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Space vehicle motion recovery in presence of actuator failure Karami, Mohammad Amin

Abstract

Recovery control methods have been proposed to tolerate the failure of the thrusters used in the attitude control system of spacecraft. Thrusters are used, in pair, in the spacecraft control system to exert external pure torques on the spacecraft. These torques can either be directly used to perform the rotational maneuvers or can be used to remove the angular momentum built up in the momentum wheels of the spacecraft. The problem of stabilizing a spacecraft subjected to disturbance torques with control torques about two of its principal axes is addressed for the first time in this research. It has been shown that a stable equilibrium, best matching the objectives of the mission, has to be found. Two control laws have been proposed to arrive at the newly defined stable equilibrium. The first law, a nonlinear kinematic control scheme, is based on the Lyapunov method. The second law, which linearizes the system about the equilibrium point, uses the pole placement method as a kinematic controller. In both control laws, after the kinematic controller is developed, the backstepping method is used to derive the control efforts at each instance of the spacecraft corrective motion. Torque thrusters are used for momentum removal of the spacecraft momentum wheels. Malfunctioning of these thrusters therefore hinders momentum dumping process. The spinning speeds of the spacecraft momentum wheels increases by time until they become saturated and the control over the attitude of the spacecraft is lost. The momentum removal procedures using external control torques about two or even one principal axis of the spacecraft is proposed for the first time in this research. All the proposed control methods have been examined using numerical simulations and are shown to achieve desired performance.

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