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Design of Nonlinear Observer and Controller for Satellite Attitude Estimation and Control

Khosravian, Alireza | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41015 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Namvar, Mehrzad
  7. Abstract:
  8. The goal of the attitude determination is to determine the orientation of a satellite with respect to a reference frame. For this purpose, gyroscopes are used to measure the satellite’s angular velocity. Also, the attitude sensors such as magnetometers, Sun sensors, Earth sensors or star trackers are employed to collect vector measurements. The aim of the attitude control is to calculate the torque which is needed to be applied to the satellite such that its orientation and angular velocity converge to their desired values. It is usual to determine the attitude of satellite first and then use it in the attitude control algorithms. When multiple independent vector measurements are available, the orientation of satellite can be calculated by the algebraic techniques, or the existing attitude estimators in literature. However, due to practical limitations, in some situations only a single vector measurement is available and hence using the mentioned methods is impossible. In this thesis, the problem of estimating and controlling the satellite’s attitude by using gyro together with a single vector measurement is discussed. The innovation presented here is to use only a single vector measurement for the attitude estimation and control. Specifically, we present some preliminary discussions on the attitude determination, and introduce the sensors and actuators used in satellites. Afterwards, a nonlinear observer is presented to estimate the satellite attitude using gyro and a single vector measurement. Globally exponentially convergence of attitude estimation error to zero is proven via the Lyapunov analysis and without demanding persistency of excitation conditions. Performance of the observer is illustrated by realistic simulations and compared with Kalman filter in the same conditions. The proposed observer is then used in a nonlinear controller to achieve attitude control using gyro and a single vector measurement. Moreover, the inertia matrix of the satellite is assumed to be unknown and consequently its estimate is adaptively used in the controller. The convergence of attitude tracking error to zero, is proven via the Lyapunov analysis. Finally, performance of the coupled attitude estimator and controller is shown in a realistic simulation.
  9. Keywords:
  10. Satellite Attitude Control ; Attitude Control ; Nonlinear Controller ; Nonlinear Observer ; Attitude Estimation ; Vector Measurement

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