Fault-tolerant spacecraft attitude control under actuator saturation and without angular velocity

In this paper, a fault-tolerant control scheme is proposed to control the attitude of a rigid spacecraft subject to external disturbances and multiple system uncertainties, as well as actuator faults and saturation. More challengingly, it is assumed that the angular velocity is unavailable. A super-twisting observer with time-varying gain is firstly designed to accurately estimate the angular velocity in finite time. The choice of the time-varying gain is dependent on a state-norm estimate. Then, using the information from the observer (estimate of angular velocity), a fault-tolerant controller is proposed, where an adaptive law is introduced to address the unknown loss of effectiveness and neural networks are used to approximate the unknown nonlinear functions. It is proved that the attitude orientations converge to the desired values at a fixed time. Finally, a simulation example is utilized to verify the effectiveness of the proposed scheme.