Sample records for attitude control method

  1. ISS Contingency Attitude Control Recovery Method for Loss of Automatic Thruster Control

    Bedrossian, Nazareth; Bhatt, Sagar; Alaniz, Abran; McCants, Edward; Nguyen, Louis; Chamitoff, Greg


    In this paper, the attitude control issues associated with International Space Station (ISS) loss of automatic thruster control capability are discussed and methods for attitude control recovery are presented. This scenario was experienced recently during Shuttle mission STS-117 and ISS Stage 13A in June 2007 when the Russian GN&C computers, which command the ISS thrusters, failed. Without automatic propulsive attitude control, the ISS would not be able to regain attitude control after the Orbiter undocked. The core issues associated with recovering long-term attitude control using CMGs are described as well as the systems engineering analysis to identify recovery options. It is shown that the recovery method can be separated into a procedure for rate damping to a safe harbor gravity gradient stable orientation and a capability to maneuver the vehicle to the necessary initial conditions for long term attitude hold. A manual control option using Soyuz and Progress vehicle thrusters is investigated for rate damping and maneuvers. The issues with implementing such an option are presented and the key issue of closed-loop stability is addressed. A new non-propulsive alternative to thruster control, Zero Propellant Maneuver (ZPM) attitude control method is introduced and its rate damping and maneuver performance evaluated. It is shown that ZPM can meet the tight attitude and rate error tolerances needed for long term attitude control. A combination of manual thruster rate damping to a safe harbor attitude followed by a ZPM to Stage long term attitude control orientation was selected by the Anomaly Resolution Team as the alternate attitude control method for such a contingency.

  2. Spacecraft methods and structures with enhanced attitude control that facilitates gyroscope substitutions

    Li, Rongsheng (Inventor); Kurland, Jeffrey A. (Inventor); Dawson, Alec M. (Inventor); Wu, Yeong-Wei A. (Inventor); Uetrecht, David S. (Inventor)


    Methods and structures are provided that enhance attitude control during gyroscope substitutions by insuring that a spacecraft's attitude control system does not drive its absolute-attitude sensors out of their capture ranges. In a method embodiment, an operational process-noise covariance Q of a Kalman filter is temporarily replaced with a substantially greater interim process-noise covariance Q. This replacement increases the weight given to the most recent attitude measurements and hastens the reduction of attitude errors and gyroscope bias errors. The error effect of the substituted gyroscopes is reduced and the absolute-attitude sensors are not driven out of their capture range. In another method embodiment, this replacement is preceded by the temporary replacement of an operational measurement-noise variance R with a substantially larger interim measurement-noise variance R to reduce transients during the gyroscope substitutions.

  3. A computed torque method based attitude control with optimal force distribution for articulated body mobile robots

    This paper introduces an attitude control scheme based in optimal force distribution using quadratic programming which minimizes joint energy consumption. This method shares similarities with force distribution for multifingered hands, multiple coordinated manipulators and legged walking robots. In particular, an attitude control scheme was introduced inside the force distribution problem, and successfully implemented for control of the articulated body mobile robot KR-II. This is an actual mobile robot composed of cylindrical segments linked in series by prismatic joints and has a long snake-like appearance. These prismatic joints are force controlled so that each segment's vertical motion can automatically follow the terrain irregularities. An attitude control is necessary because this system acts like a system of wheeled inverted pendulum carts connected in series, being unstable by nature. The validity and effectiveness of the proposed method is verified by computer simulation and experiments with the robot KR-II. (author)

  4. A computed torque method based attitude control with optimal force distribution for articulated body mobile robots

    Fukushima, Edwardo F.; Hirose, Shigeo [Tokyo Inst. of Tech. (Japan)


    This paper introduces an attitude control scheme based in optimal force distribution using quadratic programming which minimizes joint energy consumption. This method shares similarities with force distribution for multifingered hands, multiple coordinated manipulators and legged walking robots. In particular, an attitude control scheme was introduced inside the force distribution problem, and successfully implemented for control of the articulated body mobile robot KR-II. This is an actual mobile robot composed of cylindrical segments linked in series by prismatic joints and has a long snake-like appearance. These prismatic joints are force controlled so that each segment's vertical motion can automatically follow the terrain irregularities. An attitude control is necessary because this system acts like a system of wheeled inverted pendulum carts connected in series, being unstable by nature. The validity and effectiveness of the proposed method is verified by computer simulation and experiments with the robot KR-II. (author)

  5. Methods for attitude guidance and precise robust gyromoment control of large-scale agile observation spacecraft

    Somov, Sergey; Butyrin, Sergey; Somov, Yevgeny


    Problems on guidance and robust gyromoment attitude control of agile information satellite for remote sensing the Earth surface are considered. Elaborated methods for dynamic research of the spacecraft programmed angular motion at principle modes under external and parametric disturbances, partial discrete measurement of the state and digital control of the gyro moment cluster by the excessive gyrodine schemes, are presented.

  6. Composite control method for stabilizing spacecraft attitude in terms of Rodrigues parameters

    Sun Haibin; Li Shihua


    In this paper,the attitude stabilization problem of a rigid spacecraft described by Rodrigues parameters is investigated via a composite control strategy,which combines a feedback control law designed by a finite time control technique with a feedforward compensator based on a linear disturbance observer (DOB) method.By choosing a suitable coordinate transformation,the spacecraft dynamics can be divided into three second-order subsystems.Each subsystem includes a certain part and an uncertain part.By using the finite time control technique,a continuous finite time controller is designed for the certain part.The uncertain part is considered to be a lumped disturbance,which is estimated by a DOB,and a corresponding feedforward design is then implemented to compensate the disturbance.Simulation results are employed to confirm the effectiveness of the proposed approach.

  7. Spacecraft attitude control systems with dynamic methods and structures for processing star tracker signals

    Liu, Yong (Inventor); Wu, Yeong-Wei Andy (Inventor); Li, Rongsheng (Inventor)


    Methods are provided for dynamically processing successively-generated star tracker data frames and associated valid flags to generate processed star tracker signals that have reduced noise and a probability greater than a selected probability P.sub.slctd of being valid. These methods maintain accurate spacecraft attitude control in the presence of spurious inputs (e.g., impinging protons) that corrupt collected charges in spacecraft star trackers. The methods of the invention enhance the probability of generating valid star tracker signals because they respond to a current frame probability P.sub.frm by dynamically selecting the largest valid frame combination whose combination probability P.sub.cmb satisfies a selected probability P.sub.slctd. Noise is thus reduced while the probability of finding a valid frame combination is enhanced. Spacecraft structures are also provided for practicing the methods of the invention.

  8. Optimal magnetic attitude control

    Wisniewski, Rafal; Markley, F.L.


    Magnetic torquing is attractive as means of control for small satellites. The actuation principle is to use the interaction between the earth's magnetic field and a magnetic field generated by a coil set in the satellite. This control principle is inherently time-varying, 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 stabilization of a low earth orbit satellite. The problem of controlling the spacecraft attitude using only magnetic...

  9. Satellite Attitude Control System Simulator

    G.T. Conti


    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.

  10. Torque equilibrium attitude control for Skylab reentry

    Glaese, J. R.; Kennel, H. F.


    The method of torque equilibrium attitude control used to control the reentry of Skylab to an altitude below 150 km without the use of thruster fuel once the attitude was established is discussed. The Skylab attitude and pointing control system, which included rate gyros, sun sensors, star tracker, the Apollo telescope mount digital computer, control moment gyros and cold-gas attitude thrusters, is presented. The 12 torque equilibrium attitudes found at which aerodynamic, gravity gradient and gyroscopic torques would balance are indicated, and the three of those at which the solar power supply would be adequate for attitude control are illustrated. The equilibrium seeking method employed is then examined, and the operation and performance of the torque equilibrium attitude control system during the three weeks prior to Skylab reentry are discussed. It is concluded that the torque equilibrium attitude control method developed for Skylab was successful in performing its assigned mission, and will be valuable for the design of future, low-altitude spacecraft or tethered vehicles.

  11. Flexible Satellite Attitude Control via Adaptive Fuzzy Linearization

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


    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.

  12. Observer-based Satellite Attitude Control and Simulation Researches

    王子才; 马克茂


    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.

  13. Attitude control and stabilization technology discipline

    Sunkel, John W.


    Viewgraphs on attitude control and stabilization technology discipline for the Space Station Freedom are presented. Topics covered include: attitude control technologies for multi-user accommodation; flexible dynamics and control; computational control techniques; and automatic proximity operations.

  14. Fundamentals of spacecraft attitude determination and control

    Markley, F Landis


    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...

  15. Nonlinear fractional order proportion-integral-derivative active disturbance rejection control method design for hypersonic vehicle attitude control

    Song, Jia; Wang, Lun; Cai, Guobiao; Qi, Xiaoqiang


    Near space hypersonic vehicle model is nonlinear, multivariable and couples in the reentry process, which are challenging for the controller design. In this paper, a nonlinear fractional order proportion integral derivative (NFOPIλDμ) active disturbance rejection control (ADRC) strategy based on a natural selection particle swarm (NSPSO) algorithm is proposed for the hypersonic vehicle flight control. The NFOPIλDμ ADRC method consists of a tracking-differentiator (TD), an NFOPIλDμ controller and an extended state observer (ESO). The NFOPIλDμ controller designed by combining an FOPIλDμ method and a nonlinear states error feedback control law (NLSEF) is to overcome concussion caused by the NLSEF and conversely compensate the insufficiency for relatively simple and rough signal processing caused by the FOPIλDμ method. The TD is applied to coordinate the contradiction between rapidity and overshoot. By attributing all uncertain factors to unknown disturbances, the ESO can achieve dynamic feedback compensation for these disturbances and thus reduce their effects. Simulation results show that the NFOPIλDμ ADRC method can make the hypersonic vehicle six-degree-of-freedom nonlinear model track desired nominal signals accurately and fast, has good stability, dynamic properties and strong robustness against external environmental disturbances.

  16. Optimal magnetic attitude control

    Wisniewski, Rafal; Markley, F.L.


    Magnetic torquing is attractive as means of control for small satellites. The actuation principle is to use the interaction between the earth's magnetic field and a magnetic field generated by a coil set in the satellite. This control principle is inherently time-varying, 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 stabilization of a ...

  17. Nonlinear Robust Control for Spacecraft Attitude

    Wang Lina


    Full Text Available Nonlinear robust control of the spacecraft attitude with the existence of external disturbances is considered. A robust attitude controller is designed based on the passivity approach the quaternion representation, which introduces the suppression vector of external disturbance into the control law and does not need angular velocity measurement. Stability conditions of the robust attitude controller are given. And the numerical simulation results show the effectiveness of the attitude controller.

  18. Noise screen for attitude control system

    Rodden, John J. (Inventor); Stevens, Homer D. (Inventor); Hong, David P. (Inventor); Hirschberg, Philip C. (Inventor)


    An attitude control system comprising a controller and a noise screen device coupled to the controller. The controller is adapted to control an attitude of a vehicle carrying an actuator system that is adapted to pulse in metered bursts in order to generate a control torque to control the attitude of the vehicle in response to a control pulse. The noise screen device is adapted to generate a noise screen signal in response to the control pulse that is generated when an input attitude error signal exceeds a predetermined deadband attitude level. The noise screen signal comprises a decaying offset signal that when combined with the attitude error input signal results in a net attitude error input signal away from the predetermined deadband level to reduce further control pulse generation.

  19. Robust Adaptive Attitude Control for Airbreathing Hypersonic Vehicle with Attitude Constraints and Propulsive Disturbance

    Jian Fu; Liangming Wang; Mou Chen; Sijiang Chang


    A robust adaptive backstepping attitude control scheme, combined with invariant-set-based sliding mode control and fast-nonlinear disturbance observer, is proposed for the airbreathing hypersonic vehicle with attitude constraints and propulsive disturbance. Based on the positive invariant set and backstepping method, an innovative sliding surface is firstly developed for the attitude constraints. And the propulsive disturbance of airbreathing hypersonic vehicle is described as a differential ...

  20. Optimal Sliding Mode Controllers for Attitude Stabilization of Flexible Spacecraft

    Chutiphon Pukdeboon


    Full Text Available The robust optimal attitude control problem for a flexible spacecraft is considered. Two optimal sliding mode control laws that ensure the exponential convergence of the attitude control system are developed. Integral sliding mode control (ISMC is applied to combine the first-order sliding mode with optimal control and is used to control quaternion-based spacecraft attitude manoeuvres with external disturbances and an uncertainty inertia matrix. For the optimal control part the state-dependent Riccati equation (SDRE and optimal Lyapunov techniques are employed to solve the infinite-time nonlinear optimal control problem. The second method of Lyapunov is used to guarantee the stability of the attitude control system under the action of the proposed control laws. An example of multiaxial attitude manoeuvres is presented and simulation results are included to verify the usefulness of the developed controllers.

  1. Three axis attitude control system

    Studer, Philip A. (Inventor)


    A three-axis attitude control system for an orbiting body comprised of a motor driven flywheel supported by a torque producing active magnetic bearing is described. Free rotation of the flywheel is provided about its central axis and together with limited angular torsional deflections of the flywheel about two orthogonal axes which are perpendicular to the central axis. The motor comprises an electronically commutated DC motor, while the magnetic bearing comprises a radially servoed permanent magnet biased magnetic bearing capable of producing cross-axis torques on the flywheel. Three body attitude sensors for pitch, yaw and roll generate respective command signals along three mutually orthogonal axes (x, y, z) which are coupled to circuit means for energizing a set of control coils for producing torques about two of the axes (x and y) and speed control of the flywheel about the third (z) axis. An energy recovery system, which is operative during motor deceleration, is also included which permits the use of a high-speed motor to perform effectively as a reactive wheel suspended in the magnetic bearing.

  2. Chaotic attitude control of satellite using impulsive control

    Nowadays, attitude control systems of satellites demand better performance, resulting in the application of new advanced nonlinear control theory. In this paper, impulsive control is applied to a six-dimensional system which describes the attitude dynamics of a satellite subjected to deterministic external perturbations which induce chaotic motion when no control is affected. Several theorems on the stability of impulsive control systems are presented. These theorems are then used to find the conditions under which the chaotic systems can be asymptotically controlled to the origin by using impulsive control. Given the parameters of the chaotic system and the impulsive control law, an estimation of the upper bound of the impulse interval is given. Finally, we give some simulations results to visualize the effectiveness and feasibility of the proposed method.

  3. Lorentz Force Based Satellite Attitude Control

    Giri, Dipak Kumar; Sinha, Manoranjan


    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.

  4. Attitude control with active actuator saturation prevention

    Forbes, James Richard


    Spacecraft attitude control in the presence of actuator saturation is considered. The attitude controller developed has two components: a proportional component and an angular velocity component. The proportional control has a special form that depends on the attitude parameterization. The angular velocity control is realized by a strictly positive real system with its own input nonlinearity. The strictly positive real system can filter noise in the angular velocity measurement. With this control architecture the torques applied to the body are guaranteed to be below a predetermined value, thus preventing saturation of the actuators. The closed-loop equilibrium point corresponding to the desired attitude is shown to be asymptotically stable. Additionally, the control law does not require specific knowledge of the body's inertia properties, and is therefore robust to such modelling errors.

  5. Variable structure attitude maneuver and vibration control of flexible spacecraft

    HU Qing-lei; MA Cuang-fu


    A dual-stage control system design method is presented for the three-axis-rotational maneuver and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator.In this design approach,the attitude control and the vibration suppression sub-systems ale designed separately using the lower order model.The design of attitude controller is based on the variable structure control (VSC)theory leading to a discontinuous control law.This controller accomplishes asymptotic attitude maneuvering in the closed-loop system and is insensitive to the interaction of elastic modes and uncertainty in the system.To actively suppress the flexible vibrations,the modal velocity feedback control method is presented by using piezoelectric materials as additional sensor and actuator bonded on the surface of the flexible appendages.In addition,a special configuration of actuators for three-axis attitude control is also investigated:the pitch attitude controlled by a momentum wheel,and the roll/yaw control achieved by on-off thrustem.which is modulated by pulse width pulse frequency modulation technique to construct the proper control torque history.Numerical simulations performed show that the rotational maneuver and vibration suppression ale accomplished in spite of the presence of disturbance torque and parameter uncertainty.

  6. Solar Sail Attitude Control Performance Comparison

    Bladt, Jeff J.; Lawrence, Dale A.


    Performance of two solar sail attitude control implementations is evaluated. One implementation employs four articulated reflective vanes located at the periphery of the sail assembly to generate control torque about all three axes. A second attitude control configuration uses mass on a gimbaled boom to alter the center-of-mass location relative to the center-of-pressure producing roll and pitch torque along with a pair of articulated control vanes for yaw control. Command generation algorithms employ linearized dynamics with a feedback inversion loop to map desired vehicle attitude control torque into vane and/or gimbal articulation angle commands. We investigate the impact on actuator deflection angle behavior due to variations in how the Jacobian matrix is incorporated into the feedback inversion loop. Additionally, we compare how well each implementation tracks a commanded thrust profile, which has been generated to follow an orbit trajectory from the sun-earth L1 point to a sub-L1 station.

  7. A magnetic control system for attitude acquisition

    Stickler, A. C.


    A spacecraft magnetic attitude acquisition system is reported that is capable of automatically despinning a satellite from arbitrarily high rates around any axis and provides terminal orientation that makes capture by conventional fine control attitude control systems routine. The system consists of a 3-axis magnetometer, a set of 3 orthogonal magnets, and appropriate control logic. A well-configured system results in despin times of the order of 5 orbits per rpm for spacecraft in low earth orbits. Following despin, terminal orientation is achieved after another one to three orbits, depending on the capture range of the associated fine control system.

  8. Research on Attitude System of Active Magnetic Control Small Satellite

    Zhaowei, Sun; Di, Yang


    When enter orbit, small satellite often tumble as a result of disturbance. How to capture it promptly with finite magnetic torque is an important problem. Because of the coupling of dynamics and control, the small satellite control system is a nonlinear attitude control system with bounds. For high direction and steady precision, an effective method must be found. In this paper, combining with the bound conditions of magnetic torque, two methods are researched. The first is energy method. It ...

  9. Experiment D010: Ion sensing attitude control

    Sagalyn, R. C.; Smiddy, M.


    The feasibility of an attitude control system that uses environmental positive ions and an electrostatic detection system to measure spacecraft pitch and yaw is studied. The secondary objective was to measure the spatial and temporal variations of ambient positively charged particles along the orbital path of the Gemini 10 and 12 spacecrafts. The results proved that the use of a horizon detector in conjunction with pitch and yaw sensors would facilitate complete description of the spacecraft position and attitude. Furthermore, with the addition of a servosystem, the unit could be used as a complete automatic attitude-control system that would be applicable from the lowest satellite altitudes up to at least 10 earth radii. Also, results established that the charge density along the trajectory of the satellite could be determined by transmission of output voltages from the individual electrometers.

  10. Modular Attitude Control System for Microsatellites with Stringent Pointing Requirements

    Grocott, Simon


    Advancing technology has allowed for the development of low cost attitude control hardware for microsatellites. However, the attitude control design and software development remain a significant cost driver. The Dynacon High Performance Attitude Control system is a modular control system that makes use of reusable algorithm modules enabling the attitude control system to be applied to several different spacecraft missions with very different performance requirements. The High Performance Atti...

  11. SDRE Based Attitude Control Using Modified Rodriguez Parameters

    Doruk, R Ozgur


    The purpose of this paper is to present an application of the State Dependent Riccati Equation (SDRE) method to satellite attitude control where the satellite kinematics is modeled by Modified Rodriguez Parameters (MRP). The SDRE methodology is applicable on special forms of nonlinear systems where satellite model is one of the candidates. It is not easy to find an analytical solution from the SDRE. Thus point wise solutions are interpolated with respect to the operating conditions. The point wise solutions are obtained from the MATLAB algorithms which are derived from the positive definite solutions of the SDRE. The global stability analysis is difficult due to the nature of the methodology. The resultant attitude controllers outside the breakpoints (the selected operating conditions for interpolation) are suboptimal. The performance of the designs is examined by simulations on MATLAB - Simulink environment. The simulation results show that, the designed attitude controllers are working satisfactorily even i...

  12. Attitude Determination and Control Systems

    Starin, Scott R.; Eterno, John


    designing and operating spacecraft pointing (i.e. attitude) systems.

  13. Framework of Combined Adaptive and Non-adaptive Attitude Control System for a Helicopter Experimental System

    Akira Inoue; Ming-Cong Deng


    This paper presents a framework of a combined adaptive and non-adaptive attitude control system for a helicopter experimental system. The design method is based on a combination of adaptive nonlinear control and non-adaptive nonlinear control. With regard to detailed attitude control system design, two schemes are shown for different application cases.

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

    Zhigang Xing; Gangtie Zheng


    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...

  15. Modular Attitude Determination and Control System for Small Satellites

    Selby, Vaughn


    In order to meet the cost goals of small satellites, attitude determination and control problems must be solved using standardized components. Small satellite attitude control systems must feature performance, versatility, and above all, low cost Large, custom designed, high cost attitude control systems have no place in the small satellite community. A modular concept of attitude control is presented which will allow ambitious performance and cost goals to be attained. Basic building blocks ...

  16. Integrated Method - the Optimum Way to Improve the Quality of Frequency Response Characteristics of the Space Vehicle Attitude Control System

    Britova, Yu.; Dmitriev, V.; Kostyuchenko, T.


    The integrated method applied to the design of technical systems is a process in which various project, calculation and verification procedures are interconnected and interrelated. The results of procedures are used in a certain sequence, thus ensuring maximum reachable optimality of the system being designed.

  17. Prospects of Relative Attitude Control Using Coulomb Actuation

    Schaub, Hanspeter; Stevenson, Daan


    The relative attitude is studied between two charge controlled spacecraft being held at a fixed separation distance. While one body has a spherical shape, the 2nd body is assumed to be non-spherical and tumbling. The attitude control goal is to arrest the rotation of the 2nd body. While prior work has identified the existence of torques between charged bodies, this is the first analytical study on a charged feedback attitude control. Using the recently developed multi-sphere method to provide a simplified electrostatic force and torque model between non-spherical shapes, Lyapunov theory is used to develop a stabilizing attitude control using spacecraft potential as the control variable. Zero and non-zero equilibrium potentials are considered, with the later suitable for the electrostatic tug concept. With a pulling configuration, the cylinder will come to rest with the long axis aligned with the inter-vehicle axis in a stable configuration. For a pusher, the cylinder will settle 90 degrees rotated from this axis. Numerical simulations illustrate the control performance.

  18. Spacecraft attitude control momentum requirements analysis

    Robertson, Brent P.; Heck, Michael L.


    The relationship between attitude and angular momentum control requirements is derived for a fixed attitude, Earth orbiting spacecraft with large area articulating appendages. Environmental effects such as gravity gradient, solar radiation pressure, and aerodynamic forces arising from a dynamic, rotating atmosphere are examined. It is shown that, in general, each environmental effect contributes to both cyclic and secular momentum requirements both within and perpendicular to the orbit plane. The gyroscopic contribution to the angular momentum control requirements resulting from a rotating, Earth oriented spacecraft is also discussed. Special conditions are described where one or more components of the angular momentum can be made to vanish, or become purely cyclical. Computer generated plots for a candidate space station configuration are presented to supplement the analytically derived results.

  19. A novel single thruster control strategy for spacecraft attitude stabilization

    Godard; Kumar, Krishna Dev; Zou, An-Min


    Feasibility of achieving three axis attitude stabilization using a single thruster is explored in this paper. Torques are generated using a thruster orientation mechanism with which the thrust vector can be tilted on a two axis gimbal. A robust nonlinear control scheme is developed based on the nonlinear kinematic and dynamic equations of motion of a rigid body spacecraft in the presence of gravity gradient torque and external disturbances. The spacecraft, controlled using the proposed concept, constitutes an underactuated system (a system with fewer independent control inputs than degrees of freedom) with nonlinear dynamics. Moreover, using thruster gimbal angles as control inputs make the system non-affine (control terms appear nonlinearly in the state equation). This necessitates the control algorithms to be developed based on nonlinear control theory since linear control methods are not directly applicable. The stability conditions for the spacecraft attitude motion for robustness against uncertainties and disturbances are derived to establish the regions of asymptotic 3-axis attitude stabilization. Several numerical simulations are presented to demonstrate the efficacy of the proposed controller and validate the theoretical results. The control algorithm is shown to compensate for time-varying external disturbances including solar radiation pressure, aerodynamic forces, and magnetic disturbances; and uncertainties in the spacecraft inertia parameters. The numerical results also establish the robustness of the proposed control scheme to negate disturbances caused by orbit eccentricity.

  20. System and method for correcting attitude estimation

    Josselson, Robert H. (Inventor)


    A system includes an angular rate sensor disposed in a vehicle for providing angular rates of the vehicle, and an instrument disposed in the vehicle for providing line-of-sight control with respect to a line-of-sight reference. The instrument includes an integrator which is configured to integrate the angular rates of the vehicle to form non-compensated attitudes. Also included is a compensator coupled across the integrator, in a feed-forward loop, for receiving the angular rates of the vehicle and outputting compensated angular rates of the vehicle. A summer combines the non-compensated attitudes and the compensated angular rates of the to vehicle to form estimated vehicle attitudes for controlling the instrument with respect to the line-of-sight reference. The compensator is configured to provide error compensation to the instrument free-of any feedback loop that uses an error signal. The compensator may include a transfer function providing a fixed gain to the received angular rates of the vehicle. The compensator may, alternatively, include a is transfer function providing a variable gain as a function of frequency to operate on the received angular rates of the vehicle.

  1. The Magnetic Attitude Control of ABRIXAS

    Komgsmann, Hans; Wiegand, Matthias; Matthews, Oliver


    ABRIXAS is a small astronomical satellite planned by the Astrophysical Institute Potsdam (AIP) and the German Space Agency DARA. Its main scientific objective is to survey the total hemisphere; the satellite rotates once per orbit along the sun line, and after half a year the survey mission will be fulfilled. The attitude control system is one of the most critical subsystems with respect to cost and mission success, and an independent study was done. With a momentum biased system, three magne...

  2. Low cost attitude control system scanwheel development

    Bialke, William; Selby, Vaughn


    In order to satisfy a growing demand for low cost attitude control systems for small spacecraft, development of low cost scanning horizon sensor coupled to a low cost/low power consumption Reaction Wheel Assembly was initiated. This report addresses the details of the versatile design resulting from this effort. Tradeoff analyses for each of the major components are included, as well as test data from an engineering prototype of the hardware.

  3. Spacecraft Attitude Control in Hamiltonian Framework

    Wisniewski, Rafal


    The objective of this paper is to give a design scheme for attitude control algorithms of a generic spacecraft. Along with the system model formulated in the Hamilton's canonical form the algorithm uses information about a required potential energy and a dissipative term. The control action is the...... sum of the gradient of the potential energy and the dissipative force. It is shown that this control law makes the system uniformly asymptotically stable to the desired reference point. Three problems were addressed in the paper: spacecraft stabilization in the inertial frame, libration damping with...

  4. Development and Comparison of Estimation Methods for Attitude Determination

    Rinnan, Toril Bye


    The NTNU Test Satellite (NUTS) project, is part of the Norwegian Student Satellite programANSAT. The goal of the project is to design and launch a double CubeSat by the endof 2014. During earlier satellite projects at NTNU, solid work on design of the attitudedetermination and control for a small satellite has been done.One of the considered estimation methods for the attitude determination is the extendedquaternion estimation method (EQUEST). Further development and testing of themethod is d...

  5. Orbit and attitude control of spacecraft formation flying

    ZHANG Zhi-guo; LI Jun-feng


    Formation flying is a novel concept of distributing the flmctionality of large spacecraft among several smaller, less expensive, cooperative satellites. Some applica-tions require that a controllable satellite keeps relative position and attitude to observe a specific surface of another satellite among the cluster. Specially, the target space vehi- cle is malfunctioning. The present paper focuses on the problem that how to control a chaser satellite to fly around an out-of-work target satellite closely in earth orbit and to track a specific surface. Relative attitude and first approximate relative orbital dynamics equations are presented. Control strategy is derived based on feedback linearization and Lyapunov theory of stability. Further, considering the uncertainty of inertia, an adaptive control method is developed to obtain the correct inertial ratio. The numerical simulation is given to verify the validity of proposed control scheme.

  6. Coordinated Multiple Spacecraft Attitude Control with Communication Time Delays and Uncertainties

    LI Guiming; LIU Liangdong


    In this paper,we consider the coordinated attitude control problem of spacecraft formation with communication delays,model and disturbance uncertainties,and propose novel synchronized control schemes.Since the attitude motion is essential in non-Euclidean space,thus,unlike the existing designs which describe the delayed relative attitude via linear algorithm,we treat the attitude error and the local relative attitude on the nonlinear manifold-Lie group,and attempt to obtain coupling attitude information by the natural quatemion multiplication.Our main focus is to address two problems:1) Propose a coordinated attitude controller to achieve the synchronized attitude maneuver,i.e.,synchronize multiple spacecraft attitudes and track a time-varying desired attitude; 2) With known model information,we achieve the synchronized attitude maneuver with disturbances under angular velocity constraints.Especially,if the formation does not have any uncertainties,the designer can simply set the controller via an appropriate choice of control gains to avoid system actuator saturation.Our controllers are proposed based on the Lyapunov-Krasovskii method and simulation of a spacecraft formation is conducted to demonstrate the effectiveness of theoretical results.

  7. Advanced Attitude Control af Pico Sized Satellites

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


    The AAU-Cubesat project started in 2001 and led to the launch of the rst AAU-Cubesat and followed up with the second Cubesat project, AAUSAT-II, which carries a combined gamma and X-Ray detector. Due to the precision pointing requirement in the X-Ray sensor it is necessary to realize a pointing...... 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. The...

  8. Attitude control of a nano satellite


    The CubeSTAR satellite is a student satellite project at the University of Oslo. The main mission is to measure the turbulence in the electron plasma using a novel Multi Needle Langmuir Probe system developed at the University of Oslo. In order to get correct measurements, it’s important that the probes are located in the front of the satellite in the orbit velocity direction. In this thesis, the attitude control problem of the CubeSTAR nano-satellite is the main topic. The satellite wil...

  9. Local Vertical/Local Horizontal Attitude Control for Spartan Spacecraft

    Morrissey, James; Olney, David


    A Spartan spacecraft attitude control system was reconfigured to provide attitude pointing with respect to a Local Vertical/Local Horizontal reference frame even though the baseline system uses only an initial start attitude, sun sensors, and star tracker/gyros for defining the spacecraft attitude. No earth sensors of any kind are used. Deployed from the orbiter for two days, usually for solar and stellar inertial pointing, Spartan missions use pointing programs that must be written months pr...

  10. Flexible Dynamics and Attitude Control of a Square Solar Sail

    Choi, Mirue

    This thesis presents a comprehensive analysis of attitude and structural dynamics of a square solar sail. In particular, this research examines the use of corner-attached reflective vanes to control the attitude of the spacecraft. An introduction to known solar sail designs is given, then the mathematics involved in calculating solar radiation pressure forces are presented. A detailed derivation and implementation of the unconstrained nonlinear flexible structural dynamics with Finite Element Method (FEM) models are explored, with several sample simulations of published large deflection experiments used as verification measures. To simulate the inability of a thin membrane to resist compression, the sail membrane elements are augmented with a method that approximates the wrinkling and the slacking dynamics, which is followed by a simulation of another well-known experiment as a verification measure. Once the structural dynamics are established, the usage of the tip vanes is explored. Specifically, a control allocation problem formed by having two degrees of freedom for each tip vane is defined and an efficient solution to this problem is presented, allowing desired control torques to be converted to appropriate vane angles. A randomized testing mechanism is implemented to show the efficacy of this algorithm. The sail shadowing problem is explored as well, where a component of the spacecraft casts shadow upon the sail and prevents solar radiation pressure force from being produced. A method to calculate the region of shadow is presented, and two different shadowing examples are examined --- due to the spacecraft bus, and due to the sail itself. Combining all of the above, an attitude control simulation of the sail model is presented. A simple PD controller combined with the control allocation scheme is used to provide the control torque for the sail, with which the spacecraft must orient towards a number of pre-specified attitude targets. Several attitude

  11. Attitude Control System for the Extreme Ultraviolet Explorer Satellite

    Wong, E. C.


    The requirements, design, and expected performance of the Attitude Control Subsystem for the spin-stabilized Extreme Ultraviolet Explorer Satellite are presented. In the sky-mapping phase, closed-loop magnetic control keeps the spin axis pointed toward the sun. In the spectroscopy phase, the attitude control loop is closed via the ground. The satellite's attitude and spin rate are determined using periodically downlinked star data. An attitude control algorithm generates commands to be uplinked to the satellite for spin axis precession and spin rate control. Computer simulations of the satellite dynamic response, pointing error, and stability during spin axis precession are presented, and parameters that affect the pointing performance are evaluated.

  12. Position and attitude tracking control for a quadrotor UAV.

    Xiong, Jing-Jing; Zheng, En-Hui


    A synthesis control method is proposed to perform the position and attitude tracking control of the dynamical model of a small quadrotor unmanned aerial vehicle (UAV), where the dynamical model is underactuated, highly-coupled and nonlinear. Firstly, the dynamical model is divided into a fully actuated subsystem and an underactuated subsystem. Secondly, a controller of the fully actuated subsystem is designed through a novel robust terminal sliding mode control (TSMC) algorithm, which is utilized to guarantee all state variables converge to their desired values in short time, the convergence time is so small that the state variables are acted as time invariants in the underactuated subsystem, and, a controller of the underactuated subsystem is designed via sliding mode control (SMC), in addition, the stabilities of the subsystems are demonstrated by Lyapunov theory, respectively. Lastly, in order to demonstrate the robustness of the proposed control method, the aerodynamic forces and moments and air drag taken as external disturbances are taken into account, the obtained simulation results show that the synthesis control method has good performance in terms of position and attitude tracking when faced with external disturbances. PMID:24534327

  13. Attitude Controller-Observer Design for the NTNU Test Satellite

    Alvenes, Fredrik


    This report presents the results from the development and design of an Attitude Controller-Observer for the NTNU Test Satellite (NUTS). It gives an insight to mathematical modeling of satellite attitude dynamics for 3 degrees of freedom. By the different limitations of how the NUTS operates, these models are adjusted accordingly.A strategy for controlling the attitude is presented. Through an explanation of the magnetic actuators, the control laws are also adapted to work with the NUTS satell...

  14. Three-axis active magnetic attitude control asymptotical study

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


    Active magnetic attitude control system providing given inertial attitude is considered. Control algorithm is constructed on the basis of a planar motion model. It decreases attitude discrepancy. Alternative approach is based on the PD-controller design. System behavior is analyzed for specific motion cases and sometimes for specific inertia tensor (axisymmetrical satellite) using averaging technique. Overall satellite angular motion is covered. Necessary attitude is found to be accessible for some control parameters. Stability is proven and optimal algorithm parameters are obtained. Floquet-based analysis is performed to verify and broaden analytical results.

  15. Finite-time output feedback attitude coordination control for formation flying spacecraft without unwinding

    Guo, Yong; Song, Shen-Min; Li, Xue-Hui


    In this paper, two finite-time attitude coordinated controllers for formation flying spacecraft are investigated based on rotation matrix. Because rotation matrix can represent the set of attitudes both globally and uniquely, the two controllers can deal with unwinding that can result in extra fuel consumption. To address the lack of angular velocity measurement, the second attitude coordinated controller is given by using a novel filter. Through homogeneous method and Lyapunov theories, it is shown that the proposed controllers can achieve the finite-time stability. Numerical simulations also demonstrate that the proposed control schemes are effective.

  16. Attitude Control Performance of IRVE-3

    Dillman, Robert A.; Gsell, Valerie T.; Bowden, Ernest L.


    The Inflatable Reentry Vehicle Experiment 3 (IRVE-3) launched July 23, 2012, from NASA Wallops Flight Facility and successfully performed its mission, demonstrating both the survivability of a hypersonic inflatable aerodynamic decelerator in the reentry heating environment and the effect of an offset center of gravity on the aeroshell's flight L/D. The reentry vehicle separated from the launch vehicle, released and inflated its aeroshell, reoriented for atmospheric entry, and mechanically shifted its center of gravity before reaching atmospheric interface. Performance data from the entire mission was telemetered to the ground for analysis. This paper discusses the IRVE-3 mission scenario, reentry vehicle design, and as-flown performance of the attitude control system in the different phases of the mission.

  17. Motivation,Attitude and Teaching Methods



    Motivation and attitude are two important factors that influence the students' foreign language learning. This paper focuses on the diverse influences from the different types of motivation and attitude that the students have. At the same time, it provides some suggestions for the language teachers and hopes that it may be helpful for their language teaching.

  18. Spacecraft attitude control using neuro-fuzzy approximation of the optimal controllers

    Kim, Sung-Woo; Park, Sang-Young; Park, Chandeok


    In this study, a neuro-fuzzy controller (NFC) was developed for spacecraft attitude control to mitigate large computational load of the state-dependent Riccati equation (SDRE) controller. The NFC was developed by training a neuro-fuzzy network to approximate the SDRE controller. The stability of the NFC was numerically verified using a Lyapunov-based method, and the performance of the controller was analyzed in terms of approximation ability, steady-state error, cost, and execution time. The simulations and test results indicate that the developed NFC efficiently approximates the SDRE controller, with asymptotic stability in a bounded region of angular velocity encompassing the operational range of rapid-attitude maneuvers. In addition, it was shown that an approximated optimal feedback controller can be designed successfully through neuro-fuzzy approximation of the optimal open-loop controller.

  19. Algorithm of Attitude Control and Its Simulation of Free-Flying Space Robot


    Reaction wheel or reaction thruster is employed to maintain the attitude of the base of space robot fixed in attitude control of free-flying space robot.However, in this method, a large amount of fuel will be consumed, and it will shorten the on-orbit life span of space robot, it also vibrate the system and make the system unsteady.The restricted minimum disturbance map (RMDM) based algorithm of attitude control is presented to keep the attitude of the base fixed during the movement of the manipulator.In this method it is realized by planning motion trajectory of the end-effector of manipulator without using reaction wheel or reaction thruster.In order to verify the feasibility and effectiveness of the algorithm attitude control presented in this paper, computer simulation experiments have been made and the experimental results demonstrate that this algorithm is feasible.

  20. Architecture for Combined Energy and Attitude Control System

    Ibrahim M. Mehedi


    Full Text Available 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 in the torque mode. All related mathematical representation along with the relevant transfer functions and the required numerical calculation are developed. The goals are to analyze the attitude performance with respect to the ideal and non-ideal test cases for a chosen reference mission.

  1. Adaptive Jacobian Fuzzy Attitude Control for Flexible Spacecraft Combined Attitude and Sun Tracking System

    Chak, Yew-Chung; Varatharajoo, Renuganth


    Many spacecraft attitude control systems today use reaction wheels to deliver precise torques to achieve three-axis attitude stabilization. However, irrecoverable mechanical failure of reaction wheels could potentially lead to mission interruption or total loss. The electrically-powered Solar Array Drive Assemblies (SADA) are usually installed in the pitch axis which rotate the solar arrays to track the Sun, can produce torques to compensate for the pitch-axis wheel failure. In addition, the attitude control of a flexible spacecraft poses a difficult problem. These difficulties include the strong nonlinear coupled dynamics between the rigid hub and flexible solar arrays, and the imprecisely known system parameters, such as inertia matrix, damping ratios, and flexible mode frequencies. In order to overcome these drawbacks, the adaptive Jacobian tracking fuzzy control is proposed for the combined attitude and sun-tracking control problem of a flexible spacecraft during attitude maneuvers in this work. For the adaptation of kinematic and dynamic uncertainties, the proposed scheme uses an adaptive sliding vector based on estimated attitude velocity via approximate Jacobian matrix. The unknown nonlinearities are approximated by deriving the fuzzy models with a set of linguistic If-Then rules using the idea of sector nonlinearity and local approximation in fuzzy partition spaces. The uncertain parameters of the estimated nonlinearities and the Jacobian matrix are being adjusted online by an adaptive law to realize feedback control. The attitude of the spacecraft can be directly controlled with the Jacobian feedback control when the attitude pointing trajectory is designed with respect to the spacecraft coordinate frame itself. A significant feature of this work is that the proposed adaptive Jacobian tracking scheme will result in not only the convergence of angular position and angular velocity tracking errors, but also the convergence of estimated angular velocity to

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

    Luiz Carlos Gadelha de Souza


    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.

  3. Measuring attitudes: quantitative and qualitative methods

    Carrasco, Ja; Lucas, K


    In this paper, we present the discussion and main findings from the ISCTSC Workshop B3, which focused on measuring the role of attitudes and perceptions in people’s travel choices. The paper considers various issues concerning the design and use of quantitative and qualitative approaches in the measurement of attitudes and perceptions within travel surveys. It first identifies the importance of measuring the underlying psychological motivations for people’s travel choices and behaviors and pr...

  4. Method and apparatus for rate integration supplement for attitude referencing with quaternion differencing

    Rodden, John James (Inventor); Price, Xenophon (Inventor); Carrou, Stephane (Inventor); Stevens, Homer Darling (Inventor)


    A control system for providing attitude control in spacecraft. The control system comprising a primary attitude reference system, a secondary attitude reference system, and a hyper-complex number differencing system. The hyper-complex number differencing system is connectable to the primary attitude reference system and the secondary attitude reference system.

  5. Control synthesis for polynomial nonlinear systems and application in attitude control

    Chang-fei TONG; Hui ZHANG; You-xian SUN


    A method for positive polynomial validation based on polynomial decomposition is proposed to deal with control synthesis problems. Detailed algorithms for decomposition are given which mainly consider how to convert coefficients of a polynomial to a matrix with free variables. Then, the positivity of a polynomial is checked by the decomposed matrix with semidefinite programming solvers. A nonlinear control law is presented for single input polynomial systems based on the Lyapunov stability theorem. The control synthesis method is advanced to multi-input systems further. An application in attitude control is finally presented. The proposed control law achieves effective performance as illustrated by the numerical example.

  6. The Relationship between Religious Attitudes, Locus of Control and Tendency to Substace Abuse in University Students

    Farhad Asghari


    Full Text Available Aim: The purpose of this study was the study of relationship between religious attitudes, locus of control and tendency to substance abuse among students of Guilan University. Method: The research design was correlational design. For this purpose, 340 university students of Guilan University selected through Morgan table by cluster randome sampling. Allport religious orientation, Ratter locus of control and addiction potential scale administered among selected sample. Results: The results showed significant relationship between religious attitude, locus of control and tendency to substance abuse. That is religious attitude, locus of control entered in regression model as significant predictors. Also there was significant relationship between religious attitude, and locus of control. Altogheder, results showed that people with internal religious attitude have internal locus of control and lower tendency to substance abuse. Also, people with external religious attitude have external locus of control and higher tendency to substance abuse. Conclusion: According to the results, we can conclude that religious attitude and locus of control play important role on tendency to substance abuse.

  7. The Submillimeter Wave Astronomy Satellite Attitude Control Software Design

    Anderson, Mark; Wennersten, Miriam; Bonnett, Joseph; Hill, Adrian


    The Submilimeter Wave Astronomy Satellite (SWAS) was selected for flight by NASA in 1989 as a part of the Small Explorer (SMEX) program. SWAS's primary science objective is to conduct high spectral resolution surveys of galactic molecular clouds. The SWAS Attitude Control System (ACS) is three-axis controlled, zero momentum stabilized, and is capable of performing subarcminute pointing. This paper will discuss the design of the software components which comprise the Attitude Control System So...

  8. Fixed-Star Tracking Attitude Control of Spacecraft Using Single-Gimbal Control Moment Gyros

    Sangwon Kwon; Yuki Tani; Hiroshi Okubo; Takashi Shimomura


    Problem statement: A cluster of small-sized Single-Gimbal Control Moment Gyros (SGCMGs) is proposed as an attitude control actuator for high-speed maneuver of small satellites. There exists a singularity problem what is peculiar to the CMG system. Approach: This study presented a simple singularity avoidance steering law using the Singular Value Decomposition (SVD) algorithm. Results: Capability of the present steering method in singularity avoidance was demonstrated with numerical simulation...

  9. Pulsed Electrogasdynamic Thruster for Attitude Control and Orbit Maneuver Project

    National Aeronautics and Space Administration — A new pulsed electric thruster, named "pulsed electrogasdynamic thruster," for attitude control and orbit maneuver is proposed. In this thruster, propellant gas is...

  10. Pulsed Electrogasdynamic Thruster for Attitude Control and Orbit Maneuver Project

    National Aeronautics and Space Administration — In the Phase I program we successfully demonstrated the feasibility of the Pulsed ElectroGasdynamic (PEG) thruster for attitude control and orbital maneuvering. In...

  11. The Design of the OPAL Attitude Control System

    Jung, Jaewoo; Kuzuya, Naoki; Alvarez, Jaime


    OPAL's attitude is controlled by using two pairs of magnetic coils and a three axis magnetometer. One pair of coils is mounted on the side panel where the picosatellite launch window is located. The other pair is mounted on the bottom panel. The primary requirements of the attitude control system are to decease spin of the satellite with respect to its body axis to minimize disturbances during picosatellite launch, and to spin up the satellite once the picosatellite is launched to meet therma...

  12. Adaptive variable structure control based on backstepping for spacecraft with reaction wheels during attitude maneuver

    SONG Bin; MA Guang-fu; LI Chuan-jiang


    An adaptive variable structure control method based on backstepping is proposed for the attitude maneuver problem of rigid spacecraft with reaction wheel dynamics in the presence of uncertain inertia matrix and external disturbances. The proposed control approach is a combination of the backstepping and the adaptive variable structure control. The cascaded structure of the attitude maneuver control system with reaction wheel dynamics gives the advantage for applying the backstepping method to construct Lyapunov functions. The robust stability to external disturbances and parametric uncertainty is guaranteed by the adaptive variable structure control. To validate the proposed control algorithm, numerical simulations using the proposed approach are performed for the attitude maneuver mission of rigid spacecraft with a configuration consisting of four reaction wheels for actuator and three magnetorquers for momentum unloading. Simulation results verify the effectiveness of the proposed control algorithm.

  13. Attitude stabilization of electrodynamic tethers in elliptic orbits by time-delay feedback control

    Iñarrea, Manuel; Lanchares, Víctor; Pascual, Ana Isabel; Salas, José Pablo


    It is well known that libration motion of electrodynamic tethers operating in inclined orbits is affected by dynamic instability due to the electromagnetic interaction between the tether and the geomagnetic field. We study the application of two feedback control methods in order to stabilize the periodic attitude motions of electrodynamic tethers in elliptic inclined orbits. Both control schemes are based on the time-delayed autosynchronization of the system. Numerical simulations of the controlled libration motion show that both control techniques are able to transform the uncontrolled unstable periodic motions into asymptotically stable ones. Such stabilized periodic attitude motions can be taken as starting points for the operation of the tether. The control domains of both methods have been computed for different values of the system parameters, as functions of the two control parameters shared by both control schemes. The relative effectiveness of the two techniques in the stabilization of the periodic attitude motion has also been studied.

  14. Autonomous spacecraft attitude control using magnetic torquing only

    Musser, Keith L.; Ebert, Ward L.


    Magnetic torquing of spacecraft has been an important mechanism for attitude control since the earliest satellites were launched. Typically a magnetic control system has been used for precession/nutation damping for gravity-gradient stabilized satellites, momentum dumping for systems equipped with reaction wheels, or momentum-axis pointing for spinning and momentum-biased spacecraft. Although within the small satellite community there has always been interest in expensive, light-weight, and low-power attitude control systems, completely magnetic control systems have not been used for autonomous three-axis stabilized spacecraft due to the large computational requirements involved. As increasingly more powerful microprocessors have become available, this has become less of an impediment. These facts have motivated consideration of the all-magnetic attitude control system presented here. The problem of controlling spacecraft attitude using only magnetic torquing is cast into the form of the Linear Quadratic Regulator (LQR), resulting in a linear feedback control law. Since the geomagnetic field along a satellite trajectory is not constant, the system equations are time varying. As a result, the optimal feedback gains are time-varying. Orbit geometry is exploited to treat feedback gains as a function of position rather than time, making feasible the onboard solution of the optimal control problem. In simulations performed to date, the control laws have shown themselves to be fairly robust and a good candidate for an onboard attitude control system.

  15. The development and demonstration of hybrid programmable attitude control electronics

    Smith, L. S.; Kopf, E. H., Jr.


    In the course of extended life attitude control system (ELACS) research sponsored by NASA a hybrid programable attitude control electronics (HYPACE) concept was developed and demonstrated. The wide variety of future planetary missions demanded a new control approach to accommodate the automatic fault tolerance and long the life requirements of such missions. HYPACE provides an adaptable, analog/digital design approach that permits preflight and in-flight accommodation of mission changes, component performance variations, and spacecraft changes, through programing. This enabled broad multimission flexibility of application in a cost effective manner. Previously, flight control computers have not been not flown on planetary missions because of weight and power problems. These problems were resolved in the design of HYPACE. The HYPACE design, which was demonstrated in breadboard form on a single-axis gas-bearing spacecraft simulation, uses a single control channel to perform the attitude control functions sequentially, thus significantly reducing the number of component parts over hard-wired designs.

  16. Precision Integrated Power and Attitude Control System (IPACS) in the Presence of Dynamic Uncertainty

    Kim, D.; MacKunis, W.; Fitz-Coy, N.; Dixon, W. E.


    An adaptive robust integrated power and attitude control system (IPACS) is presented for a variable speed control moment gyroscope (VSCMG)-actuated satellite. The developed IPACS method is capable of achieving precision attitude control while simultaneously achieving asymptotic power tracking for a rigid-body satellite in the presence of uncertain friction in the VSCMG gimbals and wheels. In addition, the developed controller compensates for the effects of uncertain, time-varying satellite inertia properties. Some challenges encountered in the control design are that the control input is premultiplied by a nonsquare, time-varying, nonlinear, uncertain matrix and is embedded in a discontinuous nonlinear. Globally uniformly ultimately bounded attitude tracking and asymptotic power tracking results are proven via Lyapunov stability analyses, and simulation results are provided to demonstrate the performance of the controller.

  17. Propellantless Attitude Control of Solar Sail Technology Utilizing Reflective Control Devices

    Munday, Jeremy


    Solar sails offer an opportunity for a CubeSatscale, propellant-free spacecraft technology that enables long-term and long-distance missions not possible with traditional methods. Solar sails operate using the transfer of linear momentum from photons of sunlight reflected from the surface of the sail. To propel the spacecraft, no mechanically moving parts, thrusters, or propellant are needed. However, attitude control, or orientation, is still performed using traditional methods involving reaction wheels and propellant ejection, which severely limit mission lifetime. For example, the current state of the art solutions employed by upcoming missions couple solar sails with a state of the art propellant ejection gas system. Here, the use of the gas thruster has limited the lifetime of the mission. To solve the limited mission lifetime problem, the Propellantless Attitude Control of Solar Sail Technology Utilizing Reflective Control Devices project team is working on propellantless attitude control using thin layers of material, an optical film, electrically switchable from transparent to reflective. The technology is based on a polymer-dispersed liquid crystal (PDLC), which allows this switch upon application of a voltage. This technology removes the need for propellant, which reduces weight and cost while improving performance and lifetime.

  18. Rationale, design and methods for a staggered-entry, waitlist controlled clinical trial of the impact of a community-based, family-centred, multidisciplinary program focussed on activity, food and attitude habits (Curtin University’s Activity, Food and Attitudes Program—CAFAP among overweight adolescents

    Straker Leon M


    Full Text Available Abstract Background Current estimates place just under one quarter of adolescents in Australia as overweight or obese. Adolescence has been identified as a critical period for the development of obesity, yet despite this recognition, there is limited systematic research into or evaluation of interventions for overweight adolescents. Reviews have concluded that there is a substantive evidence gap for effective intervention, but physical activity, lifestyle change and family involvement have been identified as promising foci for treatment. Methods This paper reports on the development of a staggered-entry, waitlist controlled clinical trial to assess the impact of a multidisciplinary intervention aiming to change the poor health trajectory of overweight adolescents and help them avoid morbid obesity in adulthood—Curtin University’s Activity, Food and Attitudes Program (CAFAP. 96 adolescents, aged 11–16 years, and parents, will attend twice weekly during an 8 week intensive multidisciplinary program with maintenance follow-up focussed on improving activity, food and attitude habits. Follow-up assessments will be conducted immediately after completing the intensive program, and at 3, 6 and 12 months post intensive program. Main outcomes will be objectively-measured physical activity, sedentary behaviour and activity behaviours; food intake (measured by 3 day diary and food behaviours; body composition, fitness and physical function; mental and social well-being (quality of life, mood and attitudes, and family functioning. Discussion This trial will provide important information to understand whether a community based multidisciplinary intervention can have short and medium term effects on activity and food habits, attitudes, and physical and mental health status of overweight adolescents. Trial registration Australian New Zealand Clinical Trials Registry ACTRN12611001187932.

  19. A Precise Attitude Determination and Control Strategy for Small Astrometry Satellite “Nano-JASMINE”

    Hosonuma, Takayuki


    Intelligent Space Systems Laboratory (ISSL) Universityof Tokyo has developed a 35 kgastrometry satellite,“Nano-JASMINE”(Nano JAPAN Astrometry Satellite Mission for INfraredExploration)in cooperation with National Astronomical Observatoryof Japan (NAOJ). In the Nano-JASMINE mission, the satellite attitude spin rate should be controlled to an accuracy of 4 × 10−7 rad/s duringthe observation. To accomplish such severe attitude stabilization, we have developed two novelmethods. The first method i...

  20. A comparison of dysfunctional attitudes in substance abusers and control group and its psychological outcome


    Objectives: Addiction researchers find that addictive processes are influenced by patient beliefs and attitudes. This research was carried out to assess the role of dysfunctional attitudes, outcomes of psychology in substance abuse behaviors of subject were referred to addiction treatment center in the city of Bandar Abbas, and to compare the with the control group. Methods: This is a retrospective study in which 100 subject substance abusers were compared with 100 subject s of c...

  1. Robustness and Actuator Bandwidth of MRP-Based Sliding Mode Control for Spacecraft Attitude Control Problems

    Keum, Jung-Hoon; Ra, Sung-Woong


    Nonlinear sliding surface design in variable structure systems for spacecraft attitude control problems is studied. A robustness analysis is performed for regular form of system, and calculation of actuator bandwidth is presented by reviewing sliding surface dynamics. To achieve non-singular attitude description and minimal parameterization, spacecraft attitude control problems are considered based on modified Rodrigues parameters (MRP). It is shown that the derived controller ensures the sliding motion in pre-determined region irrespective of unmodeled effects and disturbances.

  2. Fuzzy robust attitude controller design for hydrofoil catamaran

    Ren Junsheng; Yang Yansheng


    A robust attitude controller for hydrofoil catamaran throughout its operating envelope is proposed, based on Tagaki-Sugeno (T-S) fuzzy model. Firstly, T-S fuzzy model and robust attitude control strategy for hydrofoil catamaran is presented by use of linear matrix inequality (LMI) techniques. Secondly, a nonlinear mathematical model of hydrofoil catamaran is established, acting as the platform for further researches. The specialty in interpolation of T-S fuzzy model guarantees that feedback gain can be obtained smoothly, while boat's speed is shifting over the operating envelope. The external disturbances are also attenuated to achieve H∞ control performance, meanwhile. Finally, based on such a boat,HC200B-A1, simulation researches demonstrate the design procedures and the effectiveness of fuzzy robust attitude controller.

  3. Global Observer-based Attitude Controller Using Direct Inertial Measurements

    Saâdi Bouhired


    Full Text Available In this work, we address the problem of global attitude control using direct inertial measurements. When using direct inertial measurement to observe the rigid body attitude, it is shown that due to a geometrical obstruction, it is impossible to achieve global asymptotic stability. In fact, for a particular initial condition the tracking error quaternion converges to a pure imaginary quaternion formed by an eigenvector of a characteristic matrix related to the inertial constant and known vectors. Our proposition consists of adding a dynamic signal to force the rigid body to escape from such a situation. The proposed observer-based controller is synthesized based on a single Lyapunov function and a stability analysis shows that the controller stabilizes globally and asymptotically the rigid body attitude at the desired one. The effectiveness of the proposed observer-based controller is confirmed by simulation results.

  4. Sliding Mode Attitude Control for Magnetic Actuated Satellite

    Wisniewski, Rafal


    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...

  5. NASA Workshop on Hybrid (Mixed-Actuator) Spacecraft Attitude Control

    Dennehy, Cornelius J.; Kunz, Nans


    At the request of the Science Mission Directorate Chief Engineer, the NASA Technical Fellow for Guidance, Navigation & Control assembled and facilitated a workshop on Spacecraft Hybrid Attitude Control. This multi-Center, academic, and industry workshop, sponsored by the NASA Engineering and Safety Center (NESC), was held in April 2013 to unite nationwide experts to present and discuss the various innovative solutions, techniques, and lessons learned regarding the development and implementation of the various hybrid attitude control system solutions investigated or implemented. This report attempts to document these key lessons learned with the 16 findings and 9 NESC recommendations.

  6. Applications software supporting the Spartan Attitude Control System

    Stone, R. W.


    The native software supporting a single mission for the Spartan Attitude Control System can require up to 40,000 lines of code. Most of this must be rewritten for each mission. Control system engineers use an array of Applications Software Packages residing in ground computers to write each mission's flight software. These Applications Packages are written in the 'C' programming language and run under the UNIX Operating System. This paper discusses each of the Attitude Control Applications Software Packages, and describes the purpose and design of each.

  7. Measuring Public Attitudes Toward Natural Resource Issues: Coyote Control

    Arthur, Louise M.


    A method to obtain quantitative information on public attitudes toward natural resource issues is described.1 The quantification depends on the structure of the entire survey instrument as well as on individual items in the survey. Items are designed and organized to facilitate (1) the summarizing of measured attitudes toward very complex resource issues, and (2) meaningful comparisons of the summary attitudinal measures to other quantified impacts --economic and physical --for policy analysi...

  8. Precision Attitude Control for the BETTII Balloon-Borne Interferometer

    Benford, Dominic J.; Fixsen, Dale J.; Rinehart. Stephen


    The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer to fly on a high altitude balloon. Operating at wavelengths of 30-90 microns, BETTII will obtain spatial and spectral information on science targets at angular resolutions down to less than half an arcsecond, a capability unmatched by other far-infrared facilities. This requires attitude control at a level ofless than a tenth of an arcsecond, a great challenge for a lightweight balloon-borne system. We have designed a precision attitude determination system to provide gondola attitude knowledge at a level of 2 milliarcseconds at rates up to 100Hz, with accurate absolute attitude determination at the half arcsecond level at rates of up to 10Hz. A mUlti-stage control system involving rigid body motion and tip-tilt-piston correction provides precision pointing stability to the level required for the far-infrared instrument to perform its spatial/spectral interferometry in an open-loop control. We present key aspects of the design of the attitude determination and control and its development status.

  9. Weight Control Beliefs, Body Shape Attitudes, and Physical Activity among Adolescents

    Martin, Scott B.; Rhea, Deborah J.; Greenleaf, Christy A.; Judd, Doryce E.; Chambliss, Heather O.


    Background: Relatively little is known about how perceived weight controllability influences important psychological health factors among adolescents. Thus, the purpose of this study is to explore adolescents' weight controllability beliefs and how those beliefs influence weight-related attitudes and behaviors. Methods: Adolescents (N = 369, mean…

  10. Direct Lyapunov-based control law design for spacecraft attitude maneuvers

    HU Likun; ANG Qingchao


    A direct Lyapunov-based control law is presented to perform on-orbit stability for spacecraft attitude maneuvers. Spacecraft attitude kinematic equations and dynamic equations are coupled, nonlinear, multi-input multi-output(MIMO), which baffles controller design. Orbit angular rates are taken into account in kinematic equations and influence of gravity gradient moments and disturbance moments on the spacecraft attitude in dynamic equations is considered to approach the practical environment, which enhance the problem complexity to some extent. Based on attitude tracking errors and angular rates, a Lyapunov function is constructed, through which the stabilizing feedback control law is deduced via Lie derivation of the Lyapunov function. The proposed method can deal with the case that the spacecraft is subjected to mass property variations or centroidal inertia matrix variations due to fuel assumption or flexibility, and disturbance moments, which shows the proposed controller is robust for spacecraft attitude maneuvers. The unlimited controller and the limited controller are taken into account respectively in simulations. Simulation results are demonstrated to validate effectiveness and feasibility of the proposed method.

  11. Crew exploration vehicle (CEV) attitude control using a neural-immunology/memory network

    Weng, Liguo; Xia, Min; Wang, Wei; Liu, Qingshan


    This paper addresses the problem of the crew exploration vehicle (CEV) attitude control. CEVs are NASA's next-generation human spaceflight vehicles, and they use reaction control system (RCS) jet engines for attitude adjustment, which calls for control algorithms for firing the small propulsion engines mounted on vehicles. In this work, the resultant CEV dynamics combines both actuation and attitude dynamics. Therefore, it is highly nonlinear and even coupled with significant uncertainties. To cope with this situation, a neural-immunology/memory network is proposed. It is inspired by the human memory and immune systems. The control network does not rely on precise system dynamics information. Furthermore, the overall control scheme has a simple structure and demands much less computation as compared with most existing methods, making it attractive for real-time implementation. The effectiveness of this approach is also verified via simulation.

  12. Sliding Mode Attitude Control for Magnetic Actuated Satellite

    Wisniewski, Rafal


    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 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...

  13. Finite-Time Reentry Attitude Control Using Time-Varying Sliding Mode and Disturbance Observer

    Xuzhong Wu


    Full Text Available This paper presents the finite-time attitude control problem for reentry vehicle with redundant actuators in consideration of planet uncertainties and external disturbances. Firstly, feedback linearization technique is used to cancel the nonlinearities of equations of motion to construct a basic mode for attitude controller. Secondly, two kinds of time-varying sliding mode control methods with disturbance observer are integrated with the basic mode in order to enhance the control performance and system robustness. One method is designed based on boundary layer technique and the other is a novel second-order sliding model control method. The finite-time stability analyses of both resultant closed-loop systems are carried out. Furthermore, after attitude controller produces the torque commands, an optimization control allocation approach is introduced to allocate them into aerodynamic surface deflections and on-off reaction control system thrusts. Finally, the numerical simulation results demonstrate that both of the time-varying sliding mode control methods are robust to uncertainties and disturbances without chattering phenomenon. Moreover, the proposed second-order sliding mode control method possesses better control accuracy.

  14. Attitude control of a space structure using a 3-R rigid manipulator

    Mukherjee, Ranjan; Zurowski, Mary

    The attitude control of space structures is an important problem. There has been considerable research in this area that has focussed on the use of momentum exchange devices. In this paper, we propose to control the attitude of space structures using a serial three-link PUMA-type manipulator that can be mounted on the space structure. This unconventional method of attitude control exploits the nonholonomic nature of the constraints that arise due to the conservation of angular momentum. We adopt a surface integral approach for the motion planning of the manipulator that will reorient the space structure in any desired way. The salient features of our algorithm are: (a) it is possible to mathematically prove the controllability of the system; (b) The motion of the manipulator can be planned amidst additional constraints like joint limits of the manipulator; and (c) the algorithm can be easily extended for application to flexible space structures.

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

    Zhang, Yang; Gan, Qingbo; Kang, Jingshu


    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.

  16. Attitude Control of a Six-Legged Robot in Consideration of Actuator Dynamics by Optimal Servo Control System

    Uchida, H.; Nonami, K.


    In the present study, we examined the attitude control method considering the delay of the hydraulic actuator whereby the mine detection six-legged robot can realize stable walking on irregular terrain without to make an orbit of the foot for irregular terrain. The following results were obtained. (1) As an attitude control method considering the delay of the actuator of the thigh links, we derive a mathematical model in which the inputs are the driving torque of the thigh links in the suppor...

  17. Active Vibration Control of Satellite Flexible Structures during Attitude Maneuvers

    Saeed Hemmati; Morteza Shahravi; Keramat Malekzadeh


    The purpose of this study is controlling active vibration of satellite flexible structures during attitude maneuvers. A smart structure is a structure which is able to sense and control active reaction to any external factors and stimulation. As it comes from the definition of smart structures, development of this knowledge depends on the materials science development, theories and strategies for control. In materials science, smart materials are developed in such a way that they are able to ...

  18. Magnetic Attitude Control System for Low-Earth Orbit Satellites

    A small spacecraft (SC) under consideration is intended for performing a scientific mission on the low-Earth orbit for a long time (a year or more). A control system of the SC provides the construction of regime of three-axis orientation of the SC in the orbital coordinate system and the stabilization of that regime, and must be autonomous, low-weight and low-cost. The magnetic control system that consists of the information subsystem based solely on three-axis magnetometer measuring and the magnetic actuators satisfies in the best way requirements mentioned above. Such system can estimate both orbital motion parameters and attitude ones of the SC. But the absence of the additional instruments and damping devices complicates the estimation since the range of initial conditions uncertainly is wide and the problem of estimating becomes essentially nonlinear. To get over these difficulties a recursive state estimation algorithm with enhanced convergence is proposed. The magnetic control moment is synthesized byte vector function Lyapunov method

  19. Cassini at Saturn Proximal Orbits - Attitude Control Challenges

    Burk, Thomas A.


    The Cassini mission at Saturn will come to an end in the spring and summer of 2017 with a series of 22 orbits that will dip inside the rings of Saturn. These are called proximal orbits and will conclude with spacecraft disposal into the atmosphere of the ringed world on September 15, 2017. These unique orbits that cross the ring plane only a few thousand kilometers above the cloud tops of the planet present new attitude control challenges for the Cassini operations team. Crossing the ring plane so close to the inner edge of the rings means that the Cassini orientation during the crossing will be tailored to protect the sensitive electronics bus of the spacecraft. This orientation will put the sun sensors at some extra risk so this paper discusses how the team prepares for dust hazards. Periapsis is so close to the planet that spacecraft controllability with RCS thrusters needs to be evaluated because of the predicted atmospheric torque near closest approach to Saturn. Radiation during the ring plane crossings will likely trigger single event transients in some attitude control sensors. This paper discusses how the attitude control team deals with radiation hazards. The angular size and unique geometry of the rings and Saturn near periapsis means that star identification will be interrupted and this paper discusses how the safe mode attitude is selected to best deal with these large bright bodies during the proximal orbits.

  20. Low cost attitude control system reaction wheel development

    Bialke, William


    In order to satisfy a growing demand for low cost attitude control systems for small spacecraft, development of a low power and low cost Reaction Wheel Assembly was initiated. The details of the versatile design resulting from this effort are addressed. Tradeoff analyses for each of the major components are included, as well as test data from an engineering prototype of the hardware.

  1. Feedforward attitude control for a TDRS with mobile antennas


    In this paper, feedforward attitude control law for a Tracking and Data Relay Satellite (TDRS) with mobile antennas is proposed. To track or point the target spacecraft with median/law orbit, the large mobile antennas have to move in a wide range. The movement of such mobile antennas disturbs the satellite attitude consequently. Conventionally, the main body of the satellite and the mobile antennas are controlled independently.The proposed controller first estimates the angular momentum which the mobile antennas will produce based on the momentum conservation equation. Next, it computes the desired velocity of reaction wheels to compensate the disturbance due to the antenna motion. It then adds the error of the wheels' velocity between a desired one and a current value as a feedforward signal to the control system. The proposed controller is demonstrated using a mathematical simulation, of which these results coincide well with analytical results.

  2. Robust attitude control for rapid multi-target tracking in spacecraft formation flying


    A robust attitude tracking control scheme for spacecraft formation flying is presented.The leader spacecraft with a.rapid mobile antenna and a camera is modeled.While the camera is tracking the ground target,the antenna is tracking the follower spacecraft.By an angular velocity constraint and an angular constraint,two methods are proposed to compute the reference attitude profiles of the camera and antenna,respectively.To simplify the control design problem,this paper first derives the desired inverse system (DIS),which can convert the attitude tracking problem of 3D space into the regulator problem.Based on DIS and sliding mode control (SMC),a robust attitude tracking controller is developed in the presence of mass parameter uncertainties and external disturbance.By Lyapunov stability theory,the closed loop system stability can be achieved.The numerical simulations show that the proposed robust control scheme exhibits significant advantages for the multi-target attitude tracking of a two-spacecraft formation.

  3. Adaptive attitude controller for a satellite based on neural network in the presence of unknown external disturbances and actuator faults

    Fazlyab, Ali Reza; Fani Saberi, Farhad; Kabganian, Mansour


    In this paper, an adaptive attitude control algorithm is developed based on neural network for a satellite. The proposed attitude control is based on nonlinear modified Rodrigues parameters feedback control in the presence of unknown terms like external disturbances and actuator faults. In order to eliminate the effect of the uncertainties, a multilayer neural network with a new learning rule will be designed appropriately. In this method, asymptotic stability of the proposed algorithm has been proven in the presence of unknown terms based on Lyapunov stability theorem. Finally, the performance of the designed attitude controller is investigated by simulations.

  4. Attitude Control on the Pico Satellite Solar Cell Testbed-2

    Janson, Siegfried; Hardy, Brian; Chin, Andrew; Rumsey, Daniel; Ehrlich, Daniel; Hinkley, David


    The Pico Satellite Solar Cell Testbed-2 (PSSCT-2) was a 5” x 5” x 10”, 3.7-kg mass nanosatellite ejected from the Space Shuttle Atlantis during the final STS-135 mission on July 20, 2011. PSSCT-2 had a three-axis attitude control system to enable firing of solid rockets for orbit raising, pointing of solar cells normal to the sun for on-orbit performance monitoring, and pointing of a GPS antenna in the anti-flight direction for radio-occultation measurements. Attitude determination and contro...

  5. Student Attitudes to Traditional and Online Methods of Delivery

    Wong, Lily; Fong, Michelle


    Rapid developments in education technology have provided educators and students new options in a constantly changing, competitive teaching and learning environment. As the number of online teaching resources continue to increase, research into student attitudes toward traditional and online methods of delivery is important in order to determine…

  6. The SAS-3 attitude control system

    Mobley, F. F.; Konigsberg, R.; Fountain, G. H.


    SAS-3 uses a reaction wheel to provide torque to control the spin rate. If the wheel speed becomes too great or too small, it must be restored to its nominal rate by momentum dumping which is done by magnetic torquing against the earth's magnetic field by the satellite's magnetic coils. A small rate-integrating gyro is used to sense the spin rate so that closed loop control of the spin rate can be achieved. These various systems are described in detail including the reaction wheel system, the gyro system, along with control modes (spin rate control and the star lock mode).

  7. Design and Stability of an On-Orbit Attitude Control System Using Reaction Control Thrusters

    Hall, Robert A.; Hough, Steven; Orphee, Carolina; Clements, Keith


    NASA is providing preliminary design and requirements for the Space Launch System Exploration Upper Stage (EUS). The EUS will provide upper stage capability for vehicle ascent as well as on-orbit control capability. Requirements include performance of on-orbit burn to provide Orion vehicle with escape velocity. On-orbit attitude control is accommodated by a on-off Reaction Control System (RCS). Paper provides overview of approaches for design and stability of an attitude control system using a RCS.

  8. Observing Mode Attitude Controller for the Lunar Reconnaissance Orbiter

    Calhoun, Philip C.; Garrick, Joseph C.


    The Lunar Reconnaissance Orbiter (LRO) mission is the first of a series of lunar robotic spacecraft scheduled for launch in Fall 2008. LRO will spend at least one year in a low altitude polar orbit around the Moon, collecting lunar environment science and mapping data to enable future human exploration. The LRO employs a 3-axis stabilized attitude control system (ACS) whose primary control mode, the "Observing mode", provides Lunar Nadir, off-Nadir, and Inertial fine pointing for the science data collection and instrument calibration. The controller combines the capability of fine pointing with that of on-demand large angle full-sky attitude reorientation into a single ACS mode, providing simplicity of spacecraft operation as well as maximum flexibility for science data collection. A conventional suite of ACS components is employed in this mode to meet the pointing and control objectives. This paper describes the design and analysis of the primary LRO fine pointing and attitude re-orientation controller function, known as the "Observing mode" of the ACS subsystem. The control design utilizes quaternion feedback, augmented with a unique algorithm that ensures accurate Nadir tracking during large angle yaw maneuvers in the presence of high system momentum and/or maneuver rates. Results of system stability analysis and Monte Carlo simulations demonstrate that the observing mode controller can meet fine pointing and maneuver performance requirements.

  9. Voyager Saturn encounter attitude and articulation control experience

    Carlisle, G.; Hill, M.


    The Voyager attitude and articulation control system is designed for a three-axis stabilized spacecraft; it uses a biasable sun sensor and a Canopus Star Tracker (CST) for celestial control, as well as a dry inertial reference unit, comprised of three dual-axis dry gryos, for inertial control. A series of complex maneuvers was required during the first of two Voyager spacecraft encounters with Saturn (November 13, 1980); these maneuvers involved rotating the spacecraft simultaneously about two or three axes while maintaining accurate pointing of the scan platform. Titan and Saturn earth occulation experiments and a ring scattering experiment are described. Target motion compensation and the effects of celestial sensor interference are also considered. Failure of the CST, which required an extensive reevaluation of the star reference and attitude control mode strategy, is discussed. Results analyzed thus far show that the system performed with high accuracy, gathering data deeper into Saturn's atmosphere than on any previous planetary encounter.

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

    Ho-Nien Shou


    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.

  11. Preliminary Attitude Control Studies for the ASTER Mission

    This work discusses an attitude control study for the ASTER mission, the first Brazilian mission to the deep space. The study is part of a larger scenario that is the development of optimal trajectories to navigate in the 2001 SN263 asteroid system, together with the generation of orbit and attitude controllers for autonomous operation. The spacecraft attitude is defined from the orientation of the body reference system to the Local Vertical Local Horizontal (LVLH) of a circular orbit around the Alpha asteroid. The rotational equations of motion involve the dynamic equations, where the three angular speeds are generated from a set of three reaction wheels and the gravitational torque. The rotational kinematics is represented in the Euler angles format. The controller is developed via the linear quadratic regulator approach with output feedback. It involves the generation of a stability augmentation (SAS) loop and a tracking outer loop, with a compensator of desired structure. It was chosen the feedback of the p, q and r angular speeds in the SAS, one for each reaction wheel. In the outer loop, it was chosen a proportional integral compensator. The parameters are tuned using a numerical minimization that represents a linear quadratic cost, with weightings in the tracking error and controls. Simulations are performed with the nonlinear model. For small angle manoeuvres, the linear results with reaction wheels or thrusters are reasonable, but, for larger manoeuvres, nonlinear control techniques shall be applied, for example, the sliding mode control

  12. Bounded attitude control of rigid bodies: Real-time experimentation to a quadrotor mini-helicopter

    Guerrero-Castellanos, Fermi; Marchand, Nicolas; Hably, Ahmad; Lesecq, Suzanne; Delamare, Jérôme


    A quaternion-based feedback is developed for the attitude stabilization of rigid bodies. The control design takes into account a priori input bounds and is based on nested saturation approach. It results in a very simple controller suitable for an embedded use with low computational resources available. The proposed method is generic not restricted to symmetric rigid bodies and does not require the knowledge of the inertia matrix of the body. The control law can be tuned to force closed-loop ...


    Majagi Suneel Ishwar; Hiremath S.V.; Torgal S.S.


    Literature review suggests the importance and the need of students’ feedback which may be used to effectively reform evaluation methods in medical sciences. The present study has been conducted to obtain student’s attitude (perception of) towards different evaluation methods of pharmacology. The sample consisted of second phase M.B.B.S (n=108) students. Students answered 115 items/questions designed according to Likert’s five point (in agreement with items) scale. These items/questions assess...

  14. Attitude-Control Algorithm for Minimizing Maneuver Execution Errors

    Acikmese, Behcet


    A G-RAC attitude-control algorithm is used to minimize maneuver execution error in a spacecraft with a flexible appendage when said spacecraft must induce translational momentum by firing (in open loop) large thrusters along a desired direction for a given period of time. The controller is dynamic with two integrators and requires measurement of only the angular position and velocity of the spacecraft. The global stability of the closed-loop system is guaranteed without having access to the states describing the dynamics of the appendage and with severe saturation in the available torque. Spacecraft apply open-loop thruster firings to induce a desired translational momentum with an extended appendage. This control algorithm will assist this maneuver by stabilizing the attitude dynamics around a desired orientation, and consequently minimize the maneuver execution errors.

  15. Satellite Attitude Control Using Only Electromagnetic Actuation

    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 of the ...

  16. Fully magnetic sliding mode control for acquiring three-axis attitude

    Ovchinnikov, M. Yu.; Roldugin, D. S.; Penkov, V. I.; Tkachev, S. S.; Mashtakov, Y. V.


    Satellite equipped with purely magnetic attitude control system is considered. Sliding mode control is used to achieve three-axis satellite attitude. Underactuation problem is solved for transient motion. Necessary attitude is acquired by proper sliding manifold construction. Satellite motion on the manifold is executed with magnetic control system. One manifold construction approach is proposed and discussed. Numerical examples are provided.

  17. Locus of Control and Attitude toward Eating in a Female College Population.

    Groth-Marnat, Gary; Scumaker, Jack F.


    Investigated relationship between locus of control and attitude to food intake in 101 female college students. Results indicated that locus of control was unable to predict attitudes toward eating and fear of becoming overweight. Thesis that locus of control would be related to attitude toward food intake was not supported. (Author/NB)

  18. Satellite Attitude Control Using Only Electromagnetic Actuation

    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 of the work was on the class of periodic systems reflecting orbital motion of the satellite. In addition to a theoretical treatment, the thesis contains a large portion of application considerations. The con...

  19. Attitude Control System Design for Fast Rest-to-Rest Attitude Maneuver

    Sakai, S.-I.; Bando, N.; Hashimoto, T.; Murata, Y.; Mochizuki, N.; Nakamura, T.; Kamiya, T.; Ogura, N.; Maeda, K.


    The VSOP-2 project is a new space VLBI (very long baseline interferometer) radio astronomy mission, proposed to inherit the fruitful success of the VSOP mission with the HALCA satellite. One of the most important advances of VSOP-2 is the use of higher observation frequency, which requires fast alternating observation of a target and calibrator in order to remove the phase changes caused by the atmosphere. Typically, both sources must be observed within 60 sec, and this switching must be carried out over many hours. ``ASTRO-G" is a satellite planned for this VSOP-2 project, and one of technical challenges is to achieve such fast rest-to-rest maneuvers, and the proper hardware must be selected to account for this fast attitude maneuver. The controlled momentum gyro (CMG) is an actuator that provides high torque with small power consumption, and the fiber optical gyro is a sensor able to measure the high angular velocity with excellent accuracy. This paper first describes these components for attitude control. Another challenge of the ASTRO-G's attitude control system is to design the switching for the flexible mode of the satellite structure, containing a large deployable reflector and a large solar panel. These produce resonances with fast switching and these must be attenuated. To achieve high agility in a flexible satellite, the controller design is crucial. One design feature is a novel robust input shaper named ``nil mode exciting profiler". Another feature is the feedback controller design. The paper describes these features and other potential problems with fast switching..

  20. Satellite Attitude Control Utilizing the Earth's Magnetic Field

    White, John S.; Shigemoto, Fred H.; Bourquin, Kent


    A study was conducted to determine the feasibility of a satellite attitude fine-control system using the interaction of the earth's magnetic field with current-carrying coils to produce torque. The approximate intensity of the earth's magnetic field was determined as a function of the satellite coordinates. Components of the magnetic field were found to vary essentially sinusoidally at approximately twice orbital frequency. Amplitude and distortion of the sinusoidal components were a function of satellite orbit. Two systems for two-axis attitude control evolved from this study, one using three coils and the other using two coils. The torques developed by the two systems differ only when the component of magnetic field along the tracking line is zero. For this case the two-coil system develops no torque whereas the three-coil system develops some effective torque which allows partial control. The equations which describe the three-coil system are complex in comparison to those of the two-coil system and require the measurement of all three components of the magnetic field as compared with only one for the two-coil case. Intermittent three-axis torquing can also be achieved. This torquing can be used for coarse attitude control, or for dumping the stored momentum of inertia reaction wheels. Such a system has the advantage of requiring no fuel aboard the satellite. For any of these magnetic torquing schemes the power required to produce the magnetic moment and the weight of the coil seem reasonable.

  1. Geometric Tracking Control of the Attitude Dynamics of a Rigid Body on SO(3)

    Lee, Taeyoung


    This paper provides new results for a tracking control of the attitude dynamics of a rigid body. Both of the attitude dynamics and the proposed control system are globally expressed on the special orthogonal group, to avoid complexities and ambiguities associated with other attitude representations such as Euler angles or quaternions. By selecting an attitude error function carefully, we show that the proposed control system guarantees a desirable tracking performance uniformly for nontrivial...

  2. Fixed-Star Tracking Attitude Control of Spacecraft Using Single-Gimbal Control Moment Gyros

    Sangwon Kwon


    Full Text Available Problem statement: A cluster of small-sized Single-Gimbal Control Moment Gyros (SGCMGs is proposed as an attitude control actuator for high-speed maneuver of small satellites. There exists a singularity problem what is peculiar to the CMG system. Approach: This study presented a simple singularity avoidance steering law using the Singular Value Decomposition (SVD algorithm. Results: Capability of the present steering method in singularity avoidance was demonstrated with numerical simulations for fixed-star tracking control of a small satellite using four SGCMGs. Conclusion: The proposed steering law utilizes the singular value decomposition to obtain singular vectors and generates the command gimbal rate that keeps the command torque in the direction orthogonal to the singular direction with a maximum gain.

  3. Attitude and Translation Control of a Solar Sail Vehicle

    Singh, Gurkirpal


    A report discusses the ability to control the attitude and translation degrees-of-freedom of a solar sail vehicle by changing its center of gravity. A movement of the spacecraft s center of mass causes solar-pressure force to apply a torque to the vehicle. At the compact core of the solar-sail vehicle lies the spacecraft bus which is a large fraction of the total vehicle mass. In this concept, the bus is attached to the spacecraft by two single degree-of-freedom linear tracks. This allows relative movement of the bus in the sail plane. At the null position, the resulting solar pressure applies no torque to the vehicle. But any deviation of the bus from the null creates an offset between the spacecraft center of mass and center of solar radiation pressure, resulting in a solar-pressure torque on the vehicle which changes the vehicle attitude. Two of the three vehicle degrees of freedom can be actively controlled in this manner. The third, the roll about the sunline, requires a low-authority vane/propulsive subsystem. Translation control of the vehicle is achieved by directing the solar-pressure-induced force in the proper inertial direction. This requires attitude control. Attitude and translation degrees-of-freedom are therefore coupled. A guidance law is proposed, which allows the vehicle to stationkeep at an appropriate point on the inertially-rotating Sun-Earth line. Power requirements for moving the bus are minimal. Extensive software simulations have been performed to demonstrate the feasibility of this concept.

  4. Stepping through versatile attitude control system design for stratospheric platforms

    Boscaleri, A.; Baldi, M; F. CALONACI; Rissone, P.; Rotini, F.


    In addition to stepping through the typical hardware parts of an Attitude Control System borne for stratospheric platform, the paper describes some fast position sensors. The use of two axis magnetometers at high latitude, even though with a lower accuracy, is analyzed. A high-accuracy motorized sun tracker based on a Position Sensitive Detector photodiode capable of driving the gondola in pointing or scanning mode in any given arbitrary anti-sun direction is also presented. Lastly, as an imp...

  5. Entry Attitude Controller for the Mars Science Laboratory

    Brugarolas, Paul B.; SanMartin, A. Miguel; Wong, Edward C.


    This paper describes the preliminary concept for the RCS 3-axis attitude controller for the exo-atmospheric and guided entry phases of the Mars Science Laboratory Entry, Descend and Landing. The entry controller is formulated as three independent channels in the control frame, which is nominally aligned with the stability frame. Each channel has a feedfoward and a feedback. The feedforward path enables fast response to large bank commands. The feedback path stabilizes the vehicle angle of attack and sideslip around its trim position, and tracks bank commands. The feedback path has a PD/D structure with deadbands that minimizes fuel usage. The performance of this design is demonstrated via simulation.

  6. Colloid Thruster for Attitude Control Systems (ACS) and Tip-off Control Applications Project

    National Aeronautics and Space Administration — We propose to develop and test key technologies needed for an integrated, high thrust colloid thruster system with no moving parts, for spacecraft attitude control...

  7. A comparison of dysfunctional attitudes in substance abusers and control group and its psychological outcome


    This research was carried out to assess the role of dysfunctional attitudes, outcomes of psychology in substance abuse behaviors of subject were referred to addiction treatment center in the city of Bandar Abbas, and to compare the with the control group. Methods: This is a retrospective study in which 100 subject substance abusers were compared with 100 subject s of control group who were selected using convenience sampling and were also demographically matched. Data were gathered using a demographic questionnaire, clinical interview, dysfunctional attitudes scale (DAS, Depression Anxiety Stress Scale (DASS. The data were analyzed via descriptive statistic method, T- Test and chi-square and variance analysis. Findings: Findings indicated that in comparison with control group, subject of substance abusers had experienced more stress, anxiety, depression, had shown a cognitively more percent of them dysfunctional attitudes in comparison with control group. Results: The results suggested that the dysfunctional attitudes could be as a Vulnerability Factor that increase abuse of substance consequently use of cognitive therapy could be helpful and effective in prevention and treatment of the addicts.


    刘延柱; 陈立群


    This paper deals with the chaotic attitude motion of a magnetic rigid spacecraft with internal damping in an elliptic orbit. The dynamical model of the spacecraft is established. The Melnikov analysis is carried out to prove the existence of a complicated nonwandering Cantor set. The dynamical behaviors are numerically investigated by means of time history, Poincare map, Lyapunov exponents and power spectrum. Numerical simulations demonstrate the chaotic motion of the system.The input-output feedback linearization method and its modified version are applied, respectively, to control the chaotic attitude motions to the given fixed point or periodic motion.

  9. Local controllability and stabilization of spacecraft attitude by two single-gimbal control moment gyros

    Gui Haichao; Jin Lei; Xu Shijie


    The attitude control problem of a spacecraft underactuated by two single-gimbal control moment gyros (SGCMGs) is investigated. Small-time local controllability (STLC) of the attitude dynamics of the spacecraft-SGCMGs system is analyzed via nonlinear controllability theory. The conditions that guarantee STLC of the spacecraft attitude by two non-coaxial SGCMGs are obtained with the momentum of the SGCMGs as inputs, implying that the spacecraft attitude is STLC when the total angular momentum of the whole system is zero. Moreover, our results indi-cate that under the zero-momentum restriction, full attitude stabilization is possible for a spacecraft using two non-coaxial SGCMGs. For the case of two coaxial SGCMGs, the STLC property of the spacecraft cannot be determined. In this case, an improvement to the previous full attitude stabiliz-ing control law, which requires zero-momentum presumption, is proposed to account for the singu-larity of SGCMGs and enhance the steady state performance. Numerical simulation results demonstrate the effectiveness and advantages of the new control law.

  10. Spacecraft attitude maneuver using two single-gimbal control moment gyros

    Kasai, Shinya; Kojima, Hirohisa; Satoh, Mitsunori


    In this paper, arbitrary rest-to-rest attitude maneuver problems for a satellite using two single-gimbal control moment gyros (2SGCMGs) are considered. Although single-gimbal control moment gyros are configured in the same manner as the traditional pyramid-array CMG, only two CMGs are assumed to be available. Attitude maneuver problems are similar to problems involving two reaction wheels (RWs) from the viewpoint of the number of actuators. In other words, the problem treated herein is a kind of underactuated problem. Although 2SGCMGs can generate torques around all axes, they cannot generate torques around each axis independently. Therefore, control methods designed for a satellite using two reaction wheels cannot be applied to three-axis attitude maneuver problems for a satellite using 2SGCMGs. In this paper, for simplicity, maneuvers around the x- and z-axes are first considered, and then a maneuver around the y-axis due to the corning effect resulting from the maneuver around the x- and z-axes is considered. Since maneuvers around each axis are established by the proposed method, arbitrary attitude maneuvers can be achieved using 2SGCMGs. In addition, the maneuvering angles around the z- and x-axes, which are required in order to maneuver around the y-axis, are analytically determined, and the total time required for maneuvering around the y-axis is then analyzed numerically.

  11. Backstepping-Based Inverse Optimal Attitude Control of Quadrotor

    An Honglei


    Full Text Available Input saturation must be taken into account for applying rapid reorientation in the large angle manoeuvre of a quadrotor. In this paper, a backstepping‐based inverse optimal attitude controller (BIOAC is derived which has the property of a maximum convergence rate in the sense of a control Lyapunov function (CLF under input torque limitation. In the controller, a backstepping technique is used for handling the complexity introducing by the unit quaternion representation of the attitude of a quadrotor with four parameters. Moreover, the inverse optimal approach is employed to circumvent the difficulty of solving the Hamilton‐Jacobi‐Bellman (HJB equation. The performance of BIOAC is compared with a PD controller in which the input torque limitation is not considered under the same unit quaternion representation using numerical simulation while the results show that BIOAC gains faster convergence with less control effort. Next, BIOAC is realized on a test bed and the effectiveness of the control law is verified by experimental studies.

  12. Observer Based Sliding Mode Attitude Control: Theoretical and Experimental Results

    U. Jørgensen


    Full Text Available In this paper we present the design of a sliding mode controller for attitude control of spacecraft actuated by three orthogonal reaction wheels. The equilibrium of the closed loop system is proved to be asymptotically stable in the sense of Lyapunov. Due to cases where spacecraft do not have angular velocity measurements, an estimator for the generalized velocity is derived and asymptotic stability is proven for the observer. The approach is tested on an experimental platform with a sphere shaped Autonomous Underwater Vehicle SATellite: AUVSAT, developed at the Norwegian University of Science and Technology.

  13. Multimode attitude and orbit control for the Atmosphere Explorer spacecraft

    Stewart, B.


    The orbit profile for the Atmosphere Explorer requires a velocity adjust capability of 2000 ft/sec/sec and individual maneuvers of up to 24 ft/sec in magnitude. This requirement is met by a monopropellant hydrazine propulsion subsystem which also provides, by virtue of the tank arrangement, a means of adjusting the spacecraft center of mass in orbit, thereby minimizing external disturbance torques. The attitude control subsystem is of the momentum bias type. A large internal flywheel furnishes gyroscopic stiffness and permits rapid changes in operating mode (despun to spinning mode) by controlled interchange of momentum between the flywheel and the spacecraft main body.

  14. UKF-based attitude determination method for gyroless satellite

    张红梅; 邓正隆


    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.

  15. 柚子包装前端姿态调整方式的研究%Research on the Method of Controlling Front-end Attitudes of Grapefruit Packaging

    李延苓; 黄志平; 张国全; 李爱华


    通过对柚子包装原理分析,提出了柚子包装材料的适宜性,研究了柚子前端姿态存在的机理,并得出了不同姿态柚子的处理方法,最后设计了一种用于柚子前端姿态调整的排序设备,且在现场验证了设备原理的可行性。%Through the theory of grapefruit packaging was analyzed , the suitability of packaging materials of the grapefruits was proposed .The mechanism of grapefruit in stance was too studied , and the grapefruit pro-cessing method in different attitude was obtained .At last, a kind of equipment for the grapefruit adjustment in attitude was designed , and the feasibility of the theory was verified on the spot .

  16. Design of Attitude Control System for UAV Based on Feedback Linearization and Adaptive Control

    Wenya Zhou


    Full Text Available Attitude dynamic model of unmanned aerial vehicles (UAVs is multi-input multioutput (MIMO, strong coupling, and nonlinear. Model uncertainties and external gust disturbances should be considered during designing the attitude control system for UAVs. In this paper, feedback linearization and model reference adaptive control (MRAC are integrated to design the attitude control system for a fixed wing UAV. First of all, the complicated attitude dynamic model is decoupled into three single-input single-output (SISO channels by input-output feedback linearization. Secondly, the reference models are determined, respectively, according to the performance indexes of each channel. Subsequently, the adaptive control law is obtained using MRAC theory. In order to demonstrate the performance of attitude control system, the adaptive control law and the proportional-integral-derivative (PID control law are, respectively, used in the coupling nonlinear simulation model. Simulation results indicate that the system performance indexes including maximum overshoot, settling time (2% error range, and rise time obtained by MRAC are better than those by PID. Moreover, MRAC system has stronger robustness with respect to the model uncertainties and gust disturbance.

  17. Cosmic Background Explorer (COBE) transfer orbit attitude control system

    Placanica, Samuel J.; Flatley, Thomas W.


    The Cosmic Background Explorer (COBE) spacecraft will be launched by the Shuttle from Vandenberg AFB into a 300 km altitude, 99 deg inclination, 6 a.m. or 6 p.m. ascending node orbit. After release from the Remote Manipulator System (RMS) arm, an on-board monopropellant hydrazine propulsion system will raise the orbit altitude to 900 km. The spacecraft continuously spins during transfer orbit operations with the spin axis nominally horizontal and in or near the orbit plane. The blowdown propulsion system consists of twelve 5 lb thrusters (3 'spin', 3 'despin', and 6 'axial') with the latter providing initially 30 lb of force parallel to the spin axis for orbit raising. The spin/despin jets provide a constant roll rate during the transfer orbit phase of the mission and the axials control pitch and yaw. The axial thrusters are pulsed on for attitude control during coast periods and are normally on- and off-modulated for control during orbit raising. Attitude sensors employed in the control loops include an array of two-axis digital sun sensors and three planar earth scanners for position measurements, as well as six gyroscopes for rate information. System redundancy is achieved by means of unique three-axes-in-a-plane geometry. This triaxial concept results in a fail-safe operational system with no performance degradation for many different component failure modes.

  18. Effects of Using Case-Study Method in Social Studies on Students' Attitudes Towards Environment

    Hamza Akengin; Gökhan Aydemir


    his study has aimed to inquired whether there was a significant difference between academic achievement and attitudes of 6th grade students who learned “The Resources of Our Country” unit of social studies through case studies and students who learned this unit with teaching based on existing unit. Besides it was aimed to present thoughts and feelings of the students about the case study method aided learning- teaching process. Pretest-posttest control group design was used in this study and...

  19. AttSim, Attitude Simulation with Control Software in the Loop

    Koenigsmann, Hans; Gurevich, Gwynne


    AttSim is a spacecraft attitude simulator that has been specifically developed to design and verify attitude control concepts and flight software architectures and algorithms. Its primary goal is to provide a generic approach to small satellite attitude control development by allowing scalable performance. AttSim specifically allows the user to develop software modules that can be used as flight code, and to verify control logic, controller gains, and other mission-critical elements. The code...

  20. Implicit and Explicit Attitudes and Interracial Interaction: The Moderating Role of Situationally Available Control Resources

    Hofmann, Wilhelm; Gschwendner, Tobias; Castelli, Luigi; Schmitt, Manfred


    Abstract The present research examined whether implicit and explicit racial attitudes predict interracial interaction behavior differently as a function of situationally available control resources. Specifically, we investigated how implicit attitudes (Implicit Association Test) and explicit attitudes (Blatant/Subtle prejudice) were related to interracial interaction behaviors of Italians toward an African ...

  1. Controlled comparison of attitudes of psychiatrists, general practitioners, homosexual doctors and homosexual men to male homosexuality.

    Bhugra, D.; King, M


    A controlled analysis of the attitudes of doctors and homosexual men to male homosexuality is reported. Not surprisingly the homosexual men held the most liberal attitudes which served as a yard-stick against which the doctors' attitudes could be assessed. The implications of these data, collected before the AIDS era, are discussed in terms of the current needs of homosexual patients.

  2. Magnetic Attitude Control System for Spinning Small Spacecraft

    Pal, Parimal; Selby, Vaughn


    A magnetic Attitude Control Subsystem (ACS) designed for minimum power weight, and cost is presented. The ACS subsystem was designed and built by ITHACO for the Small Communications Satellite Cluster (SCSC), integrated by Defense Systems Incorporated for the Defense Advanced Research Projects Agency. The basic spacecraft configuration is a flat cylinder, having a mass of 22.7 Kg with a diameter of 47.2 cm and 17.0 cm height. Hardware for the ACS design includes a two-axis magnetometer, two TO...

  3. The TUBSAT-1 Attitude Control and Stabilization System

    Ginati, Amnon


    TUBSAT-1 (Technical University Berlin Satellite) is an experimental low-cost satellite being financed by the German BMFT. The dimensions and weight are determined by the NASA Gas-Program and it will be ejected from the Space Shuttle within the German spacelab mission D2 by December 19, 1991, into a 298 km circular orbit and at a 28.5° inclination. To enable a large variety of useful experiments to fly with TUSSAT, it was necessary to develop a rather precise attitude control and stabilization...

  4. Structural control interaction for an LSS attitude control system using thrusters and reaction wheels

    da Fonseca, Ijar M.; Bainum, Peter M.; da Silva, Adenilson R.


    This work provides some important information about control structure interaction (CSI) for a large space structure (LSS) attitude control subsystem (ACS) comprised of thrusters and reaction wheels. The LSS physical model is assumed as a rigid long tubular beam as the main bus with two attached long flexible solar panels. Two thrusters (one at each tip of the LSS) are used for large amplitude maneuvers and the reaction wheels for fine control. Lagrange's formulations for generalized and quasi-coordinates were used to derive the equations of motion. The gravity gradient, the solar pressure and the drag were included in the mathematical model as external perturbations. The assumed modes discretization method has been used to model the solar array elastic displacements so as to obtain a set of ordinary differential equations to describe the LSS motion. Different control strategies were implemented to analyze the CSI for two configurations, fine and coarse control. The MatLab/Simulink platform has been used for the computational simulations. The results are in agreement with the CSI theory in that thruster firings excite the solar panel vibrations and that the elastic vibration is an important issue to be taken into account for LSS ACS performance evaluation for both fine and coarse control. In spite of the CSI the maneuver objectives have been accomplished with results that meet the mission criteria.

  5. Control system design method

    Wilson, David G.; Robinett, III, Rush D.


    A control system design method and concomitant control system comprising representing a physical apparatus to be controlled as a Hamiltonian system, determining elements of the Hamiltonian system representation which are power generators, power dissipators, and power storage devices, analyzing stability and performance of the Hamiltonian system based on the results of the determining step and determining necessary and sufficient conditions for stability of the Hamiltonian system, creating a stable control system based on the results of the analyzing step, and employing the resulting control system to control the physical apparatus.

  6. Fault Reconstruction Approach for Distributed Coordinated Spacecraft Attitude Control System

    Mingyi Huo


    Full Text Available This work presents a novel fault reconstruction approach for a large-scale system, that is, a distributed coordinated spacecraft attitude control system. The attitude of all the spacecrafts in this distributed system is controlled by using thrusters. All possible faults of thruster including thrust magnitude error and alignment error are investigated. As a stepping stone, the mathematical model of thruster is firstly established based on the thruster configuration. On the basis of this, a sliding mode observer is then proposed to reconstruct faults in each agent of the coordinated control system. A Lyapunov-based analysis shows that the observer asymptotically converges to the actual faults. The key feature of this fault reconstruction approach is that it can achieve a faster reconstruction of the fault in comparison with the conventional fault reconstruction schemes. It can globally reconstruct thruster faults with zero reconstruction error, and this is accomplished within finite time. The effectiveness of the proposed approach is analytically authenticated via simulation study.

  7. Estimating Friction Parameters in Reaction Wheels for Attitude Control

    Valdemir Carrara


    Full Text Available The ever-increasing use of artificial satellites in both the study of terrestrial and space phenomena demands a search for increasingly accurate and reliable pointing systems. It is common nowadays to employ reaction wheels for attitude control that provide wide range of torque magnitude, high reliability, and little power consumption. However, the bearing friction causes the response of wheel to be nonlinear, which may compromise the stability and precision of the control system as a whole. This work presents a characterization of a typical reaction wheel of 0.65 Nms maximum angular momentum storage, in order to estimate their friction parameters. It used a friction model that takes into account the Coulomb friction, viscous friction, and static friction, according to the Stribeck formulation. The parameters were estimated by means of a nonlinear batch least squares procedure, from data raised experimentally. The results have shown wide agreement with the experimental data and were also close to a deterministic model, previously obtained for this wheel. This model was then employed in a Dynamic Model Compensator (DMC control, which successfully reduced the attitude steady state error of an instrumented one-axis air-bearing table.

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

    Wisniewski, Rafal


    , 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, nevertheless, a solution of the riccati equation gives an excellent frame for investigations provided in this paper. An observation that geomagnetic field changes approximately periodically when satellite is on a near polar orbit is used throughout this paper. Three types of attitude controllers...

  9. An Attitude Control of Flexible Spacecraft Using Fuzzy-PID Controller

    Park, Jong-Oh; Im, Young-Do

    This primary objective of this study is to demonstrate simulation and ground-based experiment for the attitude control of flexible spacecraft. A typical spacecraft structure consists of the rigid body and flexible appendages which are large flexible solar panels, parabolic antennas built from light materials in order to reduce their weight. Therefore the attitude control has a big problem because these appendages induce structural vibration under the excitation of external forces. A single-axis rotational simulator with a flexible arm is constructed with on-off air thrusters and reaction wheel as actuation. The simulator is also equipped with payload pointing capability by simultaneous thruster and DC servo motor actuation. The experiment of flexible spacecraft attitude control is performed using only the reaction wheel. Using the reaction wheel the performance of the fuzzy-PID controller is illustrated by simulation and experimental results for a single-axis rotational simulator.

  10. Periodic H-2 Synthesis for Spacecraft Attitude Control with Magnetometers

    Wisniewski, Rafal; Stoustrup, Jakob


    A control synthesis for a spacecraft equipped with a set of magnetorquer coils is addressed. The electromagnetic actuation is particularly attractive for small low-cost spacecraft missions, due to their relatively low price, high reliability, light weight, and low power consumption. The interacti....... A linear matrix inequality-based algorithm is proposed for attitude control synthesis. Simulation results are provided, showing the prospect of the concept for onboard implementation.......A control synthesis for a spacecraft equipped with a set of magnetorquer coils is addressed. The electromagnetic actuation is particularly attractive for small low-cost spacecraft missions, due to their relatively low price, high reliability, light weight, and low power consumption. The interaction...

  11. Backup Attitude Control Algorithms for the MAP Spacecraft

    ODonnell, James R., Jr.; Andrews, Stephen F.; Ericsson-Jackson, Aprille J.; Flatley, Thomas W.; Ward, David K.; Bay, P. Michael


    The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The MAP spacecraft will perform its mission, studying the early origins of the universe, in a Lissajous orbit around the Earth-Sun L(sub 2) Lagrange point. Due to limited mass, power, and financial resources, a traditional reliability concept involving fully redundant components was not feasible. This paper will discuss the redundancy philosophy used on MAP, describe the hardware redundancy selected (and why), and present backup modes and algorithms that were designed in lieu of additional attitude control hardware redundancy to improve the odds of mission success. Three of these modes have been implemented in the spacecraft flight software. The first onboard mode allows the MAP Kalman filter to be used with digital sun sensor (DSS) derived rates, in case of the failure of one of MAP's two two-axis inertial reference units. Similarly, the second onboard mode allows a star tracker only mode, using attitude and derived rate from one or both of MAP's star trackers for onboard attitude determination and control. The last backup mode onboard allows a sun-line angle offset to be commanded that will allow solar radiation pressure to be used for momentum management and orbit stationkeeping. In addition to the backup modes implemented on the spacecraft, two backup algorithms have been developed in the event of less likely contingencies. One of these is an algorithm for implementing an alternative scan pattern to MAP's nominal dual-spin science mode using only one or two reaction wheels and thrusters. Finally, an algorithm has been developed that uses thruster one shots while in science mode for momentum management. This algorithm has been developed in case system momentum builds up faster than anticipated, to allow adequate momentum management while minimizing interruptions to science. In this paper, each mode and


    Majagi Suneel Ishwar


    Full Text Available Literature review suggests the importance and the need of students’ feedback which may be used to effectively reform evaluation methods in medical sciences. The present study has been conducted to obtain student’s attitude (perception of towards different evaluation methods of pharmacology. The sample consisted of second phase M.B.B.S (n=108 students. Students answered 115 items/questions designed according to Likert’s five point (in agreement with items scale. These items/questions assessed student’s attitude (perception of towards different constituents of evaluation methods of pharmacology like sessional exams, traditional practical exams, objective structured practical exam (OSPE, MCQs, long essays, viva voce, pharmacy practical exercise, experimental pharmacology exercise etc in relation with various aspects of pharmacology subject like understanding, retention, learning clinical applications, mechanism of action of drugs, pharmacological actions, therapeutic uses, prescribing drugs etc. Results of the present study indicated the degree to which each evaluation method like sessional/preliminary theory exams, traditional practical exams and OSPE helps to elicit different constituents of pharmacology subject (ex: mechanism of action of drugs, therapeutic uses etc and the reason for the same is discussed. Similarly usefulness of different constituents of theory exams (MCQs, long essay etc and practical exams (spotters, pharmacy exercises etc towards eliciting the understanding pharmacology is revealed. Present study indicated the merits and demerits of different evaluation methods used in pharmacology. If any reformations/changes have to be incorporated in the evaluation methods, outcomes of this study will definitely help towards improving/modifying the evaluation methods of teaching and learning of pharmacology subject.

  13. Pushing the Limits of Cubesat Attitude Control: A Ground Demonstration

    Sanders, Devon S.; Heater, Daniel L.; Peeples, Steven R.; Sules. James K.; Huang, Po-Hao Adam


    A cubesat attitude control system (ACS) was designed at the NASA Marshall Space Flight Center (MSFC) to provide sub-degree pointing capabilities using low cost, COTS attitude sensors, COTS miniature reaction wheels, and a developmental micro-propulsion system. The ACS sensors and actuators were integrated onto a 3D-printed plastic 3U cubesat breadboard (10 cm x 10 cm x 30 cm) with a custom designed instrument board and typical cubesat COTS hardware for the electrical, power, and data handling and processing systems. In addition to the cubesat development, a low-cost air bearing was designed and 3D printed in order to float the cubesat in the test environment. Systems integration and verification were performed at the MSFC Small Projects Rapid Integration & Test Environment laboratory. Using a combination of both the miniature reaction wheels and the micro-propulsion system, the open and closed loop control capabilities of the ACS were tested in the Flight Robotics Laboratory. The testing demonstrated the desired sub-degree pointing capability of the ACS and also revealed the challenges of creating a relevant environment for development testin

  14. Attitude control system of the Delfi-n3Xt satellite

    Reijneveld, J.; Choukroun, D.


    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 the associated algorithms are described. The control authority is shared between three body-mounted magnetorquers (MTQ) and three orthogonal reaction wheels. The attitude information is retrieved ...

  15. Design of the Active Attitude Determination and Control System for the e-st@r cubesat

    Stesina, Fabrizio; Corpino, Sabrina; Mozzillo, Raffaele; Obiols Rabasa, Gerard


    One of the most limiting factors which affects pico/nano satellites capabilities is the poor accuracy in attitude control. To improve mission performances of this class of satellites, the capability of controlling satellite's attitude shall be enhanced. The paper presents the design, development and verification of the Active Attitude Determination and Control System (A-ADCS) of the E-ST@R Cubesat developed at Politecnico di Torino. The heart of the system is an ARM9 microcontroller that mana...

  16. Reaction Wheel Installation Deviation Compensation for Overactuated Spacecraft with Finite-Time Attitude Control


    A novel attitude tracking control scheme is presented for overactuated spacecraft to address the attitude stabilization problem in presence of reaction wheel installation deviation, external disturbance and uncertain mass of moment inertia. An adaptive sliding mode control technique is proposed to track the uncertainty. A Lyapunov-based analysis shows that the compensation control law can guarantee that the desired attitude trajectories are followed in finite-time. The key feature of the prop...

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

    CHENG Hao; GE Sheng-min; SHEN Yi


    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.

  18. Attitude control of geostationary satellites with double gimballed momentum wheels

    Schulz, G.; Lange, T.


    Conventional control methods are generalized using state vector feedback design procedures. Alternatively, a decoupled control method using a nondiagonal inertia tensor was derived. These are confronted to modern control theory design method with observer, where especially the insensitivity with respect to variants of the moments of inertia was demonstrated.

  19. Gaining control over responses to implicit attitude tests: Implementation intentions engender fast responses on attitude-incongruent trials.

    Webb, Thomas L; Sheeran, Paschal; Pepper, John


    The present research investigated whether forming implementation intentions could promote fast responses to attitude-incongruent associations (e.g., woman-manager) and thereby modify scores on popular implicit measures of attitude. Expt 1 used the Implicit Association Test (IAT) to measure associations between gender and science versus liberal arts. Planning to associate women with science engendered fast responses to this category-attribute pairing and rendered summary scores more neutral compared to standard IAT instructions. Expt 2 demonstrated that forming egalitarian goal intentions is not sufficient to produce these effects. Expt 3 extended these findings to a different measure of implicit attitude (the Go/No-Go Association Task) and a different stereotypical association (Muslims-terrorism). In Expt 4, managers who planned to associate women with superordinate positions showed more neutral IAT scores relative to non-planners and effects were maintained 3 weeks later. In sum, implementation intentions enable people to gain control over implicit attitude responses. PMID:22435844

  20. Robust attitude control design for spacecraft under assigned velocity and control constraints.

    Hu, Qinglei; Li, Bo; Zhang, Youmin


    A novel robust nonlinear control design under the constraints of assigned velocity and actuator torque is investigated for attitude stabilization of a rigid spacecraft. More specifically, a nonlinear feedback control is firstly developed by explicitly taking into account the constraints on individual angular velocity components as well as external disturbances. Considering further the actuator misalignments and magnitude deviation, a modified robust least-squares based control allocator is employed to deal with the problem of distributing the previously designed three-axis moments over the available actuators, in which the focus of this control allocation is to find the optimal control vector of actuators by minimizing the worst-case residual error using programming algorithms. The attitude control performance using the controller structure is evaluated through a numerical example. PMID:23618744

  1. Analysis of Pan-European attitudes to the eradication and control of bovine viral diarrhoea.

    Heffernan, C; Misturelli, F; Nielsen, L; Gunn, G J; Yu, J


    At present, national-level policies concerning the eradication and control of bovine viral diarrhoea (BVD) differ widely across Europe. Some Scandinavian countries have enacted strong regulatory frameworks to eradicate the disease, whereas other countries have few formal policies. To examine these differences, the attitudes of stakeholders and policy makers in 17 European countries were investigated. A web-based questionnaire was sent to policy makers, government and private sector veterinarians, and representatives of farmers' organisations. In total, 131 individuals responded to the questionnaire and their responses were analysed by applying a method used in sociolinguistics: frame analysis. The results showed that the different attitudes of countries that applied compulsory or voluntary frameworks were associated with different views about the attribution or blame for BVD and the roles ascribed to farmers and other stakeholders in its eradication and control. PMID:19202168

  2. Nurses`knowledge of and attitude towards exercise as a treatment method for hypertensive patients

    L. Grobler


    Full Text Available Aerobic exercise is used in treating hypertension. Eventhough physiotherapists are the first choice in presenting exercise treatment, few are available to do so in primary health clinics. Nurses arepatients’ first contact and may be able to fulfil this role. Nurses’knowledge and attitude towards exercise as a treatment method for hypertensive patients was determined. This descriptive study included all nurses (n=67 working in 23 Bloemfontein clinics. Forty-three nursescompleted structured questionnaires that determined their knowledge of exercise as a treatment method. All nurses prescribed medication forhypertensive patients. Most nurses prescribed weight control (72.1%, diet control (76.7%, patient education (74.4%, and life-style modification (72.1%. Most (83.7% nurses were aware of exercise as a treatment method for hypertension. Only seven nurses, prescribing a brisk walk, recommended the correct type of exercise. The nurses’attitude towards exercise as a treatment method was determined using focus group interviews (n=16. Nurses reflected a positive attitude towards exercise with 198 positive responses. Nurses could express more than one opinion, all of which were recorded. Twenty responses reflected little or no knowledge, and four responses reflected an unsure/neutral attitude towards exercise. Ten responses reflected disinterest in prescribing exercise. Nurses do not have adequate knowledge to enable them to confidently prescribe exercise to patients. The need for more information was mentioned and some nurses were willing to present exercise classes. A training program, containing pertinent information, so that nurses can prescribe exercise for hypertension, needs to be developed.

  3. Motor Control of Two Flywheels Enabling Combined Attitude Control and Bus Regulation

    Kenny, Barbara H.


    This presentation discussed the flywheel technology development work that is ongoing at NASA GRC with a particular emphasis on the flywheel system control. The "field orientation" motor/generator control algorithm was discussed and explained. The position-sensorless angle and speed estimation algorithm was presented. The motor current response to a step change in command at low (10 kRPM) and high (60 kRPM) was discussed. The flywheel DC bus regulation control was explained and experimental results presented. Finally, the combined attitude control and energy storage algorithm that controls two flywheels simultaneously was presented. Experimental results were shown that verified the operational capability of the algorithm. shows high speed flywheel energy storage (60,000 RPM) and the successful implementation of an algorithm to simultaneously control both energy storage and a single axis of attitude with two flywheels. Overall, the presentation demonstrated that GRC has an operational facility that

  4. Sine Rotation Vector Method for Attitude Estimation of an Underwater Robot.

    Ko, Nak Yong; Jeong, Seokki; Bae, Youngchul


    This paper describes a method for estimating the attitude of an underwater robot. The method employs a new concept of sine rotation vector and uses both an attitude heading and reference system (AHRS) and a Doppler velocity log (DVL) for the purpose of measurement. First, the acceleration and magnetic-field measurements are transformed into sine rotation vectors and combined. The combined sine rotation vector is then transformed into the differences between the Euler angles of the measured attitude and the predicted attitude; the differences are used to correct the predicted attitude. The method was evaluated according to field-test data and simulation data and compared to existing methods that calculate angular differences directly without a preceding sine rotation vector transformation. The comparison verifies that the proposed method improves the attitude estimation performance. PMID:27490549

  5. Attitude Control on TET-1 - Experiences from the First Year of Operations

    Hobsch, Markus; Cossavella, Fabiana; Löw, Sebastian; Herman, Jacobus


    The micro-satellite TET-1 carries several technology experiments. It is the first in a series offering the possibility of in-orbit verification of new equipment made in Germany by the industrial and scientific aerospace community. TET-1 was launched 22nd July 2012 and is operated by the German Space Operations Center. Attitude and attitude control is influenced by several of the experiments. Special attitude control modes are required for a number of experiments in order to point the sate...

  6. Investigations of an integrated angular velocity measurement and attitude control system for spacecraft using magnetically suspended double-gimbal CMGs

    Zheng, Shiqiang; Han, Bangcheng


    This paper presents an integrated angular velocity measurement and attitude control system of spacecraft using magnetically suspended double-gimbal control moment gyros (MSDGCMGs). The high speed rotor of MSDGCMG is alleviated by a five-degree-of-freedom permanent magnet biased AMB control system. With this special rotor supported manner, the MSDGCMG has the function of attitude rate sensing as well as attitude control. This characteristic provides a new approach to a compact light-weight spacecraft design, which can combine these two functions into a single device. This paper discusses the principles and implementations of AMB-based angular velocity measurement. Spacecraft dynamics with DGMSCMG actuators, including the dynamics of magnetically suspended high-speed rotor, the dynamics of inner gimbal and outer gimbal, as well as the determination method of spacecraft angular velocity are modeled, respectively. The effectiveness of the proposed integrated system is also validated numerically and experimentally.

  7. Predicting healthcare employees' participation in an office redesign program: Attitudes, norms and behavioral control

    Lukas Carol


    Full Text Available Abstract Background The study examined the extent to which components based on a modified version of the theory of planned behavior explained employee participation in a new clinical office program designed to reduce patient waiting times in primary care clinics. Methods We regressed extent of employee participation on attitudes about the program, group norms, and perceived behavioral control along with individual and clinic characteristics using a hierarchical linear mixed model. Results Perceived group norms were one of the best predictors of employee participation. Attitudes about the program were also significant, but to a lesser degree. Behavioral control, however, was not a significant predictor. Respondents with at least one year of clinic tenure, or who were team leaders, first line supervisor, or managers had greater participation rates. Analysis at the clinic level indicated clinics with scores in the highest quartile clinic scores on group norms, attitudes, and behavioral control scores were significantly higher on levels of overall participation than clinics in the lowest quartile. Conclusion Findings suggest that establishing strong norms and values may influence employee participation in a change program in a group setting. Supervisory level was also significant with greater responsibility being associated with greater participation.

  8. Attitude control system of the Delfi-n3Xt satellite

    Reijneveld, J.; Choukroun, D.


    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

  9. Orion Launch Abort Vehicle Attitude Control Motor Testing

    Murphy, Kelly J.; Brauckmann, Gregory J.; Paschal, Keith B.; Chan, David T.; Walker, Eric L.; Foley, Robert; Mayfield, David; Cross, Jared


    Current Orion Launch Abort Vehicle (LAV) configurations use an eight-jet, solid-fueled Attitude Control Motor (ACM) to provide required vehicle control for all proposed abort trajectories. Due to the forward position of the ACM on the LAV, it is necessary to assess the effects of jet-interactions (JI) between the various ACM nozzle plumes and the external flow along the outside surfaces of the vehicle. These JI-induced changes in flight control characteristics must be accounted for in developing ACM operations and LAV flight characteristics. A test program to generate jet interaction aerodynamic increment data for multiple LAV configurations was conducted in the NASA Ames and NASA Langley Unitary Plan Wind Tunnels from August 2007 through December 2009. Using cold air as the simulant gas, powered subscale models were used to generate interaction data at subsonic, transonic, and supersonic test conditions. This paper presents an overview of the complete ACM JI experimental test program for Orion LAV configurations, highlighting ACM system modeling, nozzle scaling assumptions, experimental test techniques, and data reduction methodologies. Lessons learned are discussed, and sample jet interaction data are shown. These data, in conjunction with computational predictions, were used to create the ACM JI increments for all relevant flight databases.

  10. Tobacco control education, attitudes and beliefs of Nigerian health profession students

    Oluwatunmise Awojobi


    Full Text Available Objectives: The purpose of this study is to explore tobacco control-related education of health profession students and demonstrate variations according to course of study. Methods: This was a cross-sectional survey of 154 of third year nursing, pharmacy, medical and dental students in a tertiary institution in Lagos, Nigeria. The validated Global Health Professional Students survey questionnaire was used to collect data on recall of tobacco-related training, attitudes to tobacco control and beliefs about the role of health professionals in tobacco control. This was voluntary and anonymous. Descriptive and univariate analysis were conducted. Results: Only 11.8(n=18 of all respondents recalled being trained on all possible items of formal tobacco-related training. Pharmacy students had significantly low levels of training recall (χ[sup]2[/sup][sub](3[/sub]=9.88; p=0.02. Nursing students were reported to have the most positive attitudes to tobacco control with the highest mean score of 4.27 (95= 3.88-4.66. However, there was no significant difference in attitudes to tobacco control. Compared to other students, Nursing students were significantly less likely to believe that as health professionals they had a role in tobacco-control (χ[sup]2[/sup][sub](3[/sub] = 8.06; p=0.045. Conclusions: Many respondents believed they have a role in providing cessation interventions and that specific training should be part of the education they receive. However, fewer respondents report receiving such training. The education and training of these samples of health profession students needs to place more emphasis on their role in tobacco control if they are to effectively function as health promoting health professionals in preventing tobacco-related diseases.

  11. A study of attitude control concepts for precision-pointing non-rigid spacecraft

    Likins, P. W.


    Attitude control concepts for use onboard structurally nonrigid spacecraft that must be pointed with great precision are examined. The task of determining the eigenproperties of a system of linear time-invariant equations (in terms of hybrid coordinates) representing the attitude motion of a flexible spacecraft is discussed. Literal characteristics are developed for the associated eigenvalues and eigenvectors of the system. A method is presented for determining the poles and zeros of the transfer function describing the attitude dynamics of a flexible spacecraft characterized by hybrid coordinate equations. Alterations are made to linear regulator and observer theory to accommodate modeling errors. The results show that a model error vector, which evolves from an error system, can be added to a reduced system model, estimated by an observer, and used by the control law to render the system less sensitive to uncertain magnitudes and phase relations of truncated modes and external disturbance effects. A hybrid coordinate formulation using the provided assumed mode shapes, rather than incorporating the usual finite element approach is provided.

  12. General Attitude Control Algorithm for Spacecraft Equipped with Star Camera and Reaction Wheels

    Wisniewski, Rafal; Kulczycki, P.

    realized on an integrated circuit. This paper considers two issues: slew maneuver with a feature of avoiding direct exposure of the camera's CCD chip to the Sun %, three-axis attitude control and optimal control torque distribution in a reaction wheel assembly. The attitude controller is synthesized...... applying the energy shaping technique, where the desired potential function is carefully designed using a physical insight into the nature of the problem. The system stability is thoroughly analyzed and the control performance simulated...

  13. Knowledge, Attitude, Practice, and Status of Infection Control among Iranian Dentists and Dental Students: A Systematic Review

    Moradi Khanghahi, Behnam; Jamali, Zahra; Pournaghi Azar, Fatemeh; Naghavi Behzad, Mohammad; Azami-Aghdash, Saber


    Background and aims Infection control is an important issue in dentistry, and the dentists are primarily responsible for observing the relevant procedures. Therefore, the present study evaluated knowledge, attitude, practice, and status of infection control among Iranian dentists through systematic review of published results. Materials and methods In this systematic review, the required data was collected searching for keywords including infection, infection control, behavior, performance, p...

  14. New one-axis one-sensor magnetic attitude control theoretical and in-flight performance

    Ovchinnikov, M. Yu.; Roldugin, D. S.; Tkachev, S. S.; Karpenko, S. O.


    New one-axis magnetic attitude control is proposed. Only one attitude sensor providing any inertial direction measurements is necessary, magnetometer is not used. The control may be used as a backup capability in case main actuators or some attitude sensors fail. Sun pointing is achievable using only three-axis Sun sensor, so the control may be used to lower the power consumption during battery charging. Asymptotic stability of different equilibria depending on the satellite inertia tensor is summarized. In-flight results from "Chibis-M" microsatellite are provided proving general control performance.

  15. Attitude Stabilization Control of a Quadrotor UAV by Using Backstepping Approach

    Xing Huo


    Full Text Available The modeling and attitude stabilization control problems of a four-rotor vertical takeoff and landing unmanned air vehicle (UAV known as the quadrotor are investigated. The quadrotor’s attitude is represented by the unit quaternion rather than Euler angles to avoid singularity problem. Taking dynamical behavior of motors into consideration and ignoring aerodynamic effect, a nonlinear controller is developed to stabilize the attitude. The control design is accomplished by using backstepping control technique. The proposed control law is based on the compensation for the Coriolis and gyroscope torques. Applying Lyapunov stability analysis proves that the closed-loop attitude system is asymptotic stable. Moreover, the controller can guarantee that all the states of the system are uniformly ultimately bounded in the presence of external disturbance torque. The effectiveness of the proposed control approach is analytically authenticated and also validated via simulation study.

  16. Decentralized sliding-mode control for spacecraft attitude synchronization under actuator failures

    Wu, Baolin; Wang, Danwei; Poh, Eng Kee


    This paper examines attitude synchronization and tracking problems with model uncertainties, external disturbances, actuator failures and control torque saturation. Two decentralized sliding mode control laws are proposed and analyzed based on algebraic graph theory. Using Barbalat's Lemma, it is shown that the control laws guarantee each spacecraft approaches the desired time-varying attitude and angular velocity while maintaining attitude synchronization among the other spacecraft in the formation. The first controller is designed in the presence of model uncertainties, external disturbances, and actuator failures. The results are extended to the case with control input saturation in the second controller. Both control laws do not require online identification of failures. Numerical simulations are presented to show the effectiveness of the proposed attitude synchronization and tracking approaches.

  17. Knowledge, Attitude, Practice, and Status of Infection Control among Iranian Dentists and Dental Students: A Systematic Review

    Moradi Khanghahi, Behnam; Jamali, Zahra; Pournaghi Azar, Fatemeh; Naghavi Behzad, Mohammad; Azami-Aghdash, Saber


    Background and aims Infection control is an important issue in dentistry, and the dentists are primarily responsible for observing the relevant procedures. Therefore, the present study evaluated knowledge, attitude, practice, and status of infection control among Iranian dentists through systematic review of published results. Materials and methods In this systematic review, the required data was collected searching for keywords including infection, infection control, behavior, performance, practice, attitude, knowledge, dent*, prevention, Iran* and their Persian equivalents in PubMed, Science Direct, Iranmedex, SID, Medlib, and Magiran databases with a time limit of 1985 to 2012. Out of 698 articles, 15 completely related articles were finally considered and the rest were excluded due to lake of relev-ance to the study goals. The required data were extracted and summarized in an Extraction Table and were analyzed ma-nually. Results Evaluating the results of studies indicated inappropriate knowledge, attitude, and practice regarding infection control among Iranian dentists and dental students. Using personal protection devices and observing measures required for infection control were not in accordance with global standards. Conclusion The knowledge, attitudes, and practice of infection control in Iranian dental settings were found to be inadequate. Therefore, dentists should be educated more on the subject and special programs should be in place to monitor the dental settings for observing infection control standards. PMID:23875081

  18. Attitude dynamics and control of spacecraft using geomagnetic Lorentz force

    Attitude stabilization of a charged rigid spacecraft in Low Earth Orbit using torques due to Lorentz force in pitch and roll directions is considered. A spacecraft that generates an electrostatic charge on its surface in the Earth's magnetic field will be subject to perturbations from the Lorentz force. The Lorentz force acting on an electrostatically charged spacecraft may provide a useful thrust for controlling a spacecraft's orientation. We assume that the spacecraft is moving in the Earth's magnetic field in an elliptical orbit under the effects of gravitational, geomagnetic and Lorentz torques. The magnetic field of the Earth is modeled as a non-tilted dipole. A model incorporating all Lorentz torques as a function of orbital elements has been developed on the basis of electric and magnetic fields. The stability of the spacecraft orientation is investigated both analytically and numerically. The existence and stability of equilibrium positions is investigated for different values of the charge to mass ratio (α*). Stable orbits are identified for various values of α*. The main parameters for stabilization of the spacecraft are α* and the difference between the components of the moment of inertia for the spacecraft. (research papers)

  19. Nonlinear Attitude Control of Planar Structures in Space Using Only Internal Controls

    Reyhanoglu, Mahmut; Mcclamroch, N. Harris


    An attitude control strategy for maneuvers of an interconnection of planar bodies in space is developed. It is assumed that there are no exogeneous torques and that torques generated by joint motors are used as means of control so that the total angular momentum of the multibody system is a constant, assumed to be zero. The control strategy utilizes the nonintegrability of the expression for the angular momentum. Large angle maneuvers can be designed to achieve an arbitrary reorientation of the multibody system with respect to an inertial frame. The theoretical background for carrying out the required maneuvers is summarized.

  20. Students' Attitudes toward Statistics across the Disciplines: A Mixed-Methods Approach

    Griffith, James D.; Adams, Lea T.; Gu, Lucy L.; Hart, Christian L.; Nichols-Whitehead, Penney


    Students' attitudes toward statistics were investigated using a mixed-methods approach including a discovery-oriented qualitative methodology among 684 undergraduate students across business, criminal justice, and psychology majors where at least one course in statistics was required. Students were asked about their attitudes toward statistics and…

  1. Chattering-Free Adaptive Sliding Mode Control for Attitude Tracking of Spacecraft with External Disturbance

    Xuxi Zhang


    Full Text Available The attitude tracking problem of spacecraft in the presence of unknown disturbance is investigated. By using the adaptive control technique and the Lyapunov stability theory, a chattering-free adaptive sliding mode control law is proposed for the attitude tracking problem of spacecraft with unknown disturbance. Simulation results are employed to demonstrate the effectiveness of the proposed control design technique in this paper.

  2. Comparing Efficacy of Four Preventive Methods on Attitude of Drug Substance Abuse and Self–Esteem in Students Supported by Emdad Committee

    aziz allah agha babaei; daruosh jalali; hamid reza saeedzadeh; sohayla bagheri


    Introduction: This study was aimed to compare the efficacy of four drug substance abuse preventive methods: cognitive–behavioral social traioning, life skills training, poster presentation and short message system on attitude change and enhancement self-esteem in students supported by Emdad Committee. Method:This was a quasi experimental study. 150 students were selected and randomly assigned to the four experimental and control groups. The groups were completed attitude of drug substance ab...

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

    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, 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.

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

    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, o......, 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....

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

    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, o......, 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....

  6. Distributed event-triggered cooperative attitude control of multiple rigid bodies with leader-follower architecture

    Weng, Shengxuan; Yue, Dong


    In this note, the distributed event-triggered cooperative attitude control of multiple rigid bodies with leader-follower architecture is investigated, where both the cases of static and dynamic leaders are all considered. Two distributed triggering procedures are first introduced for the followers and leaders, and then the distributed cooperative controllers are designed under the proposed triggering schemes. Under the designed controllers with the event-triggered strategies, it is shown that the orientations of followers converge to the convex hull formed by the desired leaders' orientations with zero angular velocities. Moreover, the communication pressure in network is reduced and the energy of each agent is saved. Simulation results show the effectiveness of the proposed method.

  7. The influence of contextual teaching with the problem solving method on students' knowledge and attitudes toward horticulture, science, and school

    Whitcher, Carrie Lynn


    Adolescence is marked with many changes in the development of higher order thinking skills. As students enter high school they are expected to utilize these skills to solve problems, become abstract thinkers, and contribute to society. The goal of this study was to assess horticultural science knowledge achievement and attitude toward horticulture, science, and school in high school agriculture students. There were approximately 240 high school students in the sample including both experimental and control groups from California and Washington. Students in the experimental group participated in an educational program called "Hands-On Hortscience" which emphasized problem solving in investigation and experimentation activities with greenhouse plants, soilless media, and fertilizers. Students in the control group were taught by the subject matter method. The activities included in the Hands-On Hortscience curriculum were created to reinforce teaching the scientific method through the context of horticulture. The objectives included evaluating whether the students participating in the Hands-On Hortscience experimental group benefited in the areas of science literacy, data acquisition and analysis, and attitude toward horticulture, science, and school. Pre-tests were administered in both the experimental and control groups prior to the research activities and post-tests were administered after completion. The survey questionnaire included a biographical section and attitude survey. Significant increases in hortscience achievement were found from pre-test to post-test in both control and experimental study groups. The experimental treatment group had statistically higher achievement scores than the control group in the two areas tested: scientific method (p=0.0016) and horticulture plant nutrition (p=0.0004). In addition, the students participating in the Hands-On Hortscience activities had more positive attitudes toward horticulture, science, and school (p=0

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

    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...

  9. Venusian atmospheric and Magellan properties from attitude control data. M.S. Thesis

    Croom, Christopher A.; Tolson, Robert H.


    Results are presented of the study of the Venusian atmosphere, Magellan aerodynamic moment coefficients, moments of inertia, and solar moment coefficients. This investigation is based upon the use of attitude control data in the form of reaction wheel speeds from the Magellan spacecraft. As the spacecraft enters the upper atmosphere of Venus, measurable torques are experienced due to aerodynamic effects. Solar and gravity gradient effects also cause additional torques throughout the orbit. In order to maintain an inertially fixed attitude, the control system counteracts these torques by changing the angular rates of three reaction wheels. Model reaction wheel speeds are compared to observed Magellan reaction wheel speeds through a differential correction procedure. This method determines aerodynamic, atmospheric, solar pressure, and mass moment of inertia parameters. Atmospheric measurements include both base densities and scale heights. Atmospheric base density results confirm natural variability as measured by the standard orbital decay method. Potential inconsistencies in free molecular aerodynamic moment coefficients are identified. Moments of inertia are determined with a precision better than 1 percent of the largest principal moment of inertia.

  10. The results of flight tests of an attitude control system for the Chibis-M microsatellite

    Ivanov, D. S.; Ivlev, N. A.; Karpenko, S. O.; Ovchinnikov, M. Yu.; Roldugin, D. S.; Tkachev, S. S.


    The attitude control system of the Chibis-M microsatellite is described. Results of flight experiments on damping the initial angular velocity (made using magnetorquers) are considered, as well as stabilization in the orbital referece frame, and orientation of solar arrays toward the Sun using reaction wheels. The operation of algorithms of satellite attitude determination on sunlit and shadow segments of the orbit is also under study. The general logic of operation of the attitude control system in automatic mode is presented and discussed.

  11. Farmer attitudes to vaccination and culling of badgers in controlling bovine tuberculosis.

    Warren, M; Lobley, M; Winter, M


    Controversy persists in England, Wales and Northern Ireland concerning methods of controlling the transmission of bovine tuberculosis (bTB) between badgers and cattle. The National Trust, a major land-owning heritage organisation, in 2011, began a programme of vaccinating badgers against bTB on its Killerton Estate in Devon. Most of the estate is farmed by 18 tenant farmers, who thus have a strong interest in the Trust's approach, particularly as all have felt the effects of the disease. This article reports on a study of the attitudes to vaccination of badgers and to the alternative of a culling programme, using face-to-face interviews with 14 of the tenants. The results indicated first that the views of the respondents were more nuanced than the contemporary public debate about badger control would suggest. Secondly, the attitude of the interviewees to vaccination of badgers against bTB was generally one of resigned acceptance. Thirdly, most respondents would prefer a combination of an effective vaccination programme with an effective culling programme, the latter reducing population of density sufficiently (and preferably targeting the badgers most likely to be diseased) for vaccination to have a reasonable chance of success. While based on a small sample, these results will contribute to the vigorous debate concerning contrasting policy approaches to bTB control in England, Wales and Northern Ireland. PMID:23775132

  12. Analysis of a magnetic three-axis stabilized attitude control system for the NPSAT1 spacecraft

    Zirkle, Todd A.


    The NPSAT1 satellite uses an active magnetic torque rod system, with a magnetometer for attitude determination, to maintain 3-axis stabilization, with a slightly gravity gradient friendly structure. This thesis will examine the performance of three combinations of programs and simulation models for the NPSAT1 satellite attitude control system. The models include a magnetic control law with a reduced order estimator to generate torque commands to achieve spacecraft nadir pointing and a magneti...


    Contreras, F.; de Vicente, E; Reyes, L.; G. Bisiacchi; Prado, J; M. Mesinas; Juárez, A


    A frictionless environment simulation platform, utilized for accomplishing three-axis attitude control tests in small satellites,is introduced. It is employed to develop, improve, and carry out objective tests of sensors, actuators, and algorithms in theexperimental framework. Different sensors (i.e. sun, earth, magnetometer, and an inertial measurement unit) are utilizedto assess three-axis deviations. A set of three inertial wheels is used as primary actuators for attitude control, together...

  14. Magnetic and Momentum Bias Attitude Control Design for the HETE Small Satellite

    Chang, Daniel


    A design study of the attitude control system for the High Energy Transient Experiment (RETE) small satellite is presented. The satellite is 3-axis stabilized and sun pointing, with stringent pointing stability requirements. For actuation, magnetic torquers and a momentum wheel are chosen for their technological maturity and lack of consumables. One science instrument (CCD UV camera) and sun sensors provide attitude measurement. Two complimentary control strategies are implemented to maximize...

  15. Attitude and Vibration Control of Flexible Spacecraft Using Singular Perturbation Approach

    Morteza Shahravi; Milad Azimi


    This paper addresses a composite two-time-scale control system for simultaneous three-axis attitude maneuvering and elastic mode stabilization of flexible spacecraft. By choosing an appropriate time coordinates transformation system, the spacecraft dynamics can be divided into double time-scale subsystems using singular perturbation theory (SPT). Attitude and vibration control laws are successively designed by considering a time bandwidths separation between the oscillatory flexible parts mot...

  16. Design and Implementation of Attitude Control for 3-axes Magnetic Coil Stabilization of a Spacecraft

    Tudor, Zdenko


    Spacecrafts, especially satellites, play an ever greater rolein our daily lives as we increasingly depend on the services they provide,which in turn, more often than not, critically depend on maintainingcorrect payload attitude. As smaller educational satellites pavethe way for organization, group and privately owned pico-satellites, weexplore the possibilities of attitude control through magnetic coil actuation.We approach the whole problem, from control theory developmentto first prototype ...

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

    Peiling Cui


    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.

  18. Improved optimal steering law for SGCMG and adaptive attitude control of flexible spacecraft

    Lu Wang; Yu Guo; Liping Wu; Qingwei Chen


    The issue of attitude maneuver of a flexible spacecraft is investigated with single gimbaled control moment gyroscopes (SGCMGs) as an actuator. To solve the inertia uncertainty of the system, an adaptive attitude control algorithm is designed by ap-plying a radial basis function (RBF) neural network. An improved steering law for SGCMGs is proposed to achieve the optimal out-put torque. It enables the SGCMGs not only to avoid singularity, but also to output more precise torque. In addition, global, uniform, ultimate bounded stability of the attitude control system is proved via the Lyapunov technique. Simulation results demonstrate the effectiveness of the new steering law and the algorithm of attitude maneuver of the flexible spacecraft.

  19. Reconfigurability Analysis Method for Spacecraft Autonomous Control

    Dayi Wang


    Full Text Available As a critical requirement for spacecraft autonomous control, reconfigurability should be considered in design stage of spacecrafts by involving effective reconfigurability analysis method in guiding system designs. In this paper, a novel reconfigurability analysis method is proposed for spacecraft design. First, some basic definitions regarding spacecraft reconfigurability are given. Then, based on function tree theory, a reconfigurability modeling approach is established to properly describe system’s reconfigurability characteristics, and corresponding analysis procedure based on minimal cut set and minimal path set is further presented. In addition, indexes of fault reconfigurable degree and system reconfigurable rate for evaluating reconfigurability are defined, and the methodology for analyzing system’s week links is also constructed. Finally, the method is verified by a spacecraft attitude measuring system, and the results show that the presented method cannot only implement the quantitative reconfigurability evaluations but also find the weak links, and therefore provides significant improvements for spacecraft reconfigurability design.

  20. A method for attitude measurement of a test vehicle based on the tracking of vectors

    In the vehicle simulation test, in order to improve the measuring precision for the attitude of a test vehicle, a measuring method based on the vectors of light beams is presented, in which light beams are mounted on the test vehicle as the cooperation target, and the attitude of the test vehicle is calculated with the light beams’ vectors in the test vehicle’s coordinate system and the world coordinate system. Meanwhile, in order to expand the measuring range of the attitude parameters, cooperation targets and light beams in each cooperation target are increased. On this basis, the concept of an attitude calculation container is defined, and the selection method for the attitude calculation container that participates in the calculation is given. Simultaneously, the vectors of light beams are tracked so as to ensure the normal calculation of the attitude parameters. The experiments results show that this measuring method based on the tracking of vectors can achieve the high precision and wide range of measurement for the attitude of the test vehicle. (paper)

  1. Methods for structural control

    Baratta, A.; Bourquin, F.; CORBI, O; HOCHRAINER, M; Luo, N; MAGONETTE, G; Marazzi, F; Rodellar, J.


    In the last decades significant advances have been produced in the field of structural control. This paper focuses on some issues related with the problem of controlling (reducing) undesired vibrations, summarizing the experiences of the authors in some specific issues on specific classes of structural control systems.

  2. Attitudes of eighth-grade honors students toward the conceptual change methods of teaching science

    Heide, Clifford Lee


    The study researched the attitude of eighth grade honors science students toward the steps of the conceptual change teaching method. The attitudes of 25 students in an honors 8th grade science class in the Greater Phoenix metropolitan area were assessed using a multi-method approach. A quantitative method (student survey) and a qualitative method (focus group) were triangulated for convergence. Since conceptual change is a relatively new reform teaching modality, the study assessed students' attitudes utilizing this method. Conceptual change teaching is characterized by connections between concepts and facts which are organized around key ideas. Knowledge connected through concepts is constantly revised and edited by students as they continue to learn and add new concepts. The results of this study produced evidence that the conceptual change method of teaching science and its six process steps have qualities that foster positive student attitude. The study demonstrated that students' attitudes toward science is positively influenced through the conceptual change teaching method by enabling students to: (1) choose problems and find solutions to those problems (student directed); (2) work together in large and small groups; (3) learn through student oral presentations; (4) perform hands-on laboratory experiences; (5) learn through conceptual understanding not memorization; (6) implement higher order learning skills to make connections from the lab to the real world. Teachers can use the information in the study to become aware of the positive and negative attitudes of students taught with the conceptual change method. Even if the conceptual change teaching strategy is not the modality utilized by an educator, the factors identified by this study that affect student attitude could be used to help a teacher design lesson plans that help foster positive student attitudes.

  3. Student Compliance and Attitude: A Function of Classroom Control Technique.

    Houser, Betsy B.

    This paper examines the effects of a teacher's classroom utilization of certain means of social influence or bases of social power (reward, coercive, referent, legitimate, and informational) upon: (1) level of student compliance, and (2) attitude of the student toward the teacher. A total of 588 white, middle-class fourth, fifth, and sixth grade…

  4. Attitudes of Teachers of Arabic as a Foreign Language toward Methods of Foreign Language Teaching

    Seraj, Sami A.


    This study examined the attitude of teachers of Arabic as a foreign language toward some of the most well known teaching methods. For this reason the following eight methods were selected: (1) the Grammar-Translation Method (GTM), (2) the Direct Method (DM), (3) the Audio-Lingual Method (ALM), (4) Total Physical Response (TPR), (5) Community…

  5. Racism, gun ownership and gun control: biased attitudes in US whites may influence policy decisions.

    Kerry O'Brien

    Full Text Available OBJECTIVE: Racism is related to policies preferences and behaviors that adversely affect blacks and appear related to a fear of blacks (e.g., increased policing, death penalty. This study examined whether racism is also related to gun ownership and opposition to gun controls in US whites. METHOD: The most recent data from the American National Election Study, a large representative US sample, was used to test relationships between racism, gun ownership, and opposition to gun control in US whites. Explanatory variables known to be related to gun ownership and gun control opposition (i.e., age, gender, education, income, conservatism, anti-government sentiment, southern vs. other states, political identification were entered in logistic regression models, along with measures of racism, and the stereotype of blacks as violent. Outcome variables included; having a gun in the home, opposition to bans on handguns in the home, support for permits to carry concealed handguns. RESULTS: After accounting for all explanatory variables, logistic regressions found that for each 1 point increase in symbolic racism there was a 50% increase in the odds of having a gun at home. After also accounting for having a gun in the home, there was still a 28% increase in support for permits to carry concealed handguns, for each one point increase in symbolic racism. The relationship between symbolic racism and opposition to banning handguns in the home (OR1.27 CI 1.03,1.58 was reduced to non-significant after accounting for having a gun in the home (OR1.17 CI.94,1.46, which likely represents self-interest in retaining property (guns. CONCLUSIONS: Symbolic racism was related to having a gun in the home and opposition to gun control policies in US whites. The findings help explain US whites' paradoxical attitudes towards gun ownership and gun control. Such attitudes may adversely influence US gun control policy debates and decisions.

  6. Fault tolerant attitude control for small unmanned aircraft systems equipped with an airflow sensor array

    Inspired by sensing strategies observed in birds and bats, a new attitude control concept of directly using real-time pressure and shear stresses has recently been studied. It was shown that with an array of onboard airflow sensors, small unmanned aircraft systems can promptly respond to airflow changes and improve flight performances. In this paper, a mapping function is proposed to compute aerodynamic moments from the real-time pressure and shear data in a practical and computationally tractable formulation. Since many microscale airflow sensors are embedded on the small unmanned aircraft system surface, it is highly possible that certain sensors may fail. Here, an adaptive control system is developed that is robust to sensor failure as well as other numerical mismatches in calculating real-time aerodynamic moments. The advantages of the proposed method are shown in the following simulation cases: (i) feedback pressure and wall shear data from a distributed array of 45 airflow sensors; (ii) 50% failure of the symmetrically distributed airflow sensor array; and (iii) failure of all the airflow sensors on one wing. It is shown that even if 50% of the airflow sensors have failures, the aircraft is still stable and able to track the attitude commands. (paper)

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

    Schiehlen, W.; Popp, K.


    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.

  8. Birth control - slow release methods

    Contraception - hormonal methods; Progestin implants; Progestin injections; Skin patch; Vaginal ring ... might want to consider a different birth control method. SKIN PATCH The skin patch is placed on ...

  9. On-orbit attitude control of the Cosmic Background Explorer (COBE)

    Bramberg, B.; Croft, J.


    The way in which COBE (launched by the SS in late 1982) performs its attitude control is described, along with the design of its on-orbit system. COBE, to be situated in a 900 km high, sun-synchronous orbit, contains two unique control features: (1) the orientation of the spinning satellite is controlled to a sun-normal attitude in the sun/local vertical plane; and (2) pitch and roll control is maintained by a unique triaxial arrangement of reaction wheels, magnetic torque bars and sensors, located in the body's tranverse plane. Inherent in this triaxial configuration concept is a built-in redundancy that will maintain attitude control in the event of any single-point sensor/actuator component failure. Each of the three control drive electronics operates independently and directly of a system of dedicated sensors. This system functions independently of a computer or an ephemeris communication link, leading to greater reliability.

  10. Methods in Logic Based Control

    Christensen, Georg Kronborg


    Desing and theory of Logic Based Control systems.Boolean Algebra, Karnaugh Map, Quine McClusky's algorithm. Sequential control design. Logic Based Control Method, Cascade Control Method. Implementation techniques: relay, pneumatic, TTL/CMOS,PAL and PLC- and Soft_PLC implementation. PLC...

  11. Magnetic attitude control system for dual-spin satellites

    Alfriend, K. T.


    A closed-loop control law is developed for a dual-spin satellite control system which utilizes the interaction of the geomagnetic field with the satellite dipole parallel to the spin axis. The control law consists of the linear combination of the pitch axis component of the rate of change of the geomagnetic field and the product of the roll angle and roll axis component of the geomagnetic field. Application of the method of multiple time scales yields approximate solutions for the feedback gains in terms of the system parameters. Approximate solutions are also obtained for the response of the system to disturbance torques. A comparison of the approximate solutions and numerical solutions obtained by numerical integration of the exact equations of motion is then given.

  12. Exploiting environmental torques for attitude control and determination of spin stabilized satellites

    Gluck, R.


    Design techniques are presented which exploit environmental torques for attitude control and determination of spin stabilized satellites. The techniques are applicable to satellite missions where the dominant environmental torques are well understood and lend themselves to accurate analytical modeling. The techniques were applied to the Particles and Fields subsatellites of the Apollo 15 and 16 spacecraft and the flight results show good agreement with the attitude determination estimates obtained.

  13. Micro Sun Sensor with CMOS Imager for Small Satellite Attitude Control

    Yoshihara, Keisuke; Hashimoto, Hidekazu; Yamamoto, Toru; Saito, Hirobumi; HIROKAWA, Eiji; Mita, Makoto; Magoshi, Kota


    A new type of Micro Sun Sensor (MSS) was started development for use on JAXA’s small satellites and space exploring spacecraft as attitude sensor. In recent years, small satellites are used for various missions, such as the Earth observation and science observation, and high functional attitude control system for small satellite is also required. Therefore, the sun sensor for small satellite is required to be good balance of its dimension, mass, power consumption and performance. The detector...

  14. Development of helicopter attitude axes controlled hover flight without pilot assistance and vehicle crashes

    Simon, Miguel

    testing any one or combination of the following attitude axes controlled flight: (1) pitch, (2) roll and (3) yaw. The subsequent development of a novel method to decouple, stabilize and teach the helicopter hover flight is a primary contribution of this thesis. The novel method included the development of a non-linear modeling technique for linearizing the RPM state equation dynamics so that a simple but accurate transfer function is derivable between the "available torque of the engine" and RPM. Specifically, the main rotor and tail rotor torques are modeled accurately with a bias term plus a nonlinear term involving the product of RPM squared times the main rotor blade pitch angle raised to the three-halves power. Application of this non-linear modeling technique resulted in a simple, representative and accurate transfer function model of the open-loop plant for the entire helicopter system so that all the feedback control laws for autonomous flight purposes could be derived easily using classical control theory. This is one of the contributions of this dissertation work. After discussing the integration of hardware and software elements of our helicopter research test bed system, we perform a number of experiments and tests using the two specially built test stands. Feedback gains are derived for controlling the following: (1) engine throttle to maintain prescribed main rotor angular speed, (2) main rotor collective pitch to maintain constant elevation, (3) longitudinal cyclic pitch to maintain prescribed pitch angle, (4) lateral cyclic pitch to maintain prescribed roll angle, and (5) yaw axis to maintain prescribed compass direction. (Abstract shortened by UMI.)

  15. Impact of an Oral Health Education Workshop on Parents’ Oral Health Knowledge, Attitude, and Perceived Behavioral Control among African Immigrants

    Maryam Amin; Pawan Nyachhyon; Maryam Elyasi; Muhammed Al-Nuaimi


    Purpose. To evaluate the impact of an educational workshop on parental knowledge, attitude, and perceived behavioral control regarding their child’s oral health. Materials and Methods. A one-time oral health education workshop including audio/visual and hands-on components was conducted by a trained dentist and bilingual community workers in community locations. Participants were African parents of children who had lived in Canada for less than ten years. The impact of the workshop was evalua...

  16. The Effects of Speech Training, Guidebook and Simultaneous Method, on the Knowledge and Attitude of Students about HIV/AIDS

    Rahim Vakili


    Full Text Available Introduction: A great percentage of AIDS infections occure in adolescence and youth. since that,studing and finding the most efficient teaching methods in order to improve their information ( knowledge and attitude also to create o positive one and to creat preventive measures in the young and adolescent,is of great significance and priority. Materials and Methods: 7 school were picked randomy among different Mashhad educational districts.From these schools,650 students were  randomy  selected and divided into 4 groups:1-education with lecture, 2-education with guidebook, 3-education with lecture and guidebook,  4-without any education. Firstly ,  basic knowledge and attitude of students on AIDS were evaluated. Then their educational needs and curriculum were designed. Then 2 weeeks after cinducting the  education,student's knowledge ( study groups and attitude were evaluated. Results: Average Points for knowledge and attitude before education were 25.86 and 23.70 that were elevated to 27.68  and 25.27 after  aducation. There was no  statistical difference between average points of all 4 groups' knowledge and attitude before education. After education, average point of knowledge was 28.33+5.6 in  lecture group,28.19+6.26 in guidebook group, 29.77+4.49 in lecture and guidebook group and 26.90+4.95 in control group. After  education, average  points of attitude  was 25.77+3.7 in lecture group, 25.62+3.47 in guidebook group, 25.27+3.87 in lecture and guidebook  group  and 23.98+3.56 in  control group. Statistical analyses  showed that there is significant difference between points before and after education in the 3 study groups ( PConclusion:  To improve  student's  knowledge,  education by both lecture and guidebook, and to improve their attitude or to create a positive one, lecture method are preferred.

  17. Combined control of fast attitude maneuver and stabilization for large complex spacecraft

    Zhang, Yao; Zhang, Jing-Rui


    In remote sensing or laser communication space missions, spacecraft need fast maneuver and fast stabilization in order to accomplish agile imaging and attitude tracking tasks. However, fast attitude maneuvers can easily cause elastic deformations and vibrations in flexible appendages of the spacecraft. This paper focuses on this problem and deals with the combined control of fast attitude maneuver and stabilization for large complex spacecraft. The mathematical model of complex spacecraft with flexible appendages and momentum bias actuators on board is presented. Based on the plant model and combined with the feedback controller, modal parameters of the closed-loop system are calculated, and a multiple mode input shaper utilizing the modal information is designed to suppress vibrations. Aiming at reducing vibrations excited by attitude maneuver, a quintic polynomial form rotation path planning is proposed with constraints on the actuators and the angular velocity taken into account. Attitude maneuver simulation results of the control systems with input shaper or path planning in loop are separately analyzed, and based on the analysis, a combined control strategy is presented with both path planning and input shaper in loop. Simulation results show that the combined control strategy satisfies the complex spacecraft's requirement of fast maneuver and stabilization with the actuators' torque limitation satisfied at the same time.

  18. New optimal control laws for attitude of a rigid body motion without angular velocity measurements

    El-Gohary, Awad [Department of Statistics and Operational Research, Faculty of Science King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)] e-mail:


    In this paper we shall use the passive properties of Euler dynamic equations as well as the structural properties of kinematic equations in terms of Cayley-Rodrigues and Modified Rodrigues parameters to derive optimal control laws without any information about the angular velocity of the rigid body. The interesting difference in the current study is the assumption that only the kinematics attitude parameters are available for the control process. The optimal control laws ensure the optimal asymptotic stability of the rigid body motion and minimize a selecting performance are obtained in terms of the kinematics attitude parameters and their estimates. Numerical examples are presented to demonstrate the theoretical results.

  19. The Development of a Low Cost, Modular Attitude Determination and Control System

    Surka, Derek; Paluszek, Michael


    In an attempt to reduce the cost of future satellites, new technologies are being pursued to develop a modular attitude determination and control system that will provide three-axis control and cost less than ten percent of present systems. The low cost and modularity of this system make it especially attractive to a wide variety of small satellites. This paper will present the design and developmental status of this "plug and play" attitude control system. The general idea is to provide a co...

  20. Spacecraft Hybrid (Mixed-Actuator) Attitude Control Experiences on NASA Science Missions

    Dennehy, Cornelius J.


    There is a heightened interest within NASA for the design, development, and flight implementation of mixed-actuator hybrid attitude control systems for science spacecraft that have less than three functional reaction wheel actuators. This interest is driven by a number of recent reaction wheel failures on aging, but what could be still scientifically productive, NASA spacecraft if a successful hybrid attitude control mode can be implemented. Over the years, hybrid (mixed-actuator) control has been employed for contingency attitude control purposes on several NASA science mission spacecraft. This paper provides a historical perspective of NASA's previous engineering work on spacecraft mixed-actuator hybrid control approaches. An update of the current situation will also be provided emphasizing why NASA is now so interested in hybrid control. The results of the NASA Spacecraft Hybrid Attitude Control Workshop, held in April of 2013, will be highlighted. In particular, the lessons learned captured from that workshop will be shared in this paper. An update on the most recent experiences with hybrid control on the Kepler spacecraft will also be provided. This paper will close with some future considerations for hybrid spacecraft control.

  1. Near minimum-time feedback attitude control with multiple saturation constraints for agile satellites

    Liu Xiangdong; Xin Xing; Li Zhen; Chen Zhen; Sheng Yongzhi


    Agile satellites are of importance in modern aerospace applications, but high mobility of the satellites may cause them vulnerable to saturation during attitude maneuvers due to limited rating of actuators. This paper proposes a near minimum-time feedback control law for the agile satellite attitude control system. The feedback controller is formed by specially designed cascaded sub-units. The rapid dynamic response of the modified Bang–Bang control logic achieves the near optimal property and ensures the non-saturation properties on three-axis. To improve the dynamic performance, a model reference control strategy is proposed, in which the on-line near optimal attitude maneuver path is generated by the cascade controller and is then tracked by a nonlinear back-stepping controller. Furthermore, the accuracy and the robustness of the control system are achieved by momentum-based on-line inertial identification. The rapid attitude maneuvering can be applied for tasks including the move to move case. Numerical simulations are conducted to verify the effectiveness of the proposed control strategy in terms of the saturation-free property and rapidness.


    Orlov A. I.


    Full Text Available Statistical control is a sampling control based on the probability theory and mathematical statistics. The article presents the development of the methods of statistical control in our country. It discussed the basics of the theory of statistical control – the plans of statistical control and their operational characteristics, the risks of the supplier and the consumer, the acceptance level of defectiveness and the rejection level of defectiveness. We have obtained the asymptotic method of synthesis of control plans based on the limit average output level of defectiveness. We have also developed the asymptotic theory of single sampling plans and formulated some unsolved mathematical problems of the theory of statistical control

  3. An Aerial Image Mosaic Method Based on UAV Position and Attitude Information

    CHENG Zhenggang


    Full Text Available As the existing methods for aerial image mosaic take high computational, a fast and effective algorithm based on the position and attitude information of unmanned aerial vehicles (UAV is proposed. Firstly, the coordinates and attitude angles of UAV can be obtained by airborne GPS and inertial measurement unit (IMU, and each aerial image has a corresponding position and attitude information. The homography matrix between two aerial images with the positions and attitude information can be calculated. Then the registration of the mosaic images is obtained by the operation of homography matrix. Finally, the multiple images can be stitched and the whole panorama got. A large number of experiments demonstrate this algorithm is efficient.

  4. The Effect of Teaching Methods on Examination Performance and Attitudes in an Introductory Financial Accounting Course.

    Marcheggiani, Joseph; Davis, Karel A.; Sander, James F.


    Comparison of accounting students taught with a group Socratic method (n=22) and interactive lecture method (n=15) found no evidence that either method significantly improved examination scores. Student attitudes toward the course or the accounting profession did not differ. (SK)

  5. Maternal and Paternal Psychological Control as Moderators of the Link between Peer Attitudes and Adolescents’ Risky Sexual Behavior

    Oudekerk, Barbara A.; Allen, Joseph P.; Hafen, Christopher A.; Hessel, Elenda T.; Szwedo, David E.; Spilker, Ann


    Maternal and paternal psychological control, peer attitudes, and the interaction of psychological control and peer attitudes at age 13 were examined as predictors of risky sexual behavior before age 16 in a community sample of 181 youth followed from age 13 to 16. Maternal psychological control moderated the link between peer attitudes and sexual behavior. Peer acceptance of early sex predicted greater risky sexual behaviors, but only for teens whose mothers engaged in high levels of psycholo...

  6. An Attitude Control System for SumbandilaSAT an Earth Observation Satellite

    Steyn, W. H.


    This paper describes the attitude determination and control system to support the multi-spectral earth observation main payload of the SumbandilaSAT microsatellite. The satellite has only a single main Y- body mounted solar panel and the attitude control system must ensure a nominal sun-pointed attitude under all non-imaging conditions during the sunlit part of the orbit. The control actuators employed are 3- axis magnetic torquer rods and reaction wheels. During initial detumbling and safe mode operations a simple new magnetic control law is used to bring the satellite to a sun-pointed Y-spinning attitude for maximum solar power collection. From this sun-pointed, spinning attitude an intermediate control mode is entered when the Y-reaction wheel is utilised as a momentum wheel, to absorb the body spin rate and to inertially stabilise the angular momentum vector towards the sun direction. During the intermediate mode the magnetic rods are used to maintain the momentum vector size and direction and to do nutation damping. The pitch angle is also controlled using the Y-wheel, to keep the main imager payload as close as possible to an earth-pointed attitude and to thermally stabilise the imager telescope. The final and nominal attitude control mode is entered when a zero biased 3-axis reaction wheel controller is enabled, for: 1) sun tracking for optimal solar power collection, 2) target tracking during viewfinder use or during imaging download communication with a ground station and 3) pushbroom imager scanning with a forward motion compensation capability. During the nominal mode the magnetic rods are used to dump the angular momentum from the reaction wheels during sun tracking periods. A short introduction to the Sumbandila satellite will be given. All the control modes, the attitude sensors and estimators utilised, will be introduced in the paper. Specifically, a unique agile viewfinder control mode to manually select targets for subsequent high resolution image

  7. Space Satellite Dynamics with Applications to Sunlight Pressure Attitude Control. Ph.D. Thesis

    Stuck, B. W.


    A research program into three aspects of space satellite dynamics was carried out. First, a four-dimensional space-time formulation of Newtonian mechanics is developed. This theory allows a new physical interpretation of the conservation theorems of mechanics first derived rigorously by Noether. Second, a new concept for estimating the three angles which specify the orientation in space of a rigid body is presented. Two separate methods for implementing this concept are discussed, one based on direction cosines, the other on quaternions. Two examples are discussed: constant orientation in space, and constant rate of change of the three angles with time. Third, two synchronous equatorial orbit communication satellite designs which use sunlight pressure to control their attitude are analyzed. Each design is equipped with large reflecting surfaces, called solar sails, which can be canted in different directions to generate torques to correct pointing errors.

  8. Full quaternion based finite-time cascade attitude control approach via pulse modulation synthesis for a spacecraft.

    Mazinan, A H; Pasand, M; Soltani, B


    In the aspect of further development of investigations in the area of spacecraft modeling and analysis of the control scheme, a new hybrid finite-time robust three-axis cascade attitude control approach is proposed via pulse modulation synthesis. The full quaternion based control approach proposed here is organized in association with both the inner and the outer closed loops. It is shown that the inner closed loop, which consists of the sliding mode finite-time control approach, the pulse width pulse frequency modulator, the control allocation and finally the dynamics of the spacecraft is realized to track the three-axis referenced commands of the angular velocities. The pulse width pulse frequency modulators are in fact employed in the inner closed loop to accommodate the control signals to a number of on-off thrusters, while the control allocation algorithm provides the commanded firing times for the reaction control thrusters in the overactuated spacecraft. Hereinafter, the outer closed loop, which consists of the proportional linear control approach and the kinematics of the spacecraft is correspondingly designed to deal with the attitude angles that are presented by quaternion vector. It should be noted that the main motivation of the present research is to realize a hybrid control method by using linear and nonlinear terms and to provide a reliable and robust control structure, which is able to track time varying three-axis referenced commands. Subsequently, a stability analysis is presented to verify the performance of the overall proposed cascade attitude control approach. To prove the effectiveness of the presented approach, a thorough investigation is presented compared to a number of recent corresponding benchmarks. PMID:26142216

  9. Quaternion-based adaptive output feedback attitude control of spacecraft using Chebyshev neural networks.

    Zou, An-Min; Dev Kumar, Krishna; Hou, Zeng-Guang


    This paper investigates the problem of output feedback attitude control of an uncertain spacecraft. Two robust adaptive output feedback controllers based on Chebyshev neural networks (CNN) termed adaptive neural networks (NN) controller-I and adaptive NN controller-II are proposed for the attitude tracking control of spacecraft. The four-parameter representations (quaternion) are employed to describe the spacecraft attitude for global representation without singularities. The nonlinear reduced-order observer is used to estimate the derivative of the spacecraft output, and the CNN is introduced to further improve the control performance through approximating the spacecraft attitude motion. The implementation of the basis functions of the CNN used in the proposed controllers depends only on the desired signals, and the smooth robust compensator using the hyperbolic tangent function is employed to counteract the CNN approximation errors and external disturbances. The adaptive NN controller-II can efficiently avoid the over-estimation problem (i.e., the bound of the CNNs output is much larger than that of the approximated unknown function, and hence, the control input may be very large) existing in the adaptive NN controller-I. Both adaptive output feedback controllers using CNN can guarantee that all signals in the resulting closed-loop system are uniformly ultimately bounded. For performance comparisons, the standard adaptive controller using the linear parameterization of spacecraft attitude motion is also developed. Simulation studies are presented to show the advantages of the proposed CNN-based output feedback approach over the standard adaptive output feedback approach. PMID:20729168

  10. A distributed system adaptive control strategy. [for attitude control of large spacecraft

    Johnson, C. R., Jr.; Montgomery, R. C.


    One attitude control device being studied for large spacecraft consists of two counter-rotating rings, each designated as an annular momentum control device (AMCD), that are attached to a spacecraft using several magnetic bearings distributed along the circumference of the rings. For large spacecraft large rings are desirable. Unfortunately, for large rings flexibility is appreciable and it becomes necessary to account for the distributed nature of the rings in the design of the magnetic bearing controllers. Also ring behavior is unpredictably sensitive to ring temperature, spin rate, manufacturing imperfections, and other variables. For that reason a distributed adaptive microcomputer-based control system is being sought for ring stabilization and maneuvering. An original adaptive-control methodology for distributed-parameter systems is detailed and application to spinning ring, i.e., AMCD, stabilization is used as an illustration. The proposed methodology, presented as a step-by-step procedure, combines a lumped-parameter expansion description of distributed parameter systems with a fundamental simultaneous identification and control strategy. Simulations are presented providing preliminary evidence of the capabilities of the proposed procedure.

  11. Roles of superconducting magnetic bearings and active magnetic bearings in attitude control and energy storage flywheel

    Compared with conventional energy storage flywheel, the rotor of attitude control and energy storage flywheel (ACESF) used in space not only has high speed, but also is required to have precise and stable direction. For the presented superconducting magnetic bearing (SMB) and active magnetic bearing (AMB) suspended ACESF, the rotor model including gyroscopic couples is established originally by taking the properties of SMB and AMB into account, the forces of SMB and AMB are simplified by linearization within their own neighbors of equilibrium points. For the high-speed rigid discal rotor with large inertia, the negative effect of gyroscopic effect of rotor is prominent, the radial translation and tilting movement of rotor suspended by only SMB, SMB with equivalent PMB, or SMB together with PD controlled AMB are researched individually. These analysis results proved originally that SMB together with AMB can make the rotor be stable and make the radial amplitude of the vibration of rotor be small while the translation of rotor suspended by only SMB or SMB and PM is not stable and the amplitude of this vibration is large. For the stability of the high-speed rotor in superconducting ACESF, the AMB can suppress the nutation and precession of rotor effectively by cross-feedback control based on the separated PD type control or by other modern control methods.

  12. Attitude Control of Quad-rotor by Improving the Reliability of Multi-Sensor System

    Yu, Dong Hyeon; Chong, Kil To [Chon-bok National University, Jeonju (Korea, Republic of); Park, Jong Ho [Seonam University, Namwon (Korea, Republic of); Ryu, Ji Hyoung [ETRI, Daejeon (Korea, Republic of)


    This paper presents the results of study for improving the reliability of quadrotor attitude control by applying a multi-sensor along with a data fusion algorithm. First, a mathematical model of the quadrotor dynamics was developed. Then, using the quadrotor mathematical model, simulations were performed using the improved reliability multi-sensor data as the inputs. From the simulation results, we designed a Gimbal-equipped quadrotor system. With the quadrotor in a hover state, we performed experiments according to the angle change of the user's specifications . We then calculated the attitude control data from the actual experimental data. Furthermore, with additional simulations, we verified the performance of the designed quadrotor attitude control system with multiple sensors.

  13. Attitude Control of Quad-rotor by Improving the Reliability of Multi-Sensor System

    This paper presents the results of study for improving the reliability of quadrotor attitude control by applying a multi-sensor along with a data fusion algorithm. First, a mathematical model of the quadrotor dynamics was developed. Then, using the quadrotor mathematical model, simulations were performed using the improved reliability multi-sensor data as the inputs. From the simulation results, we designed a Gimbal-equipped quadrotor system. With the quadrotor in a hover state, we performed experiments according to the angle change of the user's specifications . We then calculated the attitude control data from the actual experimental data. Furthermore, with additional simulations, we verified the performance of the designed quadrotor attitude control system with multiple sensors

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

    Wolfe, Scott Michael


    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 responsiven...

  15. Understanding Factors that Shape Gender Attitudes in Early Adolescence Globally: A Mixed-Methods Systematic Review

    Gibbs, Susannah; Blum, Robert Wm; Moreau, Caroline; Chandra-Mouli, Venkatraman; Herbert, Ann; Amin, Avni


    Background Early adolescence (ages 10–14) is a period of increased expectations for boys and girls to adhere to socially constructed and often stereotypical norms that perpetuate gender inequalities. The endorsement of such gender norms is closely linked to poor adolescent sexual and reproductive and other health-related outcomes yet little is known about the factors that influence young adolescents’ personal gender attitudes. Objectives To explore factors that shape gender attitudes in early adolescence across different cultural settings globally. Methods A mixed-methods systematic review was conducted of the peer-reviewed literature in 12 databases from 1984–2014. Four reviewers screened the titles and abstracts of articles and reviewed full text articles in duplicate. Data extraction and quality assessments were conducted using standardized templates by study design. Thematic analysis was used to synthesize quantitative and qualitative data organized by the social-ecological framework (individual, interpersonal and community/societal-level factors influencing gender attitudes). Results Eighty-two studies (46 quantitative, 31 qualitative, 5 mixed-methods) spanning 29 countries were included. Ninety percent of studies were from North America or Western Europe. The review findings indicate that young adolescents, across cultural settings, commonly express stereotypical or inequitable gender attitudes, and such attitudes appear to vary by individual sociodemographic characteristics (sex, race/ethnicity and immigration, social class, and age). Findings highlight that interpersonal influences (family and peers) are central influences on young adolescents’ construction of gender attitudes, and these gender socialization processes differ for boys and girls. The role of community factors (e.g. media) is less clear though there is some evidence that schools may reinforce stereotypical gender attitudes among young adolescents. Conclusions The findings from this

  16. Optimal attitude determination method in presence of noise and bias on different star sensors

    Amir Moghtadaei Rad


    Full Text Available There are different attitude determination methods which have been used in satellite and spacecraft by star tracker. Each of these methods have its own advantages and disadvantages depending on their application, stochastic characteristic of noise on sensors (bias or noise, and weight of noise falling on different sensors. The present study has thus explored the major methods from two perspectives: the effect of input noise or bias on each star sensor and the corresponding weight of each noise or bias falling on each sensor. These aspects are compared in each method and the optimal method according to each condition is introduced. N Vector, Triad, Quest, Q method and least square method are the methods studied and simulated in this article. Finally, a comparison is made between the methods and the optimal method is introduced theoretically and practically.   Keywords: Attitude Determination, Celestial Navigation, Triad, Quest, Least Square, Satellite.

  17. Design and Integration of an All-Magnetic Attitude Control System for FASTSAT-HSV01's Multiple Pointing Objectives

    DeKock, Brandon; Sanders, Devon; Vanzwieten, Tannen; Capo-Lugo, Pedro


    The FASTSAT-HSV01 spacecraft is a microsatellite with magnetic torque rods as it sole attitude control actuator. FASTSAT s multiple payloads and mission functions require the Attitude Control System (ACS) to maintain Local Vertical Local Horizontal (LVLH)-referenced attitudes without spin-stabilization, while the pointing errors for some attitudes be significantly smaller than the previous best-demonstrated for this type of control system. The mission requires the ACS to hold multiple stable, unstable, and non-equilibrium attitudes, as well as eject a 3U CubeSat from an onboard P-POD and recover from the ensuing tumble. This paper describes the Attitude Control System, the reasons for design choices, how the ACS integrates with the rest of the spacecraft, and gives recommendations for potential future applications of the work.

  18. Control, Attitudes de se and Immunity to Error Through Misidentification

    Gaetano Fiorin


    Full Text Available In his work on attitudes de se, James Higginbotham has observed that the silent subject of the infinitival complements of verbs such as remember and imagine is (i unambiguously de se and (ii immune to error through misidentification relatively to the subject of the matrix clause. In this article, we review and criticize Higginbotham’s reflexive analysis of these infinitival complements. We also show that the type of criticism we raise against Higginbotham’s account applies likewise to analyses based on the use of acquaintance relations and centered possible worlds. Finally, following recent ideas in cognitive science, we propose an amendment to Higginbotham’s account based on the idea that the thematic-role “Experiencer” corresponds to a function mapping events into “minimal selves”, in the sense of Shaun Gallagher.

  19. Finite-Time Anti-Disturbance Inverse Optimal Attitude Tracking Control of Flexible Spacecraft

    Chutiphon Pukdeboon


    Full Text Available We propose a new robust optimal control strategy for flexible spacecraft attitude tracking maneuvers in the presence of external disturbances. An inverse optimal control law is designed based on a Sontag-type formula and a control Lyapunov function. An adapted extended state observer is used to compensate for the total disturbances. The proposed controller can be expressed as the sum of an inverse optimal control and an adapted extended state observer. It is shown that the developed controller can minimize a cost functional and ensure the finite-time stability of a closed-loop system without solving the associated Hamilton-Jacobi-Bellman equation directly. For an adapted extended state observer, the finite-time convergence of estimation error dynamics is proven using a strict Lyapunov function. An example of multiaxial attitude tracking maneuvers is presented and simulation results are included to show the performance of the developed controller.

  20. Efficacy of the Cooperative Learning Method on Mathematics Achievement and Attitude: A Meta-Analysis Research

    Capar, Gulfer; Tarim, Kamuran


    This research compiles experimental studies from 1988 to 2010 that examined the influence of the cooperative learning method, as compared with that of traditional methods, on mathematics achievement and on attitudes towards mathematics. The related field was searched using the following key words in Turkish "matematik ve isbirlikli ögrenme,…

  1. Design and analysis of a moment control unit for agile satellite with high attitude stability requirement

    Zhang, Yao; Li, Mou; Song, Zhuoyue; Shan, Jinjun; Guan, Xin; Tang, Liang


    A moment control unit is developed and verified by numerical simulation. This moment control unit is employed as an actuator for the satellite attitude control. It contains four control moment gyroscopes (CMGs) to realize the rapid attitude maneuver and a vibration isolation system for each CMG. This unit can not only reduce the required electronics for each CMG and thus the weight, but also improve the stability of the satellite attitude. The design of the structure is presented first. This structure not only holds and protects the CMGs, but also isolates the vibrations caused by each CMG. Then, a dynamic model of a single CMG with a vibration isolation system is formulated, and the time- and frequency-domain characteristics of this dynamic model are discussed. Numerical simulations of a satellite attitude control example are then used to evaluate the system. The new moment control unit occupies less volume than previous designs, and the results show that the new design improves satellite pointing performance because of the vibration isolation.

  2. Multivariable control theory applied to hierarchial attitude control for planetary spacecraft

    Boland, J. S., III; Russell, D. W.


    Multivariable control theory is applied to the design of a hierarchial attitude control system for the CARD space vehicle. The system selected uses reaction control jets (RCJ) and control moment gyros (CMG). The RCJ system uses linear signal mixing and a no-fire region similar to that used on the Skylab program; the y-axis and z-axis systems which are coupled use a sum and difference feedback scheme. The CMG system uses the optimum steering law and the same feedback signals as the RCJ system. When both systems are active the design is such that the torques from each system are never in opposition. A state-space analysis was made of the CMG system to determine the general structure of the input matrices (steering law) and feedback matrices that will decouple the axes. It is shown that the optimum steering law and proportional-plus-rate feedback are special cases. A derivation of the disturbing torques on the space vehicle due to the motion of the on-board television camera is presented. A procedure for computing an upper bound on these torques (given the system parameters) is included.

  3. Understanding Factors that Shape Gender Attitudes in Early Adolescence Globally: A Mixed-Methods Systematic Review.

    Anna Kågesten

    Full Text Available Early adolescence (ages 10-14 is a period of increased expectations for boys and girls to adhere to socially constructed and often stereotypical norms that perpetuate gender inequalities. The endorsement of such gender norms is closely linked to poor adolescent sexual and reproductive and other health-related outcomes yet little is known about the factors that influence young adolescents' personal gender attitudes.To explore factors that shape gender attitudes in early adolescence across different cultural settings globally.A mixed-methods systematic review was conducted of the peer-reviewed literature in 12 databases from 1984-2014. Four reviewers screened the titles and abstracts of articles and reviewed full text articles in duplicate. Data extraction and quality assessments were conducted using standardized templates by study design. Thematic analysis was used to synthesize quantitative and qualitative data organized by the social-ecological framework (individual, interpersonal and community/societal-level factors influencing gender attitudes.Eighty-two studies (46 quantitative, 31 qualitative, 5 mixed-methods spanning 29 countries were included. Ninety percent of studies were from North America or Western Europe. The review findings indicate that young adolescents, across cultural settings, commonly express stereotypical or inequitable gender attitudes, and such attitudes appear to vary by individual sociodemographic characteristics (sex, race/ethnicity and immigration, social class, and age. Findings highlight that interpersonal influences (family and peers are central influences on young adolescents' construction of gender attitudes, and these gender socialization processes differ for boys and girls. The role of community factors (e.g. media is less clear though there is some evidence that schools may reinforce stereotypical gender attitudes among young adolescents.The findings from this review suggest that young adolescents in different

  4. Hierarchical structured robust adaptive attitude controller design for reusable launch vehicles

    Guangxue Yu; Huifeng Li


    Reentry attitude control for reusable launch vehicles (RLVs) is chal enging due to the characters of fast nonlinear dy-namics and large flight envelop. A hierarchical structured attitude control system for an RLV is proposed and an unpowered RLV con-trol model is developed. Then, the hierarchical structured control frame consisting of attitude control er, compound control strategy and control al ocation is presented. At the core of the design is a robust adaptive control (RAC) law based on dual loop time-scale separation. A radial basis function neural network (RBFNN) is implemented for compensation of uncertain model dynamics and external disturbances in the inner loop. And then the robust op-timization is applied in the outer loop to guarantee performance robustness. The overal control design frame retains the simplicity in design while simultaneously assuring the adaptive and robust performance. The hierarchical structured robust adaptive con-trol er (HSRAC) incorporates flexibility into the design with regard to control er versatility to various reentry mission requirements. Simulation results show that the improved tracking performance is achieved by means of RAC.

  5. Attitude Controller for the Atmospheric Entry of the Mars Science Laboratory

    Brugarolas, Paul B.; San Martin, A. Miguel; Wong, Edward C.


    This paper describes the attitude controller for the atmospheric entry of the Mars Science Laboratory (MSL). The controller will command 8 RCS thrusters to control the 3- axis attitude of the entry capsule. The Entry Controller is formulated as three independent channels in the control frame, which is nominally aligned with the stability frame. Each channel has a feedfoward and a feedback path. The feedforward path enables fast response to large bank commands. The feedback path stabilizes the vehicle angle of attack and sideslip around its trim position, and tracks bank commands. The feedback path has a PD/D control structure with deadbands that minimizes fuel usage. The performance of this design is demonstrated via computer simulations.

  6. Attitude Estimation and Position Control of VTOL UAVs using IMU and GPS Measurements

    Roberts, Andrew


    We address two fundamental problems associated with the control of vertical take-off and landing (VTOL) unmanned airborne vehicles (UAVs): attitude estimation and position control. We propose two velocity-aided attitude observers which utilize a global-positioning system (GPS) in addition to an inertial measurement unit (IMU). The `velocity-aided' class of observer uses an accelerometer to measure the system \\emph{apparent acceleration} (instead of the gravity vector), and is therefore better suited for applications where the rigid-body (aircraft) is subjected to significant linear accelerations (which is to be expected for VTOL UAVs). We also propose a position controller which utilizes the accelerometer in a similar fashion. More precisely, rather than using the system orientation (as is usually done in the existing position controllers), we use the vector measurements (accelerometer and magnetometer measurements) directly in the position control law. Consequently, the proposed position controller does not ...


    F. Contreras


    Full Text Available A frictionless environment simulation platform, utilized for accomplishing three-axis attitude control tests in small satellites,is introduced. It is employed to develop, improve, and carry out objective tests of sensors, actuators, and algorithms in theexperimental framework. Different sensors (i.e. sun, earth, magnetometer, and an inertial measurement unit are utilizedto assess three-axis deviations. A set of three inertial wheels is used as primary actuators for attitude control, together withthree mutually perpendicular magnetic coils intended for desaturation purposes, and as a backup control system. Accuratebalancing, through the platform’s center of mass relocation into the geometrical center of the spherical air-bearing,significatively reduces gravitational torques, generating a virtually torque-free environment. A very practical balancingprocedure was developed for equilibrating the table in the local horizontal plane, with a reduced final residual torque. Awireless monitoring system was developed for on-line and post-processing analysis; attitude data are displayed and stored,allowing properly evaluate the sensors, actuators, and algorithms. A specifically designed onboard computer and a set ofmicrocontrollers are used to carry out attitude determination and control tasks in a distributed control scheme.The main components and subsystems of the simulation platform are described in detail.

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

    DeWeese, Keith


    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.

  9. Impact of an Oral Health Education Workshop on Parents’ Oral Health Knowledge, Attitude, and Perceived Behavioral Control among African Immigrants

    Maryam Amin


    Full Text Available Purpose. To evaluate the impact of an educational workshop on parental knowledge, attitude, and perceived behavioral control regarding their child’s oral health. Materials and Methods. A one-time oral health education workshop including audio/visual and hands-on components was conducted by a trained dentist and bilingual community workers in community locations. Participants were African parents of children who had lived in Canada for less than ten years. The impact of the workshop was evaluated by a questionnaire developed based on the theory of planned behavior. Results. A total of 105 parents participated in this study. Participants were mainly mothers (mean age 35.03±5.4 years who came to Canada as refugee (77.1% and had below high school education (70%. Paired t-test showed a significant difference in participants’ knowledge of caries, preventive measures, and benefits of regular dental visits after the workshop (P value<0.05. A significant improvement was also found in parental attitudes toward preventive measures and their perceived behavioral control (P<0.05. Parents’ intention to take their child to a dentist within six months significantly altered after the workshop (P value<0.05. Conclusions. A one-time hands-on training was effective in improving parental knowledge, attitude, perceived behavioral control, and intention with respect to their child’s oral health and preventive dental visits in African immigrants.

  10. Attitude Control of a Small Coaxial Helicopter with a Bell Type Stabilizer Bar

    Sunada, Shigeru; Hirosue, Wataru; Kawashima, Kenta

    We analyzed the small coaxial helicopter recently developed for entertainment. The upper rotor is connected with a stabilizer bar alone and the lower rotor is not connected with it. The cyclic pitch of the upper rotor is controlled by this stabilizer bar, and that of the lower rotor is controlled by servo motors. We investigated how this stabilizer bar varies the cyclic pitch of the upper rotor and how it contributes to attitude control of a fuselage.