Adaptive Modified Sliding-Mode-based Attitude Control of a Satellite Under Reaction Wheel Fault

In this paper, passive adaptive modified sliding-mode-based fault tolerant control is designed to track the desired attitude of a satellite with four reaction wheels in the presence of external disturbances, system uncertainties, and actuator fault. In order to achieve this goal, the adaptive modified fast terminal SMC has been used, due to its robustness against the unmodeled uncertainties and the design of control method for the nonlinear model of system. To improve the performance of the controller, the sliding surface is selected in a way that the tracking error converges in a finite time to a small neighborhood of the origin, which is proved using the extended Lyapunov law, and avoids the singularity of the control law. The adverse effects caused by the uncertainties are reduced using an adaptive parameter in the reaching phase of the control law. This reduces the tracking error and as a result, the performance of the closed loop system is improved. Also, the adaptive parameter and sliding surface are applied as a coefficient of the reaching phase to eliminate the chattering phenomenon. The simulation results indicate the high precision attitude tracking, chattering-free, and the improved performance of closed-loop system.