Fault reconstruction and fault tolerant attitude control for over-activated spacecraft under reaction wheel failure

A novel attitude control scheme is proposed for a rigid spacecraft with four reaction wheels as actuators in the presence of actuator failure and external disturbances. More specially, a sliding mode observer is firstly designed to accurately reconstruct reaction wheel faults in finite time, and it is proved from the Lyapunov analysis that the satellite attitude and the angular rate are governed in finite time to be asymptotically stable, and the proposed control law can be utilized to deal with actuator faults and external disturbances. In addition, the base sequence optimal control allocation method is also applied to accomplish the distribution from desired control torque to the commanded control torque of four reaction wheels. Finally, a numerical simulation example for a spacecraft attitude control system is included to illustrate effectiveness and feasibility of the proposed control scheme.