistant is unacceptable due to pointing accuracy impact during jet firing. The RWA is the primary set of actuators (as compared to thrusters for orbit maintenance and maneuvering) mainly responsible for the satellite mission for accurately and precisely pointing its payloads to the right targets to conduct its mission operations. The RWA consisting of either a set of four in pyramid or three in orthogonal is the primary set of actuators to allow the satellite to achieve accurate and precise pointing of the satellite payloads towards the desired targets. Future space missions will be required to achieve much longer lives and are currently perceived by the GEO satellite community as an "expected norm" of 20 years or longer. Driven by customers' demands/goals and competitive market have challenged Attitude Control Subsystems (ACS) engineers to develop better ACS algorithms to address such an emerging need. There are two main directions to design satellite's under-actuated control subsystem: (1) Attitude Feedback with Zero Momentum Principle and (2) Attitude Control by Angular Velocity Tracking via Small Time Local Controllability concept. Successful applications of these control laws have been largely demonstrated via simulation for the rest to rest case. Limited accuracy and oscillatory behaviors are observed in three axes for non-zero wheel momentum while realistic loss of a wheel scenario (i.e., fully actuated to under-actuated) has not been closely examined! This study revisits the under-actuated control design with detailed set ups of multiple scenarios reflecting real life operating conditions which have put current under-actuated control laws mentioned earlier into a re-evaluation mode

  3. Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

    Directory of Open Access Journals (Sweden)

    Liu Junhong

    2014-10-01

    Full Text Available The visibility for low earth orbit (LEO satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system (GPS. In addition, the spaceborne receivers’ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination (POD results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional (3D accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about 30 cm. As for the precise relative orbit determination (PROD, the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit (GEO satellites is illustrated for POD.

  4. Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

    Institute of Scientific and Technical Information of China (English)

    Liu Junhong; Gu Defeng; Ju Bing; Yao Jing; Duan Xiaojun; Yi Dongyun

    2014-01-01

    The visibility for low earth orbit (LEO) satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system (GPS). In addition, the spaceborne receivers’ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satel-lites orbits. The precise orbit determination (POD) results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional (3D) accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about 30 cm. As for the precise relative orbit determination (PROD), the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demon-strates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit (GEO) satellites is illustrated for POD.

  5. Orbit Determination of the SELENE Satellites Using Multi-Satellite Data Types and Evaluation of SELENE Gravity Field Models

    Science.gov (United States)

    Goossens, S.; Matsumoto, K.; Noda, H.; Araki, H.; Rowlands, D. D.; Lemoine, F. G.

    2011-01-01

    The SELENE mission, consisting of three separate satellites that use different terrestrial-based tracking systems, presents a unique opportunity to evaluate the contribution of these tracking systems to orbit determination precision. The tracking data consist of four-way Doppler between the main orbiter and one of the two sub-satellites while the former is over the far side, and of same-beam differential VLBI tracking between the two sub-satellites. Laser altimeter data are also used for orbit determination. The contribution to orbit precision of these different data types is investigated through orbit overlap analysis. It is shown that using four-way and VLBI data improves orbit consistency for all satellites involved by reducing peak values in orbit overlap differences that exist when only standard two-way Doppler and range data are used. Including laser altimeter data improves the orbit precision of the SELENE main satellite further, resulting in very smooth total orbit errors at an average level of 18m. The multi-satellite data have also resulted in improved lunar gravity field models, which are assessed through orbit overlap analysis using Lunar Prospector tracking data. Improvements over a pre-SELENE model are shown to be mostly in the along-track and cross-track directions. Orbit overlap differences are at a level between 13 and 21 m with the SELENE models, depending on whether l-day data overlaps or I-day predictions are used.

  6. Improved Orbit Determination and Forecasts with an Assimilative Tool for Satellite Drag Specification

    Science.gov (United States)

    Pilinski, M.; Crowley, G.; Sutton, E.; Codrescu, M.

    2016-09-01

    Much as aircraft are affected by the prevailing winds and weather conditions in which they fly, satellites are affected by the variability in density and motion of the near earth space environment. Drastic changes in the neutral density of the thermosphere, caused by geomagnetic storms or other phenomena, result in perturbations of LEO satellite motions through drag on the satellite surfaces. This can lead to difficulties in locating important satellites, temporarily losing track of satellites, and errors when predicting collisions in space. As the population of satellites in Earth orbit grows, higher space-weather prediction accuracy is required for critical missions, such as accurate catalog maintenance, collision avoidance for manned and unmanned space flight, reentry prediction, satellite lifetime prediction, defining on-board fuel requirements, and satellite attitude dynamics. We describe ongoing work to build a comprehensive nowcast and forecast system for specifying the neutral atmospheric state related to orbital drag conditions. The system outputs include neutral density, winds, temperature, composition, and the satellite drag derived from these parameters. This modeling tool is based on several state-of-the-art coupled models of the thermosphere-ionosphere as well as several empirical models running in real-time and uses assimilative techniques to produce a thermospheric nowcast. This software will also produce 72 hour predictions of the global thermosphere-ionosphere system using the nowcast as the initial condition and using near real-time and predicted space weather data and indices as the inputs. In this paper, we will review the driving requirements for our model, summarize the model design and assimilative architecture, and present preliminary validation results. Validation results will be presented in the context of satellite orbit errors and compared with several leading atmospheric models. As part of the analysis, we compare the drag observed by

  7. Influence of satellite aerodynamics on atmospheric density determination.

    Science.gov (United States)

    Karr, G. R.; Smith, R. E.

    1972-01-01

    Discussion of aerodynamic factors which influence the interpretation of satellite dynamic response. These factors include: (1) the influence of satellite orientation and shape on the drag coefficient; (2) the effect of changes in the gas flow properties with altitude; and (3) the influence of upper atmospheric winds on the interpretation of data. These factors represent the greatest source of error in current data reduction. For this reason, an estimate is made of a possible correction to present density models.

  8. Determining the Cost Effectiveness of Nano-Satellites

    Science.gov (United States)

    2014-09-01

    Control Network, which has eight Remote Tracking Stations around the globe to communicate with satellites ( Hodges and Woll 2008). The resulting raw...Logan, Utah: AIAA/USU, 2014. Hodges , Len, and Ron Woll. “Air Force Satellite Control Network (AFSCN) Support For Operational Responsive Space (ORS...Warfare Systems Command, 2010. Stacy, Nick . “6U Radar Altimeter Concept.” Paper presented at 6U Cubesat Low Cost Space Missions Workshop. Canberra

  9. Periodic H2 Synthesis for Spacecraft Attitude Determination and Control with a Vector Magnetometer and Magnetorquers

    DEFF Research Database (Denmark)

    Wisniewski, Rafal; Stoustrup, Jakob

    2001-01-01

    the expected magnetic field vector and the true magnetometer data is used for the attitude determination. The magnetic attitude control and determination is intrinsically periodic due to periodic nature of the geomagnetic field variation in orbit. The control performance is specified by the generalized H2...

  10. Attitude Control of Satellite With Pulse-Width Pulse- Frequency (PWPF Modulator Using Generalized Incremental Predictive Control

    Directory of Open Access Journals (Sweden)

    Ehsan Chegeni

    2014-09-01

    Full Text Available In this paper, we use generalized incremental predictive control (GIPC to stabilize attitude of satellite. We compare Generalized Predictive Control (GPC with GIPC algorithm and present that GIPC has better performance. The three-axis attitude control systems are activated in pulse mode. Consequently, a modulation of the torque command is compelling in order to avoid high non-linear control action. This work considers the Pulse-Width Pulse-Frequency modulator (PWPF is composed of a Schmitt trigger, a first order filter, and a feedback loop. PWPF modulator has several advantages over classical bang-bang controllers such as close to linear operation, high accuracy, and reduced propellant consumption

  11. Optimization of Determinant Factors of Satellite Electrical Power System with Particle Swarm Optimization (PSO Algorithm

    Directory of Open Access Journals (Sweden)

    Mojtaba Biglarahmadi

    2014-03-01

    Full Text Available Weight and dimension, cost, and performance are determinant factors for design, fabrication, and launch the satellites which are related to the mission type of the satellites. Each satellite includes several subsystems such as Electrical Power Subsystem (EPS, Navigation Subsystem, Thermal Subsystem, etc. The purpose of this paper is to optimize these determinant factors by Particle Swarm Optimization (PSO algorithm, for Electrical Power Subsystem. This paper considers the effects of selecting various types of Photovoltaic (PV cells and batteries on weight and dimension, cost, and performance of the satellite. We have used two various types of PVs and two various type of batteries in optimization of the Electrical Power Subsystem (EPS

  12. Advancements of In-Flight Mass Moment of Inertia and Structural Deflection Algorithms for Satellite Attitude Simulators

    Science.gov (United States)

    2015-03-26

    on the air-bearing satellite attitude simulator at Shenyang University of Technology. Additionally, Chesi et al., [3] advanced the EKF developed by Kim...in a disturbance torque. The data for hrw about the test axis is then used to calculate the coefficients Arw and Brw that best fit the equation hrw...oscillation; and m, b, D, and E are coefficients that best fit the 51 0 10 20 30 40 50 −0.4 −0.3 −0.2 −0.1 0 0.1 0.2 0.3 0.4 time (s) A ng ul ar M om en

  13. Attitude control system of the Delfi-n3Xt satellite

    NARCIS (Netherlands)

    Reijneveld, J.; Choukroun, D.

    2013-01-01

    This work is concerned with the development of the attitude control algorithms that will be implemented on board of the Delfi-n3xt nanosatellite, which is to be launched in 2013. One of the mission objectives is to demonstrate Sun pointing and three axis stabilization. The attitude control modes and

  14. Determinants of students' attitudes towards peers with disabilities.

    Science.gov (United States)

    Vignes, Celine; Godeau, Emmanuelle; Sentenac, Mariane; Coley, Nicola; Navarro, Felix; Grandjean, Helene; Arnaud, Catherine

    2009-06-01

    To explore factors associated with students' attitudes towards their peers with disabilities. All 7th grade students (aged 12-13y) from 12 schools in the Toulouse area were invited to participate (n=1509). Attitudes were measured using the Chedoke-McMaster Attitudes Towards Children with Handicaps (CATCH) questionnaire (affective, behavioural, cognitive, and total scores). Personal characteristics, including KIDSCREEN quality of life scores, were recorded. Data regarding information about disabilities received from parents and the media and acquaintance with people with disabilities constituted the 'disability knowledge' factors. The characteristics of the schools were obtained from the local education authority. Multivariate multilevel linear regression analyses were conducted to explore the associations between CATCH scores and these three groups of factors. Responses from 1135 students (612 females, 523 males; mean age 12y 8mo SD 7mo; age range 10y 8mo-15y) were studied (75.2% of the students approached). Factors independently associated with more positive attitudes were being a female, having a good quality of life, being friends with a child with disabilities, or having received information about disabilities from parents and the media. Presence in the school of a special class for children with cognitive disabilities was independently associated with more negative attitudes. This cross-sectional study identified different personal and environmental factors upon which interventions aimed at improving students' attitudes towards their peers with disabilities could be based.

  15. Determining the Probability of Close Approach between Two Satellites

    Science.gov (United States)

    1986-12-01

    between any two satellite, with eccentricities leos than I.U, but it can be computational!) g ."-• 5* I s expensive. For two...Bate» R.R., Mueller, D.D., and White, J.B., Fundamentals of Astrodynamics, New York: Dover Publications, Inc., 1971. 2. Brouwer D., and Clemence

  16. Onboard Supervisor for the Ørsted Satellite Attitude Control System

    DEFF Research Database (Denmark)

    Bøgh, S.A.; Izadi-Zamanabadi, Roozbeh; Blanke, M.

    1995-01-01

    The increasing operational requirements for onboard autonomy in satellite control systems necessitates structural methods that support the design of a complete and reliable supervisory system.......The increasing operational requirements for onboard autonomy in satellite control systems necessitates structural methods that support the design of a complete and reliable supervisory system....

  17. ISS Has an Attitude! Determining ISS Attitude at the ISS Window Observational Research Facility (WORF) Using Landmarks

    Science.gov (United States)

    Runco, Susan K.; Pickard,Henry; Kowtha, Vijayanand; Jackson, Dan

    2011-01-01

    Universities and secondary schools can help solve a real issue for remote sensing from the ISS WORF through hands-on engineering and activities. Remote sensing technology is providing scientists with higher resolution, higher sensitivity sensors. Where is it pointing? - To take full advantage of these improved sensors, space platforms must provide commensurate improvements in attitude determination

  18. The Determination of the Applicability of the Fishbein Model of Attitudes in Ascertaining the Attitudes Toward Science Held by High School Students.

    Science.gov (United States)

    Hartman, Dean DeVere

    This study was undertaken to determine the applicability of the Fishbein model of attitudes in ascertaining the attitudes toward science held by high school students. The model proposed assumed that attitudes involve both cognitive and affective components. Acceptability of the psychometric properties of an instrument developed in this…

  19. Robust Fault-Tolerant Control for Satellite Attitude Stabilization Based on Active Disturbance Rejection Approach with Artificial Bee Colony Algorithm

    Directory of Open Access Journals (Sweden)

    Fei Song

    2014-01-01

    Full Text Available This paper proposed a robust fault-tolerant control algorithm for satellite stabilization based on active disturbance rejection approach with artificial bee colony algorithm. The actuating mechanism of attitude control system consists of three working reaction flywheels and one spare reaction flywheel. The speed measurement of reaction flywheel is adopted for fault detection. If any reaction flywheel fault is detected, the corresponding fault flywheel is isolated and the spare reaction flywheel is activated to counteract the fault effect and ensure that the satellite is working safely and reliably. The active disturbance rejection approach is employed to design the controller, which handles input information with tracking differentiator, estimates system uncertainties with extended state observer, and generates control variables by state feedback and compensation. The designed active disturbance rejection controller is robust to both internal dynamics and external disturbances. The bandwidth parameter of extended state observer is optimized by the artificial bee colony algorithm so as to improve the performance of attitude control system. A series of simulation experiment results demonstrate the performance superiorities of the proposed robust fault-tolerant control algorithm.

  20. 76 FR 591 - Determination of Rates and Terms for Preexisting Subscription and Satellite Digital Audio Radio...

    Science.gov (United States)

    2011-01-05

    ... From the Federal Register Online via the Government Publishing Office LIBRARY OF CONGRESS Copyright Royalty Board Determination of Rates and Terms for Preexisting Subscription and Satellite Digital... subscription and satellite digital audio radio services for the digital performance of sound recordings and...

  1. BeiDou Satellites Assistant Determination by Receiving Other GNSS Downlink Signals

    Directory of Open Access Journals (Sweden)

    Lei Chen

    2016-01-01

    Full Text Available GNSS’s orbit determinations always rely on ground station or intersatellite links (ISL. In the emergency of satellite-to-ground links and ISL break-off, BeiDou navigation satellite system (BDS satellites cannot determine their orbits. In this paper, we propose to add a spaceborne annular beam antenna for receiving the global positioning system (GPS and global navigation satellite system (GLONASS signals; therefore, the BDS satellites may be capable of determining their orbits by GPS/GLONASS signals. Firstly, the spectrum selection, the power isolation, the range of Doppler frequency shift, and changing rate are taken into account for the feasibility. Specifically, the L2 band signals are chosen for receiving and processing in order to prevent the overlapping of the receiving and transmitting signals. Secondly, the minimum number of visible satellites (MNVS, carrier-to-noise ratio (C/N0, dilution of precision (GDOP, and geometric distance root-mean-square (gdrms are evaluated for acquiring the effective receiving antennas’ coverage ranges. Finally, the scheme of deploying 3 receiving antennas is proved to be optimal by analysis and simulations over the middle earth orbit (MEO, geostationary earth orbit (GEO, and the inclined geosynchronous satellite orbit (IGSO. The antennas’ structures and patterns are designed to draw a conclusion that installing GPS and GLONASS receivers on BDS satellites for emergent orbits determination is cost-effective.

  2. Attitude determination of planetary exploration rovers using solar panels characteristics and accelerometer

    Science.gov (United States)

    Ishida, Takayuki; Takahashi, Masaki

    2014-12-01

    In this study, we propose a new attitude determination system, which we call Irradiance-based Attitude Determination (IRAD). IRAD employs the characteristics and geometry of solar panels. First, the sun vector is estimated using data from solar panels including current, voltage, temperature, and the normal vectors of each solar panel. Because these values are obtained using internal sensors, it is easy for rovers to provide redundancy for IRAD. The normal vectors are used to apply to various shapes of rovers. Second, using the gravity vector obtained from an accelerometer, the attitude of a rover is estimated using a three-axis attitude determination method. The effectiveness of IRAD is verified through numerical simulations and experiments that show IRAD can estimate all the attitude angles (roll, pitch, and yaw) within a few degrees of accuracy, which is adequate for planetary explorations.

  3. Auto Code Generation for Simulink-Based Attitude Determination Control System

    Science.gov (United States)

    MolinaFraticelli, Jose Carlos

    2012-01-01

    This paper details the work done to auto generate C code from a Simulink-Based Attitude Determination Control System (ADCS) to be used in target platforms. NASA Marshall Engineers have developed an ADCS Simulink simulation to be used as a component for the flight software of a satellite. This generated code can be used for carrying out Hardware in the loop testing of components for a satellite in a convenient manner with easily tunable parameters. Due to the nature of the embedded hardware components such as microcontrollers, this simulation code cannot be used directly, as it is, on the target platform and must first be converted into C code; this process is known as auto code generation. In order to generate C code from this simulation; it must be modified to follow specific standards set in place by the auto code generation process. Some of these modifications include changing certain simulation models into their atomic representations which can bring new complications into the simulation. The execution order of these models can change based on these modifications. Great care must be taken in order to maintain a working simulation that can also be used for auto code generation. After modifying the ADCS simulation for the auto code generation process, it is shown that the difference between the output data of the former and that of the latter is between acceptable bounds. Thus, it can be said that the process is a success since all the output requirements are met. Based on these results, it can be argued that this generated C code can be effectively used by any desired platform as long as it follows the specific memory requirements established in the Simulink Model.

  4. Benefits Derived From Laser Ranging Measurements for Orbit Determination of the GPS Satellite Orbit

    Science.gov (United States)

    Welch, Bryan W.

    2007-01-01

    While navigation systems for the determination of the orbit of the Global Position System (GPS) have proven to be very effective, the current research is examining methods to lower the error in the GPS satellite ephemerides below their current level. Two GPS satellites that are currently in orbit carry retro-reflectors onboard. One notion to reduce the error in the satellite ephemerides is to utilize the retro-reflectors via laser ranging measurements taken from multiple Earth ground stations. Analysis has been performed to determine the level of reduction in the semi-major axis covariance of the GPS satellites, when laser ranging measurements are supplemented to the radiometric station keeping, which the satellites undergo. Six ground tracking systems are studied to estimate the performance of the satellite. The first system is the baseline current system approach which provides pseudo-range and integrated Doppler measurements from six ground stations. The remaining five ground tracking systems utilize all measurements from the current system and laser ranging measurements from the additional ground stations utilized within those systems. Station locations for the additional ground sites were taken from a listing of laser ranging ground stations from the International Laser Ranging Service. Results show reductions in state covariance estimates when utilizing laser ranging measurements to solve for the satellite s position component of the state vector. Results also show dependency on the number of ground stations providing laser ranging measurements, orientation of the satellite to the ground stations, and the initial covariance of the satellite's state vector.

  5. Finite-Time Control for Attitude Tracking Maneuver of Rigid Satellite

    Directory of Open Access Journals (Sweden)

    Mingyi Huo

    2014-01-01

    Full Text Available The problem of finite-time control for attitude tracking maneuver of a rigid spacecraft is investigated. External disturbance, unknown inertia parameters are addressed. As stepping stone, a sliding mode controller is designed. It requires the upper bound of the lumped uncertainty including disturbance and inertia matrix. However, this upper bound may not be easily obtained. Therefore, an adaptive sliding mode control law is then proposed to release that drawback. Adaptive technique is applied to estimate that bound. It is proved that the closed-loop attitude tracking system is finite-time stable. The tracking errors of the attitude and the angular velocity are asymptotically stabilized. Moreover, the upper bound on the lumped uncertainty can be exactly estimated in finite time. The attitude tracking performance with application of the control scheme is evaluated through a numerical example.

  6. Rest-to-Rest Attitude Naneuvers and Residual Vibration Reduction of a Finite Element Model of Flexible Satellite by Using Input Shaper

    Directory of Open Access Journals (Sweden)

    Setyamartana Parman

    1999-01-01

    Full Text Available A three-dimensional rest-to-rest attitude maneuver of flexible spacecraft equipped by on-off reaction jets is studied. Equations of motion of the spacecraft is developed by employing a hybrid system of coordinates and Lagrangian formulation. The finite element method is used to examine discrete elastic deformations of a particular model of satellite carrying flexible solar panels by modelling the panels as flat plate structures in bending. Results indicate that, under an unshaped input, the maneuvers induce undesirable attitude angle motions of the satellite as well as vibration of the solar panels. An input shaper is then applied to reduce the residual oscillation of its motion at several natural frequencies in order to get an expected pointing precision of the satellite. Once the shaped input is given to the satellite, the performance improves significantly.

  7. Attitude determination with three-axis accelerometer for emergency atmospheric entry

    Science.gov (United States)

    Garcia-Llama, Eduardo (Inventor)

    2012-01-01

    Two algorithms are disclosed that, with the use of a 3-axis accelerometer, will be able to determine the angles of attack, sideslip and roll of a capsule-type spacecraft prior to entry (at very high altitudes, where the atmospheric density is still very low) and during entry. The invention relates to emergency situations in which no reliable attitude and attitude rate are available. Provided that the spacecraft would not attempt a guided entry without reliable attitude information, the objective of the entry system in such case would be to attempt a safe ballistic entry. A ballistic entry requires three controlled phases to be executed in sequence: First, cancel initial rates in case the spacecraft is tumbling; second, maneuver the capsule to a heat-shield-forward attitude, preferably to the trim attitude, to counteract the heat rate and heat load build up; and third, impart a ballistic bank or roll rate to null the average lift vector in order to prevent prolonged lift down situations. Being able to know the attitude, hence the attitude rate, will allow the control system (nominal or backup, automatic or manual) to cancel any initial angular rates. Also, since a heat-shield forward attitude and the trim attitude can be specified in terms of the angles of attack and sideslip, being able to determine the current attitude in terms of these angles will allow the control system to maneuver the vehicle to the desired attitude. Finally, being able to determine the roll angle will allow for the control of the roll ballistic rate during entry.

  8. GNSS Single Frequency, Single Epoch Reliable Attitude Determination Method with Baseline Vector Constraint.

    Science.gov (United States)

    Gong, Ang; Zhao, Xiubin; Pang, Chunlei; Duan, Rong; Wang, Yong

    2015-12-02

    For Global Navigation Satellite System (GNSS) single frequency, single epoch attitude determination, this paper proposes a new reliable method with baseline vector constraint. First, prior knowledge of baseline length, heading, and pitch obtained from other navigation equipment or sensors are used to reconstruct objective function rigorously. Then, searching strategy is improved. It substitutes gradually Enlarged ellipsoidal search space for non-ellipsoidal search space to ensure correct ambiguity candidates are within it and make the searching process directly be carried out by least squares ambiguity decorrelation algorithm (LAMBDA) method. For all vector candidates, some ones are further eliminated by derived approximate inequality, which accelerates the searching process. Experimental results show that compared to traditional method with only baseline length constraint, this new method can utilize a priori baseline three-dimensional knowledge to fix ambiguity reliably and achieve a high success rate. Experimental tests also verify it is not very sensitive to baseline vector error and can perform robustly when angular error is not great.

  9. GNSS Single Frequency, Single Epoch Reliable Attitude Determination Method with Baseline Vector Constraint

    Directory of Open Access Journals (Sweden)

    Ang Gong

    2015-12-01

    Full Text Available For Global Navigation Satellite System (GNSS single frequency, single epoch attitude determination, this paper proposes a new reliable method with baseline vector constraint. First, prior knowledge of baseline length, heading, and pitch obtained from other navigation equipment or sensors are used to reconstruct objective function rigorously. Then, searching strategy is improved. It substitutes gradually Enlarged ellipsoidal search space for non-ellipsoidal search space to ensure correct ambiguity candidates are within it and make the searching process directly be carried out by least squares ambiguity decorrelation algorithm (LAMBDA method. For all vector candidates, some ones are further eliminated by derived approximate inequality, which accelerates the searching process. Experimental results show that compared to traditional method with only baseline length constraint, this new method can utilize a priori baseline three-dimensional knowledge to fix ambiguity reliably and achieve a high success rate. Experimental tests also verify it is not very sensitive to baseline vector error and can perform robustly when angular error is not great.

  10. Fast converging with high accuracy estimates of satellite attitude and orbit based on magnetometer augmented with gyro, star sensor and GPS via extended Kalman filter

    Directory of Open Access Journals (Sweden)

    Tamer Mekky Ahmed Habib

    2011-12-01

    Full Text Available The primary goal of this work is to extend the work done in, Tamer (2009, to provide high accuracy satellite attitude and orbit estimates needed for imaging purposes and also before execution of spacecraft orbital maneuvers for the next Egyptian scientific satellite. The problem of coarse satellite attitude and orbit estimation based on magnetometer measurements has been treated in the literature. The current research expands the field of application from coarse and slow converging estimates to accurate and fast converging attitude and orbit estimates within 0.1°, and 10 m for attitude angles and spacecraft location respectively (1-σ. The magnetometer is used for both spacecraft attitude and orbit estimation, aided with gyro to provide angular velocity measurements, star sensor to provide attitude quaternion, and GPS receiver to provide spacecraft location. The spacecraft under consideration is subject to solar radiation pressure forces and moments, aerodynamics forces and moments, earth’s oblateness till the fourth order (i.e. J4, gravity gradient moments, and residual magnetic dipole moments. The estimation algorithm developed is powerful enough to converge quickly (actually within 10 s despite very large initial estimation errors with sufficiently high accuracy estimates.

  11. The determination of infant feeding attitudes among Turkish mothers using the Iowa Infant Feeding Attitude Scale.

    Science.gov (United States)

    Topal, Sumeyra; Yuvaci, Hilal Uslu; Erkorkmaz, Unal; Cinar, Nursan; Altinkaynak, Sevin

    2017-10-01

    To assess whether the Iowa Infant Feeding Attitude Scale is a valid and reliable scale for Turkish mothers, and to assess maternal attitudes toward various aspects of infant feeding. This methodological, analytical study was conducted at the obstetrics and gynaecology department of Sakarya Training and Research Hospital, Sakarya, Turkey, from June to August 2015, and comprised mothers of newborn babies. Data was collected using the Turkish version of Iowa Infant Feeding Attitude Scale. SPSS 23 was used for data analysis. There were 391 participants in the study. Five items of the original Iowa Infant Feeding Attitude Scale were excluded due to the low correlation with the scale integrity (Cronbach's alpha=0.67). The total mean score of the mothers was 48.11±6.57. A statistically significant difference was found between the educational status, having social security, what the mothers having other children fed these children in the first 6 months and family types (p=0.05 each). Significant difference was also found between the mothers only breastfeeding and the mothers feeding with mother's milk and formula (p=0.008). The scale was found to be culturally acceptable, reliable and valid scale for Turkish mothers.

  12. Determinants of public attitudes to genetically modified salmon.

    Directory of Open Access Journals (Sweden)

    Latifah Amin

    Full Text Available The objective of this paper is to assess the attitude of Malaysian stakeholders to genetically modified (GM salmon and to identify the factors that influence their acceptance of GM salmon using a structural equation model. A survey was carried out on 434 representatives from various stakeholder groups in the Klang Valley region of Malaysia. Public attitude towards GM salmon was measured using self-developed questionnaires with seven-point Likert scales. The findings of this study have confirmed that public attitudes towards GM salmon is a complex issue and should be seen as a multi-faceted process. The most important direct predictors for the encouragement of GM salmon are the specific application-linked perceptions about religious acceptability of GM salmon followed by perceived risks and benefits, familiarity, and general promise of modern biotechnology. Encouragement of GM salmon also involves the interplay among other factors such as general concerns of biotechnology, threatening the natural order of things, the need for labeling, the need for patenting, confidence in regulation, and societal values. The research findings can serve as a database that will be useful for understanding the social construct of public attitude towards GM foods in a developing country.

  13. Determinants of Public Attitudes to Genetically Modified Salmon

    Science.gov (United States)

    Amin, Latifah; Azad, Md. Abul Kalam; Gausmian, Mohd Hanafy; Zulkifli, Faizah

    2014-01-01

    The objective of this paper is to assess the attitude of Malaysian stakeholders to genetically modified (GM) salmon and to identify the factors that influence their acceptance of GM salmon using a structural equation model. A survey was carried out on 434 representatives from various stakeholder groups in the Klang Valley region of Malaysia. Public attitude towards GM salmon was measured using self-developed questionnaires with seven-point Likert scales. The findings of this study have confirmed that public attitudes towards GM salmon is a complex issue and should be seen as a multi-faceted process. The most important direct predictors for the encouragement of GM salmon are the specific application-linked perceptions about religious acceptability of GM salmon followed by perceived risks and benefits, familiarity, and general promise of modern biotechnology. Encouragement of GM salmon also involves the interplay among other factors such as general concerns of biotechnology, threatening the natural order of things, the need for labeling, the need for patenting, confidence in regulation, and societal values. The research findings can serve as a database that will be useful for understanding the social construct of public attitude towards GM foods in a developing country. PMID:24489695

  14. Teachers' Attitude and Gender Factor as Determinant of Pupils ...

    African Journals Online (AJOL)

    Nekky Umera

    Teachers are regarded as the basic tools in education and curriculum implementations. ... respectively. Pearson moment product correlation coefficient was used to analyze the ... African Research Review Vol. 3 (1), 2009. Pp. 326- .... Discussion. The analysis in table 1 showed that teachers' attitude have significant effect.

  15. Determinant Factors of Attitude towards Quantitative Subjects: Differences between Sexes

    Science.gov (United States)

    Mondejar-Jimenez, Jose; Vargas-Vargas, Manuel

    2010-01-01

    Nowadays, almost all curricula in the social sciences contain at least one course in statistics, given the importance of this discipline as an analytical tool. This work identifies the latent factors relating to students' motivation and attitude towards statistics, tests their covariance structure for samples of both sexes, and identifies the…

  16. Determinants of public attitudes to genetically modified salmon.

    Science.gov (United States)

    Amin, Latifah; Azad, Md Abul Kalam; Gausmian, Mohd Hanafy; Zulkifli, Faizah

    2014-01-01

    The objective of this paper is to assess the attitude of Malaysian stakeholders to genetically modified (GM) salmon and to identify the factors that influence their acceptance of GM salmon using a structural equation model. A survey was carried out on 434 representatives from various stakeholder groups in the Klang Valley region of Malaysia. Public attitude towards GM salmon was measured using self-developed questionnaires with seven-point Likert scales. The findings of this study have confirmed that public attitudes towards GM salmon is a complex issue and should be seen as a multi-faceted process. The most important direct predictors for the encouragement of GM salmon are the specific application-linked perceptions about religious acceptability of GM salmon followed by perceived risks and benefits, familiarity, and general promise of modern biotechnology. Encouragement of GM salmon also involves the interplay among other factors such as general concerns of biotechnology, threatening the natural order of things, the need for labeling, the need for patenting, confidence in regulation, and societal values. The research findings can serve as a database that will be useful for understanding the social construct of public attitude towards GM foods in a developing country.

  17. Plug-and-Play Compatibility for CubeSat Attitude Determination and Control Systems Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The development of Plug-and-play Compatibility for CubeSat Attitude Determination and Control Systems (ADACS) is proposed. Existing Maryland Aerospace (MAI) ADACS...

  18. Error compensation of single-antenna attitude determination using GNSS for Low-dynamic applications

    Science.gov (United States)

    Chen, Wen; Yu, Chao; Cai, Miaomiao

    2017-04-01

    GNSS-based single-antenna pseudo-attitude determination method has attracted more and more attention from the field of high-dynamic navigation due to its low cost, low system complexity, and no temporal accumulated errors. Related researches indicate that this method can be an important complement or even an alternative to the traditional sensors for general accuracy requirement (such as small UAV navigation). The application of single-antenna attitude determining method to low-dynamic carrier has just started. Different from the traditional multi-antenna attitude measurement technique, the pseudo-attitude attitude determination method calculates the rotation angle of the carrier trajectory relative to the earth. Thus it inevitably contains some deviations comparing with the real attitude angle. In low-dynamic application, these deviations are particularly noticeable, which may not be ignored. The causes of the deviations can be roughly classified into three categories, including the measurement error, the offset error, and the lateral error. Empirical correction strategies for the formal two errors have been promoted in previous study, but lack of theoretical support. In this paper, we will provide quantitative description of the three type of errors and discuss the related error compensation methods. Vehicle and shipborne experiments were carried out to verify the feasibility of the proposed correction methods. Keywords: Error compensation; Single-antenna; GNSS; Attitude determination; Low-dynamic

  19. A fault tolerant design for autonomous attitude control of the DSCS-III communication satellite

    Science.gov (United States)

    Matijevic, J.; Mettler, E.

    1983-01-01

    The first of a new series of satellites, which will provide the principal elements in the Defense Space Communications System (DSCS), was launched on Oct. 31, 1982. This satellite, DSCS-III, is part of a system which will consist of super-high frequency communications satellites in synchronous, equatorial orbits, continuously operating in four widely separate geographic regions. The DSCS-III is designed both to maintain critical communications in the presence of an electronic jamming threat and to survive nuclear radiation exposure. The results of the present investigation are to provide a basis for the design of a spacecraft tolerant of on-board failures, survivable against external threats, and capable of performing its mission autonomously for periods as long as six months.

  20. An Attitude Heading and Reference System For Marine Satellite Tracking Antenna

    DEFF Research Database (Denmark)

    Wang, Yunlong; Soltani, Mohsen; Hussain, Dil muhammed Akbar

    2017-01-01

    conditions, an attitude estimator based on virtual horizontal reference is introduced for situations of accelerometer malfunction, where the ship is suffering from wave shocks in high sea states. The performance of the designed AHRS for MSTA is assessed through hardware experiments using a Stewart platform...

  1. Real-Time Orbit Determination for Future Korean Regional Navigation Satellite System

    Science.gov (United States)

    Shin, Kihae; Oh, Hyungjik; Park, Sang-Young; Park, Chandeok

    2016-03-01

    This paper presents an algorithm for Real-Time Orbit Determination (RTOD) of navigation satellites for the Korean Regional Navigation Satellite System (KRNSS), when the navigation satellites generate ephemeris by themselves in abnormal situations. The KRNSS is an independent Regional Navigation Satellite System (RNSS) that is currently within the basic/preliminary research phase, which is intended to provide a satellite navigation service for South Korea and neighboring countries. Its candidate constellation comprises three geostationary and four elliptical inclined geosynchronous orbit satellites. Relative distance ranging between the KRNSS satellites based on Inter-Satellite Ranging (ISR) is adopted as the observation model. The extended Kalman filter is used for real-time estimation, which includes fine-tuning the covariance, measurement noise, and process noise matrices. Simulation results show that ISR precision of 0.3-0.7 m, ranging capability of 65,000 km, and observation intervals of less than 20 min are required to accomplish RTOD accuracy to within 1 m. Furthermore, close correlation is confirmed between the dilution of precision and RTOD accuracy.

  2. Attitude Control of a Satellite Simulator Using Reaction Wheels and a PID Controller

    Science.gov (United States)

    2010-03-01

    Rohe, and Welty in the development of AFIT’s second- generation satellite simulator, SimSat II [40]. Instead of building another dumbbell-style spherical...Nathan F. Welty . A Systems Engineering Approach to the Design of a Spacecraft Dynamics and Control Testbed. MS thesis, Air Force Institute of

  3. Tilted wheel satellite attitude control with air-bearing table experimental results

    Science.gov (United States)

    Inumoh, Lawrence O.; Forshaw, Jason L.; Horri, Nadjim M.

    2015-12-01

    Gyroscopic actuators for satellite control have attracted significant research interest over the years, but their viability for the control of small satellites has only recently started to become clear. Research on variable speed gyroscopic actuators has long been focused on single gimbal actuators; double gimbal actuators typically operate at constant wheel spin rate and allow tilt angle ranges far larger than the ranges needed to operate most satellite missions. This research examines a tilted wheel, a newly proposed type of inertial actuator that can generate torques in all three principal axes of a rigid satellite using a spinning wheel and a double tilt mechanism. The tilt mechanism tilts the angular momentum vector about two axes providing two degree of freedom control, while variation of the wheel speed provides the third. The equations of motion of the system lead to a singularity-free system during nominal operation avoiding the need for complex steering logic. This paper describes the hardware design of the tilted wheel and the experimental setup behind both standalone and spherical air-bearing tables used to test it. Experimental results from the air bearing table are provided with the results depicting the high performance capabilities of the proposed actuator in torque generation.

  4. The Advanced Stellar Compass onboard the Oersted satellite

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Eisenman, Allan R.; Liebe, Carl Christian;

    1997-01-01

    In 1997 the first Danish satellite will be launched. The primarily scientific objective of the satellite is to map the magnetic field of the Earth. The attitude of the satellite is determined by an advanced stellar compass (star tracker). An advanced stellar compass consists of a CCD camera conne...

  5. Design and application of single-antenna GPS/accelerometers attitude determination system

    Institute of Scientific and Technical Information of China (English)

    He Jie; Huang Xianlin; Wang Guofeng

    2008-01-01

    In view of the problem that the current single-antenna GPS attitude determination system can only determine the body attitude when the sideslip angle is zero and the multiantenna GPS/SINS integrated navigation system is of large volume, high cost, and complex structure, this approach is presented to determine the attitude based on vector space with single-antenna GPS and accelerometers in the micro inertial measurement unit (MIMU).It can provide real-time and accurate attitude information. Subsequently, the single-antenna GPS/SINS integrated navigation system is designed based on the combination of position, velocity, and attitude. Finally the semi-physical simulations of single-antenna GPS attitude determination system and single-antenna GPS/SINS integrated navigation system are carried out. The simulation results, based on measured data, show that the single-antenna GPS/SINS system can provide more accurate navigation information compared to the GPS/SINS system, based on the combination of position and velocity. Furthermore, the single-antenna GPS/SINS system is characteristic of lower cost and simpler structure. It provides the basis for the application of a single-antenna GPS/SINS integrated navigation system in a micro aerial vehicle (MAV).

  6. Comparison of Unscented Kalman Filter and Unscented Schmidt Kalman Filter in Predicting Attitude and Associated Uncertainty of a Geosynchronous Satellite

    Science.gov (United States)

    2014-09-01

    attitude estimate. 1. INTRODUCTION The utility of using brightness ( radiometric flux intensity) measurements to determine a space object (SO)’s...a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE SEP...2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE Comparison of Unscented Kalman Filter and Unscented Schmidt

  7. Attitude and vibration control of a satellite containing flexible solar arrays by using reaction wheels, and piezoelectric transducers as sensors and actuators

    Science.gov (United States)

    da Fonseca, Ijar M.; Rade, Domingos A.; Goes, Luiz C. S.; de Paula Sales, Thiago

    2017-10-01

    The primary purpose of this paper is to provide insight into control-structure interaction for satellites comprising flexible appendages and internal moving components. The physical model considered herein aiming to attend such purpose is a rigid-flexible satellite consisting of a rigid platform containing two rotating flexible solar panels. The solar panels rotation is assumed to be in a sun-synchronous configuration mode. The panels contain surface-bonded piezoelectric patches that can be used either as sensors for the elastic displacements or as actuators to counteract the vibration motion. It is assumed that in the normal mode operation the satellite platform points towards the Earth while the solar arrays rotate so as to follow the Sun. The vehicle moves in a low Earth polar orbit. The technique used to obtain the mathematical model combines the Lagrangian formulation with the Finite Elements Method used to describe the dynamics of the solar panel. The gravity-gradient torque as well as the torque due to the interaction of the Earth magnetic field and the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control and piezoelectric actuators to control the flexible motion of the solar arrays. Computer simulations are performed using the MATLAB® software package. The following on-orbit satellite operating configurations are object of analysis: i) Satellite pointing towards the Earth (Earth acquisition maneuver) by considering the initial conditions in the elastic displacement equal to zero, aiming the assessment of the flexible modes excitation by the referred maneuver; ii) the satellite pointing towards the Earth with the assumption of an initial condition different from zero for the flexible motion such that the attitude alterations are checked against the elastic motion disturbance; and iii) attitude acquisition accomplished by taking into account initial conditions

  8. Vertical Motion Determined Using Satellite Altimetry and Tide Gauges

    Directory of Open Access Journals (Sweden)

    Chung-Yen Kuo

    2008-01-01

    Full Text Available A robust method to estimate vertical crustal motions by combining geocentric sea level measurements from decadal (1992 - 2003 TOPEX/POSEIDON satellite altimetry and long-term (> 40 years relative sea level records from tide gauges using a novel Gauss-Markov stochastic adjustment model is presented. These results represent an improvement over a prior study (Kuo et al. 2004 in Fennoscandia, where the observed vertical motions are primarily attributed to the incomplete Glacial Isostatic Adjustment (GIA in the region since the Last Glacial Maximum (LGM. The stochastic adjustment algorithm and results include a fully-populated a priori covariance matrix. The algorithm was extended to estimate vertical motion at tide gauge locations near open seas and around semi-enclosed seas and lakes. Estimation of nonlinear vertical motions, which could result from co- and postseismic deformations, has also been incorporated. The estimated uncertainties for the vertical motion solutions in coastal regions of the Baltic Sea and around the Great Lakes are in general < 0.5 mm yr-1, which is a significant improvement over existing studies. In the Baltic Sea, the comparisons of the vertical motion solution with 10 collocated GPS radial rates and with the BIFROST GIA model show differences of 0.2 ¡_ 0.9 and 1.6 ¡_ 1.8 mm yr-1, respectively. For the Great Lakes region, the comparisons with the ICE-3G model and with the relative vertical motion estimated using tide gauges only (Mainville and Craymer 2005 show differences of -0.2 ¡_ 0.6 and -0.1 ¡_ 0.5 mm yr-1, respectively. The Alaskan vertical motion solutions (linear and nonlinear models have an estimated uncertainty of ~1.2 - 1.6 mm yr-1, which agree qualitatively with GPS velocity and tide gauge-only solutions (Larsen et al. 2003. This innovative technique could potentially provide improved estimates of the vertical motion globally where long-term tide gauge records exist.

  9. RAIM Based on Single Baseline Attitude Determination%单基线姿态测量的RAIM算法研究

    Institute of Scientific and Technical Information of China (English)

    窦婧婧; 战兴群; 王博雄

    2011-01-01

    The attitude information of the vehicle could be delivered when satellite navigation receivers are equipped with multiple antennae. This paper explains the principles of a baseline constrained version of the Analytical Resolution Method (ARM). This version of the ARM is optimal by using the integrity confine of the initial integer ambiguities and the known baseline length. Once the integrity combination is fixed, the attitude information can be measured when only two satellites are captured using single differencing (SD) carrier phase equations established in local level frame (LLF). So this algorithm is capable of reducing the search integer space into countable two dimensional discrete points and ambiguity function method (AFM) resolves the ambiguity searching within the analytical solutions space. The Receiver Autonomous Integrity Monitoring (RAIM) is brought into this algorithm, and this method is useful in selecting the healthy satellites and improving AFM method. Engineering aspects of this attitude determination method are also discussed and the method is demonstrated to be effective.%当载体安装有GPS接收机和多个天线时,可以得到其姿态信息(航向角、俯仰角、横滚角);论述了利用载波相位姿态测量的解析法,利用了基线长固定的条件,在整周模糊度初始化时进行粗搜索,利用模糊度函数法进行判断筛选整周模糊度组合,减少了搜索空间;接收机自主完好性监测(RAIM)的概念被引入到姿态测量算法中,有效地剔除问题卫星,改善AFM算法;系统姿态测量结果达0.1标准差,故障卫星可由RAIM检测并剔除;结果表明RAIM算法能有效提高姿态测量结果可靠性.

  10. Cripto regulates skeletal muscle regeneration and modulates satellite cell determination by antagonizing myostatin.

    Science.gov (United States)

    Guardiola, Ombretta; Lafuste, Peggy; Brunelli, Silvia; Iaconis, Salvatore; Touvier, Thierry; Mourikis, Philippos; De Bock, Katrien; Lonardo, Enza; Andolfi, Gennaro; Bouché, Ann; Liguori, Giovanna L; Shen, Michael M; Tajbakhsh, Shahragim; Cossu, Giulio; Carmeliet, Peter; Minchiotti, Gabriella

    2012-11-20

    Skeletal muscle regeneration mainly depends on satellite cells, a population of resident muscle stem cells. However, our understanding of the molecular mechanisms underlying satellite cell activation is still largely undefined. Here, we show that Cripto, a regulator of early embryogenesis, is a novel regulator of muscle regeneration and satellite cell progression toward the myogenic lineage. Conditional inactivation of cripto in adult satellite cells compromises skeletal muscle regeneration, whereas gain of function of Cripto accelerates regeneration, leading to muscle hypertrophy. Moreover, we provide evidence that Cripto modulates myogenic cell determination and promotes proliferation by antagonizing the TGF-β ligand myostatin. Our data provide unique insights into the molecular and cellular basis of Cripto activity in skeletal muscle regeneration and raise previously undescribed implications for stem cell biology and regenerative medicine.

  11. Small satellite attitude control for sun-oriented operations utilizing a momentum bias with magnetic actuators

    Science.gov (United States)

    Wolfe, Scott M.

    1995-03-01

    The feasibility of using a three axis control, momentum bias system with magnetic actuators for sun-oriented operations is explored. Relevant equations of motion are developed for a sun-oriented coordinate system and control laws are developed for initial spacecraft capture after launch vehicle separation; reorientation from Earth oriented to a sun oriented operations mode; sun-oriented attitude control; and momentum wheel control. Simulations demonstrating the stability and time responsiveness of the system are performed. Sensor noise input tests are performed to investigate the systems susceptibility to imperfect conditions. Cross product of inertia effects are also input to test for system instability.

  12. Determination of the rotation of Mercury from satellite gravimetry

    Science.gov (United States)

    Cicalò, S.; Milani, A.

    2012-11-01

    Space missions can have as a goal the determination of the interior structure of a planet: this is the case for the ESA BepiColombo mission to Mercury. Very precise range and range-rate tracking from the Earth and onboard accelerometry will provide a huge amount of data, from which it will be possible to study the gravity field of Mercury and other parameters of interest. Gravity can be used to constrain the interior structure, but cannot uniquely determine the interior mass distribution. A much stronger constraint on the interior can be given by also determining the rotation state of the planet. If the planet is asymmetric enough, the gravity field as measured by an orbiting probe tracked from the Earth contains signatures from the rotation. Are these enough to solve for the rotation state, to the required accuracy, from tracking data alone, without measurements of the surface? In order to reach some result analytically, a simplified analytical model is developed, and the symmetry breaking, occurring when the shape of the planet deviates from spherical symmetry, is characterized by explicit formulae. Moreover, a full cycle numerical simulation of the Radio Science Experiment is performed, including the generation of simulated tracking and accelerometer data and the determination, by least-squares fit, of the Mercury-centric initial conditions of the probe, of Mercury's gravity field and its rotation state, together with other parameters affecting the dynamics. The conclusion is that there is no reason of principle prohibiting the determination of the rotation from gravimetry, and the sensitivity of the measurements and the coverage are good enough to perform the experiment at the required level of accuracy. This will be important also in ensuring independent terms of comparison for the rotation experiment performed with a high-resolution camera. The mission is currently under development and much care has to be taken in guaranteeing the scientific goals even if

  13. A Narrative Inquiry to Determine the Impact of Learning Communities on Attitude Change of Developmental College Students

    Science.gov (United States)

    Dyett, La Tonya R.

    2011-01-01

    The purpose of this narrative inquiry research study was to explore how learning communities impact attitude changes of developmental college students. The qualitative research design enabled the researcher to determine attitudes, and changes in attitudes, via narratives shared by the participants about their personal experiences. The participants…

  14. Cultural Attitudes as WTP Determinants: A Revised Cultural Worldview Scale

    Directory of Open Access Journals (Sweden)

    Andy S. Choi

    2016-06-01

    Full Text Available There has been little attention paid to the systematic measurement issue of general attitudes toward human-culture relationships. This paper applied the Cultural Worldview (CW scale that was developed by Choi et al. in 2007 (published in the Journal of Cultural Economics, and investigated its dimensionality and relationship with willingness to pay (WTP for cultural heritage protection through a sequential integration between latent variables and valuation models. A case study of 997 Korean respondents was employed to examine conservation values of cultural heritage sites using discrete choice models. Confirmatory factor analyses demonstrated that this scale can be used either as a single second-order factor or four correlated factors. A more parsimonious version of the CW scale with twelve items is endorsed in this paper and the results also confirm that it is valid for use with non-Western nations. The findings support a significant attitude–WTP relationship; there was a significant role of the CW scale that reveals unobserved factors in valuation models.

  15. An Autonomous Orbit Determination System for Earth Satellites

    Science.gov (United States)

    1989-12-01

    these points is warranted. For example, low-Earth orbits ( LEO ) can be expected to approach e - 0 with time, so it is particularly useful to examine how...0.77887 e + 0.52875 e x y z 7 Canis Major A A A Cairs) M-0.18485 e + 0.93984 e - 0.28728 e (Sirus) -xyz A A A 8 a Leo -0.86275 e + 0.46061 e...Filters for Orbit Determination and Estimation, PhD Dissertation. University of Illinois, Urbana-Champaign IL, 1986 (AD-A170680). 12. Brouwer , Dirk

  16. Glas Spacecraft Attitude Determination Using CCD Star Tracker and 3-AXIS Gyros

    Science.gov (United States)

    Bae, Sungkoo

    The main purpose of the Geoscience Laser Altimeter System (GLAS) is to determine the mass balance of the polar ice-sheets and their contributions to global sea level change. For the mission, the required accuracy for the laser altimeter height measurements is 10 cm. In this case, the direction in which the altimeter beam is pointing relative to the Terrestrial Reference Frame must be known to an accuracy of 1.5 arcseconds assuming the average slope of the ice-sheet surface is one degree. The laser pointing direction will be determined relative to the star field measured by a star tracker in the GLAS spacecraft (ICESAT). Thus, the specification of one arcsecond pointing accuracy requires that the spacecraft attitude determination has comparable accuracy. A Charge Coupled Device (CCD) star tracker and gyros will be installed in an optical bench of ICESAT to determine the spacecraft attitude. Each star position measurement from the CCD star tracker contains approximately five arcseconds position uncertainty depending on the magnitude of the observed stars. Furthermore, gyro output accuracy is corrupted by measurement noise and bias. The main purpose of this dissertation was to investigate the ability to determine the attitude to better than one arcsecond (1σ) using developed estimation algorithms. Extended Kalman Filters and a Batch method were developed and used to estimate the simulated GLAS attitude. The determined attitude showed that the root sum square of roll and pitch errors, which directly affect the laser beam pointing error, reduced to about 0.5 arcsecond (1σ), far better than one arcsecond. In order to support the study result, actual attitude data obtained from the X-ray Timing Explorer spacecraft, were processed with some of algorithms developed for this research. As a part of the generation of the measurement data, a star identification algorithm was developed.

  17. Rapid Satellite-to-Site Visibility Determination Based on Self-Adaptive Interpolation Technique

    CERN Document Server

    Han, Chao; Sun, Xiucong

    2016-01-01

    Rapid satellite-to-site visibility determination is of great significance to coverage analysis of satellite constellations as well as onboard mission planning of autonomous spacecraft. This paper presents a novel self-adaptive Hermite interpolation technique for rapid satellite-to-site visibility determination. Piecewise cubic curves are utilized to approximate the waveform of the visibility function versus time. The fourth-order derivative is used to control the approximation error and to optimize the time step for interpolation. The rise and set times are analytically obtained from the roots of cubic polynomials. To further increase the computational speed, an interval shrinking strategy is adopted via investigating the geometric relationship between the ground viewing cone and the orbit trajectory. Simulation results show a 98% decrease in computation time over the brute force method. The method is suitable for all orbital types and analytical orbit propagators.

  18. Precise orbit and attitude determination using redundant low-cost single-frequency GNSS receivers on a CubeSat

    Science.gov (United States)

    Willi, Daniel; Fisler, Michael; Hollenstein, Christine; Männel, Benjamin; Meindl, Michael; Xu, Hui; Rothacher, Markus

    2016-07-01

    CubETH is a technology demonstration mission aimed at using low-cost commercial-off-the-shelf GNSS receivers for space applications. Precise orbit and attitude determination, on-board as well as in post-processing, are the main mission goals. The one unit cube-satellite is equipped with five GNSS antennas, each of them connected to two u-blox multi-GNSS receivers. The position estimation on the satellite is based on the receiver navigation solution. We show that (1) the proper correction of the ionospheric path delay and (2) the position propagation in the Kalman filter are of uppermost importance. Based on available data from the GRACE and GOCE missions, we show how an adapted Klobuchar model leads to a better estimation of the path delay in low Earth orbits. Based on recent signal-simulator tests, we illustrate how the linear propagation in the receiver Kalman filter leads to systematic errors and exhibit a method for improvement.

  19. Periodic H2 Synthesis for Spacecraft Attitude Determination and Control with a Vector Magnetometer and Magnetorquers

    DEFF Research Database (Denmark)

    Wisniewski, Rafal; Stoustrup, Jakob

    2001-01-01

    A control synthesis for a spacecraft equipped with a set of mutually perpendicular coils and a vector magnetometer is addressed in this paper. The interaction between the Earth's magnetic field and an artificial magnetic field generated by the coils produces a control torque. Comparison between...... the expected magnetic field vector and the true magnetometer data is used for the attitude determination. The magnetic attitude control and determination is intrinsically periodic due to periodic nature of the geomagnetic field variation in orbit. The control performance is specified by the generalized H2...... operator norm. The paper proposes an LMI solution to this problem...

  20. TRMM Re-Entry Planning: Attitude Determination and Control During Thruster Modes

    Science.gov (United States)

    DeWeese, Keith

    2005-01-01

    The Tropical Rainfall Measuring Mission (TRMM) spacecraft has been undergoing design for a controlled re-entry to Earth. During simulation of the re-entry plan, there was evidence of errors in the attitude determination algorithms during thruster modes. These errors affected the bum efficiency, and thus planning, during re-entry. During thruster modes, the spacecraft attitude is controlled off of integrated Gyro Error Angles that were designed to closely follow the nominal spacecraft pointing frame (Tip Frame). These angles, however, were not exactly mapped to the Tip Frame from the Body Frame. Additionally, in the initial formulation of the thruster mode attitude determination algorithms, several assumptions and approximations were made to conserve processor speed. These errors became noticeable and significant when simulating bums of much longer duration (-10 times) than had been produced in flight. A solution is proposed that uses attitude determination information from a propagated extended Kalman filter that already exists in the TRMM thruster modes. This attitude information is then used to rotate the Gyro Error Angles into the Tip Frame. An error analysis is presented that compares the two formulations. The new algorithm is tested using the TRMM High-Fidelity Simulator and verified with the TRMM Software Testing and Training Facility. Simulation results for both configurations are also presented.

  1. Attitude determination using a MEMS-based flight information measurement unit.

    Science.gov (United States)

    Ma, Der-Ming; Shiau, Jaw-Kuen; Wang, I-Chiang; Lin, Yu-Heng

    2012-01-01

    Obtaining precise attitude information is essential for aircraft navigation and control. This paper presents the results of the attitude determination using an in-house designed low-cost MEMS-based flight information measurement unit. This study proposes a quaternion-based extended Kalman filter to integrate the traditional quaternion and gravitational force decomposition methods for attitude determination algorithm. The proposed extended Kalman filter utilizes the evolution of the four elements in the quaternion method for attitude determination as the dynamic model, with the four elements as the states of the filter. The attitude angles obtained from the gravity computations and from the electronic magnetic sensors are regarded as the measurement of the filter. The immeasurable gravity accelerations are deduced from the outputs of the three axes accelerometers, the relative accelerations, and the accelerations due to body rotation. The constraint of the four elements of the quaternion method is treated as a perfect measurement and is integrated into the filter computation. Approximations of the time-varying noise variances of the measured signals are discussed and presented with details through Taylor series expansions. The algorithm is intuitive, easy to implement, and reliable for long-term high dynamic maneuvers. Moreover, a set of flight test data is utilized to demonstrate the success and practicality of the proposed algorithm and the filter design.

  2. Attitude Determination Using a MEMS-Based Flight Information Measurement Unit

    Directory of Open Access Journals (Sweden)

    Yu-Heng Lin

    2011-12-01

    Full Text Available Obtaining precise attitude information is essential for aircraft navigation and control. This paper presents the results of the attitude determination using an in-house designed low-cost MEMS-based flight information measurement unit. This study proposes a quaternion-based extended Kalman filter to integrate the traditional quaternion and gravitational force decomposition methods for attitude determination algorithm. The proposed extended Kalman filter utilizes the evolution of the four elements in the quaternion method for attitude determination as the dynamic model, with the four elements as the states of the filter. The attitude angles obtained from the gravity computations and from the electronic magnetic sensors are regarded as the measurement of the filter. The immeasurable gravity accelerations are deduced from the outputs of the three axes accelerometers, the relative accelerations, and the accelerations due to body rotation. The constraint of the four elements of the quaternion method is treated as a perfect measurement and is integrated into the filter computation. Approximations of the time-varying noise variances of the measured signals are discussed and presented with details through Taylor series expansions. The algorithm is intuitive, easy to implement, and reliable for long-term high dynamic maneuvers. Moreover, a set of flight test data is utilized to demonstrate the success and practicality of the proposed algorithm and the filter design.

  3. GNSS space-time interference mitigation and attitude determination in the presence of interference signals.

    Science.gov (United States)

    Daneshmand, Saeed; Jahromi, Ali Jafarnia; Broumandan, Ali; Lachapelle, Gérard

    2015-05-26

    The use of Space-Time Processing (STP) in Global Navigation Satellite System (GNSS) applications is gaining significant attention due to its effectiveness for both narrowband and wideband interference suppression. However, the resulting distortion and bias on the cross correlation functions due to space-time filtering is a major limitation of this technique. Employing the steering vector of the GNSS signals in the filter structure can significantly reduce the distortion on cross correlation functions and lead to more accurate pseudorange measurements. This paper proposes a two-stage interference mitigation approach in which the first stage estimates an interference-free subspace before the acquisition and tracking phases and projects all received signals into this subspace. The next stage estimates array attitude parameters based on detecting and employing GNSS signals that are less distorted due to the projection process. Attitude parameters enable the receiver to estimate the steering vector of each satellite signal and use it in the novel distortionless STP filter to significantly reduce distortion and maximize Signal-to-Noise Ratio (SNR). GPS signals were collected using a six-element antenna array under open sky conditions to first calibrate the antenna array. Simulated interfering signals were then added to the digitized samples in software to verify the applicability of the proposed receiver structure and assess its performance for several interference scenarios.

  4. Coarse Initial Orbit Determination for a Geostationary Satellite Using Single-Epoch GPS Measurements

    Directory of Open Access Journals (Sweden)

    Ghangho Kim

    2015-04-01

    Full Text Available A practical algorithm is proposed for determining the orbit of a geostationary orbit (GEO satellite using single-epoch measurements from a Global Positioning System (GPS receiver under the sparse visibility of the GPS satellites. The algorithm uses three components of a state vector to determine the satellite’s state, even when it is impossible to apply the classical single-point solutions (SPS. Through consideration of the characteristics of the GEO orbital elements and GPS measurements, the components of the state vector are reduced to three. However, the algorithm remains sufficiently accurate for a GEO satellite. The developed algorithm was tested on simulated measurements from two or three GPS satellites, and the calculated maximum position error was found to be less than approximately 40 km or even several kilometers within the geometric range, even when the classical SPS solution was unattainable. In addition, extended Kalman filter (EKF tests of a GEO satellite with the estimated initial state were performed to validate the algorithm. In the EKF, a reliable dynamic model was adapted to reduce the probability of divergence that can be caused by large errors in the initial state.

  5. Attitudes Toward Children's Rights: Nurturance or Self-Determination?

    Science.gov (United States)

    Rogers, Carl M.; Wrightsman, Lawrence S.

    1978-01-01

    This article describes the development of a classification schema consisting of two conceptual orientations toward the rights of children (nurturance and self-determination) which cut across five different content areas. (Author)

  6. Determination for regional differences of agriculture using satellite data

    Science.gov (United States)

    Saito, G.

    2006-12-01

    swath, 2. Large wavelength and many bands, 3. High-revel of geographical location, 4. Stereo pair images, 5. High performance data searching system, 6. High speed data delivery system, 7. Cheap price, 8. Seven years observation and large volume archive. A kind of project "Determination of Local Characteristics at Global Agriculture Using Archive ASTER Data" was started at middle of November 2005. We establish data processing system and get some results. Paddy rice fields analysis was started at first, we analyze 1) the Shonai Plains in Japan, 2) the Yangtze River delta in Middle-East China, 3) Mekong Delta in South Vietnam, 4) North-east Thai Plaines, Thailand, 5) Sacrament Valley, California, USA. The results of this studies are as follows, 1) Using ASTER images, we can easily understand agricultural characteristics of each local area. 2) ASTER data are high accuracy for location, and the accuracy is suitable for global study without the fine topographical maps, 3) By five years observation of ASTER, there is huge numbers of ASTER scenes, but not enough volumes for cloud free data for seasonal analysis. It means that follow-on program of ASTER is necessary, 4) We need not only paddy field, but also all crop fields and all area, 5) The studies are necessary to international corroboration.

  7. Energy integral method for gravity field determination from satellite orbit coordinates

    NARCIS (Netherlands)

    Visser, P.N.A.M.; Sneeuw, N.; Gerlach, C.

    2003-01-01

    A fast iterative method for gravity field determination from low Earth satellite orbit coordinates has been developed and implemented successfully. The method is based on energy conservation and avoids problems related to orbit dynamics and initial state. In addition, the particular geometry of a re

  8. GPS-based precise orbit determination and accelerometry for low flying satellites

    NARCIS (Netherlands)

    Van den IJssel, J.A.A.

    2014-01-01

    Atmospheric density models are currently the limiting factor in the accuracy of the dynamic orbit determination and prediction of satellites in a low Earth orbit. Any improvement in these models would greatly aid in applications such as re-entry prediction, ground-track maintenance of Earth observat

  9. Earth rotation, station coordinates and orbit determination from satellite laser ranging

    Science.gov (United States)

    Murata, Masaaki

    The Project MERIT, a special program of international colaboration to Monitor Earth Rotation and Intercompare the Techniques of observation and analysis, has come to an end with great success. Its major objective was to evaluate the ultimate potential of space techniques such as VLBI and satellite laser ranging, in contrast with the other conventional techniques, in the determination of rotational dynamics of the earth. The National Aerospace Laboratory (NAL) has officially participated in the project as an associate analysis center for satellite laser technique for the period of the MERIT Main Campaign (September 1983-October 1984). In this paper, the NAL analysis center results are presented.

  10. The Attitude Determination Scale for Value Acquisition: A Validity and Reliability Study

    Science.gov (United States)

    Cetin, Saban

    2017-01-01

    This study aims to develop a measurement tool having measurement reliability with the aim of determining attitudes for values acquisition of secondary school students. The study was conducted on totally 325 high school senior students as 200 female and 125 male students in spring semester of 2014-2015 educational year. In the study, expert opinion…

  11. Experimental Study on the Precise Orbit Determination of the BeiDou Navigation Satellite System

    Directory of Open Access Journals (Sweden)

    Jens Wickert

    2013-03-01

    Full Text Available The regional service of the Chinese BeiDou satellite navigation system is now in operation with a constellation including five Geostationary Earth Orbit satellites (GEO, five Inclined Geosynchronous Orbit (IGSO satellites and four Medium Earth Orbit (MEO satellites. Besides the standard positioning service with positioning accuracy of about 10 m, both precise relative positioning and precise point positioning are already demonstrated. As is well known, precise orbit and clock determination is essential in enhancing precise positioning services. To improve the satellite orbits of the BeiDou regional system, we concentrate on the impact of the tracking geometry and the involvement of MEOs, and on the effect of integer ambiguity resolution as well. About seven weeks of data collected at the BeiDou Experimental Test Service (BETS network is employed in this experimental study. Several tracking scenarios are defined, various processing schemata are designed and carried out; and then, the estimates are compared and analyzed in detail. The results show that GEO orbits, especially the along-track component, can be significantly improved by extending the tracking network in China along longitude direction, whereas IGSOs gain more improvement if the tracking network extends in latitude. The involvement of MEOs and ambiguity-fixing also make the orbits better.

  12. Autonomous Sub-Pixel Satellite Track Endpoint Determination for Space Based Images

    Energy Technology Data Exchange (ETDEWEB)

    Simms, L M

    2011-03-07

    An algorithm for determining satellite track endpoints with sub-pixel resolution in spaced-based images is presented. The algorithm allows for significant curvature in the imaged track due to rotation of the spacecraft capturing the image. The motivation behind the subpixel endpoint determination is first presented, followed by a description of the methodology used. Results from running the algorithm on real ground-based and simulated spaced-based images are shown to highlight its effectiveness.

  13. Modeling determinants of medication attitudes and poor adherence in early nonaffective psychosis

    DEFF Research Database (Denmark)

    Drake, Richard J; Nordentoft, Merete; Haddock, Gillian

    2015-01-01

    the hypothesis that medication attitudes, while meaningfully different from "insight," correlated with insight and self-esteem, and change in each influenced the others. Rosenberg Self-Esteem Scale, Birchwood Insight Scale, and Positive and Negative Syndrome Scale insight were assessed at presentation, after 6......We aimed to design a multimodal intervention to improve adherence following first episode psychosis, consistent with current evidence. Existing literature identified medication attitudes, insight, and characteristics of support as important determinants of adherence to medication: we examined...... medication attitudes, self-esteem, and insight in an early psychosis cohort better to understand their relationships. Existing longitudinal data from 309 patients with early Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, nonaffective psychosis (83% first episode) were analyzed to test...

  14. CubeSat Attitude Determination and Helmholtz Cage Design

    Science.gov (United States)

    2012-03-01

    have to point and track a specific location on Earth. As a driver in a car must determine his or her location in order to decide how to get to a final...between the two coils is calculated via B = 32πNI 5 √ 5a × 10−7 (2.3) where B has units of Tesla , a is the radius of the coils, N is the number of turns...πa 2 (1 + γ2) √ 2 + γ2 (2.4) where µo is the permeability of a vacuum, 4.95e-5 Tesla -in/Amp, N is the number of wrappings, I is the current passing

  15. Multi-Aperture CMOS Sun Sensor for Microsatellite Attitude Determination

    Directory of Open Access Journals (Sweden)

    Michele Grassi

    2009-06-01

    Full Text Available This paper describes the high precision digital sun sensor under development at the University of Naples. The sensor determines the sun line orientation in the sensor frame from the measurement of the sun position on the focal plane. It exploits CMOS technology and an original optical head design with multiple apertures. This allows simultaneous multiple acquisitions of the sun as spots on the focal plane. The sensor can be operated either with a fixed or a variable number of sun spots, depending on the required field of view and sun-line measurement precision. Multiple acquisitions are averaged by using techniques which minimize the computational load to extract the sun line orientation with high precision. Accuracy and computational efficiency are also improved thanks to an original design of the calibration function relying on neural networks. Extensive test campaigns are carried out using a laboratory test facility reproducing sun spectrum, apparent size and distance, and variable illumination directions. Test results validate the sensor concept, confirming the precision improvement achievable with multiple apertures, and sensor operation with a variable number of sun spots. Specifically, the sensor provides accuracy and precision in the order of 1 arcmin and 1 arcsec, respectively.

  16. Personality traits as determinants of the attitude towards women leaders in Montenegrin society

    Directory of Open Access Journals (Sweden)

    Mašnić Jelena

    2011-01-01

    Full Text Available This research aims at defining the determining influence of some psychological characteristics (authoritarianism, self-efficacy, life satisfaction and willingness to change on the attitude towards women leaders. We have used non-experimental research on the sample of 361 respondents from four Montenegrin municipalities (Podgorica, Bar, Nikšić and Berane. Most of the observed social-status characteristics are not important determinants of the observed attitude, which could indicate the presence of traditionalist beliefs about the role of women in the society. Authoritarian people are more prone to negative attitude towards the observed phenomenon. It is also advisable to consider this attitude in light of the resistance to change. Our results suggest the importance of improving the system of professional promotion of staff in modern organizations, especially in the direction of providing gender equality training, both when it comes to overall career development and when it comes to their acceptance of women in leading roles. An equal starting point for taking the leadership position would be provided by a redefinition of gender expectations as well as by the change in the perception of features and the role of leaders. .

  17. A practical small satellite variable-speed control moment gyroscope for combined energy storage and attitude control

    Science.gov (United States)

    Richie, David J.; Lappas, Vaios J.; Prassinos, George

    2009-12-01

    A recent effort to develop single-gimbal variable-speed control moment gyroscopes (VSCMGs) for a combined energy storage and attitude control subsystem (ESACS) on small satellites has culminated in laboratory validation of the concept. A single actuator prototype comprised of a cutting-edge Carbon Fiber rotor and COTS motor/generator components has been developed, balanced, bench tested, and integrated onto a spherical air-bearing structure. This structure is used to demonstrate the primary capability of a VSCMG to act as a dynamo whilst simultaneously changing a spacecraft's orientation in a controlled fashion. As originally predicted, the actuator's flywheel spins up when energy is supplied (supported via a direct energy transfer power architecture), then spins down when the energy source is removed, porting the energy released to run a resistive load. The work presented gives an overview of the governing principles of the technology, addresses the underlying mission and design requirements, and presents the prototype design. Then, effectiveness of the prototype integrated on a three-axis test article is presented along with its associated test data. Finally, discussion of these results and identification of future research concludes the work. The benefits of this technology for future space missions are that system consolidation permits mass reduction, higher instantaneous peak power is available as compared to conventional secondary battery systems, state-of-charge measurement is readily available from wheel speed feedback, and torque amplification through gimballing permits efficient actuator control. The technology demonstrated is exciting and leaves the door open for future development via inclusion of magnetic levitation.

  18. Precise orbit determination of the Fengyun-3C satellite using onboard GPS and BDS observations

    Science.gov (United States)

    Li, Min; Li, Wenwen; Shi, Chuang; Jiang, Kecai; Guo, Xiang; Dai, Xiaolei; Meng, Xiangguang; Yang, Zhongdong; Yang, Guanglin; Liao, Mi

    2017-04-01

    The GNSS Occultation Sounder instrument onboard the Chinese meteorological satellite Fengyun-3C (FY-3C) tracks both GPS and BDS signals for orbit determination. One month's worth of the onboard dual-frequency GPS and BDS data during March 2015 from the FY-3C satellite is analyzed in this study. The onboard BDS and GPS measurement quality is evaluated in terms of data quantity as well as code multipath error. Severe multipath errors for BDS code ranges are observed especially for high elevations for BDS medium earth orbit satellites (MEOs). The code multipath errors are estimated as piecewise linear model in 2° × 2° grid and applied in precise orbit determination (POD) calculations. POD of FY-3C is firstly performed with GPS data, which shows orbit consistency of approximate 2.7 cm in 3D RMS (root mean square) by overlap comparisons; the estimated orbits are then used as reference orbits for evaluating the orbit precision of GPS and BDS combined POD as well as BDS-based POD. It is indicated that inclusion of BDS geosynchronous orbit satellites (GEOs) could degrade POD precision seriously. The precisions of orbit estimates by combined POD and BDS-based POD are 3.4 and 30.1 cm in 3D RMS when GEOs are involved, respectively. However, if BDS GEOs are excluded, the combined POD can reach similar precision with respect to GPS POD, showing orbit differences about 0.8 cm, while the orbit precision of BDS-based POD can be improved to 8.4 cm. These results indicate that the POD performance with onboard BDS data alone can reach precision better than 10 cm with only five BDS inclined geosynchronous satellite orbit satellites and three MEOs. As the GNOS receiver can only track six BDS satellites for orbit positioning at its maximum channel, it can be expected that the performance of POD with onboard BDS data can be further improved if more observations are generated without such restrictions.

  19. Estimation of Vegetation Aerodynamic Roughness of Natural Regions Using Frontal Area Density Determined from Satellite Imagery

    Science.gov (United States)

    Jasinski, Michael F.; Crago, Richard

    1994-01-01

    Parameterizations of the frontal area index and canopy area index of natural or randomly distributed plants are developed, and applied to the estimation of local aerodynamic roughness using satellite imagery. The formulas are expressed in terms of the subpixel fractional vegetation cover and one non-dimensional geometric parameter that characterizes the plant's shape. Geometrically similar plants and Poisson distributed plant centers are assumed. An appropriate averaging technique to extend satellite pixel-scale estimates to larger scales is provided. ne parameterization is applied to the estimation of aerodynamic roughness using satellite imagery for a 2.3 sq km coniferous portion of the Landes Forest near Lubbon, France, during the 1986 HAPEX-Mobilhy Experiment. The canopy area index is estimated first for each pixel in the scene based on previous estimates of fractional cover obtained using Landsat Thematic Mapper imagery. Next, the results are incorporated into Raupach's (1992, 1994) analytical formulas for momentum roughness and zero-plane displacement height. The estimates compare reasonably well to reference values determined from measurements taken during the experiment and to published literature values. The approach offers the potential for estimating regionally variable, vegetation aerodynamic roughness lengths over natural regions using satellite imagery when there exists only limited knowledge of the vegetated surface.

  20. Precise orbit determination of a maneuvered GEO satellite using CAPS ranging data

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Wheel-off-loadings and orbital maneuvers of the GEO satellite result in additional accelerations to the satellite itself. Complex and difficult to model, these time varying accelerations are an important error source of precise orbit determination (POD). In most POD practices, only non-maneuver orbital arcs are treated. However, for some applications such as satellite navigation RDSS services, uninterrupted orbital ephemeris is demanded, requiring the development of POD strategies to be processed both during and after an orbital maneuver. We in this paper study the POD for a maneuvered GEO satellite, using high precision and high sampling rate ranging data obtained with Chinese Area Positioning System (CAPS). The strategy of long arc POD including maneuver arcs is studied by using telemetry data to model the maneuver thrust process. Combining the thrust and other orbital perturbations, a long arc of 6 days’ CAPS ranging data is analyzed. If the telemetry data are not available or contain significant errors, attempts are made to estimate thrusting parameters using CAPS ranging data in the POD as an alternative to properly account for the maneuver. Two strategies achieve reasonably good data fitting level in the tested arc with the maximal position difference being about 20 m.

  1. Precise orbit determination of a maneuvered GEO satellite using CAPS ransing data

    Institute of Scientific and Technical Information of China (English)

    HUANG Yong; HU XiaoGong; HUANG Cheng; YANG QiangWen; JIAO WenHai

    2009-01-01

    Wheel-off-loadings and orbital maneuvers of the GEO satellite result in additional accelerations to the satellite itself.Complex and difficult to model,these time varying accelerations are an important error source of precise orbit determination (POD).In most POD practices,only non-maneuver orbital arcs are treated.However,for some applications such as satellite navigation RDSS services,uninterrupted orbital ephemeris is demanded,requiring the development of POD strategies to be processed both during and after an orbital maneuver.We in this paper study the POD for a maneuvered GEO satellite,using high precision and high sampling rate ranging data obtained with Chinese Area Positioning System (CAPS).The strategy of long arc POD including maneuver arcs is studied by using telemetry data to model the maneuver thrust process.Combining the thrust and other orbital perturbations,a long arc of 6 days' CAPS ranging data is analyzed.If the telemetry data are not available or contain significant errors,attempts are made to estimate thrusting parameters using CAPS ranging data in the POD as an alternative to properly account for the maneuver.Two strategies achieve reasonably good data fitting level in the tested arc with the maximal position difference being about 20m.

  2. Precise orbit determination of a maneuvered GEO satellite using CAPS ranging data

    Science.gov (United States)

    Huang, Yong; Hu, Xiaogong; Huang, Cheng; Yang, Qiangwen; Jiao, Wenhai

    2009-03-01

    Wheel-off-loadings and orbital maneuvers of the GEO satellite result in additional accelerations to the satellite itself. Complex and difficult to model, these time varying accelerations are an important error source of precise orbit determination (POD). In most POD practices, only non-maneuver orbital arcs are treated. However, for some applications such as satellite navigation RDSS services, uninterrupted orbital ephemeris is demanded, requiring the development of POD strategies to be processed both during and after an orbital maneuver. We in this paper study the POD for a maneuvered GEO satellite, using high precision and high sampling rate ranging data obtained with Chinese Area Positioning System (CAPS). The strategy of long arc POD including maneuver arcs is studied by using telemetry data to model the maneuver thrust process. Combining the thrust and other orbital perturbations, a long arc of 6 days’ CAPS ranging data is analyzed. If the telemetry data are not available or contain significant errors, attempts are made to estimate thrusting parameters using CAPS ranging data in the POD as an alternative to properly account for the maneuver. Two strategies achieve reasonably good data fitting level in the tested arc with the maximal position difference being about 20 m.

  3. Tests of daily time variable Earth gravity field solutions for precise orbit determination of altimetry satellites

    Science.gov (United States)

    Rudenko, Sergei; Gruber, Christian

    2016-04-01

    This study makes use of current GFZ monthly and daily gravity field products from 2002 to 2014 based on radial basis functions (RBF) instead of time variable gravity field modeling for precise orbit determination of altimetry satellites. Since some monthly solutions are missing in the GFZ GRACE RL05a solution and in order to reach a better quality for the precise orbit determination, daily generated RBF solutions obtained from Kalman filtered GRACE data processing and interpolated in case of gaps have been used. Moreover, since the geopotential coefficients of low degrees are better determined using SLR observations to geodetic satellites like Lageos, Stella, Starlette and Ajisai than from GRACE observations, these terms are co-estimated in the RBF solutions by using apriori SLR-derived values up to degree and order 4. Precise orbits for altimetry satellites Envisat (2002-2012), Jason-1 (2002-2013) and Jason-2 (2008-2014) are then computed over the given time intervals using this approach and compared with the orbits obtained when using other models such as EIGEN-6S4. An analysis of the root-mean-square values of the observation fits of SLR and DORIS observations and the orbit arcs overlaps will allow us to draw a conclusion on the quality of the RBF solution and to use these new trajectories for sea level trend estimates and geophysical application.

  4. Precise Orbit Determination of the two LAGEOS and LARES satellites and the LARASE activities

    Science.gov (United States)

    Massimo Lucchesi, David; Peron, Roberto; Anselmo, Luciano; Bassan, Massimo; Magnafico, Carmelo; Nobili, Anna Maria; Pardini, Carmen; Pucacco, Giuseppe; Stanga, Ruggero; Visco, Massimo

    2016-04-01

    The LAser RAnged Satellites Experiment (LARASE) research program aims to provide an original contribution in testing and verifying Einstein's theory of General Relativity (GR) in its Weak-Field and Slow-Motion (WFSM) limit by means of the powerful Satellite Laser Ranging (SLR) technique. Therefore, in this perspective, a Precise Orbit Determination (POD) of a dedicated set of passive laser-ranged satellites is required. In particular, the joint analysis of the orbit of the two LAGEOS (LAser GEOdynamic Satellite) satellites with that of the more recently launched LARES (LAser RElativity Satellite) satellite will be exploited in order to obtain precise measurements of the gravitational interaction in the field of the Earth. A major point to be reached within the activities of LARASE is to provide the relativistic measurements with an error budget of the various systematic effects (both gravitational and non-gravitational) that be robust and reliable. This requires a careful analysis of the various disturbing effects on the orbit of the considered satellites, especially for the new LARES. This activity has been planned both for the gravitational and the non-gravitational perturbations (NGP). Therefore, we started to re-visit, update and improve previous dynamical models, especially for the NGP, and we also developed new models in such a way to improve the current dynamical models used in space geodesy to account for the main perturbations acting on the orbit of LAGEOS and LARES. We focused especially on the spin dynamics, the drag effects (especially for LARES, because of its much lower height with respect to the two LAGEOS) and, at a preliminary level, the thermal ones that, as it is well known from the literature, are very important for the LAGEOS satellites. These studies are of fundamental importance not only for the objective of a reliable error budget, but also in order to improve the POD. In this context, because of the importance of the LAGEOS satellites in

  5. Satellite Control Laboratory

    DEFF Research Database (Denmark)

    Wisniewski, Rafal; Bak, Thomas

    2001-01-01

    The Satellite Laboratory at the Department of Control Engineering of Aalborg University (SatLab) is a dynamic motion facility designed for analysis and test of micro spacecraft. A unique feature of the laboratory is that it provides a completely gravity-free environment. A test spacecraft...... of the laboratory is to conduct dynamic tests of the control and attitude determination algorithms during nominal operation and in abnormal conditions. Further it is intended to use SatLab for validation of various algorithms for fault detection, accommodation and supervisory control. Different mission objectives...... can be implemented in the laboratory, e.g. three-axis attitude control, slew manoeuvres, spins stabilization using magnetic actuation and/or reaction wheels. The spacecraft attitude can be determined applying magnetometer measurements...

  6. DETERMINANTS OF EMPLOYEES’ ATTITUDE TOWARD UNION MEMBERSHIP (Study Case In A Logistics Company In Indonesia)

    OpenAIRE

    Dewantoro, Ranggapati Siswara; Sobri, Riani Rachmawati; Syaebani, Muhammad Irfan

    2015-01-01

    This research examines the determinants of employees’ attitude toward union membership.These factors are represented by job-related predictor such as; employees’ jobdissatisfaction, job stress, and consultative managerial style. Apart from these job-relatedpredictor variables, the cultural orientation played a role in this research such as;individualism and collectivism both horizontal and vertical. After performing resgressiontesting, the result shows that almost all variables are affecting ...

  7. First Attempt of Orbit Determination of SLR Satellites and Space Debris Using Genetic Algorithms

    Science.gov (United States)

    Deleflie, F.; Coulot, D.; Descosta, R.; Fernier, A.; Richard, P.

    2013-08-01

    We present an orbit determination method based on genetic algorithms. Contrary to usual estimation methods mainly based on least-squares methods, these algorithms do not require any a priori knowledge of the initial state vector to be estimated. These algorithms can be applied when a new satellite is launched or for uncatalogued objects that appear in images obtained from robotic telescopes such as the TAROT ones. We show in this paper preliminary results obtained from an SLR satellite, for which tracking data acquired by the ILRS network enable to build accurate orbital arcs at a few centimeter level, which can be used as a reference orbit ; in this case, the basic observations are made up of time series of ranges, obtained from various tracking stations. We show as well the results obtained from the observations acquired by the two TAROT telescopes on the Telecom-2D satellite operated by CNES ; in that case, the observations are made up of time series of azimuths and elevations, seen from the two TAROT telescopes. The method is carried out in several steps: (i) an analytical propagation of the equations of motion, (ii) an estimation kernel based on genetic algorithms, which follows the usual steps of such approaches: initialization and evolution of a selected population, so as to determine the best parameters. Each parameter to be estimated, namely each initial keplerian element, has to be searched among an interval that is preliminary chosen. The algorithm is supposed to converge towards an optimum over a reasonable computational time.

  8. Determination of the Impact of Urbanization on Agricultural Lands using Multi-temporal Satellite Sensor Images

    Science.gov (United States)

    Kaya, S.; Alganci, U.; Sertel, E.; Ustundag, B.

    2015-12-01

    Throughout the history, agricultural activities have been performed close to urban areas. Main reason behind this phenomenon is the need of fast marketing of the agricultural production to urban residents and financial provision. Thus, using the areas nearby cities for agricultural activities brings out advantage of easy transportation of productions and fast marketing. For decades, heavy migration to cities has directly and negatively affected natural grasslands, forests and agricultural lands. This pressure has caused agricultural lands to be changed into urban areas. Dense urbanization causes increase in impervious surfaces, heat islands and many other problems in addition to destruction of agricultural lands. Considering the negative impacts of urbanization on agricultural lands and natural resources, a periodic monitoring of these changes becomes indisputably important. At this point, satellite images are known to be good data sources for land cover / use change monitoring with their fast data acquisition, large area coverages and temporal resolution properties. Classification of the satellite images provides thematic the land cover / use maps of the earth surface and changes can be determined with GIS based analysis multi-temporal maps. In this study, effects of heavy urbanization over agricultural lands in Istanbul, metropolitan city of Turkey, were investigated with use of multi-temporal Landsat TM satellite images acquired between 1984 and 2011. Images were geometrically registered to each other and classified using supervised maximum likelihood classification algorithm. Resulting thematic maps were exported to GIS environment and destructed agricultural lands by urbanization were determined using spatial analysis.

  9. Mean Sea Surface (mss) Model Determination for Malaysian Seas Using Multi-Mission Satellite Altimeter

    Science.gov (United States)

    Yahaya, N. A. Z.; Musa, T. A.; Omar, K. M.; Din, A. H. M.; Omar, A. H.; Tugi, A.; Yazid, N. M.; Abdullah, N. M.; Wahab, M. I. A.

    2016-09-01

    The advancement of satellite altimeter technology has generated many evolutions to oceanographic and geophysical studies. A multi-mission satellite altimeter consists with TOPEX, Jason-1 and Jason-2, ERS-2, Envisat-1, CryoSat-2 and Saral are extracted in this study and has been processed using Radar Altimeter Database System (RADS) for the period of January 2005 to December 2015 to produce the sea surface height (hereinafter referred to SSH). The monthly climatology data from SSH is generated and averaged to understand the variation of SSH during monsoon season. Then, SSH data are required to determine the localised and new mean sea surface (MSS). The differences between Localised MSS and DTU13 MSS Global Model is plotted with root mean square error value is 2.217 metres. The localised MSS is important towards several applications for instance, as a reference for sea level variation, bathymetry prediction and derivation of mean dynamic topography.

  10. MEAN SEA SURFACE (MSS MODEL DETERMINATION FOR MALAYSIAN SEAS USING MULTI-MISSION SATELLITE ALTIMETER

    Directory of Open Access Journals (Sweden)

    N. A. Z. Yahaya

    2016-09-01

    Full Text Available The advancement of satellite altimeter technology has generated many evolutions to oceanographic and geophysical studies. A multi-mission satellite altimeter consists with TOPEX, Jason-1 and Jason-2, ERS-2, Envisat-1, CryoSat-2 and Saral are extracted in this study and has been processed using Radar Altimeter Database System (RADS for the period of January 2005 to December 2015 to produce the sea surface height (hereinafter referred to SSH. The monthly climatology data from SSH is generated and averaged to understand the variation of SSH during monsoon season. Then, SSH data are required to determine the localised and new mean sea surface (MSS. The differences between Localised MSS and DTU13 MSS Global Model is plotted with root mean square error value is 2.217 metres. The localised MSS is important towards several applications for instance, as a reference for sea level variation, bathymetry prediction and derivation of mean dynamic topography.

  11. Satellite techniques for determining the geopotential for sea-surface elevations

    Science.gov (United States)

    Pisacane, V. L.

    1984-01-01

    Spaceborne altimetry with measurement accuracies of a few centimeters which has the potential to determine sea surface elevations necessary to compute accurate three-dimensonal geostrophic currents from traditional hydrographic observation is discussed. The limitation in this approach is the uncertainties in knowledge of the global and ocean geopotentials which produce satellite and height uncertainties about an order of magnitude larger than the goal of about 10 cm. The quantative effects of geopotential uncertainties on processing altimetry data are described. Potential near term improvements, not requiring additional spacecraft, are discussed. Even though there is substantial improvements at the longer wavelengths, the oceanographic goal will be achieved. The geopotential research mission (GRM) is described which should produce goepotential models that are capable of defining the ocean geid to 10 cm and near-Earth satellite position. The state of the art and the potential of spaceborne gravimetry is described as an alternative approach to improve our knowledge of the geopotential.

  12. Precise Orbit Determination of BeiDou Satellites with Contributions from Chinese National Continuous Operating Reference Stations

    Directory of Open Access Journals (Sweden)

    Ming Chen

    2017-08-01

    Full Text Available The precise orbit determination (POD for BeiDou satellites is usually limited by the insufficient quantity and poor distribution of ground tracking stations. To cope with this problem, this study used the GPS and BeiDou joint POD method based on Chinese national continuous operating reference stations (CNCORS and IGS/MGEX stations. The results show that the 3D RMS of the differences of overlapping arcs is better than 22 cm for geostationary orbit (GEO satellites and better than 10 cm for inclined geosynchronous orbit (IGSO and medium earth orbit (MEO satellites. The radial RMS is better than 2 cm for all three types of BeiDou satellites. The results of satellite laser ranging (SLR residuals show that the RMS of the IGSO and MEO satellites is better than 5 cm, whereas the GEO satellite has a systematic bias. This study investigates the contributions of CNCORS to the POD of BeiDou satellites. The results show that after the incorporation of CNCORS, the precision of overlapping arcs of the GEO, IGSO, and MEO satellites is improved by 15.5%, 57.5%, and 5.3%, respectively. In accordance with the improvement in the precision of overlapping arcs, the accuracy of the IGSO and MEO satellites assessed by the SLR is improved by 30.1% and 4.8%, respectively. The computation results and analysis demonstrate that the inclusion of CNCORS yields the biggest contribution in the improvement of orbit accuracy for IGSO satellites, when compared to GEO satellites, while the orbit improvement for MEO satellites is the lowest due to their global coverage.

  13. Formulation of geopotential difference determination using optical-atomic clocks onboard satellites and on ground based on Doppler cancellation system

    Science.gov (United States)

    Shen, Ziyu; Shen, Wen-Bin; Zhang, Shuangxi

    2016-08-01

    In this study, we propose an approach for determining the geopotential difference using high-frequency-stability microwave links between satellite and ground station based on Doppler cancellation system. Suppose a satellite and a ground station are equipped with precise optical-atomic clocks (OACs) and oscillators. The ground oscillator emits a signal with frequency fa towards the satellite and the satellite receiver (connected with the satellite oscillator) receives this signal with frequency fb which contains the gravitational frequency shift effect and other signals and noises. After receiving this signal, the satellite oscillator transmits and emits, respectively, two signals with frequencies fb and fc towards the ground station. Via Doppler cancellation technique, the geopotential difference between the satellite and the ground station can be determined based on gravitational frequency shift equation by a combination of these three frequencies. For arbitrary two stations on ground, based on similar procedures as described above, we may determine the geopotential difference between these two stations via a satellite. Our analysis shows that the accuracy can reach 1 m2 s- 2 based on the clocks' inaccuracy of about 10-17 (s s-1) level. Since OACs with instability around 10-18 in several hours and inaccuracy around 10-18 level have been generated in laboratory, the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.

  14. GPS卫星导航系统多频姿态测量技术研究%Research on GPS Satellite Navigation System Multi-frequency Attitude Determinat ion Technology

    Institute of Scientific and Technical Information of China (English)

    李献球; 甘兴利; 李隽

    2012-01-01

    GPS modernization provides a foundation for developing multi-frequency a ttitude determination receiver.To satisfy the attitude determination requiremen ts of platforms such as low orbit satellites,missiles,aircrafts and naval vess els,a general design scheme for multi-frequency attitude determination receive r is given,which is composed of antenna unit,measurement unit and attitude comp utation unit.Then,some key technologies are investigated,including real-time cycle slip detection and correction based on GPS multi-frequency combination no i se residual,and the ambiguity resolution algorithm for single epoch using geome try restriction.The computation equations and flows are described in detail.Fi nally,a static test is carried out for the GPS-based single frequency receiver and multi-frequency receiver for attitude determination.The test results indic a te that,as for the attitude determination accuracy and computation success rati o,the multi-frequency receiver shows better performance than that of the singl e-frequency receiver.%GPS全球卫星导航系统现代化工作,为多频姿态测量接收机的研制提供了基础条件。针对低轨卫星、导弹、飞机和舰艇等平台对姿态测量的使用需求,给出了由天线单元、测量单元和姿态解算单元构成的多频姿态测量接收机总体方案。研究了基于GPS多频组合噪声残差法实时探测与修复周跳、基于几何约束的单历元模糊度解算等关键技术,并给出了详细的计算方程和流程。对GPS单频定姿接收机和多频定姿接收机进行静态试验,证明后者在测姿精度和解算成功率方面都优于前者。

  15. Determining Prospective Elementary Teachers' Attitudes Towards Computer: A Sample from Turkey

    Directory of Open Access Journals (Sweden)

    S. Birisci

    2009-06-01

    Full Text Available The aim of this study is to determine prospective elementary teachers’ attitudes towards computers. This research was carried out in fall semester of 2007 at a small university in northeastern Turkey with 248 prospective elementary teachers. In order to get general results about the sample survey methodology was used. Results show that computer attitudes of prospective elementary teachers are at medium level. No significant differences were found between gender, high school type and monthly family income independent variables and computer liking, computer anxiety and use of computers in education/instruction sub-scales. However, a significant difference was found between high school type and computer anxiety and computers in education/instruction sub-scales.

  16. FACOTRS TO DETERMINE RISK PERCEPTION OF CLIMATE CHANGE, AND ATTITUDE TOWARD ADAPTATION POLICY OF THE PUBLIC

    Science.gov (United States)

    Baba, Kenshi; Sugimoto, Takuya; Kubota, Hiromi; Hijioka, Yasuaki; Tanaka, Mitsuru

    This study clarifies the factors to determine risk perception of climate change and attitudes toward adaptation policy by analyzing the data collecting from Internet survey to the general public. The results indicate the followings: 1) more than 70% people perceive some sort of risk of climate change, and most people are awaken to wind and flood damage. 2) most people recognize that mitigation policy is much more important than adaptation policy, whereas most people assume to accept adaptation policy as self-reponsibility, 3) the significant factors to determinane risk perception of climate chage and attitude towerd adaptation policy are cognition of benefits on the policy and procedural justice in the policy process in addion to demographics such as gender, experience of disaster, intension of inhabitant.

  17. A remark on the GNSS single difference model with common clock scheme for attitude determination

    Science.gov (United States)

    Chen, Wantong

    2016-09-01

    GNSS-based attitude determination technique is an important field of study, in which two schemes can be used to construct the actual system: the common clock scheme and the non-common clock scheme. Compared with the non-common clock scheme, the common clock scheme can strongly improve both the reliability and the accuracy. However, in order to gain these advantages, specific care must be taken in the implementation. The cares are thus discussed, based on the generating technique of carrier phase measurement in GNSS receivers. A qualitative assessment of potential phase bias contributes is also carried out. Possible technical difficulties are pointed out for the development of single-board multi-antenna GNSS attitude systems with a common clock.

  18. Baseline configuration for GNSS attitude determination with an analytical least-squares solution

    Science.gov (United States)

    Chang, Guobin; Xu, Tianhe; Wang, Qianxin

    2016-12-01

    The GNSS attitude determination using carrier phase measurements with 4 antennas is studied on condition that the integer ambiguities have been resolved. The solution to the nonlinear least-squares is often obtained iteratively, however an analytical solution can exist for specific baseline configurations. The main aim of this work is to design this class of configurations. Both single and double difference measurements are treated which refer to the dedicated and non-dedicated receivers respectively. More realistic error models are employed in which the correlations between different measurements are given full consideration. The desired configurations are worked out. The configurations are rotation and scale equivariant and can be applied to both the dedicated and non-dedicated receivers. For these configurations, the analytical and optimal solution for the attitude is also given together with its error variance-covariance matrix.

  19. An improved quaternion Gauss–Newton algorithm for attitude determination using magnetometer and accelerometer

    Directory of Open Access Journals (Sweden)

    Liu Fei

    2014-08-01

    Full Text Available For the vector attitude determination, the traditional optimal algorithms which are based on quaternion estimator (QUEST measurement noise model are complicated for just two observations. In our application, the magnetometer and accelerometer are not two comparable kinds of sensors and both are not small field-of-view sensors as well. So in this paper a new unit measurement model is derived. According to the Wahba problem, the optimal weights for each measurement are obtained by the error variance researches. Then an improved quaternion Gauss–Newton method is presented and adopted to acquire attitude. Eventually, simulation results and experimental validation employed to test the proposed method demonstrate the usefulness of the improved algorithm.

  20. An improved quaternion Gauss-Newton algorithm for attitude determination using magnetometer and accelerometer

    Institute of Scientific and Technical Information of China (English)

    Liu Fei; Li Jie; Wang Haifu; Liu Chang

    2014-01-01

    For the vector attitude determination, the traditional optimal algorithms which are based on quaternion estimator (QUEST) measurement noise model are complicated for just two observa-tions. In our application, the magnetometer and accelerometer are not two comparable kinds of sen-sors and both are not small field-of-view sensors as well. So in this paper a new unit measurement model is derived. According to the Wahba problem, the optimal weights for each measurement are obtained by the error variance researches. Then an improved quaternion Gauss-Newton method is presented and adopted to acquire attitude. Eventually, simulation results and experimental valida-tion employed to test the proposed method demonstrate the usefulness of the improved algorithm.

  1. Determination of the tectonic plate motion by satellite laser ranging in 1999-2003

    Science.gov (United States)

    Schillak, S.; Wnuk, E.

    The paper presents results of the tectonic plates motion determination from satellite laser ranging in the period 1999-2003 The SLR station velocities were calculated from station geocentric coordinates determined from one month orbital arcs of Lageos-1 and Lageos-2 satellites for the first day of each arc The mean orbital RMS-of-fit for 5 years was equal to 15 mm The station velocities were determined for 29 stations and points in 1999-2003 it means for all SLR stations with data time span longer than 20 months The accuracy of station velocities determination varied from 0 4 mm year to 3 mm year dependent on quality of data and data span The difference of station velocities between ITRF2000 and the presented results were in the range 0-5 mm year Only for four stations Riyad Maidanak-2 Beijng and Arequipa after earthquake in 2001 the differences were statistically significant For the most stations is a good agreement with the NUVEL1A model of tectonic plates motion The significant differences were detected for stations Arequipa Concepcion Shanghai and Simosato The results differs from the model NUVEL1A in the station velocities and azimuths for South America tectonic plate and Japan

  2. A new method to determine eroded areas in arid environment using Landsat satellite imagery

    Science.gov (United States)

    A, Aydda; Ah, Algouti; Ab, Algouti; M, Essemani; Y, Taghya

    2014-06-01

    Erosion (by water or wind) is an increasing problem for many local authorities and government agencies throughout the world. The identification of eroded areas in arid and humid regions can be very useful for environmental planning and can help reduce soil and sediment degradation in these regions. In this work we present a new method to determine eroded areas in arid environment. In this method were explored lithological data to determine eroded areas. These data were collected in the field using GPS (Global Positioning System) checkpoints and geological maps. For that, two lithological maps of the study areas were analysed to determine lithological data change. Those two maps were obtained from the classification algorithm by applying the maximum likelihood on two Landsat satellite images. After images classification and validation a change detection technique was adopted to determine eroded areas. This method was applied in northern part of Atlantic Sahara desert to confirm their potentiality.

  3. Real-time precise orbit determination of LEO satellites using a single-frequency GPS receiver: Preliminary results of Chinese SJ-9A satellite

    Science.gov (United States)

    Sun, Xiucong; Han, Chao; Chen, Pei

    2017-10-01

    Spaceborne Global Positioning System (GPS) receivers are widely used for orbit determination of low-Earth-orbiting (LEO) satellites. With the improvement of measurement accuracy, single-frequency receivers are recently considered for low-cost small satellite missions. In this paper, a Schmidt-Kalman filter which processes single-frequency GPS measurements and broadcast ephemerides is proposed for real-time precise orbit determination of LEO satellites. The C/A code and L1 phase are linearly combined to eliminate the first-order ionospheric effects. Systematic errors due to ionospheric delay residual, group delay variation, phase center variation, and broadcast ephemeris errors, are lumped together into a noise term, which is modeled as a first-order Gauss-Markov process. In order to reduce computational complexity, the colored noise is considered rather than estimated in the orbit determination process. This ensures that the covariance matrix accurately represents the distribution of estimation errors without increasing the dimension of the state vector. The orbit determination algorithm is tested with actual flight data from the single-frequency GPS receiver onboard China's small satellite Shi Jian-9A (SJ-9A). Preliminary results using a 7-h data arc on October 25, 2012 show that the Schmidt-Kalman filter performs better than the standard Kalman filter in terms of accuracy.

  4. Determination of Pole and Rotation Period of not Stabilized Artificial Satellite by Use of Model "diffuse Cylinder"

    Science.gov (United States)

    Kolesnik, S. Ya.; Dobrovolsky, A. V.; Paltsev, N. G.

    The algorithm of determination of orientation of rotation axis (pole) and rotation period of satellite, simulated by a cylinder, which is precessing around of vector of angular moment of pulse with constant nutation angle is offered. The Lambert's law of light reflection is accepted. Simultaneously, dependence of light reflection coefficient versus phase angle is determined. The model's simulation confirm applicability of this method. Results of the calculations for artificial satellite No 28506 are carried out.

  5. Determination of the position of the station Borowiec Nr 7811 by satellite laser observations

    Science.gov (United States)

    Dobaczewska, W.; Drozyner, A.; Rutkowska, M.; Schillak, S.; Zielinski, J. B.

    Laser observations during 1977-1979 of the GEOS-1 and GEOS-3 satellites, used to determine the geocentric position of the Astronomical Latitude Observatory in Borowiec (station No. 7811) are examined. The data are processed by means of the ORBITA program and the GRIPE program elaborated at the Smithsonian Astrophysical Observatory. The coordinates of the station are calculated by a dynamical orbital method. Results of the ORBITA and GRIPE solutions are presented in tables. A comparison of these two solutions with the Wettzel-Borowiec translocation solution is considered.

  6. Determination of Land Use from Satellite Imagery for Input to Hydrologic Models.

    Science.gov (United States)

    1980-04-01

    Symposium on Remote Sensing of thieK Environment, 23-30 April 1980, San Jose, Costa Rica 19. KEY WORDS - C=Wm*. eO I.W. EII..e.wvm I*FS Week atfm...Fourteenth International Symposium on Remote Sensing of the Environment, 23-30 April 1980, San Jose, Costa Rica DETERMINATION OF LAND USE FROM SATELLITE...Factors in Small Hydropower Planning, Darryl W. Davis, February 1979, 38 pages. #62 Flood Hydrograph and Peak Flow Frequency Analysis, Arlen D. Feldman

  7. The Three-Dimensional Spatial Structure of Cirrus Clouds Determined from Lidar Satellite Observations

    Science.gov (United States)

    Eloranta, E. W.; Wylie, D.; Wolf, W.

    1996-01-01

    Simultaneous imagery from the University of Wisconsin Volume Imaging Lidar (VIL) and meteorological satellites were used to quantify the spatial structure of cirrus clouds with 60 m resolution. This data was used to determine the spatial distributions of cloud base altitude, cloud top altitude, and mid-cloud altitude. Two dimensional auto-correlation functions describing the mean shape of cirrus clouds were computed. Because cirrus clouds seldom have distinct edges, these correlation functions are derived as a function of a threshold value which defines the cloud edge.

  8. Preliminary Study of Satellite Attitude Determination for the LANDSAT 7 Spacecraft

    Science.gov (United States)

    1994-04-01

    ROBERT BOSCH STRASSE 5 D 6100 DARMSTADT GERMANY ATTN PROF ALFRED LEICK 1 DEPARTMENT OF SURVEYING ATTN G SEEBER 1 ENGINEERING UNIVERSITY OF HANOVER...20771 K14 5 K40 1 ATTN B SCHUTZ 1 K43 2 CENTER FOR SPACE RESEARCH N74 GIDEP 1 WRW402 UNIVERSITY OF TEXAS AT AUSTIN AUSTIN TX 78712 DEFENSE TECHNICAL

  9. Determination of quasi-static microaccelerations onboard a satellite using video images of moving objects

    Science.gov (United States)

    Levtov, V. L.; Romanov, V. V.; Boguslavsky, A. A.; Sazonov, V. V.; Sokolov, S. M.; Glotov, Yu. N.

    2009-12-01

    A space experiment aimed at determination of quasi-static microaccelerations onboard an artificial satellite of the Earth using video images of the objects executing free motion is considered. The experiment was carried out onboard the Foton M-3 satellite. Several pellets moved in a cubic box fixed on the satellite’s mainframe and having two transparent adjacent walls. Their motion was photographed by a digital video camera. The camera was installed facing one of the transparent walls; a mirror was placed at an angle to another transparent wall. Such an optical system allowed us to have in a single frame two images of the pellets from differing viewpoints. The motion of the pellets was photographed on time intervals lasting 96 s. Pauses between these intervals were also equal to 96 s. A special processing of a separate image allowed us to determine coordinates of the pellet centers in the camera’s coordinate system. The sequence of frames belonging to a continuous interval of photography was processed in the following way. The time dependence of each coordinate of every pellet was approximated by a second degree polynomial using the least squares method. The coefficient of squared time is equal to a half of the corresponding microacceleration component. As has been shown by processing made, the described method of determination of quasi-static microaccelerations turned out to be sufficiently sensitive and accurate.

  10. Equilibria of a charged artificial satellite subject to gravitational and Lorentz torques

    CERN Document Server

    Abdel-Aziz, Yehia A

    2014-01-01

    Attitude Dynamics of a rigid artificial satellite subject to gravity gradient and Lorentz torques in a circular orbit is considered. Lorentz torque is developed on the basis of the electrodynamic effects of the Lorentz force acting on the charged satellite's surface. We assume that the satellite is moving in Low Earth Orbit (LEO) in the geomagnetic field which is considered as a dipole model. Our model of the torque due to the Lorentz force is developed for a general shape of artificial satellite, and the nonlinear differential equations of Euler are used to describe its attitude orientation. All equilibrium positions are determined and {their} existence conditions are obtained. The numerical results show that the charge $q$ and radius $\\rho_0$ of the charged center of satellite provide a certain type of semi passive control for the attitude of satellite. The technique for such kind of control would be to increase or decrease the electrostatic radiation screening of the satellite. The results {obtained} confi...

  11. Determination of Destructed and Infracted Forest Areas with Multi-temporal High Resolution Satellite Images

    Science.gov (United States)

    Seker, D. Z.; Unal, A.; Kaya, S.; Alganci, U.

    2015-12-01

    Migration from rural areas to city centers and their surroundings is an important problem of not only our country but also the countries that under development stage. This uncontrolled and huge amount of migration brings out urbanization and socio - economic problems. The demand on settling the industrial areas and commercial activities nearby the city centers results with a negative change in natural land cover on cities. Negative impacts of human induced activities on natural resources and land cover has been continuously increasing for decades. The main human activities that resulted with destruction and infraction of forest areas can be defined as mining activities, agricultural activities, industrial / commercial activities and urbanization. Temporal monitoring of the changes in spatial distribution of forest areas is significantly important for effective management and planning progress. Changes can occur as spatially large destructions or small infractions. Therefore there is a need for reliable, fast and accurate data sources. At this point, satellite images proved to be a good data source for determination of the land use /cover changes with their capability of monitoring large areas with reasonable temporal resolutions. Spectral information derived from images provides discrimination of land use/cover types from each other. Developments in remote sensing technology in the last decade improved the spatial resolution of satellites and high resolution images were started to be used to detect even small changes in the land surface. As being the megacity of Turkey, Istanbul has been facing a huge migration for the last 20 years and effects of urbanization and other human based activities over forest areas are significant. Main focus of this study is to determine the destructions and infractions in forest areas of Istanbul, Turkey with 2.5m resolution SPOT 5 multi-temporal satellite imagery. Analysis was mainly constructed on threshold based classification of

  12. A MEMS-based Adaptive AHRS for Marine Satellite Tracking Antenna

    DEFF Research Database (Denmark)

    Wang, Yunlong; Hussain, Dil Muhammed Akbar; Soltani, Mohsen

    2015-01-01

    Satellite tracking is a challenging task for marine applications. An attitude determination system should estimate the wave disturbances on the ship body accurately. To achieve this, an Attitude Heading Reference System (AHRS) based on Micro-Electro-Mechanical Systems (MEMS) sensors, composed...... of three-axis gyroscope, accelerometer and magnetometer, is developed for Marine Satellite Tracking Antenna (MSTA). In this paper, the attitude determination algorithm is improved using an adaptive mechanism that tunes the attitude estimator parameters based on an estimation of ship motion frequency...

  13. DETERMINATION OF FACULTY OF EDUCATION STUDENTS’ ATTITUDES AS REGARDS LEVEL OF THE RECOGNITION OF HACI BEKTAS VELI AND ATTITUDES ON BEKTASHISM

    Directory of Open Access Journals (Sweden)

    Recep Özkan

    2014-04-01

    Full Text Available There are some significant characters shaping the life of societies. Introducing these characters to young generations plays an important role for their upbringing. Hacı Bektasi Veli comes to the fore as one of these characters. The purpose of this study is to determine the Faculty of Education of Nigde University students’ recognition level of Haci Bektas Veli and their attitudes about the Bektashism. In this study, questionnaire and literature review techniques have been applied. According to t test results, male students’ positive attitudes about Hacı Bektasi Veli are higher than female students. Positive attitudes of daytime and evening education students don’t show significant difference. According to one-way variance analysis test results, students of primary school teaching account for 33.61, social sciences teaching account for 34.03, Turkish teaching account for 34.27 and it is observed that there is no statistically significant difference between mean points of students.

  14. The ST5000: An Attitude Determination System with Low-Bandwidth Digital Imaging

    Science.gov (United States)

    Percival, J. W.; Nordsieck, K. H.

    The Space Astronomy Laboratory is building an attitude determination and digital imaging system with embedded compression. The attitude determination system uses a 30-square-degree field of view and an embedded star catalog to determine the Right Ascension and Declination of its line of sight to better than 5 arcseconds. The digital imaging subsystem uses a scheme of ``progressive image transmission'' in which the image is sent out over a very-low-bandwidth channel, such as a spacecraft telemetry downlink, in such a way that it can be reconstructed ``on the fly'' and updated as more data arrive. Large (768×474) useful images can be obtained over a 4-kbit downlink in as little as 10 seconds. In addition to its use in sounding rockets and spacecraft, we are planning to use it for two ground-based applications at the Southern Africa Large Telescope (SALT). We will explore its use in generating real-time measurements of the telescope pointing, independent of the telescope control system, and we will use the low bandwidth imaging capability for public outreach.

  15. Real-time single-frequency GPS/MEMS-IMU attitude determination of lightweight UAVs.

    Science.gov (United States)

    Eling, Christian; Klingbeil, Lasse; Kuhlmann, Heiner

    2015-10-16

    In this paper, a newly-developed direct georeferencing system for the guidance, navigation and control of lightweight unmanned aerial vehicles (UAVs), having a weight limit of 5 kg and a size limit of 1.5 m, and for UAV-based surveying and remote sensing applications is presented. The system is intended to provide highly accurate positions and attitudes (better than 5 cm and 0.5°) in real time, using lightweight components. The main focus of this paper is on the attitude determination with the system. This attitude determination is based on an onboard single-frequency GPS baseline, MEMS (micro-electro-mechanical systems) inertial sensor readings, magnetic field observations and a 3D position measurement. All of this information is integrated in a sixteen-state error space Kalman filter. Special attention in the algorithm development is paid to the carrier phase ambiguity resolution of the single-frequency GPS baseline observations. We aim at a reliable and instantaneous ambiguity resolution, since the system is used in urban areas, where frequent losses of the GPS signal lock occur and the GPS measurement conditions are challenging. Flight tests and a comparison to a navigation-grade inertial navigation system illustrate the performance of the developed system in dynamic situations. Evaluations show that the accuracies of the system are 0.05° for the roll and the pitch angle and 0.2° for the yaw angle. The ambiguities of the single-frequency GPS baseline can be resolved instantaneously in more than 90% of the cases.

  16. The GLAS Algorithm Theoretical Basis Document for Precision Attitude Determination (PAD)

    Science.gov (United States)

    Bae, Sungkoo; Smith, Noah; Schutz, Bob E.

    2013-01-01

    The Geoscience Laser Altimeter System (GLAS) was the sole instrument for NASAs Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry mission. The primary purpose of the ICESat mission was to make ice sheet elevation measurements of the polar regions. Additional goals were to measure the global distribution of clouds and aerosols and to map sea ice, land topography and vegetation. ICESat was the benchmark Earth Observing System (EOS) mission to be used to determine the mass balance of the ice sheets, as well as for providing cloud property information, especially for stratospheric clouds common over polar areas.

  17. 75 FR 5513 - Determination of Rates and Terms for Preexisting Subscription Services and Satellite Digital...

    Science.gov (United States)

    2010-02-03

    ... Services and Satellite Digital Audio Radio Services AGENCY: Copyright Royalty Board, Library of Congress... rates for the preexisting satellite digital audio radio services' use of the ephemeral recordings... preexisting satellite digital audio radio services (``SDARS''). 73 FR 4080. In SoundExchange, Inc....

  18. Attitude and Trajectory Estimation Using Earth Magnetic Field Data

    Science.gov (United States)

    Deutschmann, Julie; Bar-Itzhack, Itzhack Y.

    1996-01-01

    The magnetometer has long been a reliable, inexpensive sensor used in spacecraft momentum management and attitude estimation. Recent studies show an increased accuracy potential for magnetometer-only attitude estimation systems. Since the Earth's magnetic field is a function of time and position, and since time is known quite precisely, the differences between the computer and measured magnetic field components, as measured by the magnetometers throughout the entire spacecraft orbit, are a function of both the spacecraft trajectory and attitude errors. Therefore, these errors can be used to estimate both trajectory and attitude. Traditionally, satellite attitude and trajectory have been estimated with completely separate system, using different measurement data. Recently, trajectory estimation for low earth orbit satellites was successfully demonstrated in ground software using only magnetometer data. This work proposes a single augmented extended Kalman Filter to simultaneously and autonomously estimate both spacecraft trajectory and attitude with data from a magnetometer and either dynamically determined rates or gyro-measured body rates.

  19. Determination of poles and zeros of transfer functions for flexible spacecraft attitude control

    Science.gov (United States)

    Ohkami, Y.; Likins, P. W.

    1976-01-01

    The transfer function matrix is obtained for a three-input and three-output model of minimum sensors and actuators for the attitude control system of flexible spacecraft, and a method is described for determining the poles and zeros of this transfer function. Three cases are considered: (1) the actuators and the sensors are all attached to the primary body, (2) the actuators are on the primary body and the sensors are on the sub-body, and (3) the actuators are on the sub-body and the sensors are on the primary body. The zero-determination problem is shown to reduce to eigenvalue calculations of a matrix which is constructed from the inertial and modal matrices in a simple fashion.

  20. The use of satellites in gravity field determination and model adjustment

    Science.gov (United States)

    Visser, Petrus Nicolaas Anna Maria

    1992-06-01

    Methods to improve gravity field models of the Earth with available data from satellite observations are proposed and discussed. In principle, all types of satellite observations mentioned give information of the satellite orbit perturbations and in conjunction the Earth's gravity field, because the satellite orbits are affected most by the Earth's gravity field. Therefore, two subjects are addressed: representation forms of the gravity field of the Earth and the theory of satellite orbit perturbations. An analytical orbit perturbation theory is presented and shown to be sufficiently accurate for describing satellite orbit perturbations if certain conditions are fulfilled. Gravity field adjustment experiments using the analytical orbit perturbation theory are discussed using real satellite observations. These observations consisted of Seasat laser range measurements and crossover differences, and of Geosat altimeter measurements and crossover differences. A look into the future, particularly relating to the ARISTOTELES (Applications and Research Involving Space Techniques for the Observation of the Earth's field from Low Earth Orbit Spacecraft) mission, is given.

  1. TOURISM SATELLITE ACCOUNT - STATISTICAL METHOD FOR DETERMINING THE ECONOMIC IMPACT OF TOURISM

    Directory of Open Access Journals (Sweden)

    OANA MARIA MILEA

    2012-05-01

    Full Text Available The permanent concerns of analysts to determine how accurately the real economic benefits of tourism, not stopping at only the direct costs of international and domestic visitors but to consider their indirect effects have made them believe that tourism statistics are not comprehensive enough.This is both because they fail to provide a concrete or in respect of costs incurred by tourists on their own and to some extent to those seeking semi-organized tourism and because the economic effects of spending tourist receipts go beyond statistics reported by service providers. As a result, the World Tourism Organization (UNWTO in collaboration with the World Travel and Tourism Council (WTTO, the European Union Statistical Office (EUROSTST and other regional statistical bodies initiated the Tourism Satellite Account system, UNWTO recommending its adoption by all countries.

  2. Earth's lithospheric magnetic field determined to spherical harmonic degree 90 from CHAMP satellite measurements

    DEFF Research Database (Denmark)

    Maus, S.; Rother, M.; Hemant, K.;

    2006-01-01

    The CHAMP magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy. Using almost 5 yr of data, we derive our fourth generation lithospheric field model termed MF4, which is expanded...... to spherical harmonic degree and order 90. After subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15, an external field model up to degree two, and the predicted magnetic field signatures for the eight dominant ocean tidal constituents, we fit...... of the lithospheric field down to an altitude of about 50 km at lower latitudes, with reduced accuracy in the polar regions. Crustal features come out significantly sharper than in previous models. In particular, bands of magnetic anomalies along subduction zones become visible by satellite for the first time....

  3. Cooperative attitude and translation control of satellite formation flying using consensus algorithm%基于一致性算法的卫星编队姿轨耦合的协同控制

    Institute of Scientific and Technical Information of China (English)

    周稼康; 胡庆雷; 马广富; 吕跃勇

    2011-01-01

    针对卫星编队一主多从结构的相对轨迹、姿态的协同控制问题,提出了一种基于Lyapunov方法的编队飞行协同控制策略.该控制策略将分布式控制思想引入卫星编队飞行的相对轨迹、姿态的动力学系统中,使各从星保持编队构型的同时沿期望轨迹相对主星绕飞.从理论上证明了系统的渐近稳定以及对外部干扰的抑制,并基于一致性算法理论定量地分析了通信拓扑结构为有向图情况下控制器参数的选择范围.此外,利用星星间的相对位置信息确定各从星的期望姿态和角速度,以确保对卫星编队进行姿态协同控制,达到跟踪同步的目的.最后将提出的算法应用于卫星三角形编队飞行的协同控制,仿真结果表明该方法的可行性与有效性,具有潜在的应用前景.%This paper proposes a Lyapunov based cooperative control for the coupling of the rotational and translational motion of the satellite formation flying, in which one leader multi-follower satellite formation structure is adopted. More specifically, using the information of the inter-satellite position, the desired attitude quaternion and angular velocity of the followers are determined, such that the desired attitude and position trajectories could be tracked, while simultaneously the synchronized motion among all spacecraft in formation is guaranteed. The stability analysis of the closed-loop system is performed using Lyapunov stability theorem and the range of the control parameters are determined by using consensus algorithm even in the presence of external disturbances. Numerical simulation results are presented to show the effectiveness of the proposed controller.

  4. Orbit Determination with Angle-only Data from the First Korean Optical Satellite Tracking System, OWL-Net

    Science.gov (United States)

    Choi, J.; Jo, J.

    2016-09-01

    The optical satellite tracking data obtained by the first Korean optical satellite tracking system, Optical Wide-field patrol - Network (OWL-Net), had been examined for precision orbit determination. During the test observation at Israel site, we have successfully observed a satellite with Laser Retro Reflector (LRR) to calibrate the angle-only metric data. The OWL observation system is using a chopper equipment to get dense observation data in one-shot over 100 points for the low Earth orbit objects. After several corrections, orbit determination process was done with validated metric data. The TLE with the same epoch of the end of the first arc was used for the initial orbital parameter. Orbit Determination Tool Kit (ODTK) was used for an analysis of a performance of orbit estimation using the angle-only measurements. We have been developing batch style orbit estimator.

  5. Determination Gradients of the Earth's Magnetic Field from the Measurements of the Satellites and Inversion of the Kursk Magnetic Anomaly

    Science.gov (United States)

    Karoly, Kis; Taylor, Patrick T.; Geza, Wittmann

    2014-01-01

    We computed magnetic field gradients at satellite altitude, over Europe with emphasis on the Kursk Magnetic Anomaly (KMA). They were calculated using the CHAMP satellite total magnetic anomalies. Our computations were done to determine how the magnetic anomaly data from the new ESA/Swarm satellites could be utilized to determine the structure of the magnetization of the Earths crust, especially in the region of the KMA. Since the ten years of 2 CHAMP data could be used to simulate the Swarm data. An initial East magnetic anomaly gradient map of Europe was computed and subsequently the North, East and Vertical magnetic gradients for the KMA region were calculated. The vertical gradient of the KMA was determined using Hilbert transforms. Inversion of the total KMA was derived using Simplex and Simulated Annealing algorithms. Our resulting inversion depth model is a horizontal quadrangle with upper 300-329 km and lower 331-339 km boundaries.

  6. Testing of the on-board attitude determination and control algorithms for SAMPEX

    Science.gov (United States)

    McCullough, Jon D.; Flatley, Thomas W.; Henretty, Debra A.; Markley, F. Landis; San, Josephine K.

    1993-02-01

    Algorithms for on-board attitude determination and control of the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) have been expanded to include a constant gain Kalman filter for the spacecraft angular momentum, pulse width modulation for the reaction wheel command, an algorithm to avoid pointing the Heavy Ion Large Telescope (HILT) instrument boresight along the spacecraft velocity vector, and the addition of digital sun sensor (DSS) failure detection logic. These improved algorithms were tested in a closed-loop environment for three orbit geometries, one with the sun perpendicular to the orbit plane, and two with the sun near the orbit plane - at Autumnal Equinox and at Winter Solstice. The closed-loop simulator was enhanced and used as a truth model for the control systems' performance evaluation and sensor/actuator contingency analysis. The simulations were performed on a VAX 8830 using a prototype version of the on-board software.

  7. Attitude determination and calibration using a recursive maximum likelihood-based adaptive Kalman filter

    Science.gov (United States)

    Kelly, D. A.; Fermelia, A.; Lee, G. K. F.

    1990-01-01

    An adaptive Kalman filter design that utilizes recursive maximum likelihood parameter identification is discussed. At the center of this design is the Kalman filter itself, which has the responsibility for attitude determination. At the same time, the identification algorithm is continually identifying the system parameters. The approach is applicable to nonlinear, as well as linear systems. This adaptive Kalman filter design has much potential for real time implementation, especially considering the fast clock speeds, cache memory and internal RAM available today. The recursive maximum likelihood algorithm is discussed in detail, with special attention directed towards its unique matrix formulation. The procedure for using the algorithm is described along with comments on how this algorithm interacts with the Kalman filter.

  8. Survey of HIV/AIDS-related Knowledge, Attitude and Determinants in Urban Residents

    Institute of Scientific and Technical Information of China (English)

    何群; 杨放; 林鹏; 王晔; 刘勇鹰; 付笑冰; 赵茜茜

    2003-01-01

    Objectives: To provide references for HIV/AIDS-re-lated health education strategies through survey on HIV/AIDS-related knowledge, attitude and determi-nants of HIV/AIDS awareness.Methods: The study subjects were selected by ran-dom interception in a downtown street of Guangzhou city on World AIDS Day-December 1,2002. The uni-form questionnaires were finished by means of self-administration.Results: Two hundred questionnaires were distrib-uted and 147 qualified questionnaires were collected.The results showed, the awareness rate of HIV/AIDS-related knowledge was 63.3%, and awareness rate of transmission routes was 76.2 %, whilst non-transmis-sion route was 60.5 %; the awareness rate of trans-mission was 59.2%; the awareness rate of prevention was 47.0%; the positive attitude to people living with HIV/AIDS was 65.6%. Multiple variable Logistic re-gression analysis showed the determinants of HIV/AIDS-related knowledge were education level, age,marital status and gender, of which people with high level of education, young age and the group of male and married had better awareness of HIV/AIDS.Conclusion: Current HIV/AIDS-related knowledge of urban residents is relativly low, especially for the non-transmission route, hence further HIV/AIDS-re-lated education should be strengthened, especially fo-cusing on non-transmission route to eliminate dis-crimination over people living with HIV/AIDS.Further, education efforts also should be put on fe-male population, unmarried population and poorly edu-cated population.

  9. Determination of External Forces in Alpine Skiing Using a Differential Global Navigation Satellite System

    Directory of Open Access Journals (Sweden)

    Erich Müller

    2013-08-01

    Full Text Available In alpine ski racing the relationships between skier kinetics and kinematics and their effect on performance and injury-related aspects are not well understood. There is currently no validated system to determine all external forces simultaneously acting on skiers, particularly under race conditions and throughout entire races. To address the problem, this study proposes and assesses a method for determining skier kinetics with a single lightweight differential global navigation satellite system (dGNSS. The dGNSS kinetic method was compared to a reference system for six skiers and two turns each. The pattern differences obtained between the measurement systems (offset ± SD were −26 ± 152 N for the ground reaction force, 1 ± 96 N for ski friction and −6 ± 6 N for the air drag force. The differences between turn means were small. The error pattern within the dGNSS kinetic method was highly repeatable and precision was therefore good (SD within system: 63 N ground reaction force, 42 N friction force and 7 N air drag force allowing instantaneous relative comparisons and identification of discriminative meaningful changes. The method is therefore highly valid in assessing relative differences between skiers in the same turn, as well as turn means between different turns. The system is suitable to measure large capture volumes under race conditions.

  10. Nonhydrostatic Effects and the Determination of Icy Satellites' Moment of Inertia

    CERN Document Server

    Gao, Peter

    2013-01-01

    We compare the moment of inertia (MOI) of a simple hydrostatic, two layer body as determined by the Radau-Darwin Approximation (RDA) to its exact hydrostatic MOI calculated to first order in the parameter q = w^2R^3/GM, where w, R, and M are the spin angular velocity, radius, and mass of the body, and G is the gravitational constant. RDA is in error by less than 1% for many configurations of core sizes and layer densities congruent with those of solid bodies in the Solar System. We determine the error in the MOI of icy satellites calculated with the RDA due to nonhydrostatic effects by using a simple model in which the core and outer shell have slight degree 2 distortions away from their expected hydrostatic shapes. Since the hydrostatic shape has an associated stress of order pw^2R^2 (where p is density) it follows that the importance of nonhydrostatic effects scales with the dimensionless number s/pw^2R^2, where s is the nonhydrostatic stress. This highlights the likely importance of this error for slowly r...

  11. MicroRNA-133 Controls Brown Adipose Determination in Skeletal Muscle Satellite Cells by Targeting Prdm16

    DEFF Research Database (Denmark)

    Yin, Hang; Pasut, Alessandra; Soleimani, Vahab D

    2013-01-01

    (satellite cells) have long been considered uniformly determined toward the myogenic lineage. Here, we report that adult satellite cells give rise to brown adipocytes and that microRNA-133 regulates the choice between myogenic and brown adipose determination by targeting the 3'UTR of Prdm16. Antagonism...... are downregulated in mice exposed to cold, resulting in de novo generation of satellite cell-derived brown adipocytes. Therefore, microRNA-133 represents an important therapeutic target for the treatment of obesity....... of microRNA-133 during muscle regeneration increases uncoupled respiration, glucose uptake, and thermogenesis in local treated muscle and augments whole-body energy expenditure, improves glucose tolerance, and impedes the development of diet-induced obesity. Finally, we demonstrate that miR-133 levels...

  12. Determination of gravitational potential distribution over a geocentric quasi- sphere based on links between GRACE- and GNSS-type satellites

    Science.gov (United States)

    Shen, Ziyu; Shen, Wen-Bin

    2017-04-01

    We provide a formulation of determining the Earth's gravitational potential distribution over a geocentric quasi-sphere (QS) that is constructed by a GRACE-type satellite (GTS), based on frequency signal transmission between the GTS and a cluster of GNSS satellites (CGS). By emitting and receiving frequency signals between the GTS and a GNSS satellite, we can determine the gravitational potential at the GTS orbit. For a near-polar GTS with height about 350 km above the geoid, we choose sufficient GNSS satellites to determine the gravitational potential at the GTS position. Simulation results show that the accuracy of the determined gravitational potential distribution over the QS can achieve centimeter level if (1) the accuracy of the given potentials at GDSs is about 1 cm level, and (2) optical atomic clocks with instability of 1*10E-18 are available. Our final purpose is to determine the Earth's external gravity field based on the potential distribution on the QS. This study is supported by National 973 Project China (grant No. 2013CB733301 and 2013CB733305) and NSFCs (grant Nos. 41174011, 41429401, 41210006, 41128003, 41021061)

  13. Application of Magnetically Suspended Gimbaling Flywheel in Satellite Attitude Maneuver%磁悬浮万向飞轮在卫星姿态机动中的应用

    Institute of Scientific and Technical Information of China (English)

    李丽君; 樊亚洪; 袁军

    2015-01-01

    Attitude maneuver control of high-earth-orbit satellite at roll and yaw axes with magnetically suspended gimbaling flywheel(MSGFW) is presented. The dynamic equations of satellite with MSGFW as actuator are developed. The control torque generates in roll and yaw axis when the gamble angles of flywheel change. Double MSGFWs mounted on the satellite with opposite rotation direction comprise the double MSGFWs attitude control system. The attitude control system works at zero momentum mode. Simulation results show that the satellite achieves attitude angle maneuver of 5° in 20 s with the gimbal angle of 3°. When the gimbal angle is 6° the satellite can achieve attitude angle maneuver of 12°. The future application of MSGFW on low-orbiting satellite is analyzed and the new concept in rapid maneuver and stabilization of satellite attitude control is proposed.%针对基于磁悬浮万向飞轮的高轨卫星姿态机动控制问题,建立磁悬浮万向飞轮和卫星的姿态动力学方程,通过磁悬浮万向飞轮转子的偏转控制实现卫星滚动和偏航轴的姿态机动。由两个磁悬浮万向飞轮反向安装,组成双轮控制构型,实现整星零动量控制。仿真结果表明,在双磁悬浮万向飞轮系统控制下,卫星在20 s内可实现5°的姿态机动,所需要的框架角为3°;当磁悬浮万向飞轮达到最大框架角6°时,卫星可实现12°的姿态机动。分析磁悬浮万向飞轮在低轨卫星中应用的前景,为实现卫星的快速机动和快速稳定控制提供新的思路。

  14. Investigating On-Orbit Attitude Determination Anomalies for the Solar Dynamics Observatory Mission

    Science.gov (United States)

    Vess, Melissa F.; Starin, Scott R.; Chia-Kuo, Alice Liu

    2011-01-01

    The Solar Dynamics Observatory (SDO) was launched on February 11, 2010 from Kennedy Space Center on an Atlas V launch vehicle into a geosynchronous transfer orbit. SDO carries a suite of three scientific instruments, whose observations are intended to promote a more complete understanding of the Sun and its effects on the Earth's environment. After a successful launch, separation, and initial Sun acquisition, the launch and flight operations teams dove into a commissioning campaign that included, among other things, checkout and calibration of the fine attitude sensors and checkout of the Kalman filter (KF) and the spacecraft s inertial pointing and science control modes. In addition, initial calibration of the science instruments was also accomplished. During that process of KF and controller checkout, several interesting observations were noticed and investigated. The SDO fine attitude sensors consist of one Adcole Digital Sun Sensor (DSS), two Galileo Avionica (GA) quaternion-output Star Trackers (STs), and three Kearfott Two-Axis Rate Assemblies (hereafter called inertial reference units, or IRUs). Initial checkout of the fine attitude sensors indicated that all sensors appeared to be functioning properly. Initial calibration maneuvers were planned and executed to update scale factors, drift rate biases, and alignments of the IRUs. After updating the IRU parameters, the KF was initialized and quickly reached convergence. Over the next few hours, it became apparent that there was an oscillation in the sensor residuals and the KF estimation of the IRU bias. A concentrated investigation ensued to determine the cause of the oscillations, their effect on mission requirements, and how to mitigate them. The ensuing analysis determined that the oscillations seen were, in fact, due to an oscillation in the IRU biases. The low frequencies of the oscillations passed through the KF, were well within the controller bandwidth, and therefore the spacecraft was actually

  15. Young Adults' Belief in Genetic Determinism, and Knowledge and Attitudes towards Modern Genetics and Genomics: The PUGGS Questionnaire.

    Science.gov (United States)

    Carver, Rebecca Bruu; Castéra, Jérémy; Gericke, Niklas; Evangelista, Neima Alice Menezes; El-Hani, Charbel N

    2017-01-01

    In this paper we present the development and validation a comprehensive questionnaire to assess college students' knowledge about modern genetics and genomics, their belief in genetic determinism, and their attitudes towards applications of modern genetics and genomic-based technologies. Written in everyday language with minimal jargon, the Public Understanding and Attitudes towards Genetics and Genomics (PUGGS) questionnaire is intended for use in research on science education and public understanding of science, as a means to investigate relationships between knowledge, determinism and attitudes about modern genetics, which are to date little understood. We developed a set of core ideas and initial items from reviewing the scientific literature on genetics and previous studies on public and student knowledge and attitudes about genetics. Seventeen international experts from different fields (e.g., genetics, education, philosophy of science) reviewed the initial items and their feedback was used to revise the questionnaire. We validated the questionnaire in two pilot tests with samples of university freshmen students. The final questionnaire contains 45 items, including both multiple choice and Likert scale response formats. Cronbach alpha showed good reliability for each section of the questionnaire. In conclusion, the PUGGS questionnaire is a reliable tool for investigating public understanding and attitudes towards modern genetics and genomic-based technologies.

  16. Young Adults’ Belief in Genetic Determinism, and Knowledge and Attitudes towards Modern Genetics and Genomics: The PUGGS Questionnaire

    Science.gov (United States)

    Carver, Rebecca Bruu; Castéra, Jérémy; Gericke, Niklas; Evangelista, Neima Alice Menezes

    2017-01-01

    In this paper we present the development and validation a comprehensive questionnaire to assess college students’ knowledge about modern genetics and genomics, their belief in genetic determinism, and their attitudes towards applications of modern genetics and genomic-based technologies. Written in everyday language with minimal jargon, the Public Understanding and Attitudes towards Genetics and Genomics (PUGGS) questionnaire is intended for use in research on science education and public understanding of science, as a means to investigate relationships between knowledge, determinism and attitudes about modern genetics, which are to date little understood. We developed a set of core ideas and initial items from reviewing the scientific literature on genetics and previous studies on public and student knowledge and attitudes about genetics. Seventeen international experts from different fields (e.g., genetics, education, philosophy of science) reviewed the initial items and their feedback was used to revise the questionnaire. We validated the questionnaire in two pilot tests with samples of university freshmen students. The final questionnaire contains 45 items, including both multiple choice and Likert scale response formats. Cronbach alpha showed good reliability for each section of the questionnaire. In conclusion, the PUGGS questionnaire is a reliable tool for investigating public understanding and attitudes towards modern genetics and genomic-based technologies. PMID:28114357

  17. Determination of attitudes with gynecologic examination and anxiety of Turkish women before gynecologic examination

    Directory of Open Access Journals (Sweden)

    Nülüfer Erbil

    2008-05-01

    Full Text Available Objective: This study was planned with the purpose determination of attitudes with gynecologic examination and anxiety of Turkish women before gynecologic examination.Material & Methods: The sample of this descriptive and cross-sectional constituted by 240 women, applying for gynecologic examination in Gynecologic Policlinic of Ordu Maternity-Gynecologic and Child Hospital of who accepted to participate in the research. The data were collected with of a questionnarie form and State Anxiety Inventory. This study was made between the dates of 4 April- 30 May 2006. In the analysis of data, frequency, percentage, standart deviation, arithmetic mean, Kruskal wallis test, t test, ANOVA varience analysis, Mann –Whitney U test and Chi square test were used.Results: In the research, it was determined that the state axiety average point of women is 43.85±5,41. It was been that level anxiety of women before gynecologic examination was “middle level anxiety”. It was found that there is a significant between state anxiety inventory points according to the job and gynecologic examination experience of women order in the family with state anxiety (P=,000. Doctor’s knowledge and capability (63,8%, doctor’s knowledge giving (44,6% and doctor’s complaisant (41,7% were important in women’ doctor preferring for gynecologic examination. It was found that 37,5% of the women desired only doctor and 37,1% of the women desired their husband during gynecologic examination. It was determined that women felt uncomfortable because of nakedness genital organs of them (67,1% and negatif communication between doctor and women (39,6% in previously gynecologic examination. Women perceived feelings as embarrassment (62,5%, distress (38,8%, fear (37,9%, pain (21,7% during gynecologic examination. Expectations of women from health professionals during gynecologic examination were complaisant (45,0%, interest (28,3%, perceptiveness (24,2%.Conclusion: This study

  18. Migration and wintering sites of Pelagic Cormorants determined by satellite telemetry

    Science.gov (United States)

    Hatch, Shyla A.; Gill, V.A.; Mulcahy, D.M.

    2011-01-01

    Factors affecting winter survival may be key determinants of status and population trends of seabirds, but connections between breeding sites and wintering areas of most populations are poorly known. Pelagic Cormorants (Phalacrocorax pelagicus; N= 6) surgically implanted with satellite transmitters migrated from a breeding colony on Middleton Island, northern Gulf of Alaska, to wintering sites in southeast Alaska and northern British Columbia. Winter locations averaged 920 km (range = 600-1190 km) from the breeding site. Migration flights in fall and spring lasted ???5 d in four instances. After reaching wintering areas, cormorants settled in narrowly circumscribed inshore locations (~10-km radius) and remained there throughout the nonbreeding period (September- March). Two juveniles tagged at the breeding colony as fledglings remained at their wintering sites for the duration of the tracking interval (14 and 22 mo, respectively). Most cormorants used multiple sites within their winter ranges for roosting and foraging. Band recoveries show that Pelagic Cormorants in southern British Columbia and Washington disperse locally in winter, rather than migrating like the cormorants in our study. Radio-tagging and monitoring cormorants and other seabirds from known breeding sites are vital for understanding migratory connectivity and improving conservation strategies for local populations. ?? 2011 The Authors. Journal of Field Ornithology ?? 2011 Association of Field Ornithologists.

  19. Determination of mangrove change in Matang Mangrove Forest using multi temporal satellite imageries

    Science.gov (United States)

    Ibrahim, N. A.; Mustapha, M. A.; Lihan, T.; Ghaffar, M. A.

    2013-11-01

    Mangrove protects shorelines from damaging storm and hurricane winds, waves, and floods. Mangroves also help prevent erosion by stabilizing sediments with their tangled root systems. They maintain water quality and clarity, filtering pollutants and trapping sediments originating from land. However, mangrove has been reported to be threatened by land conversion for other activities. In this study, land use and land cover changes in Matang Mangrove Forest during the past 18 years (1993 to 2011) were determined using multi-temporal satellite imageries by Landsat TM and RapidEye. In this study, classification of land use and land cover approach was performed using the maximum likelihood classifier (MCL) method along with vegetation index differencing (NDVI) technique. Data obtained was evaluated through Kappa coefficient calculation for accuracy and results revealed that the classification accuracy was 81.25% with Kappa Statistics of 0.78. The results indicated changes in mangrove forest area to water body with 2,490.6 ha, aquaculture with 890.7 ha, horticulture with 1,646.1 ha, palm oil areas with 1,959.2 ha, dry land forest with 2,906.7 ha and urban settlement area with 224.1 ha. Combinations of these approaches were useful for change detection and for indication of the nature of these changes.

  20. US Female College Students' Breast Health Knowledge, Attitudes, and Determinants of Screening Practices: New Implications for Health Education

    Science.gov (United States)

    Early, Jody; Armstrong, Shelley Nicole; Burke, Sloane; Thompson, Doris Lee

    2011-01-01

    Objective: This study examined female college students' knowledge, attitudes, and breast cancer screening and determined significant predictors of breast self-examination, clinical breast examination, and mammography among this population. Participants: A convenience sample of 1,074 college women from 3 universities participated in the research.…

  1. US Female College Students' Breast Health Knowledge, Attitudes, and Determinants of Screening Practices: New Implications for Health Education

    Science.gov (United States)

    Early, Jody; Armstrong, Shelley Nicole; Burke, Sloane; Thompson, Doris Lee

    2011-01-01

    Objective: This study examined female college students' knowledge, attitudes, and breast cancer screening and determined significant predictors of breast self-examination, clinical breast examination, and mammography among this population. Participants: A convenience sample of 1,074 college women from 3 universities participated in the research.…

  2. Determining the Pixel-to-Pixel Uncertainty in Satellite-Derived SST Fields

    Directory of Open Access Journals (Sweden)

    Fan Wu

    2017-08-01

    Full Text Available The primary measure of the quality of sea surface temperature (SST fields obtained from satellite-borne infrared sensors has been the bias and variance of matchups with co-located in-situ values. Because such matchups tend to be widely separated, these bias and variance estimates are not necessarily a good measure of small scale (several pixels gradients in these fields because one of the primary contributors to the uncertainty in satellite retrievals is atmospheric contamination, which tends to have large spatial scales compared with the pixel separation of infrared sensors. Hence, there is not a good measure to use in selecting SST fields appropriate for the study of submesoscale processes and, in particular, of processes associated with near-surface fronts, both of which have recently seen a rapid increase in interest. In this study, two methods are examined to address this problem, one based on spectra of the SST data and the other on their variograms. To evaluate the methods, instrument noise was estimated in Level-2 Visible-Infrared Imager-Radiometer Suite (VIIRS and Advanced Very High Resolution Radiometer (AVHRR SST fields of the Sargasso Sea. The two methods provided very nearly identical results for AVHRR: along-scan values of approximately 0.18 K for both day and night and along-track values of 0.21 K for day and night. By contrast, the instrument noise estimated for VIIRS varied by method, scan geometry and day-night. Specifically, daytime, along-scan (along-track, spectral estimates were found to be approximately 0.05 K (0.08 K and the corresponding nighttime values of 0.02 K (0.03 K. Daytime estimates based on the variogram were found to be 0.08 K (0.10 K with the corresponding nighttime values of 0.04 K (0.06 K. Taken together, AVHRR instrument noise is significantly larger than VIIRS instrument noise, along-track noise is larger than along-scan noise and daytime levels are higher than nighttime levels. Given the similarity of

  3. Study to forecast and determine characteristics of world satellite communications market

    Science.gov (United States)

    Filep, R. T.; Schnapf, A.; Fordyce, S. W.

    1983-01-01

    The world commercial communications satellite market during the spring and summer of 1983 was examined and characteristics and forecasts of the market extending to the year 2000 were developed. Past, present and planned satellites were documented in relation to frequencies, procurement and launch dates, costs, transponders, and prime contractor. Characteristics of the market are outlined for the periods 1965 - 1985, 1986 - 1989, and 1990 - 2000. Market share forecasts, discussions of potential competitors in various world markets, and profiles of major communication satellite manufacturing and user countries are documented.

  4. Satellite Control Laboratory

    DEFF Research Database (Denmark)

    Wisniewski, Rafal; Bak, Thomas

    2001-01-01

    The Satellite Laboratory at the Department of Control Engineering of Aalborg University (SatLab) is a dynamic motion facility designed for analysis and test of micro spacecraft. A unique feature of the laboratory is that it provides a completely gravity-free environment. A test spacecraft...... is suspended on an air bearing, and rotates freely in 3 degrees of freedom. In order to avoid any influence of the gravitational force the centre of mass of the satellite is placed in the geometric centre of the air bearing by an automatic balancing system. The test spacecraft is equipped with a three...... of the laboratory is to conduct dynamic tests of the control and attitude determination algorithms during nominal operation and in abnormal conditions. Further it is intended to use SatLab for validation of various algorithms for fault detection, accommodation and supervisory control. Different mission objectives...

  5. Dynamic attitude command and control of the TOPEX/Poseidon spacecraft

    Science.gov (United States)

    Zimbelman, D. F.; Lee, B. B.; Welch, R. V.

    1991-01-01

    The dynamic control laws utilized by the TOPEX/Poseidon (T/P) spacecraft attitude determination and control subsystem to command and maneuver the satellite during normal mission mode (NMM) laws are described. Results show that the vehicle is able to respond to the dynamic attitude commands while at the same time providing ample disturbance rejection capability.

  6. The determinations of remote sensing satellite data delivery service quality: A positivistic case study in Chinese context

    Science.gov (United States)

    Jin, Jiahua; Yan, Xiangbin; Tan, Qiaoqiao; Li, Yijun

    2014-03-01

    With the development of remote sensing technology, remote-sensing satellite has been widely used in many aspects of national construction. Big data with different standards and massive users with different needs, make the satellite data delivery service to be a complex giant system. How to deliver remote-sensing satellite data efficiently and effectively is a big challenge. Based on customer service theory, this paper proposes a hierarchy conceptual model for examining the determinations of remote-sensing satellite data delivery service quality in the Chinese context. Three main dimensions: service expectation, service perception and service environment, and 8 sub-dimensions are included in the model. Large amount of first-hand data on the remote-sensing satellite data delivery service have been obtained through field research, semi-structured questionnaire and focused interview. A positivist case study is conducted to validate and develop the proposed model, as well as to investigate the service status and related influence mechanisms. Findings from the analysis demonstrate the explanatory validity of the model, and provide potentially helpful insights for future practice.

  7. Research on long-term autonomous orbit determination for navigation constellation using inter-satellite orientation observation information

    Science.gov (United States)

    Li, Bo; Xu, Bo; Wang, Hai-Hong

    2009-12-01

    Long-term autonomous orbit determination is one of the key techniques of autonomous navigation for navigation constellation. Based only on cross-link range observation, which is not able to overcome the defect of entire constellation rotation and translation relative to inertial reference frame, the accuracy of autonomous orbit determination is reduced with time. In order to solve this problem, the approach of using inter-satellite orientation observation is put forward to estimate the constellation rotation and translation with the benefit of absolute position information provided by stars. In view of the fact that most navigation satellites moving in near circular orbits, and also in order to reduce the calculation burden of onboard computer, nonsingular orbital elements are chosen as state variables and analytical method is used to calculate the transition matrix in this paper. In addition, the extended Kalman filter is designed to fuse information of satellite dynamic model, cross-link range observation and inter-satellite orientation observation to determine the orbit. The simulation results based on the IGS Final Products of GPS constellation indicate that, at the certain error condition of range and orientation measurement, the URE of constellation is better than 2 meters within 120 days.

  8. Phase Error Modeling and Its Impact on Precise Orbit Determination of GRACE Satellites

    Directory of Open Access Journals (Sweden)

    Jia Tu

    2012-01-01

    Full Text Available Limiting factors for the precise orbit determination (POD of low-earth orbit (LEO satellite using dual-frequency GPS are nowadays mainly encountered with the in-flight phase error modeling. The phase error is modeled as a systematic and a random component each depending on the direction of GPS signal reception. The systematic part and standard deviation of random part in phase error model are, respectively, estimated by bin-wise mean and standard deviation values of phase postfit residuals computed by orbit determination. By removing the systematic component and adjusting the weight of phase observation data according to standard deviation of random component, the orbit can be further improved by POD approach. The GRACE data of 1–31 January 2006 are processed, and three types of orbit solutions, POD without phase error model correction, POD with mean value correction of phase error model, and POD with phase error model correction, are obtained. The three-dimensional (3D orbit improvements derived from phase error model correction are 0.0153 m for GRACE A and 0.0131 m for GRACE B, and the 3D influences arisen from random part of phase error model are 0.0068 m and 0.0075 m for GRACE A and GRACE B, respectively. Thus the random part of phase error model cannot be neglected for POD. It is also demonstrated by phase postfit residual analysis, orbit comparison with JPL precise science orbit, and orbit validation with KBR data that the results derived from POD with phase error model correction are better than another two types of orbit solutions generated in this paper.

  9. Improved Orbit Determination and Forecasts with an Assimilative Tool for Atmospheric Density and Satellite Drag Specification

    Science.gov (United States)

    Crowley, G.; Pilinski, M.; Sutton, E. K.; Codrescu, M.; Fuller-Rowell, T. J.; Matsuo, T.; Fedrizzi, M.; Solomon, S. C.; Qian, L.; Thayer, J. P.

    2016-12-01

    Much as aircraft are affected by the prevailing winds and weather conditions in which they fly, satellites are affected by the variability in density and motion of the near earth space environment. Drastic changes in the neutral density of the thermosphere, caused by geomagnetic storms or other phenomena, result in perturbations of LEO satellite motions through drag on the satellite surfaces. This can lead to difficulties in locating important satellites, temporarily losing track of satellites, and errors when predicting collisions in space. We describe ongoing work to build a comprehensive nowcast and forecast system for specifying the neutral atmospheric state related to orbital drag conditions. The system outputs include neutral density, winds, temperature, composition, and the satellite drag derived from these parameters. This modeling tool is based on several state-of-the-art coupled models of the thermosphere-ionosphere as well as several empirical models running in real-time and uses assimilative techniques to produce a thermospheric nowcast. This software will also produce 72 hour predictions of the global thermosphere-ionosphere system using the nowcast as the initial condition and using near real-time and predicted space weather data and indices as the inputs. Features of this technique include: • Satellite drag specifications with errors lower than current models • Altitude coverage up to 1000km • Background state representation using both first principles and empirical models • Assimilation of satellite drag and other datatypes • Real time capability • Ability to produce 72-hour forecasts of the atmospheric state In this paper, we will summarize the model design and assimilative architecture, and present preliminary validation results. Validation results will be presented in the context of satellite orbit errors and compared with several leading atmospheric models including the High Accuracy Satellite Drag Model, which is currently used

  10. Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Haley 2

    Science.gov (United States)

    Luna, Michael E.; Collins, Stephen M.

    2011-01-01

    On November 4, 2010 the already "in-flight" Deep Impact spacecraft flew within 700km of comet 103P/Hartley 2 as part of its extended mission EPOXI, the 5th time to date any spacecraft visited a comet. In 2005, the spacecraft had previously imaged a probe impact comet Tempel 1. The EPOXI flyby marked the first time in history that two comets were explored with the same instruments on a re-used spacecraft-with hardware and software originally designed and optimized for a different mission. This made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby. As part of the spacecraft team preparations, the ADCS team had to perform thorough sequence reviews, key spacecraft activities and onboard calibrations. These activities included: review of background sequences for the initial conditions vector, sun sensor coefficients, and reaction wheel assembly (RWA) de-saturations; design and execution of 10 trajectory correction maneuvers; science calibration of the two telescope instruments; a flight demonstration of the fastest turns conducted by the spacecraft between Earth and comet point; and assessment of RWA health (given RWA problems on other spacecraft).

  11. Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Hartley 2

    Science.gov (United States)

    Luna, Michael E.; Collins, Steven M.

    2011-01-01

    On November 4, 2010 the former "Deep Impact" spacecraft, renamed "EPOXI" for its extended mission, flew within 700km of comet 103P/Hartley 2. In July 2005, the spacecraft had previously imaged a probe impact of comet Tempel 1. The EPOXI flyby was the fifth close encounter of a spacecraft with a comet nucleus and marked the first time in history that two comet nuclei were imaged at close range with the same suite of onboard science instruments. This challenging objective made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby.As part of the spacecraft flyby preparations, the ADCS operations team had to perform meticulous sequence reviews, implement complex spacecraft engineering and science activities and perform numerous onboard calibrations. ADCS contributions included design and execution of 10 trajectory correction maneuvers, the science calibration of the two telescopic instruments, an in-flight demonstration of high-rate turns between Earth and comet point, and an ongoing assessment of reaction wheel health. The ADCS team was also responsible for command sequences that included updates to the onboard ephemeris and sun sensor coefficients and implementation of reaction wheel assembly (RWA) de-saturations.

  12. Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Haley 2

    Science.gov (United States)

    Luna, Michael E.; Collins, Stephen M.

    2011-01-01

    On November 4, 2010 the already "in-flight" Deep Impact spacecraft flew within 700km of comet 103P/Hartley 2 as part of its extended mission EPOXI, the 5th time to date any spacecraft visited a comet. In 2005, the spacecraft had previously imaged a probe impact comet Tempel 1. The EPOXI flyby marked the first time in history that two comets were explored with the same instruments on a re-used spacecraft-with hardware and software originally designed and optimized for a different mission. This made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby. As part of the spacecraft team preparations, the ADCS team had to perform thorough sequence reviews, key spacecraft activities and onboard calibrations. These activities included: review of background sequences for the initial conditions vector, sun sensor coefficients, and reaction wheel assembly (RWA) de-saturations; design and execution of 10 trajectory correction maneuvers; science calibration of the two telescope instruments; a flight demonstration of the fastest turns conducted by the spacecraft between Earth and comet point; and assessment of RWA health (given RWA problems on other spacecraft).

  13. Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Hartley 2

    Science.gov (United States)

    Luna, Michael E.; Collins, Steven M.

    2011-01-01

    On November 4, 2010 the former "Deep Impact" spacecraft, renamed "EPOXI" for its extended mission, flew within 700km of comet 103P/Hartley 2. In July 2005, the spacecraft had previously imaged a probe impact of comet Tempel 1. The EPOXI flyby was the fifth close encounter of a spacecraft with a comet nucleus and marked the first time in history that two comet nuclei were imaged at close range with the same suite of onboard science instruments. This challenging objective made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby.As part of the spacecraft flyby preparations, the ADCS operations team had to perform meticulous sequence reviews, implement complex spacecraft engineering and science activities and perform numerous onboard calibrations. ADCS contributions included design and execution of 10 trajectory correction maneuvers, the science calibration of the two telescopic instruments, an in-flight demonstration of high-rate turns between Earth and comet point, and an ongoing assessment of reaction wheel health. The ADCS team was also responsible for command sequences that included updates to the onboard ephemeris and sun sensor coefficients and implementation of reaction wheel assembly (RWA) de-saturations.

  14. Coupled GPS/MEMS IMU Attitude Determination of Small UAVs with COTS

    Directory of Open Access Journals (Sweden)

    Michael Strohmeier

    2017-02-01

    Full Text Available This paper proposes an attitude determination system for small Unmanned Aerial Vehicles (UAV with a weight limit of 5 kg and a small footprint of 0.5m x 0.5 m. The system is realized by coupling single-frequency Global Positioning System (GPS code and carrier-phase measurements with the data acquired from a Micro-Electro-Mechanical System (MEMS Inertial Measurement Unit (IMU using consumer-grade Components-Off-The-Shelf (COTS only. The sensor fusion is accomplished using two Extended Kalman Filters (EKF that are coupled by exchanging information about the currently estimated baseline. With a baseline of 48 cm, the static heading accuracy of the proposed system is comparable to the one of a commercial single-frequency GPS heading system with an accuracy of approximately 0.25°/m. Flight testing shows that the proposed system is able to obtain a reliable and stable GPS heading estimation without an aiding magnetometer.

  15. Determination of SLR station coordinates on the basis of tracking 45 GNSS satellites: benefits for future ITRF realizations

    Science.gov (United States)

    Sośnica, Krzysztof; Bury, Grzegorz; Zajdel, Radosław; Kaźmierski, Kamil; Drożdżewski, Mateusz

    2017-04-01

    The SLR station coordinates and SLR-derived Earth Rotation Parameters (ERPs) are typically derived on the basis of SLR tracking of four spherical geodetic satellites: two LAGEOS and two Etalons. Between 2014 and 2016, the International Laser Ranging Service (ILRS) initiated four intensive SLR tracking campaigns for Galileo and three campaigns devoted to tracking all GNSS spacecraft. As a result, the number of SLR observations and the number of tracked GNSS satellites have dramatically increased allowing for determining SLR station coordinates and ERPs solely on the basis of SLR tracking of GNSS satellites. This paper shows, for the first time, the solution in which the SLR station coordinates, geocenter motion, and ERPs are determined using the SLR observations to 26 GLONASS, 14 Galileo, 2 BeiDou IGSO, 2 BeiDou MEO, and 1 QZSS satellite. We compare the SLR station coordinate stability derived from GNSS-based results to the LAGEOS-only solution and from a combined 'SLR to GNSS+LAGEOS' solution. We address the issues related to the GNSS orbit determination using sparse SLR data and the issues related to handling range biases in the GNSS solutions. We found that the coordinate stability of those SLR stations which provide a large number of GNSS observations can remarkably be improved. The Length-of-day parameter can be derived from SLR-GNSS solutions with a much better accuracy than from the LAGEOS-only solutions. Finally, we show that the SLR tracking of GNSS satellites improves the consistency between SLR and GNSS solutions, and thus, can be beneficial for the future ITRF realizations.

  16. Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations

    Directory of Open Access Journals (Sweden)

    R. Lindsay

    2014-08-01

    Full Text Available Sea ice thickness is a fundamental climate state variable that provides an integrated measure of changes in the high-latitude energy balance. However, observations of ice thickness have been sparse in time and space making the construction of observation-based time series difficult. Moreover, different groups use a variety of methods and processing procedures to measure ice thickness and each observational source likely has different and poorly characterized measurement and sampling biases. Observational sources include upward looking sonars mounted on submarines or moorings, electromagnetic sensors on helicopters or aircraft, and lidar or radar altimeters on airplanes or satellites. Here we use a curve-fitting approach to evaluate the systematic differences between eight different observation systems in the Arctic Basin. The approach determines the large-scale spatial and temporal variability of the ice thickness as well as the mean differences between the observation systems using over 3000 estimates of the ice thickness. The thickness estimates are measured over spatial scales of approximately 50 km or time scales of 1 month and the primary time period analyzed is 2000–2013 when the modern mix of observations is available. Good agreement is found between five of the systems, within 0.15 m, while systematic differences of up to 0.5 m are found for three others compared to the five. The trend in annual mean ice thickness over the Arctic Basin is −0.58 ± 0.07 m decade−1 over the period 2000–2013, while the annual mean ice thickness for the central Arctic Basin alone (the SCICEX Box has decreased from 3.45 m in 1975 to 1.11 m in 2013, a 68% reduction. This is nearly double the 36% decline reported by an earlier study. These results provide additional direct observational confirmation of substantial sea ice losses found in model analyses.

  17. Bi-satellite formation relative position and attitude measurement based on Dual quaternion%基于对偶四元数的双星编队相对位姿测量

    Institute of Scientific and Technical Information of China (English)

    李静; 王惠南; 付世勇; 刘海颖

    2011-01-01

    为了描述编队卫星中主从星的相对位置和姿态信息,提出了基于对偶四元数的编队卫星相对位姿测量算法.以双星编队飞行的位姿运动为主线,运用对偶四元数工具,充分发挥其能以最简洁的形式表示一般性刚体运动的优点,对卫星轨道和姿态进行分析并建立了对偶四元数位姿模型.同时设计类GPS测量技术来测量编队卫星的相对位置和姿态,该技术载波相位波长和伪码码元比GPS的更短,可获得更高精度的相对测量信号.由于状态方程和观测方程的非线性特征,使用UKF滤波来消除随机噪声对量测过程的干扰.实验结果表明,所设计的算法能够有效估计系统误差,卫星的位置误差为10-3 m左右,四元教误差为10-15左右,验证了该算法的有效性.%In order to describe relative position and attitude information of formation flying satellites, a novel dual quaternion based satellite formation flying position and attitude measurement technique is put forward. Guided by bi-satellite formation flying position and attitude movement, and under the help of dual quaternion, the complex satellite formation flying position and attitude measurement model is constructed which has such merits as simple form of rigid body movement expression. Then a GPS-like measurement modal is put forward, and the observation equation is constructed for the position and attitude measurement, which owns shorter carrier phase wavelength and pseudo code symbol than those of GPS. At last, a refined UKF filter is applied to eliminate the system noise during the measurement process. Simulation is added to further improve its correctness and efficiency in solving formation flying satellite relative position and attitude measurement problem, in which the relative position error and the quaternion error are 10~3mand 10-15.

  18. Determination of the position of the Station Borowiec No. 7811 by satellite laser observations.

    Science.gov (United States)

    Dobaczewská, W.; Drozyner, A.; Rutkowska, M.; Schillak, S.; Zieliňski, J. B.

    Laser observations were performed in Borowiec in three years 1977 - 79 of the satellites Geos A and Geos C. These data were processed by means of the program ORBITA and station coordinates were calculated by dynamical methods. Another solution was found with the processing by the program GRIPE of SAO. These two dynamical solutions are compared with the translocation solution Wettzel-Borowiec.

  19. Towards an improved determination of Earth’s lithospheric field from satellite observations

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Olsen, Nils; Finlay, Chris

    the lithospheric signal is contaminated by much larger and highly time-dependent contributions from sources in the ionosphere and magnetosphere. Simultaneous, high-quality measurements from different locations as well as gradient estimates provided by the three Swarm satellites open new possibilities...

  20. Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

    DEFF Research Database (Denmark)

    Aakjær, Cecilie Drost; Olsen, Nils; Finlay, Chris

    2016-01-01

    currents at 110 km altitude (corresponding to the ionospheric E-layer) perpendicular to the satellite orbit, separated by 1° (about 113 km). We assess the reliability of our method, with the aim of a possible near-real-time application. A study of the effect of different regularization methods is therefore...

  1. Satellite-based assessment of yield variation and its determinants in smallholder African systems

    Science.gov (United States)

    Lobell, David B.

    2017-01-01

    The emergence of satellite sensors that can routinely observe millions of individual smallholder farms raises possibilities for monitoring and understanding agricultural productivity in many regions of the world. Here we demonstrate the potential to track smallholder maize yield variation in western Kenya, using a combination of 1-m Terra Bella imagery and intensive field sampling on thousands of fields over 2 y. We find that agreement between satellite-based and traditional field survey-based yield estimates depends significantly on the quality of the field-based measures, with agreement highest (R2 up to 0.4) when using precise field measures of plot area and when using larger fields for which rounding errors are smaller. We further show that satellite-based measures are able to detect positive yield responses to fertilizer and hybrid seed inputs and that the inferred responses are statistically indistinguishable from estimates based on survey-based yields. These results suggest that high-resolution satellite imagery can be used to make predictions of smallholder agricultural productivity that are roughly as accurate as the survey-based measures traditionally used in research and policy applications, and they indicate a substantial near-term potential to quickly generate useful datasets on productivity in smallholder systems, even with minimal or no field training data. Such datasets could rapidly accelerate learning about which interventions in smallholder systems have the most positive impact, thus enabling more rapid transformation of rural livelihoods. PMID:28202728

  2. CARTEL: A method to calibrate S-band ranges with geostationary satellites. Results of orbit determination

    Science.gov (United States)

    Guitart, A.; Mesnard, B.

    1986-05-01

    A satellite tracking campaign was organized, with 4 S-band stations, for 1 wk. The relative geometry of the network with respect to the satellites was an opportunity to show how the most precise orbit can be computed with the operational software. This precise orbit served as a reference to evaluate what can be achieved with one station with range and angular measurements, a typical configuration used for stationkeeping of geostationary satellites. Orbit computation implied numerical integration with gravitational (Earth, Moon, and Sun) and solar radiation pressure forces acting on the satellite. Arc lengths of 2 days gave initial state vectors which were compared every day. Precision of 10 m is achieved. However, an analysis of the influence of parameters in the orbit computations reveals that the absolute accuracy is of the order of 100 m, since modeling perturbations were neglected in the operational software (e.g., polar motion). In a relative sense, the reference orbit allows estimation of systematic errors for other tracking antennas.

  3. Women with gestational diabetes in Vietnam: a qualitative study to determine attitudes and health behaviours

    Directory of Open Access Journals (Sweden)

    Hirst Jane E

    2012-08-01

    Full Text Available Abstract Background Diabetes is increasing in prevalence globally, notably amongst populations from low- and middle- income countries. Gestational Diabetes Mellitus(GDM, a precursor for type 2 diabetes, is increasing in line with this trend. Few studies have considered the personal and social effects of GDM on women living in low and middle-income countries. The aim of this study was determine attitudes and health behaviours of pregnant women with GDM in Vietnam. Methods This was a qualitative study using focus group methodology conducted in Ho Chi Minh City. Pregnant women, aged over 18 years, with GDM were eligible to participate. Women were purposely sampled to obtain a range of gestational ages and severity of disease. They were invited to attend a 1-hour focus group. Questions were semi structured around six themes. Focus groups were recorded, transcribed, translated and cross-referenced. Non-verbal and group interactions were recorded. Thematic analysis was performed using a theoretical framework approach. Results From December 2010 to February 2011, four focus groups were conducted involving 34 women. Median age was 31.5 years (range 23 to 44, median BMI 21.8 kg/m2. Women felt confusion, anxiety and guilt about GDM. Many perceived their baby to be at increased risk of death. Advice to reduce dietary starch was confusing. Women reported being ‘hungry’ or ‘starving’ most of the time, unaware of appropriate food substitutions. They were concerned about transmission of GDM through breast milk. Several women planned not to breastfeed. All felt they needed more information. Current sources of information included friends, magazines, a health phone line or the Internet. Women felt small group sessions and information leaflets could benefit them. Conclusions This study highlights the need for culturally appropriate clinical education and health promotion activities for women with GDM in Vietnam.

  4. Evaluation of GPS position and attitude determination for automated rendezvous and docking missions. M.S. Thesis

    Science.gov (United States)

    Diprinzio, Marc D.; Tolson, Robert H.

    1994-01-01

    The use of the Global Positioning System for position and attitude determination is evaluated for an automated rendezvous and docking mission. The typical mission scenario involves the chaser docking with the target for resupply or repair purposes, and is divided into three sections. During the homing phase, the chaser utilizes coarse acquisition pseudorange data to approach the target; guidance laws for this stage are investigated. In the second phase, differential carrier phase positioning is utilized. The chaser must maintain a quasiconstant distance from the target, in order to resolve the initial integer ambiguities. Once the ambiguities are determined, the terminal phase is entered, and the rendezvous is completed with continuous carrier phase tracking. Attitude knowledge is maintained in all phases through the use of the carrier phase observable. A Kalman filter is utilized to estimate all states from the noisy measurement data. The effects of selective availability and cycle slips are also investigated.

  5. Attitudes towards Immigrant Workers and Asylum Seekers in Eastern Croatia: Dimensions, Determinants and Differences

    Directory of Open Access Journals (Sweden)

    Margareta Gregurović

    2016-04-01

    Full Text Available Croatia’s accession to the EU has brought new challenges and issues in researching and analysing migration flows and trends as well as attitudes and perceptions of real and potential newcomers. The aim of this paper is to explore attitudes of the residents of the two most easterly Croatian counties towards two distinct categories of newcomers: immigrant workers and asylum seekers. The research was conducted shortly after Croatia’s entry into the EU, in September 2013, and the presented data are a part of a larger survey that included various migration and ethnicity issues. The survey was applied on a convenience sample of 1 110 adult respondents in two counties: Osijek-Baranja and Vukovar-Srijem. Data were analysed in a series of multivariate procedures. Results indicated significant perceptions of immigrant workers within the dimension of cultural threat, along with the expression of a considerable degree of social distance towards them. Asylum seekers were further perceived as a security and economic threat. Within two analysed regression models, the effects on attitudes towards immigrant workers and asylum seekers were similar. Among the spectrum of socio-demographic variables, a statistically significant effect on both dependent variables came from age and political orientation, indicating that older and politically right-oriented respondents expressed more negative attitudes towards both groups. Among other socio-demographic variables, education was significant in predicting attitudes towards immigrant workers, while ethnicity was significant in predicting the attitudes towards asylum seekers. The second model analysed the effect of selected political attitudes and value orientations resulting in significant prediction of negative attitudes towards both groups by pronounced conservativism, support of aggression and submission, social-dominance, dominant submissive authoritarianism and social alienation, rejecting socially oriented

  6. A Comparative Accuracy Analysis of Classification Methods in Determination of Cultivated Lands with Spot 5 Satellite Imagery

    Science.gov (United States)

    kaya, S.; Alganci, U.; Sertel, E.; Ustundag, B.

    2013-12-01

    A Comparative Accuracy Analysis of Classification Methods in Determination of Cultivated Lands with Spot 5 Satellite Imagery Ugur ALGANCI1, Sinasi KAYA1,2, Elif SERTEL1,2,Berk USTUNDAG3 1 ITU, Center for Satellite Communication and Remote Sensing, 34469, Maslak-Istanbul,Turkey 2 ITU, Department of Geomatics, 34469, Maslak-Istanbul, Turkey 3 ITU, Agricultural and Environmental Informatics Research Center,34469, Maslak-Istanbul,Turkey alganci@itu.edu.tr, kayasina@itu.edu.tr, sertele@itu.edu.tr, berk@berk.tc ABSTRACT Cultivated land determination and their area estimation are important tasks for agricultural management. Derived information is mostly used in agricultural policies and precision agriculture, in specifically; yield estimation, irrigation and fertilization management and farmers declaration verification etc. The use of satellite image in crop type identification and area estimate is common for two decades due to its capability of monitoring large areas, rapid data acquisition and spectral response to crop properties. With launch of high and very high spatial resolution optical satellites in the last decade, such kind of analysis have gained importance as they provide information at big scale. With increasing spatial resolution of satellite images, image classification methods to derive the information form them have become important with increase of the spectral heterogeneity within land objects. In this research, pixel based classification with maximum likelihood algorithm and object based classification with nearest neighbor algorithm were applied to 2012 dated 2.5 m resolution SPOT 5 satellite images in order to investigate the accuracy of these methods in determination of cotton and corn planted lands and their area estimation. Study area was selected in Sanliurfa Province located on Southeastern Turkey that contributes to Turkey's agricultural production in a major way. Classification results were compared in terms of crop type identification using

  7. Determinants of consumer attitudes and purchase intentions with regard to genetically modifed foods

    DEFF Research Database (Denmark)

    Bredahl, Lone

    2001-01-01

    Previous research has shown consumers to be highly sceptical towards genetic modification in food production. So far, however, little research has tried to explain how consumers form attitudes and make decisions with regard to genetically modified foods. The paper presents the results of a survey...... which was carried out in Denmark, Germany, Italy and the United Kingdom to investigate the formation of consumer attitudes towards genetic modification in food production and of purchase decisions with regard to genetically modified yoghurt and beer. Altogether, 2031 consumers were interviewed...... in the four countries. Results show that attitude formation and decision-making are more comparable among Danish, German and British consumers than with Italian consumers. Italian consumers turned out to be significantly less negative towards genetic modification in foods than particularly Danish and German...

  8. Error analysis for satellite gravity field determination based on two-dimensional Fourier methods

    CERN Document Server

    Cai, Lin; Hsu, Houtse; Gao, Fang; Zhu, Zhu; Luo, Jun

    2012-01-01

    The time-wise and space-wise approaches are generally applied to data processing and error analysis for satellite gravimetry missions. But both the approaches, which are based on least-squares collocation, address the whole effect of measurement errors and estimate the resolution of gravity field models mainly from a numerical point of indirect view. Moreover, requirement for higher accuracy and resolution gravity field models could make the computation more difficult, and serious numerical instabilities arise. In order to overcome the problems, this study focuses on constructing a direct relationship between power spectral density of the satellite gravimetry measurements and coefficients of the Earth's gravity potential. Based on two-dimensional Fourier transform, the relationship is analytically concluded. By taking advantage of the analytical expression, it is efficient and distinct for parameter estimation and error analysis of missions. From the relationship and the simulations, it is analytically confir...

  9. H-- Filtering Algorithms Case Study GPS-Based Satellite Orbit Determination

    Science.gov (United States)

    Kuang, Jinlu; Tan, Soonhie

    In this paper the new Hfiltering algorithms for the design of navigation systems for autonomous LEO satellite is introduced. The nominal orbit (i.e., position and velocity) is computed by integrating the classical orbital differential equations of the LEO satellite by using the 7th-8th order Runge- Kutta algorithms. The perturbations due to the atmospheric drag force, the lunar-solar attraction and the solar radiation pressure are included together with the Earth gravity model (EGM-96). The spherical harmonic coefficients of the EGM-96 are considered up to 72 for the order and degree. By way of the MATLAB GPSoft software, the simulated pseudo ranges between the user LEO satellite and the visible GPS satellites are generated when given the appropriate angle of mask. The effects of the thermal noises, tropospheric refraction, ionospheric refraction, and multipath of the antenna are also compensated numerically in the simulated pseudo ranges. The dynamic Position-Velocity (PV) model is obtained by modeling the velocity as nearly constant being the white noise process. To further accommodate acceleration in the process model, the Position-Velocity-Acceleration (PVA) model is investigated by assuming the acceleration to be the Gaussian- Markov process. The state vector for the PV model becomes 8-dimensional (3-states for positions, 3-states for velocities, 1-state for range (clock) bias error, 1-state for range (clock) drift error). The state vector for the PV model becomes 11-dimensional with the addition of three more acceleration states. Three filtering approaches are used to smooth the orbit solution based upon the GPS pseudo range observables. The numerical simulation shows that the observed orbit root-mean-square errors of 60 meters by using the least squares adjustment method are improved to be less than 5 meters within 16 hours of tracking time by using the Hfiltering algorithms. The results are compared with the ones obtained by using the Extended Kalman

  10. Knowledge, attitude, practice, and determinants emergency contraceptive use among women seeking abortion services in Dire Dawa, Ethiopia.

    Directory of Open Access Journals (Sweden)

    Meskerem Abate

    Full Text Available BACKGROUND: Unplanned pregnancy from casual sex, unplanned sexual activity, and sexual violence are increasing. Emergency Contraceptives (EC are used to prevent unplanned pregnancies thereby preventing the occurrence and consequences of unplanned pregnancy. Emergency contraception is widely available in Ethiopia particularly in major cities. Yet the use of EC is very low and abortion rate in cities is high compared to the national average. OBJECTIVES: To assess knowledge, attitude and practice and determinants on the use of emergency contraception among women obtaining abortion service at selected health institutions in Dire Dawa, Eastern Ethiopia. METHODS: A facility based cross-sectional study was conducted on 390 women selected by multi-stage random sampling technique. The samples were generated from government and private for non profit health facilities. Participant's knowledge and attitude towards emergency contraception were measured using composite index based on 7 and 9 questions, respectively and analyzed using mean score to classify them as knowledgeable or not, and have positive attitude or not. Practice was assessed if the women reported ever use of emergency contraception. Determinants of use of emergency contraception were analyzed using logistic regression. RESULT: Out of 390 women interviewed, 162 women (41.5% heard about EC, only 133 (34.1% had good knowledge, and 200 (51.3% of the respondents had positive attitudes towards to EC. Ever use of EC was reported by 38 (9.7%. Age, living arrangement, education, marital status, religion were found to be significantly associated with the use of emergency contraceptives. Women with poor knowledge were less likely to use EC compared to the knowledgeable ones [AOR = 0.027, 95% CI (0.007, 0.105]. CONCLUSION: The study identified that most respondents lack adequate knowledge on the method of EC. In addition ever use of EC is very low. RECOMMENDATIONS: Health professions should give

  11. Integrated GNSS attitude determination and positioning for direct geo-referencing

    NARCIS (Netherlands)

    Nadarajah, N.; Paffenholz, J.A.; Teunissen, P.J.G.

    2014-01-01

    Direct geo-referencing is an efficient methodology for the fast acquisition of 3D spatial data. It requires the fusion of spatial data acquisition sensors with navigation sensors, such as Global Navigation Satellite System (GNSS) receivers. In this contribution, we consider an integrated GNSS naviga

  12. Centimeter-level precise orbit determination for the HY-2A satellite using DORIS and SLR tracking data

    Science.gov (United States)

    Kong, Qiaoli; Guo, Jinyun; Sun, Yu; Zhao, Chunmei; Chen, Chuanfa

    2017-01-01

    The HY-2A satellite is the first ocean dynamic environment monitoring satellite of China. Centimeter-level radial accuracy is a fundamental requirement for its scientific research and applications. To achieve this goal, we designed the strategies of precise orbit determination (POD) in detail. To achieve the relative optimal orbit for HY-2A, we carried out POD using DORIS-only, SLR-only, and DORIS + SLR tracking data, respectively. POD tests demonstrated that the consistency level of DORIS-only and SLR-only orbits with respect to the CNES orbits were about 1.81 cm and 3.34 cm in radial direction in the dynamic sense, respectively. We designed 6 cases of different weight combinations for DORIS and SLR data, and found that the optimal relative weight group was 0.2 mm/s for DORIS and 15.0 cm for SLR, and RMS of orbit differences with respect to the CNES orbits in radial direction and three-dimensional (3D) were 1.37 cm and 5.87 cm, respectively. These tests indicated that the relative radial and 3D accuracies computed using DORIS + SLR data with the optimal relative weight set were obviously higher than those computed using DORIS-only and SLR-only data, and satisfied the requirement of designed precision. The POD for HY-2A will provide the invaluable experience for the following HY-2B, HY-2C, and HY-2D satellites.

  13. Precise orbit determination for Jason-1 satellite using on-board GPS data with cm-level accuracy

    Institute of Scientific and Technical Information of China (English)

    PENG DongJu; WU Bin

    2009-01-01

    The joint US/French Jason-1 satellite altimeter mission, launched from the Vandenberg Air Force Base on December 7, 2001, continues the time series of centimeter-level ocean topography observations as the follow-on to the highly successful T/P radar altimeter satellite. Orbit error especially the radial orbit error is a major component in the overall budget of all altimeter satellite missions, in order to continue the T/P standard of observations. Jason-1 has a radial orbit error budget requirement of 2.5 cm. in this work, two cycles (December 19, 2002 to January 7, 2003) of the Jason-1 on-board GPS data were processed using the zero-difference (ZD) dynamic precise orbit determination (POD) technique. The resulting Jason-1 orbit accuracy was assessed by comparison with the precise orbit ephemeris (POE)produced by JPL, orbit overlaps and SLR residuals. These evaluations indicate that the RMS radial accuracy is in the range of 1-2 cm.

  14. Spin-Stabilized Spacecrafts: Analytical Attitude Propagation Using Magnetic Torques

    Directory of Open Access Journals (Sweden)

    Roberta Veloso Garcia

    2009-01-01

    Full Text Available An analytical approach for spin-stabilized satellites attitude propagation is presented, considering the influence of the residual magnetic torque and eddy currents torque. It is assumed two approaches to examine the influence of external torques acting during the motion of the satellite, with the Earth's magnetic field described by the quadripole model. In the first approach is included only the residual magnetic torque in the motion equations, with the satellites in circular or elliptical orbit. In the second approach only the eddy currents torque is analyzed, with the satellite in circular orbit. The inclusion of these torques on the dynamic equations of spin stabilized satellites yields the conditions to derive an analytical solution. The solutions show that residual torque does not affect the spin velocity magnitude, contributing only for the precession and the drift of the spacecraft's spin axis and the eddy currents torque causes an exponential decay of the angular velocity magnitude. Numerical simulations performed with data of the Brazilian Satellites (SCD1 and SCD2 show the period that analytical solution can be used to the attitude propagation, within the dispersion range of the attitude determination system performance of Satellite Control Center of Brazil National Research Institute.

  15. Satellite-derived determination of PM10 concentration and of the associated risk on public health

    Science.gov (United States)

    Sarigiannis, Dimosthenis; Sifakis, Nicolaos I.; Soulakellis, Nikos; Tombrou, Maria; Schaefer, Klaus P.

    2004-02-01

    Recent studies worldwide have revealed the relation between urban air pollution, particularly fine aerosols, and human health. The current state of the art in air quality assessment, monitoring and management comprises analytical measurements and atmospheric transport modeling. Earth observation from satellites provides an additional information layer through the calculation of synoptic air pollution indicators, such as atmospheric turbidity. Fusion of these data sources with ancillary data, including classification of population vulnerability to the adverse health effects of fine particulate and, especially, PM10 pollution, in the ambient air, integrates them into an optimally managed environmental information processing tool. Several algorithms pertaining to urban air pollution assessment using HSR satellite imagery have been developed and applied to urban sites in Europe such as Athens, Greece, the Po valley in Northern Italy, and Munich, Germany. Implementing these computational procedures on moderate spatial resolution (MSR) satellite data and coupling the result with the output of HSR data processing provides comprehensive and dynamic information on the spatial distribution of PM10 concentration. The result of EO data processing is corrected to account for the relative importance of the signal due to anthropogenic fine particles, concentrated in the lower troposphere. Fusing the corrected maps of PM10 concentration with data on vulnerable population distribution and implementation of epidemiology-derived exposure-response relationships results in the calculation of indices of the public health risk from PM10 concentration in the ambient air. Results from the pilot application of this technique for integrated environmental and health assessment in the urban environment are given.

  16. Characterizing the Effects of Low Order Perturbations on Geodetic Satellite Precision Orbit Determination

    Science.gov (United States)

    2015-08-07

    relativistic corrections comprise of Schwarzschild terms, Lense- Thirring precession (frame-dragging), and de Sitter ( geodesic ) precession. The Schwarzschild...Lense-Thirring, and de Sitter terms can be seen on lines 1, 2, and 3 respectively in Equation 1.13 ∆ −→̈ r = GME c2r3 {[ 2(β + γ) GME r − γ−→̇r · −→̇r...satellite. Figure 3. RSS Position Differences for Various Lunar Gravity Field Model Solutions It can be seen that all four lines representing each RSS

  17. The combination of satellite and topographic/isostatic potential models for mean anomaly determinations

    Science.gov (United States)

    Rapp, Richard H.; Pavlis, Nikolaos

    A method is presented for the estimation of a global gravity anomaly field using the combination of satellite-derived potential coefficient models and the coefficients implied by the Airy-Heiskanen topographic/isostatic potential (Rummel et al., 1988) from topographic models with a 30-km depth of compensation. Gravity anomalies calculated with this method are compared with a terrestrial 1 x 1 degree anomaly file where the anomaly standard deviations were less than 10 mgals. Using the GEM T1 model (Marsh et al., 1988) to degree 36, the rms anomaly discrepency was + or - 19 mgals, while the rms values for the terrestrial anomalies was + or - 28 mgals.

  18. Design and Test of an Attitude Determination and Control System for a 6U CubeSat using AFIT’s CubeSat Testbed

    Science.gov (United States)

    2015-03-01

    DESIGN AND TEST OF AN ATTITUDE DETERMINATION AND CONTROL SYSTEM FOR A 6U CUBESAT USING AFIT’S CUBESAT TESTBED THESIS Michael L. Tibbs, 2nd Lieutenant...work of the U.S. Government and is not subject to copyright protection in the United States. AFIT-ENY-MS-15-M-240 DESIGN AND TEST OF AN ATTITUDE ...DISTRIBUTION STATEMENT A APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT-ENY-MS-15-M-240 DESIGN AND TEST OF AN ATTITUDE DETERMINATION AND CONTROL

  19. Knowledge, Attitude and Determinants of Safe Abortion among first year students in Mekelle University, Tigray, Ethiopia

    Directory of Open Access Journals (Sweden)

    Selam Desalegn

    2015-01-01

    Full Text Available Introduction: students are becoming aware of the availability and seeking of safe abortion services in their communities. However, unsafe abortion still remains globally major health problem especially in developing countries like Ethiopia. It is becoming one of the leading direct obstetric causes of maternal morbidity and mortality. In many low income countries lack of knowledge about the consequences of unsafe abortion and having negative attitude towards abortion service resulted in unsafe abortion practices. This study is important to identify area for improvement and encourage better communication with student clients who need safe abortion services. Objective: The aim of this study is to assess knowledge, attitude and factors associated with safe abortion among first year students in Mekelle University, Tigray, Ethiopia. Methods: Institution based-cross-sectional study design involving both quantitative and qualitative methods was employed. The sample size was 772 and the sampling technique used was multistage cluster sampling technique. To proportionally allocate the sample size to each department, population proportion to size allocation was used. Data was analyzed using SPSS version 16.0. Bivariate analysis was made to see the relations of independent variables with knowledge and attitude towards safe abortion. At bivariate logistic regression analysis, independent variables with cut off P-value<0.25 was included. In the multivariable binary logistic regression, P- value< 0.05 was used to declare the significance of the variables. Thematic analysis was used for the Qualitative method. Finally both qualitative and quantitative data was triangulated. The analyzed data was presented using figures, tables, graphs and texts. Result: Out of 752 students who heard about safe abortion, more than half 300 (55.9% have inadequate knowledge. Sex, (AOR= 1.7, 95% CI: 1.160-2.725, department (AOR=0.37, 95% CI: 0.169-0.809, family education level (AOR

  20. Determination of global Earth outgoing radiation at high temporal resolution using a theoretical constellation of satellites

    Science.gov (United States)

    Gristey, Jake J.; Chiu, J. Christine; Gurney, Robert J.; Han, Shin-Chan; Morcrette, Cyril J.

    2017-01-01

    New, viable, and sustainable observation strategies from a constellation of satellites have attracted great attention across many scientific communities. Yet the potential for monitoring global Earth outgoing radiation using such a strategy has not been explored. To evaluate the potential of such a constellation concept and to investigate the configuration requirement for measuring radiation at a time resolution sufficient to resolve the diurnal cycle for weather and climate studies, we have developed a new recovery method and conducted a series of simulation experiments. Using idealized wide field-of-view broadband radiometers as an example, we find that a baseline constellation of 36 satellites can monitor global Earth outgoing radiation reliably to a spatial resolution of 1000 km at an hourly time scale. The error in recovered daily global mean irradiance is 0.16 W m-2 and -0.13 W m-2, and the estimated uncertainty in recovered hourly global mean irradiance from this day is 0.45 W m-2 and 0.15 W m-2, in the shortwave and longwave spectral regions, respectively. Sensitivity tests show that addressing instrument-related issues that lead to systematic measurement error remains of central importance to achieving similar accuracies in reality. The presented error statistics therefore likely represent the lower bounds of what could currently be achieved with the constellation approach, but this study demonstrates the promise of an unprecedented sampling capability for better observing the Earth's radiation budget.

  1. Determination of health-care workers' attitudes toward people with AIDS.

    Science.gov (United States)

    Hunter, C E; Ross, M W

    1991-06-01

    One hundred and thirty-four health professionals read one of 12 fictional case histories in which the patient was diagnosed as being either HIV- or Hepatitis B-positive. For each diagnosis infection was attributed to sexual contact, IV drug use, or a transfusion of contaminated blood. Within each diagnostic category, and for each source of infection, the patient was identified as either heterosexual or homosexual. Although homophobia has been suggested as a major contributor to negative attitudes toward people with AIDS, the present results remained significant even after homophobia, as measured by Hudson and Ricketts (1980), had been controlled for statistically. Regardless of disease, patients infected through IV drug use or sexual contact were seen as equally culpable and more responsible for their condition than those infected by transfusion. HIV, but not Hepatitis B, patients infected by sex or IV drug use were perceived as having less moral integrity than those infected by transfusion. Source of infection also influenced respondents' desire for close personal interaction. Negativity toward particular patient groups based merely on information about patient lifestyles was clearly demonstrated and it is suggested that negative attitudes toward people with AIDS may be a reflection of negative attitudes toward sexuality generally, rather than homosexuality.

  2. Determinants of drug abuse in high school students and their related knowledge and attitude.

    Science.gov (United States)

    Geramian, Nahid; Akhavan, Shohreh; Gharaat, Leila; Tehrani, Afsaneh Malekpour; Farajzadegan, Ziba

    2012-03-01

    The aim of the current study is to evaluate the knowledge and attitude of high school students toward addicting drugs. Thus, the interventions, which are more appropriate for this age group can be designed and applied. This cross-sectional study was carried out in 2009 in Isfahan province. The study population was high school students, who were randomly selected by multi-stage cluster sampling. The evaluation tool was an author-devised questionnaire, which was filled out by the students. The data obtained was analyzed using SPSS software, version 16. Among 6998 students who filled out the questionnaire, 50.1% were female. The mean knowledge scores were 58.7 +/- 10.3 and 57.9 +/- 10.2 for girls and boys, respectively, which were significantly different (p = 0.002). Considering the scores students obtained in attitude toward inclination to drug abuse, the most important factors in this regard were parents' divorce, familial conflicts, seeking pleasure, adolescents' curiosity, availability of the drugs, peer pressure, low levels of self-confidence, psychological disorders, and strict parents. With respect to the results obtained, promoting the knowledge and modifying the attitude of students, and increasing their self-confidence particularly in schools can play an important role in decreasing drug abuse in this age group. Moreover, policymakers should consider the strategies, which can support the family structure and reduce the harms in unstable families.

  3. Some Methodological Aspects Concerning the Use of Satellite Images and Maps in the Physico-Geographical Regional Determination of the Romania Territory

    Directory of Open Access Journals (Sweden)

    VASILE LOGHIN

    2005-01-01

    Full Text Available This paper presents some methodological aspects concerning the use of satellite images and maps in the physico-geographical region determination of Romania's territory, as well as some results that can be obtained using this method. In order to determine the physico-geographical units and sub-units using satellite maps (Bucharest page, 1:1.500.000 and satellite images (Landsat, IRS we have analyzed, from the geographical point of view, some samples of such documents. The resulting maps were compared with the already existing physico-geographical region determination maps. Our results show that the method under consideration has both advantages and disadvantages. One conclusion is sure: satellite images and maps can be used for this purpose together with traditional maps.

  4. On determining the large-scale ocean circulation from satellite altimetry

    Science.gov (United States)

    Tai, C.-K.

    1983-01-01

    It is contended that a spherical harmonic expansion of the difference between the altimeter-derived mean sea surface and the geoid estimate should reveal the large-scale circulation of the ocean surface layer when the low-degree terms are examined. Methods based on this principle are proposed and partially demonstrated over the Pacific Ocean with the aid of the mean sea surface derived from the Seasat altimeter and the Goddard Earth Model 9 earth gravity model. The preliminary results reveal a well-defined clockwise gyre in the North Pacific and a much less well defined counterclockwise gyre in the South Pacific. When the dynamic topography thus obtained is compared with Wyrtki's (1975) dynamic topography derived from hydrographic data, the agreement is found to be within the limit of geoid uncertainties and satellite orbital errors.

  5. Vertical crustal motion determined by satellite altimetry and tide gauge data in Fennoscandia

    Science.gov (United States)

    Kuo, C. Y.; Shum, C. K.; Braun, A.; Mitrovica, J. X.

    2004-01-01

    We present a new method of combining satellite altimetry and tide gauge data to obtain improved estimates of absolute (or geocentric) vertical crustal motion at tide gauges within a semi-enclosed sea. As an illustration, we combine TOPEX/POSEIDON altimetry data (1992-2001) and 25 long-term (>40 years) tide gauge records around the Baltic Sea region of Fennoscandia, an area where crustal deformation is dominated by glacial isostatic adjustment (GIA). A comparison of the estimated vertical motion, at 1-11 mm/yr, with independent solutions from 10 collocated BIFROST GPS sites, shows a difference of 0.2 +/- 0.9 mm/yr, thus verifying the accuracy and robustness of the procedure. The solution uncertainty is estimated at 0.4 mm/yr, which is significantly lower than previous analyses of this type. We conclude that our technique can potentially provide accurate vertical motion observations globally where long-term tide gauge records exist.

  6. Determining economic benefits of satellite data in short-range forecasting

    Science.gov (United States)

    Suchman, D.; Auvine, B.; Hinton, B.

    1981-01-01

    The chances of enhanced short term weather predictions and economic benefits from the use of GOES satellite data were examined. Results for a meteorological consulting firm before and after the introduction of GOES data were chosen as the method, and monetary benefits were selected as the measure. Services were provided for use by road and street departments, commodities dealers, and marine clients of the consulting firm. The Man-computer Interactive Data Access Program (McIDAS) was employed to furnish 1/2 hour visual or IR imagery for remote access. The commodities clients reconnected the GOES real-time imagery once the study was completed, while the consulting firm, which was personnel and not equipment intensive, did not. Further development of the flexibility of access to the GOES data and improvements in the projected grids are indicated.

  7. Multisensor satellite data integration for sea surface wind speed and direction determination

    Science.gov (United States)

    Glackin, D. L.; Pihos, G. G.; Wheelock, S. L.

    1984-01-01

    Techniques to integrate meteorological data from various satellite sensors to yield a global measure of sea surface wind speed and direction for input to the Navy's operational weather forecast models were investigated. The sensors were launched or will be launched, specifically the GOES visible and infrared imaging sensor, the Nimbus-7 SMMR, and the DMSP SSM/I instrument. An algorithm for the extrapolation to the sea surface of wind directions as derived from successive GOES cloud images was developed. This wind veering algorithm is relatively simple, accounts for the major physical variables, and seems to represent the best solution that can be found with existing data. An algorithm for the interpolation of the scattered observed data to a common geographical grid was implemented. The algorithm is based on a combination of inverse distance weighting and trend surface fitting, and is suited to combing wind data from disparate sources.

  8. Attitude pointing enhancement for combined energy and attitude control system

    Science.gov (United States)

    Varatharajoo, Renuganth; Tech Wooi, Choo; Mailah, Musa

    2011-06-01

    This paper extends the previous works that appeared in Acta Astronautica. An approach that incorporates the Active Force Control (AFC) technique into a conventional Proportional-Derivative (PD) controller is proposed for a 50 kg small satellite. Numerical treatments are performed to validate the effectiveness of AFC. The attitude control capability of the combined energy and attitude control system (CEACS) is expected to improve. The result shows an important attitude pointing enhancement for the CEACS attitude control task.

  9. An Efficient and Robust Singular Value Method for Star Pattern Recognition and Attitude Determination

    Science.gov (United States)

    Juang, Jer-Nan; Kim, Hye-Young; Junkins, John L.

    2003-01-01

    A new star pattern recognition method is developed using singular value decomposition of a measured unit column vector matrix in a measurement frame and the corresponding cataloged vector matrix in a reference frame. It is shown that singular values and right singular vectors are invariant with respect to coordinate transformation and robust under uncertainty. One advantage of singular value comparison is that a pairing process for individual measured and cataloged stars is not necessary, and the attitude estimation and pattern recognition process are not separated. An associated method for mission catalog design is introduced and simulation results are presented.

  10. 基于机械飞轮干扰补偿的小卫星自适应滑模变结构姿态控制%The Small Satellite Adaptive Sliding Mode Attitude Controller with Mechanical Flywheels Disturbance Compensation

    Institute of Scientific and Technical Information of China (English)

    杨宁宁; 杨照华; 余远金

    2013-01-01

    针对机械飞轮内干扰可能导致小卫星姿态控制系统性能下降问题,提出了一种加入机械飞轮干扰补偿的自适应滑模变结构姿态控制方法.本文针对基于机械飞轮的三轴稳定卫星姿态控制系统,首先建立系统详细的数学模型,包括基于机械飞轮的三轴稳定卫星姿态动力学方程和机械飞轮控制系统模型,然后针对此系统设计了一种基于机械飞轮干扰补偿的自适应滑模变结构控制器,其中通过设计一种状态观测器得到机械飞轮摩擦干扰的估计值,用于对机械飞轮摩擦干扰的补偿,并通过Lyapunov定理证明了此控制律能保证系统的渐近稳定性.最后仿真结果显示,此方法缩短了飞轮转速过零时间,降低了最大的姿态扰动量且提高了卫星姿态控制的精度和稳定度.%An adaptive sliding mode control law with disturbance compensation is proposed for small satellite attitude control system to overcome the deterioration of performance under mechanical flywheel disturbance. According to the small 3-axis stabilization satellite attitude control system with mechanical flywheels as actuators, the dynamic model of the system is firstly given, including attitude dynamic equations of a satellite with mechanical flywheels and the mechanical flywheels control system model. Secondly, an adaptive sliding mode control law which takes wheel disturbances into account is given and state observer is used to estimate wheels friction disturbance for compensation. The stability of the system is proven by using Lya- punov theorem. Finally, the simulation results show that this method shortens flywheel speed zero-crossing time, decreases the largest attitude disturbance value and effectively improves attitude control accuracy and stability.

  11. Fault Diagnosis Based on RO-NUIO/LMI for Flexible Satellite Attitude Control Systems during Orbit Control%基于RO-NUIO/LMI的挠性卫星轨控期间姿控系统故障诊断

    Institute of Scientific and Technical Information of China (English)

    侯倩; 程月华; 姜斌; 陆宁云

    2011-01-01

    During satellite orbit maneuver, the orbit control force causes disturbing torque and affects attitude of a satellite if the control force does not pass through the mass center of the satellite. In this paper, a set of reduced order nonlinear unknown input observers (RO-NUIO) are designed to detect and isolate faults. During the design process, the system is divided into three sub-systems to ensure that some states are not affected by the disturbance. Observers are designed by using the observable information. Meanwhile, some parameters of the observers can be obtained by using the LMI approach to reduce effects of nonlinear part on observers. The existence conditions of the observer proposed in this paper only depend on the inherent feature of the system. Combination of the reduced order idea and the LMI method make the structure of observers easy to be applied to nonlinear satellite attitude control systems. Numerical simulation is carried out to demonstrate the efficiency of the proposed fault diagnosis scheme for satellite attitude control systems.%卫星轨控期间,由于推力偏心,会产生较大的干扰力矩,直接影响卫星姿态.针对轨道控制期间的挠性卫星姿态控制系统,设计了干扰解耦的降阶非线性未知输入观测器(RO-NUIO),用于故障检测与故障隔离.在设计过程中,首先通过坐标变换,使得不可观的状态及部分可观状态不受干扰影响,然后针对不可观的子系统利用可观状态的信息设计观测器,观测器中的部分参数利用LMI方法获得,可以弱化非线性部分对观测器的影响.所设计观测器的存在条件仅依赖于系统本身特性,无需在线验证.观测器采用降阶设计,同时借助LMI思想,结构简单,适合于非线性卫星姿态控制系统.仿真结果验证了降阶非线性未知输入观测器实现卫星姿态控制故障诊断的可行性与有效性.

  12. Mesoscale ionospheric electrodynamics of omega bands determined from ground-based electromagnetic and satellite optical observations

    Directory of Open Access Journals (Sweden)

    O. Amm

    2005-02-01

    Full Text Available We present ground-based electromagnetic data from the MIRACLE and BEAR networks and satellite optical observations from the UVI and PIXIE instruments on the Polar satellite of an omega band event over Northern Scandinavia on 26 June 1998, which occured close to the morning side edge of a substorm auroral bulge. Our analysis of the data concentrates on one omega band period from 03:18-03:27 UT, for which we use the method of characteristics combined with an analysis of the UVI and PIXIE data to derive a time series of instantaneous, solely data-based distributions of the mesoscale ionospheric electrodynamic parameters with a 1-min time resolution. In addition, the AMIE method is used to derive global Hall conductance patterns. Our results show that zonally alternating regions of enhanced ionospheric conductances ("tongues" up to ~60S and low conductance regions are associated with the omega bands. The tongues have a poleward extension of ~400km from their base and a zonal extension of ~380km. While they are moving coherently eastward with a velocity of ~770ms-1, the structures are not strictly stationary. The current system of the omega band can be described as a superposition of two parts: one consists of anticlockwise rotating Hall currents around the tongues, along with Pedersen currents, with a negative divergence in their centers. The sign of this system is reversing in the low conductance areas. It causes the characteristic ground magnetic signature. The second part consists of zonally aligned current wedges of westward flowing Hall currents and is mostly magnetically invisible below the ionosphere. This system dominates the field-aligned current (FAC pattern and causes alternating upward and downward FAC at the flanks of the tongues with maximum upward FAC of ~25µA m-2. The total FAC of ~2MA are comparable to the ones diverted inside a westward traveling surge. Throughout the event, the overwhelming part of the FAC

  13. Evaluating Ultraviolet Radiation Exposures Determined from TOMS Satellite Data at Sites of Amphibian Declines in Central and South America

    Science.gov (United States)

    Middleton, Elizabeth M.; Smith, David E. (Technical Monitor)

    2000-01-01

    Many amphibian species have experienced substantial population declines, or have disappeared altogether, during the last several decades at a number of amphibian census sites in Central and South America. This study addresses the use of satellite-derived trends in solar ultraviolet-B (UV-B; 280-320 nm) radiation exposures at these sites over the last two decades, and is intended to demonstrate a role for satellite observations in determining whether UV-B radiation is a contributing factor in amphibian declines. UV-B radiation levels at the Earth's surface were derived from the Total Ozone Mapping Spectrometer (TOMS) satellite data, typically acquired daily since 1979. These data were used to calculate the daily erythemal (sunburning) UV-B, or UV-B(sub ery), exposures at the latitude, longitude, and elevation of each of 20 census sites. The annually averaged UV-B(sub ery) dose, as well as the maximum values, have been increasing in both Central and South America, with higher levels received at the Central American sites. The annually averaged UV-B(sub ery) exposures increased significantly from 1979-1998 at all 11 Central American sites examined (r(exp 2) = 0.60 - 0.79; Pexposure levels (>= 6750 J/sq m*d) to the annual UV-B(sub ery) total has increased from approx. 5% to approx. 15% in Central America over the 19 year period, but actual daily exposures for each species are unknown. Synergy among UV-B radiation and other factors, especially those associated with alterations of water chemistry (e.g., acidification) in aqueous habitats is discussed. These findings justify further research concerning whether UV-B(sub ery) radiation plays a role in amphibian population declines and extinctions.

  14. Retreat of glaciers on Puncak Jaya, Irian Jaya, determined from 2000 and 2002 IKONOS satellite images

    Science.gov (United States)

    Klein, Andrew G.; Kincaid, Joni L.

    Puncak Jaya, Irian Jaya, Indonesia, contains the only remaining tropical glaciers in East Asia. The extent of the ice masses on Puncak Jaya has been mapped from high-resolution IKONOS satellite images acquired on 8 June 2000 and 11 June 2002. Exclusive of Southwall Hanging Glacier, the ice extent on Puncak Jaya was 2.326 km2 and 2.152 km2 in 2000 and 2002, respectively. From 2000 to 2002, the Puncak Jaya glaciers lost a surface area of 0.174 km2 or 7.48% of their 2000 ice extent. Comparison of the IKONOS-based glacier extents with previous glacier extents demonstrates a continuing reduction of ice area on Puncak Jaya. By 2000, ice extent on Puncak Jaya had reduced by 88% of its maximum neoglacial extent. Between 1992 and 2000 Meren Glacier disappeared entirely. All remaining ice masses on Puncak Jaya continue their retreat from their neoglacial maxima. Comparison of 2000/2002 ice extents with previous extents suggests that these glaciers have not experienced accelerating rates of retreat during the last half of the 20th century. If the recession rates observed from 2000 to 2002 continue, the remaining ice masses on Puncak Jaya will melt within 50 years.

  15. Determination of the centre of mass kinematics in alpine skiing using differential global navigation satellite systems.

    Science.gov (United States)

    Gilgien, Matthias; Spörri, Jörg; Chardonnens, Julien; Kröll, Josef; Limpach, Philippe; Müller, Erich

    2015-01-01

    In the sport of alpine skiing, knowledge about the centre of mass (CoM) kinematics (i.e. position, velocity and acceleration) is essential to better understand both performance and injury. This study proposes a global navigation satellite system (GNSS)-based method to measure CoM kinematics without restriction of capture volume and with reasonable set-up and processing requirements. It combines the GNSS antenna position, terrain data and the accelerations acting on the skier in order to approximate the CoM location, velocity and acceleration. The validity of the method was assessed against a reference system (video-based 3D kinematics) over 12 turn cycles on a giant slalom skiing course. The mean (± s) position, velocity and acceleration differences between the CoM obtained from the GNSS and the reference system were 9 ± 12 cm, 0.08 ± 0.19 m · s(-1) and 0.22 ± 1.28 m · s(-2), respectively. The velocity and acceleration differences obtained were smaller than typical differences between the measures of several skiers on the same course observed in the literature, while the position differences were slightly larger than its discriminative meaningful change. The proposed method can therefore be interpreted to be technically valid and adequate for a variety of biomechanical research questions in the field of alpine skiing with certain limitations regarding position.

  16. Solution Method and Precision Analysis of Double-difference Dynamic Precise Orbit Determination of BeiDou Navigation Satellite System

    Directory of Open Access Journals (Sweden)

    LIU Weiping

    2016-02-01

    Full Text Available To resolve the high relativity between the transverse element of GEO orbit and double-difference ambiguity, the classical double-difference dynamic method is improved and the method, which is to determine precise BeiDou satellite orbit using carrier phase and pseudo-range smoothed by phase, is proposed. The feasibility of the method is discussed and the influence of the method about ambiguity fixing is analyzed. Considering the characteristic of BeiDou, the method, which is to fix double-difference ambiguity of BeiDou satellites by QIF, is derived. The real data analysis shows that the new method, which can reduce the relativity and assure the precision, is better than the classical double-difference dynamic method. The result of ambiguity fixing is well by QIF, but the ambiguity fixing success rate is not high on the whole. So the precision of BeiDou orbit can't be improved clearly after ambiguity fixing.

  17. Kinematic Orbit Determination Method Optimization and Test Analysis for BDS Satellites with Short-arc Tracking Data

    Directory of Open Access Journals (Sweden)

    GUO Rui

    2017-04-01

    Full Text Available Rapid orbit recovery is a puzzle for the BDS satellites after orbit maneuvers. Two kinematic orbit determination methods are studied, with two orbit determination models being established. The receiver system error and serious multipath error exist in the BDS system. The co-location method is proposed to estimate and calibrate the receiver system errors. A CNMC (code noise and multipath correction method is introduced to weaken the multipath error. Therefore the data quality is controlled efficiently for the receivers in the short tracking arc. The GEO/IGSO/MEO real data is emploied to carry out tests and validation. Using 10 min short tracking arc, the kinematic precise orbit determination accuracy is about 3.27 m for the GEOs, and 8.19 m for the IGSOs, and 5.9 m for the MEOs. Rapid orbit determination is achieved, which satisfying the orbit requirements from the BDS RDSS services. The kinematic precise orbit determination method also supports the RDSS service walking up to the global world.

  18. Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking

    Science.gov (United States)

    Vander Zanden, Hannah B.; Tucker, Anton D.; Hart, Kristen M.; Lamont, Margaret M.; Fujisaki, Ikuko; Addison, David S.; Mansfield, Katherine L.; Phillips, Katrina F.; Wunder, Michael B.; Bowen, Gabriel J.; Pajuelo, Mariela; Bolten, Alan B.; Bjorndal, Karen A.

    2015-01-01

    Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: 1) a nominal approach through discriminant analysis and 2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to inexpensively

  19. Study on feasibility of laser reflective tomography with satellite-accompany

    Science.gov (United States)

    Gu, Yu; Hu, Yi-hua; Hao, Shi-qi; Gu, You-lin; Zhao, Nan-xiang; Wang, Yang-yang

    2015-10-01

    Laser reflective tomography is a long-range, high-resolution active detection technology, whose advantage is that the spatial resolution is unrelated with the imaging distance. Accompany satellite is a specific satellite around the target spacecraft with encircling movement. When using the accompany satellite to detect the target aircraft, multi-angle echo data can be obtained with the application of reflective tomography imaging. The feasibility of such detection working mode was studied in this article. Accompany orbit model was established with horizontal circular fleet and the parameters of accompany flight was defined. The simulation of satellite-to-satellite reflective tomography imaging with satellite-accompany was carried out. The operating mode of reflective tomographic data acquisition from monostatic laser radar was discussed and designed. The flight period, which equals to the all direction received data consuming time, is one of the important accompany flight parameters. The azimuth angle determines the plane of image formation while the elevation angle determines the projection direction. Both of the azimuth and elevation angles guide the satellite attitude stability controller in order to point the laser radar spot on the target. The influences of distance between accompany satellite and target satellite on tomographic imaging consuming time was analyzed. The influences of flight period, azimuth angle and elevation angle on tomographic imaging were analyzed as well. Simulation results showed that the satellite-accompany laser reflective tomography is a feasible and effective method to the satellite-to-satellite detection.

  20. DFH-3 Satellite Platform

    Institute of Scientific and Technical Information of China (English)

    RenShufang

    2005-01-01

    The DFH-3 satellite platform is designed and developed by China Academy of Space Technology (CAST). It is a medium capability communications satellite platform. The platform adopts threeaxis attitude stabilization control system, having solar array output power of 1.7kW by the end of its design lifetime of 8 years. Its mass is 2100kg with payload capacity of 220kg.

  1. Phase Residual Estimations for PCVs of Spaceborne GPS Receiver Antenna and Their Impacts on Precise Orbit Determination of GRACE Satellites

    Institute of Scientific and Technical Information of China (English)

    TU Jia; GU Defeng; WU Yi; YI Dongyun

    2012-01-01

    In-flight phase center systematic errors of global positioning system (GPS) receiver antenna are the main restriction for improving the precision of precise orbit determination using dual-frequency GPS.Residual approach is one of the valid methods for in-flight calibration of GPS receiver antenna phase center variations (PCVs) from ground calibration.In this paper,followed by the correction model of spaceborne GPS receiver antenna phase center,ionosphere-free PCVs can be directly estimated by ionosphere-free carrier phase post-fit residuals of reduced dynamic orbit determination.By the data processing of gravity recovery and climate experiment (GRACE) satellites,the following conclusions are drawn.Firstly,the distributions of ionosphere-free carrier phase post-fit residuals from different periods have the similar systematic characteristics.Secondly,simulations show that the influence of phase residual estimations for ionosphere-free PCVs on orbit determination can reach the centimeter level.Finally,it is shown by in-flight data processing that phase residual estimations of current period could not only be used for the calibration for GPS receiver antenna phase center of foretime and current period,but also be used for the forecast of ionosphere-free PCVs in future period,and the accuracy of orbit determination can be well improved.

  2. Ionospheric refraction effects on TOPEX orbit determination accuracy using the Tracking and Data Relay Satellite System (TDRSS)

    Science.gov (United States)

    Radomski, M. S.; Doll, C. E.

    1991-01-01

    This investigation concerns the effects on Ocean Topography Experiment (TOPEX) spacecraft operational orbit determination of ionospheric refraction error affecting tracking measurements from the Tracking and Data Relay Satellite System (TDRSS). Although tracking error from this source is mitigated by the high frequencies (K-band) used for the space-to-ground links and by the high altitudes for the space-to-space links, these effects are of concern for the relatively high-altitude (1334 kilometers) TOPEX mission. This concern is due to the accuracy required for operational orbit-determination by the Goddard Space Flight Center (GSFC) and to the expectation that solar activity will still be relatively high at TOPEX launch in mid-1992. The ionospheric refraction error on S-band space-to-space links was calculated by a prototype observation-correction algorithm using the Bent model of ionosphere electron densities implemented in the context of the Goddard Trajectory Determination System (GTDS). Orbit determination error was evaluated by comparing parallel TOPEX orbit solutions, applying and omitting the correction, using the same simulated TDRSS tracking observations. The tracking scenarios simulated those planned for the observation phase of the TOPEX mission, with a preponderance of one-way return-link Doppler measurements. The results of the analysis showed most TOPEX operational accuracy requirements to be little affected by space-to-space ionospheric error. The determination of along-track velocity changes after ground-track adjustment maneuvers, however, is significantly affected when compared with the stringent 0.1-millimeter-per-second accuracy requirements, assuming uncoupled premaneuver and postmaneuver orbit determination. Space-to-space ionospheric refraction on the 24-hour postmaneuver arc alone causes 0.2 millimeter-per-second errors in along-track delta-v determination using uncoupled solutions. Coupling the premaneuver and postmaneuver solutions

  3. Determinants, attitudes and willingness of private forest owners to produce goods and services: a review of the international literature

    Directory of Open Access Journals (Sweden)

    Mozzato D

    2016-12-01

    Full Text Available Determinants, attitudes and willingness of private forest owners to produce goods and services: a review of the international literature. There is an information gap in the Italian literature with regards to private forest ownership, while several analysis are available on the characteristics and the management systems of public forest ownership. To address this gap, this paper presents the characteristics of private forest owners and their evolution in time by reviewing the international literature in the last three decades. The examined studies are reported according to four perspectives: (i the available classifications and/or typologies of private forest owners; (ii the determinants of different forest owners’ behaviors, especially in relation to their objectives; (iii the attitudes of forest owners and the motivations behind their management decisions; (iv the valuation of the willingness to accept monetary compensations in return for the provision of ecosystem services. The results show a very complex picture, varying both in space and time. However, some recurring features can be identified: (i not only are forest owners motivated by timber production goals, but also by other reasons, often very diversified and detached from market considerations; (ii a “multi-functional” forest owner is by no means less active, but, conversely, is more active than a forest owner whose sole objective is timber production; (iii in general, the active owner is a farmer whose family has owned the forest for many generations (and in this case he/she is more market-oriented, or is a new entry in the forestry sector; (iv the “passive” owner is usually elderly, non-farmer and resides far from the property. In addition, the “absent” owner is a common problem to several of the examined geographical contexts. Although the results of the review cannot be transferred as such, they represent a useful starting point for similar analyses in the Italian

  4. Communication, Ethics and Values: The Effect of Attitude toward Capital Punishment on the Evaluation of Evidence and the Determination of Guilt.

    Science.gov (United States)

    Taylor, K. Phillip; Buchanan, Raymond W.

    A study examined the effect of attitude toward capital punishment on the evaluation of evidence and the determination of guilt. Subjects were 224 undergraduate students who read a description of a murder. They then received two, four, or six items of evidence relevant to the defendant's guilt. Subjects were asked to determine a verdict and…

  5. Qualitative – Attitude Research To Determine the Employee Opinion of a Business Hotel in Istanbul - Turkey

    Directory of Open Access Journals (Sweden)

    Ahmet Ferda Seymen

    2015-07-01

    Full Text Available Qualitative research is concerned with qualitative phenomenon, i.e., phenomena relating to or involving quality or kind. For instance, when we are interested in investigating the reasons for human behavior (i.e., why people think or do certain things, we quite often talk of ‘Motivation Research’, an important type of qualitative research. This type of research aims at discovering the underlying motives and desires, using in depth interviews for the purpose. Other techniques of such research are word association tests, sentence completion tests, story completion tests and similar other projective techniques. Attitude or opinion research i.e., research designed to find out how people feel or what they think about a particular subject or institution is also qualitative research. Qualitative research is especially important in the behavioral sciences where the aim is to discover the underlying motives of human behavior. Through such research we can analyze the various factors which motivate people to behave in a particular manner or which make people like or dislike a particular thing. In this study; main issues identified by employees were: That the functions of the human resources department was none existent within the company. Recruitment, Reward and Reprimand, Career Development, Performance Evaluation System, Lack of proper orientation, on the job trainings and self-improvement courses needed to be developed and implemented in order to raise the declined motivation of employees and the deteriorating relations between the two sides.

  6. Snow melt on sea ice surfaces as determined from passive microwave satellite data

    Science.gov (United States)

    Anderson, Mark R.

    1987-01-01

    SMMR data for the year 1979, 1980 and 1984 have been analyzed to determine the variability in the onset of melt for the Arctic seasonal sea ice zone. The results show melt commencing in either the Kara/Barents Seas or Chukchi Sea and progressing zonally towards the central Asian coast (Laptev Sea). Individual regions had interannual variations in melt onset in the 10-20 day range. To determine whether daily changes occur in the sea ice surface melt, the SMMR 18 and 37 GHz brightness temperature data are analyzed at day/night/twilight periods. Brightness temperatures illustrate diurnal variations in most regions during melt. In the East Siberian Sea, however, daily variations are observed in 1979, throughout the analysis period, well before any melt would usually have commenced. Understanding microwave responses to changing surface conditions during melt will perhaps give additional information about energy budgets during the winter to summer transition of sea ice.

  7. Error Modeling and Analysis for InSAR Spatial Baseline Determination of Satellite Formation Flying

    Directory of Open Access Journals (Sweden)

    Jia Tu

    2012-01-01

    Full Text Available Spatial baseline determination is a key technology for interferometric synthetic aperture radar (InSAR missions. Based on the intersatellite baseline measurement using dual-frequency GPS, errors induced by InSAR spatial baseline measurement are studied in detail. The classifications and characters of errors are analyzed, and models for errors are set up. The simulations of single factor and total error sources are selected to evaluate the impacts of errors on spatial baseline measurement. Single factor simulations are used to analyze the impact of the error of a single type, while total error sources simulations are used to analyze the impacts of error sources induced by GPS measurement, baseline transformation, and the entire spatial baseline measurement, respectively. Simulation results show that errors related to GPS measurement are the main error sources for the spatial baseline determination, and carrier phase noise of GPS observation and fixing error of GPS receiver antenna are main factors of errors related to GPS measurement. In addition, according to the error values listed in this paper, 1 mm level InSAR spatial baseline determination should be realized.

  8. Investigation of Adaptive-threshold Approaches for Determining Area-Time Integrals from Satellite Infrared Data to Estimate Convective Rain Volumes

    Science.gov (United States)

    Smith, Paul L.; VonderHaar, Thomas H.

    1996-01-01

    The principal goal of this project is to establish relationships that would allow application of area-time integral (ATI) calculations based upon satellite data to estimate rainfall volumes. The research is being carried out as a collaborative effort between the two participating organizations, with the satellite data analysis to determine values for the ATIs being done primarily by the STC-METSAT scientists and the associated radar data analysis to determine the 'ground-truth' rainfall estimates being done primarily at the South Dakota School of Mines and Technology (SDSM&T). Synthesis of the two separate kinds of data and investigation of the resulting rainfall-versus-ATI relationships is then carried out jointly. The research has been pursued using two different approaches, which for convenience can be designated as the 'fixed-threshold approach' and the 'adaptive-threshold approach'. In the former, an attempt is made to determine a single temperature threshold in the satellite infrared data that would yield ATI values for identifiable cloud clusters which are closely related to the corresponding rainfall amounts as determined by radar. Work on the second, or 'adaptive-threshold', approach for determining the satellite ATI values has explored two avenues: (1) attempt involved choosing IR thresholds to match the satellite ATI values with ones separately calculated from the radar data on a case basis; and (2) an attempt involved a striaghtforward screening analysis to determine the (fixed) offset that would lead to the strongest correlation and lowest standard error of estimate in the relationship between the satellite ATI values and the corresponding rainfall volumes.

  9. Determinants of Knowledge and Attitudes Regarding Pain among Nurses in a University Hospital: A Cross-sectional Study.

    Science.gov (United States)

    Gretarsdottir, Elfa; Zoëga, Sigridur; Tomasson, Gunnar; Sveinsdottir, Herdis; Gunnarsdottir, Sigridur

    2017-06-01

    The aim of this cross-sectional study was to evaluate the primary determinants of knowledge and attitudes regarding pain among nurses in a hospital setting. All registered nurses employed at participating units at a university hospital were invited to participate. Information on work experience, education, and hospital unit was evaluated using a questionnaire. The Knowledge and Attitude Survey Regarding Pain instrument was used to assess knowledge on pain management. The difference in knowledge between nurses with different levels of education was assessed with analysis of variance. The discriminatory ability of each question was determined with item response theory, and the association between correct answers to individual items and the total score were calculated using linear regression. Participants were 235 nurses, 51% of the 459 invited. The overall pain knowledge score was 26.1 (standard deviation 5.3, range 8-38) out of a total of 40 possible. Those with an advanced degree in nursing scored on average 2.9 points higher than those who did not have an advance degree (95% confidence interval: 0.9-4.7). Responses to clinical vignette questions showed more difference between nurses with different levels of knowledge of pain management than the other questions. Participants with the correct response to the best discriminatory item had 5.35 (95% confidence interval 4.08-6.61) points higher total score than those with an incorrect answer. Higher education is associated with better knowledge on pain management. To assess pain knowledge, the ability to interpret and solve a clinical vignette leads to better results than answering direct questions. Copyright © 2017 American Society for Pain Management Nursing. Published by Elsevier Inc. All rights reserved.

  10. On the determination of the global cloud feedback from satellite measurements

    Directory of Open Access Journals (Sweden)

    T. Masters

    2012-08-01

    Full Text Available A detailed analysis is presented in order to determine the sensitivity of the estimated short-term cloud feedback to choices of temperature datasets, sources of top-of-atmosphere (TOA clear-sky radiative flux data, and temporal averaging. It is shown that the results of a previous analysis, which suggested a likely positive value for the short-term cloud feedback, depended upon combining all-sky radiative fluxes from NASA's Clouds and Earth's Radiant Energy System (CERES with reanalysis clear-sky forecast fluxes when determining the cloud radiative forcing (CRF. These results are contradicted when ΔCRF is derived using both all-sky and clear-sky measurements from CERES over the same period. The differences between the radiative flux data sources are thus explored, along with the potential problems in each. The largest discrepancy is found when including the first two years (2000–2002, and the diagnosed cloud feedback from each method is sensitive to the time period over which the regressions are run. Overall, there is little correlation between the changes in the ΔCRF and surface temperatures on these timescales, suggesting that the net effect of clouds varies during this time period quite apart from global temperature changes. Given the large uncertainties generated from this method, the limited data over this period are insufficient to rule out either the positive feedback present in most climate models or a strong negative cloud feedback.

  11. Onboard and Real-Time Artificial Satellite Orbit Determination Using GPS

    Directory of Open Access Journals (Sweden)

    Ana Paula Marins Chiaradia

    2013-01-01

    Full Text Available An algorithm for real-time and onboard orbit determination applying the Extended Kalman Filter (EKF method is developed. Aiming at a very simple and still fairly accurate orbit determination, an analysis is performed to ascertain an adequacy of modeling complexity versus accuracy. The minimum set of to-be-estimated states to reach the level of accuracy of tens of meters is found to have at least the position, velocity, and user clock offset components. The dynamical model is assessed through several tests, covering force model, numerical integration scheme and step size, and simplified variational equations. The measurement model includes only relevant effects to the order of meters. The EKF method is chosen to be the simplest real-time estimation algorithm with adequate tuning of its parameters. In the developed procedure, the obtained position and velocity errors along a day vary from 15 to 20 m and from 0.014 to 0.018 m/s, respectively, with standard deviation from 6 to 10 m and from 0.006 to 0.008 m/s, respectively, with the SA either on or off. The results, as well as analysis of the final adopted models used, are presented in this work.

  12. Attitudes and attitude change.

    Science.gov (United States)

    Bohner, Gerd; Dickel, Nina

    2011-01-01

    Attitudes and attitude change remain core topics of contemporary social psychology. This selective review emphasizes work published from 2005 to 2009. It addresses constructionist and stable-entity conceptualizations of attitude, the distinction between implicit and explicit measures of attitude, and implications of the foregoing for attitude change. Associative and propositional processes in attitude change are considered at a general level and in relation to evaluative conditioning. The role of bodily states and physical perceptions in attitude change is reviewed. This is followed by an integrative perspective on processing models of persuasion and the consideration of meta-cognitions in persuasion. Finally, effects of attitudes on information processing, social memory, and behavior are highlighted. Core themes cutting across the areas reviewed are attempts at integrative theorizing bringing together formerly disparate phenomena and viewpoints.

  13. Coronal magnetic field and the plasma beta determined from radio and multiple satellite observations

    CERN Document Server

    Iwai, Kazumasa; Nozawa, Satoshi; Takahashi, Takuya; Sawada, Shinpei; Kitagawa, Jun; Miyawaki, Shun; Kashiwagi, Hirotaka

    2014-01-01

    We derived the coronal magnetic field, plasma density, and temperature from the observation of polarization and intensity of radio thermal free-free emission using the Nobeyama Radioheliograph (NoRH) and extreme ultraviolet (EUV) observations. We observed a post-flare loop on the west limb 11 April 2013. The line-of-sight magnetic field was derived from the circularly polarized free-free emission observed by NoRH. The emission measure and temperature were derived from the Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO). The derived temperature was used to estimate the emission measure from the NoRH radio free-free emission observations. The derived density from NoRH was larger than that determined using AIA, which can be explained by the fact that the low temperature plasma is not within the temperature coverage of the AIA filters used in this study. We also discuss the other observation of the post-flare loops by the EUV Imager onboard the Solar Terrestrial Relations Observatory (...

  14. Simulation of 3-Axis Stable Satellite Attitude Control System Based on Modularization%基于模块化的三轴稳定卫星姿控系统仿真

    Institute of Scientific and Technical Information of China (English)

    梁骁俊

    2012-01-01

    研究卫星姿控系统快速建模问题,根据姿态控制原理以及控制系统的基本结构,遵循“开放性”、“集成性”和“模块化”等原则,提出建立了三轴稳定卫星姿态控制系统仿真通用模块库,并通过一个仿真算例验证了模块库的有效性.该库划分为执行机构、代数法姿态确定、常用模块、控制器、动力学与运动学、敏感器、空间环境和状态估计姿态确定等八大类功能模块,可嵌入到MATLAB平台中,使用方便,而且可以对模块库不断扩展改进,为三轴稳定卫星姿态控制系统设计与仿真验证提供了一个快速有效方法.%According to the principle and the structure of 3 梐xis stable satellite attitude control system, a unitized MATLAB/Simulink modules library for 3-axis stable satellite attitude control system was build to resolve the problem of fleetly modeling. It was designed following three rules: openness, integration and modularization, then its validity was proved by a simulation example. The library can be embedded into the platform of MATLAB/Simulink, which includes eight blocks; Actuators, Algebra AD Blocks, Commonly Used Blocks, Controllers, Dynamics and Kinematics, Sensor Models, Space Environment Blocks and State Estimation Blocks. So it is easy to use and can be serially improved. This method will be helpful for 3-axis stable satellite attitude control system design and simulation.

  15. Analysis of GRACE attitude variations based on characteristics of the AOCS sensors and actuators

    Science.gov (United States)

    Bandikova, Tamara; Flury, Jakob; Ko, Ung-Dai

    Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has provided the infor-mation about variations in the Earth's gravity field with unprecedented accuracy. Although this mission is in operation for more than 8 years, the onboard sensor behavior is not yet fully understood. The focus of this study is on GRACE satellite dynamics and the operation of attitude determination and control sensors. The goal is to better understand the onboard pro-cesses leading to certain systematic attitude variations which might influence the gravity field solution. Systematic patterns in long-time series of relative and absolute attitude variations of both GRACE spacecrafts during the different AOCS operational modes are investigated. They are put into connection with attitude determination sensors such as star camera and inertial measurement unit, to attitude control systems i.e. magnetic torquers and cold gas thrusters, and to other onboard sensors and satellite environment. Besides, some of the parameters used for the gravity field determination such as KBR geometric correction are analyzed with respect to the above mentioned attitude variations. The emphasis is put on the analysis of the star camera operation and on fuel consumption which are both very crucial topics not only for current but also for the future satellite missions.

  16. Melt ponds on Arctic sea ice determined from MODIS satellite data using an artificial neural network

    Directory of Open Access Journals (Sweden)

    A. Rösel

    2012-04-01

    Full Text Available Melt ponds on sea ice strongly reduce the surface albedo and accelerate the decay of Arctic sea ice. Due to different spectral properties of snow, ice, and water, the fractional coverage of these distinct surface types can be derived from multispectral sensors like the Moderate Resolution Image Spectroradiometer (MODIS using a spectral unmixing algorithm. The unmixing was implemented using a multilayer perceptron to reduce computational costs.

    Arctic-wide melt pond fractions and sea ice concentrations are derived from the level 3 MODIS surface reflectance product. The validation of the MODIS melt pond data set was conducted with aerial photos from the MELTEX campaign 2008 in the Beaufort Sea, data sets from the National Snow and Ice Data Center (NSIDC for 2000 and 2001 from four sites spread over the entire Arctic, and with ship observations from the trans-Arctic HOTRAX cruise in 2005. The root-mean-square errors range from 3.8 % for the comparison with HOTRAX data, over 10.7 % for the comparison with NSIDC data, to 10.3 % and 11.4 % for the comparison with MELTEX data, with coefficient of determination ranging from R2=0.28 to R2=0.45. The mean annual cycle of the melt pond fraction per grid cell for the entire Arctic shows a strong increase in June, reaching a maximum of 15 % by the end of June. The zonal mean of melt pond fractions indicates a dependence of the temporal development of melt ponds on the geographical latitude, and has its maximum in mid-July at latitudes between 80° and 88° N.

    Furthermore, the MODIS results are used to estimate the influence of melt ponds on retrievals of sea ice concentrations from passive microwave data. Results from a case study comparing sea ice concentrations from ARTIST Sea Ice-, NASA Team 2-, and Bootstrap-algorithms with MODIS sea ice concentrations indicate an underestimation of around 40 % for sea ice concentrations retrieved with microwave

  17. Melt ponds on Arctic sea ice determined from MODIS satellite data using an artificial neural network

    Science.gov (United States)

    Rösel, A.; Kaleschke, L.; Birnbaum, G.

    2012-04-01

    Melt ponds on sea ice strongly reduce the surface albedo and accelerate the decay of Arctic sea ice. Due to different spectral properties of snow, ice, and water, the fractional coverage of these distinct surface types can be derived from multispectral sensors like the Moderate Resolution Image Spectroradiometer (MODIS) using a spectral unmixing algorithm. The unmixing was implemented using a multilayer perceptron to reduce computational costs. Arctic-wide melt pond fractions and sea ice concentrations are derived from the level 3 MODIS surface reflectance product. The validation of the MODIS melt pond data set was conducted with aerial photos from the MELTEX campaign 2008 in the Beaufort Sea, data sets from the National Snow and Ice Data Center (NSIDC) for 2000 and 2001 from four sites spread over the entire Arctic, and with ship observations from the trans-Arctic HOTRAX cruise in 2005. The root-mean-square errors range from 3.8 % for the comparison with HOTRAX data, over 10.7 % for the comparison with NSIDC data, to 10.3 % and 11.4 % for the comparison with MELTEX data, with coefficient of determination ranging from R2=0.28 to R2=0.45. The mean annual cycle of the melt pond fraction per grid cell for the entire Arctic shows a strong increase in June, reaching a maximum of 15 % by the end of June. The zonal mean of melt pond fractions indicates a dependence of the temporal development of melt ponds on the geographical latitude, and has its maximum in mid-July at latitudes between 80° and 88° N. Furthermore, the MODIS results are used to estimate the influence of melt ponds on retrievals of sea ice concentrations from passive microwave data. Results from a case study comparing sea ice concentrations from ARTIST Sea Ice-, NASA Team 2-, and Bootstrap-algorithms with MODIS sea ice concentrations indicate an underestimation of around 40 % for sea ice concentrations retrieved with microwave algorithms.

  18. Attitudes and attitude change

    DEFF Research Database (Denmark)

    Scholderer, Joachim

    2010-01-01

    attitude theory. Why is this important? Attitudinal concepts can be found in every area of marketing. Concepts like ad liking, brand attitude, quality perception, product preference, perceived benefit, perceived risk, perceived value, and customer satisfaction can all be understood as particular types......, attitude objects are simply the things we like or dislike. Consumer researchers are mainly interested in attitude objects of two classes, products and services, including the attributes, issues, persons, communications, situations, and behaviours related to them. Research on consumer attitudes takes two...

  19. Hybrid spacecraft attitude control system

    Directory of Open Access Journals (Sweden)

    Renuganth Varatharajoo

    2016-02-01

    Full Text Available The hybrid subsystem design could be an attractive approach for futurespacecraft to cope with their demands. The idea of combining theconventional Attitude Control System and the Electrical Power System ispresented in this article. The Combined Energy and Attitude ControlSystem (CEACS consisting of a double counter rotating flywheel assemblyis investigated for small satellites in this article. Another hybrid systemincorporating the conventional Attitude Control System into the ThermalControl System forming the Combined Attitude and Thermal ControlSystem (CATCS consisting of a "fluid wheel" and permanent magnets isalso investigated for small satellites herein. The governing equationsdescribing both these novel hybrid subsystems are presented and theironboard architectures are numerically tested. Both the investigated novelhybrid spacecraft subsystems comply with the reference missionrequirements.The hybrid subsystem design could be an attractive approach for futurespacecraft to cope with their demands. The idea of combining theconventional Attitude Control System and the Electrical Power System ispresented in this article. The Combined Energy and Attitude ControlSystem (CEACS consisting of a double counter rotating flywheel assemblyis investigated for small satellites in this article. Another hybrid systemincorporating the conventional Attitude Control System into the ThermalControl System forming the Combined Attitude and Thermal ControlSystem (CATCS consisting of a "fluid wheel" and permanent magnets isalso investigated for small satellites herein. The governing equationsdescribing both these novel hybrid subsystems are presented and theironboard architectures are numerically tested. Both the investigated novelhybrid spacecraft subsystems comply with the reference missionrequirements.

  20. Attitudes of Academic Staff towards Their Own Work and towards External Evaluation, from the Perspective of Self-Determination Theory: Estonian Case

    Science.gov (United States)

    Seema, Riin; Udam, Maiki; Mattisen, Heli

    2016-01-01

    The purpose of this study was to ascertain the attitudes of academic staff towards their own work as well as towards external evaluations. The study was based on (1) an analysis of assessment reports of institutional accreditations conducted by the Estonian Quality Agency for Higher and Vocational Education and (2) self-determination theory on…

  1. Attitudes of Academic Staff towards Their Own Work and towards External Evaluation, from the Perspective of Self-Determination Theory: Estonian Case

    Science.gov (United States)

    Seema, Riin; Udam, Maiki; Mattisen, Heli

    2016-01-01

    The purpose of this study was to ascertain the attitudes of academic staff towards their own work as well as towards external evaluations. The study was based on (1) an analysis of assessment reports of institutional accreditations conducted by the Estonian Quality Agency for Higher and Vocational Education and (2) self-determination theory on…

  2. Determination of Motivation of 5th Grade Students Living in Rural and Urban Environments towards Science Learning and Their Attitudes towards Science-Technology Course

    Science.gov (United States)

    Kenar, Ismail; Köse, Mücahit; Demir, Halil Ibrahim

    2016-01-01

    In this research, determination of motivation of 5th grade students living in rural and urban environments towards science learning and their attitudes towards science-technology course is aimed. This research is conducted based on descriptive survey model. Samples are selected through teleological model in accordance with the aim of this…

  3. Habitat use and movement patterns of bull sharks Carcharhinus leucas determined using pop-up satellite archival tags.

    Science.gov (United States)

    Carlson, J K; Ribera, M M; Conrath, C L; Heupel, M R; Burgess, G H

    2010-08-01

    Habitat use, movement and residency of bull sharks Carcharhinus leucas were determined using satellite pop-up archival transmitting (PAT) tags throughout coastal areas in the U.S., Gulf of Mexico and waters off the south-east U.S. From 2005 to 2007, 18 fish (mean size = 164 cm fork length, L(F)) were tagged over all seasons. Fish retained tags for up to 85 days (median = 30 days). Based on geolocation data from initial tagging location to pop-off location, C. leucas generally travelled c. 5-6 km day(-1) and travelled an average of 143.6 km. Overall, mean proportions of time at depth revealed C. leucas spent the majority of their time in waters up the east coast of the U.S. to South Carolina. Data on C. leucas movements indicated that they are found primarily in shallower waters and tend to remain in the same location over long periods. While some individuals made large-scale movements over open ocean areas, the results emphasize the importance of the coastal zone for this species as potential essential habitat, particularly in areas of high freshwater inflow.

  4. Access to Attitude-Relevant Information in Memory as a Determinant of Persuasion: The Role of Message and Communicator Attributes.

    Science.gov (United States)

    Wood, Wendy; And Others

    Research literature shows that people with access to attitude-relevant information in memory are able to draw on relevant beliefs and prior experiences when analyzing a persuasive message. This suggests that people who can retrieve little attitude-relevant information should be less able to engage in systematic processing. Two experiments were…

  5. Mother Tongue as a Determining Variable in Language Attitudes. The Case of Immigrant Latin American Students in Spain

    Science.gov (United States)

    Huguet, Angel; Janes, Judit

    2008-01-01

    Bearing in mind the relevance of immigration in Spain, we consider the linguistic idiosyncrasy of the autonomous community of Catalonia in the present study to describe and analyse language attitudes to Catalan and Spanish in a sample of 225 students of immigrant origin living in different parts of the region. We focus on language attitudes in so…

  6. Access to Attitude-Relevant Information in Memory as a Determinant of Persuasion: The Role of Message and Communicator Attributes.

    Science.gov (United States)

    Wood, Wendy; And Others

    Research literature shows that people with access to attitude-relevant information in memory are able to draw on relevant beliefs and prior experiences when analyzing a persuasive message. This suggests that people who can retrieve little attitude-relevant information should be less able to engage in systematic processing. Two experiments were…

  7. To Determine Some Knowledge and Attitudes Related to the Social Hand Washing of Individuals who Apply to a Primary Health Center

    Directory of Open Access Journals (Sweden)

    Funda Sevencan

    2009-06-01

    Full Text Available AIM: The aim of this study is to determine some knowledge and attitudes related to the social hand washing of individuals who apply to a health center and to examine the relationships with some socio-demographic characteristic. METHODS: The universe of this epidemiological descriptive study was applicants (over 18 years old of a primary health center in five business days. A questionnaire, which was prepared by the researchers, was applied to the applicants who agree to participate in the survey with face to face interview method. The mean scores of the knowledge and positive attitude of participants were calculated and the percentage distribution, t-test and One Way Anova were used in analysis. RESULTS: 77.9% of participants in research were female, 31.0% were primary school graduate and 75.5% were married. Of the participants, 41.5% were washing hands 11 times and over in a day. The mean scores of the knowledge and positive attitudes of participants were 61.6±21.4 and 61.9±13.4, respectively. The mean knowledge and positive attitudes scores were significantly different increases with education (p=0.002, p=0.013 respectively. The mean scores of positive attitudes of females were higher than males and difference is statistically significant (p=0.001. CONCLUSION: According to the results of this study, it can be said that the knowledge and positive attitudes about hand washing influenced by socio-demographic characteristics. It can be concluded that the most appropriate solution for improving knowledge and positive attitudes about hand washing is to increase the level of education. [TAF Prev Med Bull 2009; 8(3.000: 207-216

  8. Accurate Determination of Impact Epoch and Coordinate of Chang' E - 1 Satellite on the Moon%嫦娥一号卫星撞月时刻与坐标精确分析

    Institute of Scientific and Technical Information of China (English)

    马茂莉; 郑为民; 李金岭; 王广利

    2011-01-01

    The impact epoch and coordinates of the Chang ' e - 1 satellite on the moon are obtained through several techniques. The local correlation technique is used to determine the time when the carrier signals disappeared at VLBI stations, and the impact epoch on the moon. Real-time doppler data iS analyzed to examine the flight attitude evolution of the satellite during the landing arc section. Position reduction for the VLBI delay and the USB ranging data is uaed to determine the impact coordinates. The uncertainty of the impact epoch is ± 5μs, and the lunar tangential linear and three dimensional coordinate accuracy are ahout 0.274km and 0.319km ( 1σ) respectively.%针对CE-1卫星精确的撞月时刻与撞月点坐标,首先通过探测器载波信号的本地相关处理技术,精确分析了载波信号在VLBI各测站的消失时刻,进而推算了卫星的撞月时刻;通过实时单向多普勒频移测量的事后分析,核实了卫星撞月过程中的飞行姿态演化;最后结合VLBI互相关时延与测距资料,经定位归算确定撞月点坐标.分析表明,CE-1卫星撞月时刻的误差为±5μs,撞月点坐标月面切向和三维定位误差分别约为0.274km和0.319km(1σ).

  9. Characterization and compensation of thermo-elastic instability of SWARM optical bench on Micro Advanced Stellar Compass attitude observations

    DEFF Research Database (Denmark)

    Herceg, Matija; Jørgensen, Peter Siegbjørn; Jørgensen, John Leif

    2017-01-01

    Launched into orbit on November 22, 2013, the Swarm constellation of three satellites precisely measures magnetic signal of the Earth. To ensure the high accuracy of magnetic observation by vector magnetometer (VFM), its inertial attitude is precisely determined by µASC (micro Advanced Stellar...... Compass). Each of the three Swarm satellites is equipped with three µASC Camera Head Units (CHU) mounted on a common optical bench (OB), which has a purpose of transference of the attitude from the star trackers to the magnetometer measurements. Although substantial pre-launch analyses were made...... can be predicted and corrected in the Swarm data processing. The results after applying thermal corrections show decrease in IBA RMS from 6.41 to 2.58 arc-seconds. The model significantly improves attitude determination which, after correction, meets the requirements of Swarm satellite mission...

  10. Optimal magnetic attitude control

    DEFF Research Database (Denmark)

    Wisniewski, Rafal; Markley, F.L.

    1999-01-01

    because control torques can only be generated perpendicular to the local geomagnetic field vector. This has been a serious obstacle for using magnetorquer based control for three-axis stabilization of a low earth orbit satellite. The problem of controlling the spacecraft attitude using only magnetic...

  11. A Three Degrees of Freedom Test-Bed for Nanosatellite and CubeSat Attitude Dynamics, Determination, and Control

    Science.gov (United States)

    2009-12-01

    Tactical Imaging Nano-sat Yielding Small-Cost Operations and Persistent Earth-coverage UFO UHF Follow On UHF Ultra-High Frequency USCG United...replaced by UHF Follow On ( UFO ) satellites in the 1990s. The UFO satellites are being updated and scheduled for replacement by the Mobile User

  12. Attitude Design for the LADEE Mission

    Science.gov (United States)

    Galal, Ken; Nickel, Craig; Sherman, Ryan

    2015-01-01

    The Lunar Atmosphere and Dust Environment Explorer (LADEE) satellite successfully completed its 148-day science investigation in a low-altitude, near-equatorial lunar orbit on April 18, 2014. The LADEE spacecraft was built, managed and operated by NASA's Ames Research Center (ARC). The Mission Operations Center (MOC) was located at Ames and was responsible for activity planning, command sequencing, trajectory and attitude design, orbit determination, and spacecraft operations. The Science Operations Center (SOC) was located at Goddard Space Flight Center and was responsible for science planning, data archiving and distribution. This paper details attitude design and operations support for the LADEE mission. LADEE's attitude design was shaped by a wide range of instrument pointing requirements that necessitated regular excursions from the baseline one revolution per orbit "Ram" attitude. Such attitude excursions were constrained by a number of flight rules levied to protect instruments from the Sun, avoid geometries that would result in simultaneous occlusion of LADEE's two star tracker heads, and maintain the spacecraft within its thermal and power operating limits. To satisfy LADEE's many attitude requirements and constraints, a set of rules and conventions was adopted to manage the complexity of this design challenge and facilitate the automation of ground software that generated pointing commands spanning multiple days of operations at a time. The resulting LADEE Flight Dynamics System (FDS) that was developed used Visual Basic scripts that generated instructions to AGI's Satellite Tool Kit (STK) in order to derive quaternion commands at regular intervals that satisfied LADEE's pointing requirements. These scripts relied heavily on the powerful "align and constrain" capability of STK's attitude module to construct LADEE's attitude profiles and the slews to get there. A description of the scripts and the attitude modeling they embodied is provided. One particular

  13. Galileo satellite antenna modeling

    Science.gov (United States)

    Steigenberger, Peter; Dach, Rolf; Prange, Lars; Montenbruck, Oliver

    2015-04-01

    The space segment of the European satellite navigation system Galileo currently consists of six satellites. Four of them belong to the first generation of In-Orbit Validation (IOV) satellites whereas the other two are Full Operational Capability (FOC) satellites. High-precision geodetic applications require detailed knowledge about the actual phase center of the satellite and receiver antenna. The deviation of this actual phase center from a well-defined reference point is described by phase center offsets (PCOs) and phase center variations (PCVs). Unfortunately, no public information is available about the Galileo satellite antenna PCOs and PCVs, neither for the IOV, nor the FOC satellites. Therefore, conventional values for the IOV satellite antenna PCOs have been adopted for the Multi-GNSS experiment (MGEX) of the International GNSS Service (IGS). The effect of the PCVs is currently neglected and no PCOs for the FOC satellites are available yet. To overcome this deficiency in GNSS observation modeling, satellite antenna PCOs and PCVs are estimated for the Galileo IOV satellites based on global GNSS tracking data of the MGEX network and additional stations of the legacy IGS network. Two completely independent solutions are computed with the Bernese and Napeos software packages. The PCO and PCV values of the individual satellites are analyzed and the availability of two different solutions allows for an accuracy assessment. The FOC satellites are built by a different manufacturer and are also equipped with another type of antenna panel compared to the IOV satellites. Signal transmission of the first FOC satellite has started in December 2014 and activation of the second satellite is expected for early 2015. Based on the available observations PCO estimates and, optionally PCVs of the FOC satellites will be presented as well. Finally, the impact of the new antenna model on the precision and accuracy of the Galileo orbit determination is analyzed.

  14. Attitudes and attitude change

    DEFF Research Database (Denmark)

    Scholderer, Joachim

    2010-01-01

    attitude theory. Why is this important? Attitudinal concepts can be found in every area of marketing. Concepts like ad liking, brand attitude, quality perception, product preference, perceived benefit, perceived risk, perceived value, and customer satisfaction can all be understood as particular types...... of attitudes. This is the reason why a thorough understanding of attitudes is one of the most important skills a marketer can have. That same is true in related areas such as communications research: concepts like public opinion, corporate reputation, and corporate image are nothing more than particular types...

  15. Attitude Perturbation of Spin-Stabilized Satellites Caused by Gravity Gradient Moment%重力梯度力矩引起的自旋稳定卫星姿态摄动

    Institute of Scientific and Technical Information of China (English)

    隋起胜; 袁建平; 姜宇

    2011-01-01

    A mathematical model and numerical method for attitude perturbation of spin-stabilized satellites are presented. With highlight on gravity gradient moment, the precession angle, nutation angle, longitude and latitude of the spin axis in the earth-centered inertial frame are computed and analyzed. The attitude perturbation of spin-stabilized satellites caused by gravity gradient moment is studied. The paper points out that with the attitude perturbation of the gravity gradient moment, precession of the spin axis follows the normal line of the orbital plane and the nutation velocity is much smaller than the precession velocity. If the orbital velocity augments, the precession velocity and nutation velocity of the spin axis relative to the earth-centered inertial frame will increase and the longitude and latitude of the spin axis in the earth-centered inertial frame will increase. If the spin velocity augments, the rate of change of the longitude and latitude of the spin axis will decrease and the precession velocity and nutation velocity of the spin axis relative to the earth-centered inertial frame will decrease.%建立了自旋稳定卫星姿态摄动的数值分析方法及模型,对重力梯度力矩作用下自旋卫星自旋轴相对于地心惯性系进动和章动以及赤经和赤纬的变化进行了仿真分析.对重力梯度力矩引起的自旋稳定卫星姿态摄动的演化规律进行了研究.指出在重力梯度力矩的作用下:自旋轴指向绕轨道面法线进动;章动角速度远小于进动角速度;轨道角速度越大,星体相对于地心惯性系的进动角速度和章动角速度越大,赤经和赤纬的变化率越大;自旋角速度越大,星体相对于地心惯性系的进动角速度和章动角速度越小,赤经和赤纬的变化率越小.

  16. A drift line bias estimator: ARMA-based filter or calibration method, and its application in BDS/GPS-based attitude determination

    Science.gov (United States)

    Liang, Zhang; Yanqing, Hou; Jie, Wu

    2016-06-01

    The multi-antenna synchronized receiver (using a common clock) is widely applied in GNSS-based attitude determination (AD) or terrain deformations monitoring, and many other applications, since the high-accuracy single-differenced carrier phase can be used to improve the positioning or AD accuracy. Thus, the line bias (LB) parameter (fractional bias isolating) should be calibrated in the single-differenced phase equations. In the past decades, all researchers estimated the LB as a constant parameter in advance and compensated it in real time. However, the constant LB assumption is inappropriate in practical applications because of the physical length and permittivity changes of the cables, caused by the environmental temperature variation and the instability of receiver-self inner circuit transmitting delay. Considering the LB drift (or colored LB) in practical circumstances, this paper initiates a real-time estimator using auto regressive moving average-based (ARMA) prediction/whitening filter model or Moving average-based (MA) constant calibration model. In the ARMA-based filter model, four cases namely AR(1), ARMA(1, 1), AR(2) and ARMA(2, 1) are applied for the LB prediction. The real-time relative positioning model using the ARMA-based predicting LB is derived and it is theoretically proved that the positioning accuracy is better than the traditional double difference carrier phase (DDCP) model. The drifting LB is defined with a phase temperature changing rate integral function, which is a random walk process if the phase temperature changing rate is white noise, and is validated by the analysis of the AR model coefficient. The auto covariance function shows that the LB is indeed varying in time and estimating it as a constant is not safe, which is also demonstrated by the analysis on LB variation of each visible satellite during a zero and short baseline BDS/GPS experiment. Compared to the DDCP approach, in the zero-baseline experiment, the LB constant

  17. A drift line bias estimator: ARMA-based filter or calibration method, and its application in BDS/GPS-based attitude determination

    Science.gov (United States)

    Liang, Zhang; Yanqing, Hou; Jie, Wu

    2016-12-01

    The multi-antenna synchronized receiver (using a common clock) is widely applied in GNSS-based attitude determination (AD) or terrain deformations monitoring, and many other applications, since the high-accuracy single-differenced carrier phase can be used to improve the positioning or AD accuracy. Thus, the line bias (LB) parameter (fractional bias isolating) should be calibrated in the single-differenced phase equations. In the past decades, all researchers estimated the LB as a constant parameter in advance and compensated it in real time. However, the constant LB assumption is inappropriate in practical applications because of the physical length and permittivity changes of the cables, caused by the environmental temperature variation and the instability of receiver-self inner circuit transmitting delay. Considering the LB drift (or colored LB) in practical circumstances, this paper initiates a real-time estimator using auto regressive moving average-based (ARMA) prediction/whitening filter model or Moving average-based (MA) constant calibration model. In the ARMA-based filter model, four cases namely AR(1), ARMA(1, 1), AR(2) and ARMA(2, 1) are applied for the LB prediction. The real-time relative positioning model using the ARMA-based predicting LB is derived and it is theoretically proved that the positioning accuracy is better than the traditional double difference carrier phase (DDCP) model. The drifting LB is defined with a phase temperature changing rate integral function, which is a random walk process if the phase temperature changing rate is white noise, and is validated by the analysis of the AR model coefficient. The auto covariance function shows that the LB is indeed varying in time and estimating it as a constant is not safe, which is also demonstrated by the analysis on LB variation of each visible satellite during a zero and short baseline BDS/GPS experiment. Compared to the DDCP approach, in the zero-baseline experiment, the LB constant

  18. Attitude Control and Orbital Dynamics Challenges of Removing the First 3-Axis Stabilized Tracking and Data Relay Satellite from the Geosynchronous ARC

    Science.gov (United States)

    Benet, Charles A.; Hofman, Henry; Williams, Thomas E.; Olney, Dave; Zaleski, Ronald

    2011-01-01

    Launched on April 4, 1983 onboard STS 6 (Space Shuttle Challenger), the First Tracking and Data Relay Satellite (TDRS 1) was retired above the Geosynchronous Orbit (GEO) on June 27, 2010 after having provided real-time communications with a variety of low-orbiting spacecraft over a 26-year period. To meet NASA requirements limiting orbital debris 1, a team of experts was assembled to conduct an End-Of-Mission (EOM) procedure to raise the satellite 350 km above the GEO orbit. Following the orbit raising via conventional station change maneuvers, the team was confronted with having to deplete the remaining propellant and passivate all energy storage or generation sources. To accomplish these tasks within the time window, communications (telemetry and control links), electrical power, propulsion, and thermal constraints, a spacecraft originally designed as a three-axis stabilized satellite was turned into a spinner. This paper (a companion paper to Innovative Approach Enabled the Retirement of TDRS 1, paper # 1699, IEEE 2011 Aerospace Conference, March 5-12, 2011 sup 2) focuses on the challenges of maintaining an acceptable spinning dynamics, while repetitively firing thrusters. Also addressed are the effects of thruster firings on the orbit characteristics and how they were mitigated by a careful scheduling of the fuel depletion operations. Periodic thruster firings for spin rate adjustment, nutation damping, and precession of the momentum vector were also required in order to maintain effective communications with the satellite. All operations were thoroughly rehearsed and supported by simulations thus lending a high level of confidence in meeting the NASA EOM goals.

  19. Determinants of Public Attitudes towards Euthanasia in Adults and Physician-Assisted Death in Neonates in Austria: A National Survey.

    Directory of Open Access Journals (Sweden)

    Erwin Stolz

    Full Text Available Euthanasia remains a controversial topic in both public discourses and legislation. Although some determinants of acceptance of euthanasia and physician-assisted death have been identified in previous studies, there is still a shortage of information whether different forms of euthanasia are supported by the same or different sub-populations and whether authoritarian personality dispositions are linked to attitudes towards euthanasia.A large, representative face-to-face survey was conducted in Austria in 2014 (n = 1,971. Respondents faced three scenarios of euthanasia and one of physician assisted death differing regarding the level of specificity, voluntariness and subject, requiring either approval or rejection: (1 abstract description of euthanasia, (2 abstract description of physician-assisted suicide, (3 the case of euthanasia of a terminally-ill 79-year old cancer patient, and (4 the case of non-voluntary, physician assisted death of a severely disabled or ill neonate. A number of potential determinants for rejection ordered in three categories (socio-demographic, personal experience, orientations including authoritarianism were tested via multiple logistic regression analyses.Rejection was highest in the case of the neonate (69% and lowest for the case of the older cancer patient (35%. A consistent negative impact of religiosity on the acceptance across all scenarios and differential effects for socio-economic status, area of residence, religious confession, liberalism, and authoritarianism were found. Individuals with a stronger authoritarian personality disposition were more likely to reject physician-assisted suicide for adults but at the same time also more likely to approve of physician-assisted death of a disabled neonate.Euthanasia in adults was supported by a partially different sub-population than assisted death of disabled neonates.

  20. Determinants of Public Attitudes towards Euthanasia in Adults and Physician-Assisted Death in Neonates in Austria: A National Survey.

    Science.gov (United States)

    Stolz, Erwin; Burkert, Nathalie; Großschädl, Franziska; Rásky, Éva; Stronegger, Willibald J; Freidl, Wolfgang

    2015-01-01

    Euthanasia remains a controversial topic in both public discourses and legislation. Although some determinants of acceptance of euthanasia and physician-assisted death have been identified in previous studies, there is still a shortage of information whether different forms of euthanasia are supported by the same or different sub-populations and whether authoritarian personality dispositions are linked to attitudes towards euthanasia. A large, representative face-to-face survey was conducted in Austria in 2014 (n = 1,971). Respondents faced three scenarios of euthanasia and one of physician assisted death differing regarding the level of specificity, voluntariness and subject, requiring either approval or rejection: (1) abstract description of euthanasia, (2) abstract description of physician-assisted suicide, (3) the case of euthanasia of a terminally-ill 79-year old cancer patient, and (4) the case of non-voluntary, physician assisted death of a severely disabled or ill neonate. A number of potential determinants for rejection ordered in three categories (socio-demographic, personal experience, orientations) including authoritarianism were tested via multiple logistic regression analyses. Rejection was highest in the case of the neonate (69%) and lowest for the case of the older cancer patient (35%). A consistent negative impact of religiosity on the acceptance across all scenarios and differential effects for socio-economic status, area of residence, religious confession, liberalism, and authoritarianism were found. Individuals with a stronger authoritarian personality disposition were more likely to reject physician-assisted suicide for adults but at the same time also more likely to approve of physician-assisted death of a disabled neonate. Euthanasia in adults was supported by a partially different sub-population than assisted death of disabled neonates.

  1. Determinants of consumer attitudes and purchase intentions with regard to genetically modified foods - Results of a cross-national survey

    OpenAIRE

    2000-01-01

    1. Previous research has shown consumers to be highly sceptical towards genetic modification in food production. So far, however, little research has tried to explain how consumers form attitudes and make decisions with regard to genetically modified foods. 2. The paper presents the results of a survey which was carried out in Denmark, Germany, Italy and the United Kingdom to investigate the formation of consumer attitudes towards genetic modification in food production and of purchase decisi...

  2. Determinants of consumer attitudes and purchase intentions with regard to genetically modified foods: Results of a cross-national survey

    OpenAIRE

    2000-01-01

    Executive summary 1. Previous research has shown consumers to be highly sceptical towards genetic modification in food production. So far, however, little research has tried to explain how consumers form attitudes and make decisions with regard to genetically modified foods. 2. The paper presents the results of a survey which was carried out in Denmark, Germany, Italy and the United Kingdom to investigate the formation of consumer attitudes towards genetic modification in food production and ...

  3. Satellite Communication.

    Science.gov (United States)

    Technology Teacher, 1985

    1985-01-01

    Presents a discussion of communication satellites: explains the principles of satellite communication, describes examples of how governments and industries are currently applying communication satellites, analyzes issues confronting satellite communication, links mathematics and science to the study of satellite communication, and applies…

  4. Farmer’s Attitude on Sustainable Agriculture and its Determinants: A Case Study in Behbahan County of Iran

    Directory of Open Access Journals (Sweden)

    S. Abolhasan Sadati

    2010-08-01

    Full Text Available The purpose of this study was to conduct a descriptive survey to study the attitudes and perceptions of Iranian farmers on the concepts and thoughts of sustainable agriculture and identifying effective factors on their attitude. The target population of this study consisted of 7314 Behbahan farmers of Khuzestan province of Iran. A sample consisting of 208 respondents was selected through Stratified Sampling. The instrument used for assessing the attitude of respondents on the concepts of sustainable agriculture was a questionnaire by reliability 0.78. Responses were grouped based on the differences in standard deviation of mean, which revealed that 73.4% of respondents had moderate attitude towards concepts of sustainable agriculture. The results of study showed that there is positive correlation between literacy, participation in extension courses, off-farm income, farmer's knowledge about sustainable agriculture, level of use of sustainable agriculture methods, extension contacts and job satisfaction and negative correlation between age, experience in agricultural activities, family size and agrarian land with attitude toward sustainable agriculture. According to result of regression the ‘extension contacts’, ‘Farmers knowledge about sustainable agriculture’, ‘Job satisfaction’ and ‘literacy’ are effective factors on farmers attitude toward sustainable agriculture and explained 52.6% of this scale.

  5. 载噪比加权的GPS单频单历元定姿算法%Carrier to Noise Ratio Weighted Algorithm in GPS Single Epoch Single Frequency Attitude Determination

    Institute of Scientific and Technical Information of China (English)

    金天; 原青; 郑光辉; 张立杨; 张军

    2014-01-01

    In GPS attitude determination system to deal with the problem that the traditional elevation weighted algorithm can’t reflect the situation of occlusion effectively,the accuracy of carrier phase by the satellite carrier to noise ratio of receiver is analyzed in this paper,and a new algorithm based on weighted matrixW is proposed.In the new algorithm,the leastGsquares (ILS)are used to estimate ambiguity and baseline vector.The proposed algorithm can improve the success rate under situation when satellite signal is weak and precision of carrier phase is low.By comparative experiments,it is verified the rationality and effectiveness of the proposed algorithm.Simulation results show that the proposed CN0 weighted algorithm can increase the success rate of single epoch attitude determination by 5 percent compared to the traditional algorithm,1~2 percent compared to the elevation weighted algorithm.%针对GPS定姿系统中,传统的利用高度角的加权不能有效反映遮挡情况的问题,从接收机的卫星载噪比出发,对载波相位精度进行分析,提出新的权重矩阵W,对观测模型进行加权。加权后模型根据最小二乘得到整周模糊度和基线矢量的浮点解。加权方法能够降低弱信号卫星的载波相位观测值对姿态测量成功率的影响。通过对比试验验证了加权算法的合理性和有效性。部分试验结果表明,相比于未加权算法,载噪比加权算法可以使单历元定姿成功率提高5个百分点;相比于高度角加权算法,载噪比加权可以使成功率提高1~2个百分点。

  6. Model of the Availability of Satellite Navigational Systems Asg-Eupos and Rtk Services in Poland

    Science.gov (United States)

    Oszczak, Bartlomiej; Maciejczyk, Olga

    Geodetic precision gravity field satellite missions are to determine Earth gravity field with a high spatial resolution and accuracy. In order to carry out a successful gravity field stallite mission non-gravitational forces acting upon the spacecraft need to be either compensated or measured and thereafter corrected as they distort the actual gravity signal. These non-gravitational forces can be detected and determined by an onboard accelerometer. However, in many cases not only non-gravitational effects are detected, but also noise signals which are self-induced by the satellites onboard instruments. This study shall give a brief overview about the effects acting upon geodetic precision space laboratories, that ought to be regarded in order to realise a smooth functioning of a gravity field mission. Abstract In this study the focus will be upon the GRACE (Gravity Recovery And Climate Experiment) gravity field satellite mission, concerning the impacts that onboard instruments used for attitude and orbit control as well as thermal control have onto the accelerometer and what impact this can have onto the gravity field determined by the GRACE twin satellites. As the GRACE twin satellites can only operate successfully if they are maintained in the same orbit and in a certrain orientation to each other, the Attitude and Orbit Control System (AOCS) is mandatory. This AOCS determines whether the onboard cold-gas thrusters, which are used for both orbit and attitude recovery, are fired and also the duration of the firing event. Moreover, the AOCS controls the three onboard magnetic torquers, which only can be used for attitude restorage. The acceleration disturbances induced by instruments for attitude and orbit restorage can be as high as 20 nm/s2 due to magnetic torquer activity and 0.6 µm/s2 due to thruster firing events.

  7. Consumers’ attitudes towards green food in China

    DEFF Research Database (Denmark)

    Perrea, Toula; Grunert, Klaus G; Krystallis Krontalis, Athanasios

    Green food is perceived by Chinese consumers as environmentally friendly and safe to consume. Through a Value-Attitude model, the paper examines the degree to which attitudes towards green food is determined by consumers’ values and their general attitudes towards environment and technology....... The link between collectivism, attitudes towards environment and attitudes towards green food is the strongest one. Collectivism also influences attitudes towards technology, which in turn influence attitudes towards green food. However, the lack of significant relationship between individualism...

  8. Consumers’ attitudes towards green food in China

    DEFF Research Database (Denmark)

    Perrea, Toula; Grunert, Klaus G; Krystallis Krontalis, Athanasios

    Green food is perceived by Chinese consumers as environmentally friendly and safe to consume. Through a Value-Attitude model, the paper examines the degree to which attitudes towards green food is determined by consumers’ values and their general attitudes towards environment and technology....... The link between collectivism, attitudes towards environment and attitudes towards green food is the strongest one. Collectivism also influences attitudes towards technology, which in turn influence attitudes towards green food. However, the lack of significant relationship between individualism...

  9. Pre-flyby Determination Of The Size, Shape, Pole, Density, And Satellites Of (21) Lutetia From Ground-based Observations

    Science.gov (United States)

    Merline, William J.; Carry, B.; Drummond, J. D.; Conrad, A.; Chapman, C. R.; Kaasalainen, M.; Leyrat, C.; Weaver, H. A.; Tamblyn, P. M.; Christou, J. C.; Dumas, C.; Kryszczynska, A.; Colas, F.; Bernasconi, L.; Behrend, R.; Vachier, F.; Polinska, M.; Roy, R.; Naves, R.; Poncy, R.; Wiggins, P.

    2010-10-01

    Prior to the flyby of (21) Lutetia by Rosetta, we initiated a campaign of observations to characterize the system, primarily using ground-based adaptive optics (AO) on large telescopes, including Keck, Gemini, and VLT. We coordinated these efforts with HST observations (Weaver et al. 2010 A&A in press) made in support of the Rosetta ALICE UV spectrometer. Lutetia was 0.10" in diameter, allowing disk-resolved imaging with AO and tracking of its shape during rotation. We modeled the shape using both a triaxial-ellipsoid model (Drummond et al. 2010 A&A submitted) and a full 3D radius-vector model (Carry et al. 2010 A&A submitted, in which we combine AO imaging with decades of lightcurve data to produce an improved 3D model using our inversion algorithm KOALA). To overcome limitations in each model, we combined the best aspects of each to produce our best-estimate 3D shape model, a hybrid having ellipsoid-equivalent dimensions of 124 x 101 x 93 km (± 5 x 4 x 13 km) and effective diameter 105 ± 7 km. We find the spin axis of Lutetia to lie within 5 deg of [long, lat (52,-6)] or [RA DEC (52,+12)], and determine an improved sidereal period of 8.168270 ± 0.000001 h. We predicted the geometry of Lutetia during the flyby and showed that the southern hemisphere would be in seasonal shadow at that time. The model suggests the presence of several concavities that may be associated with large impacts. Using two separately determined masses and the volume of our hybrid model, we estimate a density of 3.5 ± 1.1 or 4.3 ± 0.8 g/cc, favoring an enstatite-chondrite composition for this large M-type asteroid, although other compositions are formally allowed. No satellites larger than 1 km diameter were detected in the AO-data over a significant fraction of the Hill sphere (10-240 asteroid radii).

  10. Architecture for Combined Energy and Attitude Control System

    OpenAIRE

    Ibrahim M. Mehedi; Renuganth Varatharajoo; Harlisya Harun; Mohd N. Filipski

    2005-01-01

    Combining the energy and attitude control system is a feasible technology for small satellites to improve the space missions. In this Combined Energy and Attitude Control System (CEACS) a double rotating flywheel is used to replace the conventional battery for energy storage as well as to control the attitude of an earth oriented satellite. Each flywheel is to be controlled in the torque mode. The energy and attitude inputs for the flywheels' control architecture are also ...

  11. Beliefs in genetic determinism and attitudes towards psychiatric genetic research: psychometric scale properties, construct associations, demographic correlates, and cross-cultural comparisons.

    Science.gov (United States)

    Voracek, Martin; Swami, Viren; Loibl, Lisa Mariella; Furnham, Adrian

    2007-12-01

    Using two new scales, this study examined beliefs in genetic determinism and attitudes towards psychiatric genetic research in student samples from Austria, Malaysia, Romania, and the United Kingdom. For both constructs, effects of culture were detectable, whereas those related to key demographics were either small and inconsistent across samples (political orientation and religiosity) or zero (sex and age). Judged from factorial dimensionality and internal consistency, the psychometric properties of both scales were satisfactory. Belief in genetic determinism had lower prevalence and corresponded only modestly to positive attitudes towards psychiatric genetic research which had higher prevalence. The correlations of both constructs with a preference of inequality among social groups (social dominance orientation) were modest and inconsistent across samples. Both scales appear appropriate for cross-cultural applications, in particular for research into lay theories and public perceptions regarding genetic vs environmental effects on human behavior, mental disorders, and behavioral and psychiatric genetic research related to these.

  12. IDENTIFICATION OF OCEANOGRAPHIC PARAMETERS FOR DETERMINING PELAGIC TUNA FISHING GROUND IN THE NORTH PAPUA WATERS USING MULTI-SENSOR SATELLITE DATA

    Directory of Open Access Journals (Sweden)

    VlNCENTIUS SlREGAR

    2006-01-01

    Full Text Available The North Papua waters as one of the important fi shing grounds in the world contribute approximately 75% of world production of pelagic tunas. These fishing grounds are still determined by hunting method. This method is time consuming and costly. However, in many areas determination of fishing ground using satellited data lias been applied by detecting the important oceanographic parameter of the presence of fish schooling such as, sea surface temperature and chlorophyl. Mostly these parameters are used integrat edly. The aim of this study is to assess the important oceanographic parameters detected from mu lti-sensor satellites (NO AA/AVHRR, Seawifs and Topex Poisedon for determining fishing ground of pelagic tunas in the North Papua waters at east season. The parameters include Sea Surface Temperature (STT, chlorophyl-a and currents. The ava ilability of data from optic sensor (Seawifs: chl-a and AVHRR: Thermal is limited by the presence of cloud cover. In that case, Topex Poseidon satellite data can be used to provide the currents data. The integration of data from multi-sensors increases the availability of the oceanographic parameters for prediction of the potential fishing zones in the study area.

  13. Determination of regional surface heat fluxes over heterogeneous landscapes by integrating satellite remote sensing with boundary layer observations

    NARCIS (Netherlands)

    Ma, Y.M.

    2006-01-01

    Keywords: satellite remote sensing, surface layer observations, atmospheric boundary layer observations, land surface variables, vegetation variables, land surface heat fluxes, validation, heterogeneous landscape, GAME/Tibet

  14. Water Quality Determination of Küçükçekmece Lake, Turkey by Using Multispectral Satellite Data

    Directory of Open Access Journals (Sweden)

    Erhan Alparslan

    2009-01-01

    Full Text Available This study focuses on the analysis of the Landsat-5 TM + SPOT-Pan (1992, IRS-1C/D LISS + Pan (2000, and Landsat-5 TM (2006 satellite images that reflect the drastic land use/land cover changes in the Küçükçekmece Lake region, Istanbul. Landsat-5 TM satellite data dated 2006 was used for mapping water quality. A multiple regression analysis was carried out between the unitless planetary reflectance values derived from the satellite image and in situ water quality parameters chlorophyll a, total phosphorus, total nitrogen, turbidity, and biological and chemical oxygen demand measured at a number of stations homogenously distributed over the lake surface. The results of this study provided valuable information to local administrators on the water quality of Küçükçekmece Lake, which is a large water resource of the Istanbul Metropolitan Area. Results also show that such a methodology structured by use of reflectance values provided from satellite imagery, in situ water quality measurements, and basin land use/land cover characteristics obtained from images can serve as a powerful and rapid monitoring tool for the drinking water basins that suffer from rapid urbanization and pollution, all around the world.

  15. Eating on impulse: Implicit attitudes, self-regulatory resources, and trait self-control as determinants of food consumption.

    Science.gov (United States)

    Wang, Yan; Wang, Lei; Cui, Xianghua; Fang, Yuan; Chen, Qianqiu; Wang, Ya; Qiang, Yao

    2015-12-01

    Self-regulatory resources and trait self-control have been found to moderate the impulse-behavior relationship. The current study investigated whether the interaction of self-regulatory resources and trait self-control moderates the association between implicit attitudes and food consumption. One hundred twenty female participants were randomly assigned to either a depletion condition in which their self-regulatory resources were reduced or a no-depletion condition. Participants' implicit attitudes for chocolate were measured with the Single Category Implicit Association Test and self-report measures of trait self-control were collected. The dependent variable was chocolate consumption in an ostensible taste and rate task. Implicit attitudes predicted chocolate consumption in depleted participants but not in non-depleted participants. However, this predictive power of implicit attitudes on eating in depleted condition disappeared in participants with high trait self-control. Thus, trait self-control and self-regulatory resources interact to moderate the prediction of implicit attitude on eating behavior. Results suggest that high trait self-control buffers the effect of self-regulatory depletion on impulsive eating.

  16. Low-frequency Periodic Error Identification and Compensation for Star Tracker Attitude Measurement

    Institute of Scientific and Technical Information of China (English)

    WANG Jiongqi; XIONG Kai; ZHOU Haiyin

    2012-01-01

    The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequency periodic error for star tracker in attitude measurement.The analytical expression between the estimated gyro drift and the low-frequency periodic error of star tracker is derived firstly.And then the low-frequency periodic error,which can be expressed by Fourier series,is identified by the frequency spectrum of the estimated gyro drift according to the solution of the first step.Furthermore,the compensated model of the low-frequency periodic error is established based on the identified parameters to improve the attitude determination accuracy.Finally,promising simulated experimental results demonstrate the validity and effectiveness of the proposed method.The periodic error for attitude determination is eliminated basically and the estimation precision is improved greatly.

  17. Solar disc radius determined from observations made during eclipses with bolometric and photometric instruments on board the PICARD satellite

    Science.gov (United States)

    Thuillier, G.; Zhu, P.; Shapiro, A. I.; Sofia, S.; Tagirov, R.; van Ruymbeke, M.; Perrin, J.-M.; Sukhodolov, T.; Schmutz, W.

    2017-07-01

    Context. Despite the importance of having an accurate measurement of the solar disc radius, there are large uncertainties of its value due to the use of different measurement techniques and instrument calibration. An item of particular importance is to establish whether the value of the solar disc radius correlates with the solar activity level. Aims: The main goal of this work is to measure the solar disc radius in the near-UV, visible, and near-IR regions of the solar spectrum. Methods: Three instruments on board the PICARD spacecraft, namely the Bolometric Oscillations Sensor (BOS), the PREcision MOnitoring Sensor (PREMOS), and a solar sensor (SES), are used to derive the solar disc radius using the light curves produced when the Sun is occulted by the Moon. Nine eclipses, from 2010 to 2013, resulted in 17 occultations as viewed from the moving satellite. The calculation of the solar disc radius uses a simulation of the light curve taking into account the center-to-limb variation provided by the Non-local thermodynamic Equilibrium Spectral SYnthesis (NESSY) code. Results: We derive individual values for the solar disc radius for each viewed eclipse. Tests for a systematic variation of the radius with the progression of the solar cycle yield no significant results during the three years of measurements within the uncertainty of our measurements. Therefore, we derive a more precise radius value by averaging these values. At one astronomical unit, we obtain 959.79 arcseconds (arcsec) from the bolometric experiment; from PREMOS measurements, we obtain 959.78 arcsec at 782 nm and 959.76 arcsec at 535 nm. We found 960.07 arcsec at 210 nm, which is a higher value than the other determinations given the photons at this wavelength originate from the upper photosphere and lower chromosphere. We also give a detailed comparison of our results with those previously published using measurements from space-based and ground-based instruments using the Moon angular radius

  18. Coupled simulation of mixture plume for attitude-control satellite thruster%卫星姿控发动机混合物羽流场分区耦合计算研究

    Institute of Scientific and Technical Information of China (English)

    李志辉; 李中华; 杨东升; 毕林; 张顺玉

    2012-01-01

    研究求解喷管内流场N-S方程数值计算方法,发展基于N-S方程物面边界滑移流理论计算技术.提出求解羽流核心区轴对称DSMC模拟方法与远场三维DSMC仿真方案,发展多组元混合物羽流DSMC仿真方法.研究求解卫星姿控发动机内外近场、远场、倒流区和物面相互作用影响区多流域流场分区耦合计算技术,建立了一套用于求解混合物燃气羽流及对太阳电池帆板与卫星体表面撞击污染影响数值模拟方法.通过对分别安装于某在轨卫星不同位置两个典型姿控发动机燃气五组元混合物羽流计算研究及相关结果对比分析,证实本文数值方法可靠性.%The numerical method for the steady Navier-Stokes equations is studied to solve the inner flow field of the nozzle. The N-S computing technique with the slip-boundary theory is developed for the near-continuum slip flow near the nozzle exit. The DSMC method for the flow of axial symmetry is studied to simulate the core plume?the DSMC scheme for the simulation of three-dimensional far-field plume flow is developed, and the DSMC method is studied for multi-species mixture plume. Then, the multiregion decomposing and coupling technique is developed to solve the inside and outside flow of the thruster including the near-field, far-field, backflow and gas-surface infected regions. As a result, the numerical simulation method has been presented to compute the gas-fired mixture plume from the attitude-control thruster of the satellite and the impinging contamination on the surface of the solar array panel and satellite. To study the contamination effects produced by the five-species mixture plume from two representative attitude-control thrusters installed in different locations of the satellite in orbit, the present method is adopted to simulate the nozzle inflow, tremendous plume flowfield of five-species mixture including the impinging contamination of the particles from the gas

  19. [3-nitrotyrosine determination as nitrosative stress marker and health attitudes of medical students considering exposure to environmental tobacco smoke].

    Science.gov (United States)

    Szumska, Magdalena; Wielkoszyński, Tomasz; Tyrpień, Krystyna

    2012-01-01

    Negative attitudes in health such as cigarette smoking and imbalanced diet play important role in pathogenesis of various diseases. Cigarette smoking constitutes one of the main sources of exposure to cancerogenic and procancerogenic xenobiotics among adults as well as among young people. Many studies have proven that cigarettes smokers more frequently follow less varied diet in comparison to non-smokers. Despite increasing knowledge of Poles regarding harmful effects of cigarettes smoking and numerous antinicotine campaigns, still high number of women and men smoke and the smoking percentage among young people remains high and has not decreased in the recent years. The ongoing research shows that free radicals -the man cause of exposure to oxidative stress- play the seminal role in pathogenesis of civilisation diseases and physiological cell aging processes. Reactive oxygen and nitrogen species present in cigarette smoke due to induced toxic compounds formation, are closely connected with observed increased risk of cancer, Chronic Obstructive Pulmonary Disease (COPD) and arteriosclerosis incidents. Malondialdehyde is one of the most studied product of lipid peroxidation and biomarker of oxidative stress. However, 3-nitrotyrosine is one of the most promising biomarkers regarding changes caused by oxidative stress in living organisms. The presence of 3-nitrotyrosine was observed in many diseases such as coronary artery disease, cancer and diabetes. The aim of the study was the evaluation of free radical processes increase related to tobacco smoke exposure and chosen diet habits by determination of 3-nitrotyrosine in plasma samples collected from the group of medicine students. In our investigation we used an author's questionnaire which served to estimate the exposure to tobacco smoke among medicine students. It took also into account the knowledge of the exposure to other xenobiotics and unhealthy habits/behaviours. The investigated group included 150 students of 1

  20. Evaluation of Aerosol Pollution Determination From MODIS Satellite Retrievals for Semi-Arid Reno, NV, USA with In-Situ Measurements

    Science.gov (United States)

    Loria-Salazar, S. Marcela

    The aim of the present work is to carry out a detailed analysis of ground and columnar aerosol properties obtained by in-situ Photoacoustic and Integrated Nephelometer (PIN), Cimel CE-318 sunphotometer and MODIS instrument onboard Aqua and Terra satellites, for semi-arid Reno, Nevada, USA in the local summer months of 2012. Satellite determination of local aerosol pollution is desirable because of the potential for broad spatial and temporal coverage. However, retrieval of quantitative measures of air pollution such as Aerosol Optical Depth (AOD) from satellite measurements is challenging because of the underlying surface albedo being heterogeneous in space and time. Therefore, comparisons of satellite retrievals with measurements from ground-based sun photometers are crucial for validation, testing, and further development of instruments and retrieval algorithms. Ground-based sunphotometry and in-situ ground observations show that seasonal weather changes and fire plumes have great influence on the atmosphere aerosol optics. The Apparent Optical Height (AOH) follows the shape of the development of the Convective Boundary Layer (CBL) when fire conditions were not present. However, significant fine particle optical depth was inferred beyond the CBL thereby complicating the use of remote sensing measurements for near-ground aerosol pollution measurements. A meteorological analysis was performed to help diagnose the nature of the aerosols above Reno. The calculation of a Zephyr index and back trajectory analysis demonstrated that a local circulation often induces aerosol transport from Northern CA over the Sierra Nevada Mountains that doubles the Aerosol Optical Depth (AOD) at 500 nm. Sunphotometer measurements were used as a `ground truth' for satellite retrievals to evaluate the current state of the science retrievals in this challenging location. Satellite retrieved for AOD showed the presence of wild fires in Northern CA during August. AOD retrieved using the

  1. Earth Oblateness and Relative Sun Motion Considerations in the Determination of an Ideal Orbit for the Nimbus Meteorological Satellite

    Science.gov (United States)

    Bandeen, William R.

    1961-01-01

    It is desired that the Nimbus meteorological satellite always cross the equator around local noon and, half-an-orbit later, cross the equator in the other direction around local midnight. The application of the phenomenon of nodal regression toward this end is discussed, and an analysis of the parameters angles of inclination, periods, and heights of such "ideal" circular orbits is presented. Also, the relative motion of the apparent versus the fictitious mean sun is briefly discussed.

  2. Design, dynamics and control of an Adaptive Singularity-Free Control Moment Gyroscope actuator for microspacecraft Attitude Determination and Control System

    Science.gov (United States)

    Viswanathan, Sasi Prabhakaran

    how they lead to CMG singularities, are described. General ideas on control of the angular momentum of the spacecraft using changes in the momentum variables of a finite number of ASCMGs, are provided. Control schemes for agile and precise attitude maneuvers using ASCMG cluster in the absence of external torques and when the total angular momentum of the spacecraft is zero, is presented for both constant speed and variable speed modes. A Geometric Variational Integrator (GVI) that preserves the geometry of the state space and the conserved norm of the total angular momentum is constructed for numerical simulation and microcontroller implementation of the control scheme. The GVI is obtained by discretizing the Lagrangian of the rnultibody systems, in which the rigid body attitude is globally represented on the Lie group of rigid body rotations. Hardware and software architecture of a novel spacecraft Attitude Determination and Control System (ADCS) based on commercial smartphones and a bare minimum hardware prototype of an ASCMG using low cost COTS components is also described. A lightweight, dynamics model-free Variational Attitude Estimator (VAE) suitable for smartphone implementation is employed for attitude determination and the attitude control is performed by ASCMG actuators. The VAE scheme presented here is implemented and validated onboard an Unmanned Aerial Vehicle (UAV) platform and the real time performance is analyzed. On-board sensing, data acquisition, data uplink/downlink, state estimation and real-time feedback control objectives can be performed using this novel spacecraft ADCS. The mechatronics realization of the attitude determination through variational attitude estimation scheme and control implementation using ASCMG actuators are presented here. Experimental results of the attitude estimation (filtering) scheme using smartphone sensors as an Inertial Measurement Unit (IMU) on the Hardware In the Loop (HIL) simulator testbed are given. These

  3. Improving Preschool Teachers Attitude towards the Persona Doll Approach and Determining the Effectiveness of Persona Doll Training Procedures

    Science.gov (United States)

    Acar, Ebru Aktan; Çetin, Hilal

    2017-01-01

    The study features two basic steps. The first step of the research aims to develop a scale to measure the attitude of preschool teachers towards the Persona Dolls Approach and to verify its validity/reliability through a general survey. The cohort employed in the research was drawn from a pool of preschool teachers working in and around the cities…

  4. Determinants of consumer attitudes and purchase intentions with regard to genetically modified foods: Results of a cross-national survey

    DEFF Research Database (Denmark)

    Bredahl, Lone

    2000-01-01

    Executive summary 1. Previous research has shown consumers to be highly sceptical towards genetic modification in food production. So far, however, little research has tried to explain how consumers form attitudes and make decisions with regard to genetically modified foods. 2. The paper presents...

  5. Determining the area of influence of depression cone in the vicinity of lignite mine by means of triangle method and LANDSAT TM/ETM+ satellite images.

    Science.gov (United States)

    Zawadzki, Jarosław; Przeździecki, Karol; Miatkowski, Zygmunt

    2016-01-15

    Problems with lowering of water table are common all over the world. Intensive pumping of water from aquifers for consumption, irrigation, industrial or mining purposes often causes groundwater depletion and results in the formation of cone of depression. This can severely decrease water pressure, even over vast areas, and can create severe problems such as degradation of agriculture or natural environment sometimes depriving people and animals of water supply. In this paper, the authors present a method for determining the area of influence of a groundwater depression cone resulting from prolonged drainage, by means of satellite images in optical, near infrared and thermal infrared bands from TM sensor (Thematic Mapper) and ETM+ sensor (Enhanced Thematic Mapper +) placed on Landsat 5 and Landsat 7 satellites. The research area was Szczercowska Valley (Pol. Kotlina Szczercowska), Central Poland, located within a range of influence of a groundwater drainage system of the lignite coal mine in Belchatow. It is the biggest lignite coal mine in Poland and one of the largest in Europe exerting an enormous impact on the environment. The main method of satellite data analysis for determining soil moisture, was the so-called triangle method. This method, based on TVDI (Temperature Vegetation Dryness Index) was supported by additional spatial analysis including ordinary kriging used in order to combine fragmentary information obtained from areas covered by meadows. The results obtained are encouraging and confirm the usefulness of the triangle method not only for soil moisture determination but also for assessment of the temporal and spatial changes in the area influenced by the groundwater depression cone. The range of impact of the groundwater depression cone determined by means of above-described remote sensing analysis shows good agreement with that determined by ground measurements. The developed satellite method is much faster and cheaper than in-situ measurements

  6. The accuracy of satellite radar altimeter data over the Greenland ice sheet determined from airborne laser data

    DEFF Research Database (Denmark)

    Bamber, J.L.; Ekholm, Simon; Krabill, W.

    1998-01-01

    The 336 days of the geodetic phase of ERS-1 provides dense coverage, by satellite radar altimetry, of the whole of the Greenland ice sheet. These data have been used to produce a digital elevation model of the ice sheet. The errors present in the altimeter data were investigated via a comparison...... with airborne laser altimeter data an absolute accuracy typically in the range 2-10 cm +/- 10 cm. Comparison of differences between the radar and laser derived elevations, showed a correlation with surface slope. The difference between the two data sets ranged from 84 cm +/- 79 cm for slopes below 0.1 degrees...

  7. Determinants of households’ investment in energy efficiency and renewables: evidence from the OECD survey on household environmental behaviour and attitudes

    Science.gov (United States)

    Ameli, Nadia; Brandt, Nicola

    2015-04-01

    This paper provides novel evidence on the main factors behind consumer choices regarding investments in energy efficiency and renewable energy technologies using the OECD Survey on Household Environmental Behaviour and Attitudes. The empirical analysis is based on the estimation of binary logit regression models. Empirical results suggest that households’ propensity to invest in clean energy technologies depends mainly on home ownership, income, social context and household energy conservation practices. Indeed, home owners and high-income households are more likely to invest than renters and low-income households. In addition, environmental attitudes and beliefs, as manifest in energy conservation practices or membership in an environmental non-governmental organisation, also play a relevant role in technology adoption.

  8. Orbit Determination of KOMPSAT-1 and Cryosat-2 Satellites Using Optical Wide-field Patrol Network (OWL-Net) Data with Batch Least Squares Filter

    Science.gov (United States)

    Lee, Eunji; Park, Sang-Young; Shin, Bumjoon; Cho, Sungki; Choi, Eun-Jung; Jo, Junghyun; Park, Jang-Hyun

    2017-03-01

    The optical wide-field patrol network (OWL-Net) is a Korean optical surveillance system that tracks and monitors domestic satellites. In this study, a batch least squares algorithm was developed for optical measurements and verified by Monte Carlo simulation and covariance analysis. Potential error sources of OWL-Net, such as noise, bias, and clock errors, were analyzed. There is a linear relation between the estimation accuracy and the noise level, and the accuracy significantly depends on the declination bias. In addition, the time-tagging error significantly degrades the observation accuracy, while the time-synchronization offset corresponds to the orbital motion. The Cartesian state vector and measurement bias were determined using the OWL-Net tracking data of the KOMPSAT-1 and Cryosat-2 satellites. The comparison with known orbital information based on two-line elements (TLE) and the consolidated prediction format (CPF) shows that the orbit determination accuracy is similar to that of TLE. Furthermore, the precision and accuracy of OWL-Net observation data were determined to be tens of arcsec and sub-degree level, respectively.

  9. Design and Analysis of an Attitude Determination and Control Subsystem (ADCS) for AFIT’s 6U Standard Bus

    Science.gov (United States)

    2014-03-27

    EKF). The model, developed in 2009, runs in the MATLAB and Simulink environments. An overview of the Simulink model is shown in Figure 2.6. The model...Figure 2.6: NPS TINYSCOPE Simulink Model Overview [45] 2.2.1.2 NTNU Satellite Model. NTNU developed a MATLAB and Simulink model in support of their NTNU...Surrounding Magnetic Coils (b) Air Bearing Solidworks Model Figure 2.14: MIT Spherical Air Bearing [18] The MATLAB Simulink simulation models the

  10. 3-Axis magnetic control: flight results of the TANGO satellite in the PRISMA mission

    Science.gov (United States)

    Chasset, C.; Noteborn, R.; Bodin, P.; Larsson, R.; Jakobsson, B.

    2013-09-01

    PRISMA implements guidance, navigation and control strategies for advanced formation flying and rendezvous experiments. The project is funded by the Swedish National Space Board and run by OHB-Sweden in close cooperation with DLR, CNES and the Danish Technical University. The PRISMA test bed consists of a fully manoeuvrable MANGO satellite as well as a 3-axis controlled TANGO satellite without any Δ V capability. PRISMA was launched on the 15th of June 2010 on board DNEPR. The TANGO spacecraft is the reference satellite for the experiments performed by MANGO, either with a "cooperative" or "non-cooperative" behaviour. Small, light and low-cost were the keywords for the TANGO design. The attitude determination is based on Sun sensors and magnetometers, and the active attitude control uses magnetic torque rods only. In order to perform the attitude manoeuvres required to fulfil the mission objectives, using any additional gravity gradient boom to passively stabilize the spacecraft was not allowed. After a two-month commissioning phase, TANGO separated from MANGO on the 11th of August 2010. All operational modes have been successfully tested, and the pointing performance in flight is in accordance with expectations. The robust Sun Acquisition mode reduced the initial tip-off rate and placed TANGO into a safe attitude in TANGO points its GPS antenna towards zenith with sufficient accuracy to track as many GPS satellites as MANGO. At the same time, it points its solar panel towards the Sun, and all payload equipments can be switched on without any restriction. This paper gives an overview of the TANGO Attitude Control System design. It then presents the flight results in the different operating modes. Finally, it highlights the key elements at the origin of the successful 3-axis magnetic control strategy on the TANGO satellite.

  11. Biased momentum satellite attitude tracking control based on sliding mode observer%基于滑模观测器的偏置动量卫星姿态跟踪控制

    Institute of Scientific and Technical Information of China (English)

    郝勇; 闫鑫; 苏中华

    2012-01-01

    针对在偏航姿态测量信息未知时偏置动量卫星姿态跟踪控制,提出了一种新的滑模观测器及其对应的自适应滑模控制器设计方法.基于滚动轴和俯仰轴信息,设计了一种经过平滑的滑模观测器,抑制高频抖震的同时提高状态估计的鲁棒性;设计的比例-积分滑模面,能实现积分滑模控制,抑制稳态误差,优化滑模的全程鲁棒性,并采用自适应方法,对不确定参数进行在线更新,补偿不确定参数的影响.数值仿真结果表明,相对于龙伯格观测器,该方法能提高偏航姿态信息估计精度,在保证系统鲁棒性的同时,滚动和偏航轴姿态跟踪精度分别提高约50%.%A method for design of the novel adaptive sliding mode observer and its corresponding controller is proposed for momentum biased satellite at titude tracking control with unknown measure yaw attitude. The smooth sliding mode observer is designed by using roll and pitch information so as to improve the state estimation robustness while suppressing high-frequency chattering. A proportional and integral sliding mode surface is proposed to implement an integral sliding mode control which could mitigate the steady-state error and optimize the global robustness of sliding mode. With purpose of compensating the passive effect of uncertain parameters, an adaptive update law is presented based on an adaptive method. Numerical simulation results show that, compared with Luenberger observer, the proposed method could improve the yaw attitude estimation accuracy and improve the pitch-yaw axis tracking precision by 50% as well as the guaranty of the robustness.

  12. Determining the Suitability of Different Digital Elevation Models and Satellite Images for Fancy Maps. An Example of Cyprus

    Science.gov (United States)

    Drachal, J.; Kawel, A. K.

    2016-06-01

    The article describes the possibility of developing an overall map of the selected area on the basis of publicly available data. Such a map would take the form designed by the author with the colors that meets his expectations and a content, which he considers to be appropriate. Among the data available it was considered the use of satellite images of the terrain in real colors and, in the form of shaded relief, digital terrain models with different resolutions of the terrain mesh. Specifically the considered data were: MODIS, Landsat 8, GTOPO-30, SRTM-30, SRTM-1, SRTM-3, ASTER. For the test area the island of Cyprus was chosen because of the importance in tourism, a relatively small area and a clearly defined boundary. In the paper there are shown and discussed various options of the Cyprus terrain image obtained synthetically from variants of Modis, Landsat and digital elevation models of different resolutions.

  13. Determination of the Earth gravity Field Parameters in Persian Gulf and Oman Sea with the Satellite Altimetry Data

    Science.gov (United States)

    Emadi, S. R.; Najafi-Alamardi, M.; Toosi, K. N.; Sedighi, M.; Nankali, H. R.

    2006-07-01

    Satellite altimetry provides continuous, accur ate, and homogenous data ser ies in marine areas .Th e Sea Surf ace Heigh ts (SSH) ex tracted from altimetry data w as used in a method sear ching for the least squares of the sea surface topography to simultaneously d etermine the geoidal height and the sea surface topography as well in the Persian Gulf and the Oman sea. This is contrary to th e methods wh ich r equire the knowledge of one parameter to estimate the other. The North and East componen ts of the deflections of vertical w ere also estimated by differentiating the der ived geoid al heights in the corresponding directions, and finally the free- air grav ity anomalies w ere computed utilizing the inverse V ening- Meinesz integral.

  14. 卫星轨道Kalman滤波稳健估计%obust Kalman Filtering for Satellite Orbit Determination

    Institute of Scientific and Technical Information of China (English)

    文援兰; 王威; 杨元喜

    2001-01-01

    Kalman filtering is affected by the gross error that is inevitable in the observation of satellite. First robust kalman filtering is derived and its robustness is analyzed, then the observations of Lageos is processed. It verifies that robust kalman filtering has the capability to resist the gross error.%卫星观测数据中不可避免地存在着粗差,一般的Kalman滤波易受观测粗差的影响。首先推导Kalman滤波稳健估计公式,并分析了它的稳健性。然后用Kalman滤波稳健估计对Lageos卫星的激光实测资料进行了处理,证明它具有明显的抗粗差的能力和稳健性。

  15. Biological satellite Kosmos-936

    Science.gov (United States)

    Vedeshin, L. A.

    1978-01-01

    A description is given of physiological experiments performed on the biological satellite Kosmos-936. Other experiments to determine the electrostatic and dielectric responses to the effects of cosmic radiation are discussed.

  16. Small Satellite Transporter Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The primary objective is to determine whether this small satellite transporter is capable of transporting at least four 6U CubeSats is possible for a given set of...

  17. Characterization and compensation of thermo-elastic instability of SWARM optical bench on micro Advanced Stellar Compass attitude observations

    Science.gov (United States)

    Herceg, M.; Jørgensen, P. S.; Jørgensen, J. L.

    2017-08-01

    Launched into orbit on November 22, 2013, the Swarm constellation of three satellites precisely measures magnetic signal of the Earth. To ensure the high accuracy of magnetic observation by vector magnetometer (VFM), its inertial attitude is precisely determined by μASC (micro Advanced Stellar Compass). Each of the three Swarm satellites is equipped with three μASC Camera Head Units (CHU) mounted on a common optical bench (OB), which has a purpose of transference of the attitude from the star trackers to the magnetometer measurements. Although substantial pre-launch analyses were made to maximize thermal and mechanical stability of the OB, significant signal with thermal signature is discovered when comparing relative attitude between the three CHU's (Inter Boresight Angle, IBA). These misalignments between CHU's, and consequently geomagnetic reference frame, are found to be correlated with the period of angle between Swarm orbital plane and the Sun (ca. 267 days), which suggests sensitivity of optical bench system on temperature variation. In this paper, we investigate the propagation of thermal effects into the μASC attitude observations and demonstrate how thermally induced attitude variation can be predicted and corrected in the Swarm data processing. The results after applying thermal corrections show decrease in IBA RMS from 6.41 to 2.58″. The model significantly improves attitude determination which, after correction, meets the requirements of Swarm satellite mission. This study demonstrates the importance of the OB pre-launch analysis to ensure minimum thermal gradient on satellite optical system and therefore maximum attitude accuracy.

  18. An Empirical Approach to Determining the Boundary Layer Bromine Monoxide (BrO) Abundance from Satellite Total Column Measurements

    Science.gov (United States)

    Simpson, W. R.; Donohoue, D.; Carlson, D. A.

    2009-12-01

    Unique chemistry in the Arctic boundary layer during springtime liberates bromine from sea salt, producing reactive halogen gases (e.g. atomic bromine and bromine monoxide radicals) that then drastically alter atmospheric oxidation pathways. This phenomenon causes ozone depletion events and affects mercury deposition to the snowpack. Satellite remote sensing (e.g. OMI and GOME2 observations) techniques can detect the total column abundance of BrO, which is generally the primary species of the reactive bromine family. However, BrO is also present in the stratosphere, so it is necessary to partition the satellite-observed BrO column abundance into boundary layer and non-boundary layer (primarily stratospheric) partial columns to be able to infer boundary layer abundances and hence chemical affects near the Earth's surface (i.e. ozone and mercury impacts). In this presentation, we describe an empirical method for partitioning the BrO total column and apply it globally during spring 2008. The method indicates that some BrO total column enhancements ("hotspots") are not actually enhancements in the boundary layer BrO abundance but occur aloft. Movies and a statistical analysis of the inferred boundary layer BrO abundance are presented. The method has been tested and performs well at the Barrow field site. However, in areas that lack routine ground truth BrO measurements (e.g. Hudson Bay, Canada), large tropospheric BrO abundances are indicated. It is not clear if these inferred boundary layer BrO events are real or if the simple empirical method described here is failing in those locations. Verification of this method over large spatial regions of the Arctic is needed.

  19. Effects of magnetometer calibration and maneuvers on accuracies of magnetometer-only attitude-and-rate determination

    Science.gov (United States)

    Challa, M.; Natanson, G.

    1998-01-01

    Two different algorithms - a deterministic magnetic-field-only algorithm and a Kalman filter for gyroless spacecraft - are used to estimate the attitude and rates of the Rossi X-Ray Timing Explorer (RXTE) using only measurements from a three-axis magnetometer. The performance of these algorithms is examined using in-flight data from various scenarios. In particular, significant enhancements in accuracies are observed when' the telemetered magnetometer data are accurately calibrated using a recently developed calibration algorithm. Interesting features observed in these studies of the inertial-pointing RXTE include a remarkable sensitivity of the filter to the numerical values of the noise parameters and relatively long convergence time spans. By analogy, the accuracy of the deterministic scheme is noticeably lower as a result of reduced rates of change of the body-fixed geomagnetic field. Preliminary results show the filter-per-axis attitude accuracies ranging between 0.1 and 0.5 deg and rate accuracies between 0.001 deg/sec and 0.005 deg./sec, whereas the deterministic method needs a more sophisticated techniques for smoothing time derivatives of the measured geomagnetic field to clearly distinguish both attitude and rate solutions from the numerical noise. Also included is a new theoretical development in the deterministic algorithm: the transformation of a transcendental equation in the original theory into an 8th-order polynomial equation. It is shown that this 8th-order polynomial reduces to quadratic equations in the two limiting cases-infinitely high wheel momentum, and constant rates-discussed in previous publications.

  20. Multi-antenna synchronized global navigation satellite system receiver and its advantages in high-precision positioning applications

    Science.gov (United States)

    Dong, Danan; Chen, Wen; Cai, Miaomiao; Zhou, Feng; Wang, Minghua; Yu, Chao; Zheng, Zhengqi; Wang, Yuanfei

    2016-12-01

    The multi-antenna synchronized global navigation satellite system receiver is a high precision, low cost, and widely used emerging receiver. Using this type of receiver, the satellite and receiver clock errors can be eliminated simultaneously by forming between antenna single-differences, which is equivalent to the conventional double-difference model. However, current multi-antenna synchronized global navigation satellite system receiver products have not fully realized their potential to achieve better accuracy, efficiency, and broader applications. This paper introduces the conceptual design and derivable products of multi-antenna synchronized global navigation satellite system receivers involving the aspects of attitude determination, multipath effect mitigation, phase center variation correction, and ground-based carrier phase windup calibration. Through case studies, the advantages of multi-antenna synchronized global navigation satellite system receivers in high-precision positioning applications are demonstrated.

  1. A satellite anemometer

    Science.gov (United States)

    Hanson, W. B.; Heelis, R. A.

    1995-01-01

    This report describes the design, development, and testing of components of a satellite anemometer, an instrument for measuring neutral winds in the upper atmosphere from a satellite platform. The device, which uses four nearly identical pressure sensors, measures the angle of arrival of the bulk neutral flow in the satellite frame of reference. It could also be used in a feedback loop to control spacecraft attitude with respect to the ram velocity direction. We have now developed miniaturized ionization pressure gauges that will work well from the slip flow region near 115 km up to the base of the exosphere, which covers the entire altitude range currently being considered for Tether. Laboratory tests have demonstrated a very linear response to changes in ram angle out to +/- 20 deg. (transverse wind component of 2.7 km s(exp -1)) from the ram, and a monotonic response to out beyond 45 deg. Pitch (vertical wind) and yaw (horizontal wind) can be sampled simultaneously and meaningfully up to 10 Hz. Angular sensitivity of 30 arc seconds (approximately 1 ms(exp -1) is readily attainable, but absolute accuracy for winds will be approximately 1 deg (130 m/s) unless independent attitude knowledge is available. The critical elements of the design have all been tested in the laboratory.

  2. Attitude Strength.

    Science.gov (United States)

    Howe, Lauren C; Krosnick, Jon A

    2017-01-03

    Attitude strength has been the focus of a huge volume of research in psychology and related sciences for decades. The insights offered by this literature have tremendous value for understanding attitude functioning and structure and for the effective application of the attitude concept in applied settings. This is the first Annual Review of Psychology article on the topic, and it offers a review of theory and evidence regarding one of the most researched strength-related attitude features: attitude importance. Personal importance is attached to an attitude when the attitude is perceived to be relevant to self-interest, social identification with reference groups or reference individuals, and values. Attaching personal importance to an attitude causes crystallizing of attitudes (via enhanced resistance to change), effortful gathering and processing of relevant information, accumulation of a large store of well-organized relevant information in long-term memory, enhanced attitude extremity and accessibility, enhanced attitude impact on the regulation of interpersonal attraction, energizing of emotional reactions, and enhanced impact of attitudes on behavioral intentions and action. Thus, important attitudes are real and consequential psychological forces, and their study offers opportunities for addressing behavioral change.

  3. Beginnings of Satellite Navigation

    Directory of Open Access Journals (Sweden)

    Miljenko Solarić

    2008-05-01

    Full Text Available The first satellite navigation system called the Navy Navigation Satellite System (NNSS or TRANSIT was planned in the USA in 1958. It consisted of 5-6 artificial Earth satellites, was set in motion for the USA military in 1964, and in 1967 for civilian purposes. The frequency shift of received radio waves emitted from the satellite and caused by the Doppler effect was measured. The TRANSIT satellite speed of approaching or moving away was derived from that; the TRANSIT satellites emmited also their own coordinates. Then the ship's position was determined by an intersection of three hyperboloids, which were determined from differences of distances in three time intervals. Maintenance of this navigation system was stopped in 1996, but it is still being used in the USA Navy for exploring the ionosphere. Furthermore, results of Doppler measurements in international projects at the Hvar Observatory from 1982 and 1983. This was the first time in Croatia and the former country that the coordinates of the Hvar Observatory were determined in the unique world coordinate system WGS'72. The paper ends with a brief representation of the Tsiklon Doppler navigation system produced in the former Soviet Union, and there is a list of some of numerous produced and designed satellite navigation systems.Ključne riječi

  4. Determining spatio-temporal distribution of bee forage species of Al-Baha region based on ground inventorying supported with GIS applications and Remote Sensed Satellite Image analysis.

    Science.gov (United States)

    Adgaba, Nuru; Alghamdi, Ahmed; Sammoud, Rachid; Shenkute, Awraris; Tadesse, Yilma; Ansari, Mahammad J; Sharma, Deepak; Hepburn, Colleen

    2017-07-01

    In arid zones, the shortage of bee forage is critical and usually compels beekeepers to move their colonies in search of better forages. Identifying and mapping the spatiotemporal distribution of the bee forages over given area is important for better management of bee colonies. In this study honey bee plants in the target areas were inventoried following, ground inventory work supported with GIS applications. The study was conducted on 85 large plots of 50 × 50 m each. At each plot, data on species name, height, base diameter, crown height, crown diameter has been taken for each plant with their respective geographical positions. The data were stored, and processed using Trimble GPS supported with ArcGIS10 software program. The data were used to estimate the relative frequency, density, abundance and species diversity, species important value index and apicultural value of the species. In addition, Remotely Sensed Satellite Image of the area was obtained and processed using Hopfield Artificial Neural Network techniques. During the study, 182 species from 49 plant families were identified as bee forages of the target area. From the total number of species; shrubs, herbs and trees were accounting for 61%, 27.67%, and 11.53% respectively. Of which Ziziphus spina-christi, Acacia tortilis, Acacia origina, Acacia asak, Lavandula dentata, and Hypoestes forskaolii were the major nectar source plants of the area in their degree of importance. The average vegetation cover values of the study areas were low (place. The Remote Sensed Satellite Image analysis confirmed the spatial distribution of the bee forage resources as determined by the ground inventory work. An integrated approach, combining the ground inventory work with GIS and satellite image processing techniques could be an important tool for characterizing and mapping the available bee forage resources leading to their efficient and sustainable utilization.

  5. Multi-agent robotic systems and applications for satellite missions

    Science.gov (United States)

    Nunes, Miguel A.

    A revolution in the space sector is happening. It is expected that in the next decade there will be more satellites launched than in the previous sixty years of space exploration. Major challenges are associated with this growth of space assets such as the autonomy and management of large groups of satellites, in particular with small satellites. There are two main objectives for this work. First, a flexible and distributed software architecture is presented to expand the possibilities of spacecraft autonomy and in particular autonomous motion in attitude and position. The approach taken is based on the concept of distributed software agents, also referred to as multi-agent robotic system. Agents are defined as software programs that are social, reactive and proactive to autonomously maximize the chances of achieving the set goals. Part of the work is to demonstrate that a multi-agent robotic system is a feasible approach for different problems of autonomy such as satellite attitude determination and control and autonomous rendezvous and docking. The second main objective is to develop a method to optimize multi-satellite configurations in space, also known as satellite constellations. This automated method generates new optimal mega-constellations designs for Earth observations and fast revisit times on large ground areas. The optimal satellite constellation can be used by researchers as the baseline for new missions. The first contribution of this work is the development of a new multi-agent robotic system for distributing the attitude determination and control subsystem for HiakaSat. The multi-agent robotic system is implemented and tested on the satellite hardware-in-the-loop testbed that simulates a representative space environment. The results show that the newly proposed system for this particular case achieves an equivalent control performance when compared to the monolithic implementation. In terms on computational efficiency it is found that the multi

  6. Design and Implementation of a Space Environment Simulation Toolbox for Small Satellites

    DEFF Research Database (Denmark)

    Amini, Rouzbeh; Larsen, Jesper A.; Izadi-Zamanabadi, Roozbeh

    This paper presents a developed toolbox for space environment model in SIMULINK that facilitates development and design of Attitude Determination and Control Systems (ADCS) for a Low Earth Orbit (LEO) spacecraft. The toolbox includes, among others, models of orbit propagators, disturbances, Earth...... gravity field, Earth magnetic field and eclipse. The structure and facilities within the toolbox are described and exemplified using a student satellite case (AAUSAT-II). The validity of developed models is confirmed by comparing the simulation results with the realistic data obtained from the Danish...... Ørsted satellite....

  7. Design and Implementation of a Space Environment Simulation Toolbox for Small Satellites

    DEFF Research Database (Denmark)

    Amini, Rouzbeh; Larsen, Jesper A.; Izadi-Zamanabadi, Roozbeh

    2005-01-01

    This paper presents a developed toolbox for space environment model in SIMULINK that facilitates development and design of Attitude Determination and Control Systems (ADCS) for a Low Earth Orbit (LEO) spacecraft. The toolbox includes, among others, models of orbit propagators, disturbances, Earth...... gravity field, Earth magnetic field and eclipse. The structure and facilities within the toolbox are described and exemplified using a student satellite case (AAUSAT-II). The validity of developed models is confirmed by comparing the simulation results with the realistic data obtained from the Danish...... Ørsted satellite....

  8. Epistemics and attitudes

    Directory of Open Access Journals (Sweden)

    Pranav Anand

    2013-10-01

    Full Text Available This paper investigates the distribution of epistemic modals in attitude contexts in three Romance languages, as well as their potential interaction with mood selection. We show that epistemics can appear in complements of attitudes of acceptance (Stalnaker 1984, but not desideratives or directives; in addition, emotive doxastics (hope, fear and dubitatives (doubt permit epistemic possibility modals, but not their necessity counterparts. We argue that the embedding differences across attitudes indicate that epistemics are sensitive to the type of attitude an attitude predicate reports. We show that this sensitivity can be derived by adopting two types of proposals from the literature on epistemic modality and on attitude verbs: First, we assume that epistemics do not target knowledge uniformly, but rather quantify over an information state determined by the content of the embedding attitude (Hacquard 2006, 2010, Yalcin 2007. In turn, we adopt a fundamental split in the semantics of attitude verbs between ‘representational’ and ‘non-representational’ attitudes (Bolinger 1968: representational attitudes quantify over an information state (e.g., a set of beliefs for believe, which, we argue, epistemic modals can be anaphoric to. Non-representational attitudes do not quantify over an information state; instead, they combine with their complement via a comparison with contextually-provided alternatives using a logic of preference (cf. Bolinger 1968, Stalnaker 1984, Farkas 1985, Heim 1992, Villalta 2000, 2008. Finally, we argue that emotive doxastics and dubitatives have a hybrid semantics, which combines a representational component (responsible for licensing epistemic possibility modals, and a preference component (responsible for disallowing epistemic necessity modals. http://dx.doi.org/10.3765/sp.6.8 BibTeX info

  9. Is Socio-Economic Status a Determinant of HIV-Related Stigma Attitudes in Zimbabwe? Findings from Project Accept.

    Science.gov (United States)

    Mateveke, Kudzanai; Singh, Basant; Chingono, Alfred; Sibanda, E; Machingura, Ian

    2016-08-17

    HIV related stigma and discrimination is a known barrier for HIV prevention and care. We aimed to assess the relationship between socio-economic status (SES) and HIV related stigma in Zimbabwe. This paper uses data from Project Accept, which examined the impact of community-based voluntary counseling and testing intervention on HIV incidence and stigma. Total of 2522 eligible participants responded to a psychometric assessment tool, which assessed HIV related stigma and discrimination attitudes on 4 point Likert scale. The tool measured three components of HIV-related stigma: shame, blame and social isolation, perceived discrimination, and equity. Participants' ownership of basic assets was used to assess the socio-economic status. Shame, blame and social isolation component of HIV related stigma was found to be significantly associated with medium [odds ratio (OR)=1.73, Psocio-economic context of target population.

  10. Centimeter Precise Orbit Determination for SWARM Satellite via Reduced-dynamic Method%SWARM卫星简化动力学厘米级精密定轨

    Institute of Scientific and Technical Information of China (English)

    张兵兵; 聂琳娟; 吴汤婷; 冯建迪; 邱耀东

    2016-01-01

    联合星载GPS双频观测值与简化的动力学模型,在卫星运动方程中引入适当的伪随机脉冲参数,对SWARM卫星进行精密定轨.采用星载GPS相位观测值残差、重叠轨道以及与外部轨道对比等3种方法对SWARM卫星简化动力学定轨结果进行检核.结果表明:SWARM星载GPS相位观测值残差RMS为7~10mm;径向、切向以及法向6h重叠轨道差值RMS均在1cm左右,3个方向均无明显的系统误差.通过与欧空局(ESA)发布的精密轨道进行对比分析,径向轨道差值RMS为2~5cm,切向轨道差值RMS为2~5cm,法向轨道差值RMS为2~4cm,3D轨道差值RMS为4~7cm;SWARM-B定轨精度优于SWARM-A与SWARM-C.因此,采用简化动力学法与本文提供的定轨策略进行SWARM卫星精密定轨是切实可行的,定轨结果良好且稳定,定轨精度达到厘米级.%Combining dual-frequency satellite-borne GPS observations with reduced dynamic models,and introducing proper pseudo-stochastic pulse parameters into the satellite’s motion equation,SWARM satellite precise orbit determination is implemented.The orbit accuracy is assessed using three methods, which include analysis satellite-borne GPS phase observation residuals,orbit overlaps and external orbit comparisons.The results indicate that the SWARM satellite-borne GPS phase observation residual RMS is in the range of 7 to 10 mm,radial,along-track and cross-track orbit overlap difference RMS of 6 hours are about 1 cm,three directions have no significant systematic errors,comparisons with orbits computed by European Space Agency (ESA),Radial orbit difference RMS is in the range of 2 to 5 cm,along-track orbit difference RMS is in the range of 2 to 5 cm,cross-track orbit difference RMS is in the range of 2 to 4 cm,3D orbit difference RMS is in the range of 4 to 7 cm,SWARM-B orbit accuracy is better than SWARM-A and SWARM-C.This evaluations indicate that SWARM satellite precise orbit determination is practicable by using reduced

  11. Satellite RNAs and Satellite Viruses.

    Science.gov (United States)

    Palukaitis, Peter

    2016-03-01

    Satellite RNAs and satellite viruses are extraviral components that can affect either the pathogenicity, the accumulation, or both of their associated viruses while themselves being dependent on the associated viruses as helper viruses for their infection. Most of these satellite RNAs are noncoding RNAs, and in many cases, have been shown to alter the interaction of their helper viruses with their hosts. In only a few cases have the functions of these satellite RNAs in such interactions been studied in detail. In particular, work on the satellite RNAs of Cucumber mosaic virus and Turnip crinkle virus have provided novel insights into RNAs functioning as noncoding RNAs. These effects are described and potential roles for satellite RNAs in the processes involved in symptom intensification or attenuation are discussed. In most cases, models describing these roles involve some aspect of RNA silencing or its suppression, either directly or indirectly involving the particular satellite RNA.

  12. The role of the curriculum and other factors in determining the medium- to long-term attitude of the practicing dentist towards life-long learning.

    LENUS (Irish Health Repository)

    Polyzois, I

    2010-05-01

    To investigate the significance of the undergraduate dental curriculum on the medium- to long-term attitudes of the clinician to life-long learning, and to identify demographical and professional characteristics which may influence this attitude.

  13. Enhanced solar radiation pressure modeling for Galileo satellites

    Science.gov (United States)

    Montenbruck, O.; Steigenberger, P.; Hugentobler, U.

    2015-03-01

    This paper introduces a new approach for modeling solar radiation pressure (SRP) effects on Global Navigation Satellite Systems (GNSSs). It focuses on the Galileo In-Orbit Validation (IOV) satellites, for which obvious SRP modeling deficits can be identified in presently available precise orbit products. To overcome these problems, the estimation of empirical accelerations in the Sun direction (D), solar panel axis (Y) and the orthogonal (B) axis is complemented by an a priori model accounting for the contribution of the rectangular spacecraft body. Other than the GPS satellites, which comprise an almost cubic body, the Galileo IOV satellites exhibit a notably rectangular shape with a ratio of about 2:1 for the main body axes. Use of the a priori box model allows to properly model the varying cross section exposed to the Sun during yaw-steering attitude mode and helps to remove systematic once-per-revolution orbit errors that have so far affected the Galileo orbit determination. Parameters of a simple a priori cuboid model suitable for the IOV satellites are established from the analysis of a long-term set of GNSS observations collected with the global network of the Multi-GNSS Experiment of the International GNSS Service. The model is finally demonstrated to reduce the peak magnitude of radial orbit errors from presently 20 cm down to 5 cm outside eclipse phases.

  14. Centriolar satellites

    DEFF Research Database (Denmark)

    Tollenaere, Maxim A X; Mailand, Niels; Bekker-Jensen, Simon

    2015-01-01

    Centriolar satellites are small, microscopically visible granules that cluster around centrosomes. These structures, which contain numerous proteins directly involved in centrosome maintenance, ciliogenesis, and neurogenesis, have traditionally been viewed as vehicles for protein trafficking...... highlight newly discovered regulatory mechanisms targeting centriolar satellites and their functional status, and we discuss how defects in centriolar satellite components are intimately linked to a wide spectrum of human diseases....

  15. Satellite theory

    Science.gov (United States)

    Kozai, Y.

    1981-04-01

    The dynamical characteristics of the natural satellite of Mars, Jupiter, Saturn, Uranus and Neptune are analyzed on the basis of the solar tidal perturbation factor and the oblateness factor of the primary planet for each satellite. For the inner satellites, for which the value of the solar tidal factor is much smaller than the planetary oblateness factor, it is shown that the eccentricity and inclination of satellite orbits are generally very small and almost constant; several pairs of inner satellites are also found to exhibit commensurable mean motions, or secular accelerations in mean longitude. In the case of the outer satellites, for which solar perturbations are dominant, secular perturbations and long-period perturbations may be derived by the solution of equations of motion reduced to one degree of freedom. The existence of a few satellites, termed intermediary satellites, for which the solar tidal perturbation is on the order of the planetary oblateness factor, is also observed, and the pole of the orbital plane of the satellite is noted to execute a complex motion around the pole of the planet or the orbital plane of the planet.

  16. Miniaurizable, High Performance, Fiber-Optic Gyroscopes for Small Satellites Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Small satellites require much lighter weight, smaller, and long life Attitude control components that can withstand stressing launch conditions and space vibration...

  17. Side-effects of a bad attitude: How GNSS spacecraft orientation errors affect solar radiation pressure modelling

    Science.gov (United States)

    Dilssner, Florian; Springer, Tim; Schönemann, Erik; Zandbergen, Rene; Enderle, Werner

    2015-04-01

    Solar radiation pressure (SRP) is the largest non-gravitational perturbation for Global Navigation Satellite System (GNSS) satellites, and can therefore have substantial impact on their orbital dynamics. Various SRP force models have been developed over the past 30 years for the purpose of precise orbit determination. They all rely upon the assumption that the satellites continuously maintain a Sun-Nadir pointing attitude with the navigation antenna boresight (body-fixed z-axis) pointing towards Earth center, and the solar panel rotation axis (body-fixed y-axis) being normal to the Sun direction. However, in reality, this is not perfectly the case. Reasons for a non-nominal spacecraft attitude may be eclipse maneuvers, commanded attitude biases and Sun/horizon sensor measurement errors, for example due to mounting misalignment or incorrectly calibrated sensor electronics. In this work the effect of GNSS spacecraft orientation errors on SRP modelling is investigated. Simplified mathematical functions describing the SRP force acting on the solar arrays in the presence of yaw-, pitch- and roll-biases are derived. Special attention is paid to the yaw-bias and its relationship to the SRP dynamics, particular in direction of the spacecraft y-axis ("y-bias force"). Analytical and experimental results gathered from orbit and attitude analyses of GPS Block II/IIA/IIF satellites demonstrate how sensitive the SRP coefficients are to changes in yaw.

  18. Low-Frequency Error Extraction and Compensation for Attitude Measurements from STECE Star Tracker.

    Science.gov (United States)

    Lai, Yuwang; Gu, Defeng; Liu, Junhong; Li, Wenping; Yi, Dongyun

    2016-10-12

    The low frequency errors (LFE) of star trackers are the most penalizing errors for high-accuracy satellite attitude determination. Two test star trackers- have been mounted on the Space Technology Experiment and Climate Exploration (STECE) satellite, a small satellite mission developed by China. To extract and compensate the LFE of the attitude measurements for the two test star trackers, a new approach, called Fourier analysis, combined with the Vondrak filter method (FAVF) is proposed in this paper. Firstly, the LFE of the two test star trackers' attitude measurements are analyzed and extracted by the FAVF method. The remarkable orbital reproducibility features are found in both of the two test star trackers' attitude measurements. Then, by using the reproducibility feature of the LFE, the two star trackers' LFE patterns are estimated effectively. Finally, based on the actual LFE pattern results, this paper presents a new LFE compensation strategy. The validity and effectiveness of the proposed LFE compensation algorithm is demonstrated by the significant improvement in the consistency between the two test star trackers. The root mean square (RMS) of the relative Euler angle residuals are reduced from [27.95'', 25.14'', 82.43''], 3σ to [16.12'', 15.89'', 53.27''], 3σ.

  19. Unscented Kalman Filter Applied to the Spacecraft Attitude Estimation with Euler Angles

    Directory of Open Access Journals (Sweden)

    Roberta Veloso Garcia

    2012-01-01

    Full Text Available The aim of this work is to test an algorithm to estimate, in real time, the attitude of an artificial satellite using real data supplied by attitude sensors that are on board of the CBERS-2 satellite (China Brazil Earth Resources Satellite. The real-time estimator used in this work for attitude determination is the Unscented Kalman Filter. This filter is a new alternative to the extended Kalman filter usually applied to the estimation and control problems of attitude and orbit. This algorithm is capable of carrying out estimation of the states of nonlinear systems, without the necessity of linearization of the nonlinear functions present in the model. This estimation is possible due to a transformation that generates a set of vectors that, suffering a nonlinear transformation, preserves the same mean and covariance of the random variables before the transformation. The performance will be evaluated and analyzed through the comparison between the Unscented Kalman filter and the extended Kalman filter results, by using real onboard data.

  20. Geostationary Operational Environmental Satellite (GOES)-8 mission flight experience

    Science.gov (United States)

    Noonan, C. H.; McIntosh, R. J.; Rowe, J. N.; Defazio, R. L.; Galal, K. F.

    1995-05-01

    The Geostationary Operational Environmental Satellite (GOES)-8 spacecraft was launched on April 13, 1994, at 06:04:02 coordinated universal time (UTC), with separation from the Atlas-Centaur launch vehicle occurring at 06:33:05 UTC. The launch was followed by a series of complex, intense operations to maneuver the spacecraft into its geosynchronous mission orbit. The Flight Dynamics Facility (FDF) of the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) was responsible for GOES-8 attitude, orbit maneuver, orbit determination, and station acquisition support during the ascent phase. This paper summarizes the efforts of the FDF support teams and highlights some of the unique challenges the launch team faced during critical GOES-8 mission support. FDF operations experience discussed includes: (1) The abort of apogee maneuver firing-1 (AMF-1), cancellation of AMF-3, and the subsequent replans of the maneuver profile; (2) The unexpectedly large temperature dependence of the digital integrating rate assembly (DIRA) and its effect on GOES-8 attitude targeting in support of perigee raising maneuvers; (3) The significant effect of attitude control thrusting on GOES-8 orbit determination solutions; (4) Adjustment of the trim tab to minimize torque due to solar radiation pressure; and (5) Postlaunch analysis performed to estimate the GOES-8 separation attitude. The paper also discusses some key FDF GOES-8 lessons learned to be considered for the GOES-J launch which is currently scheduled for May 19, 1995.