Fault tolerant nano-satellite attitude control by adaptive modified nonsingular fast terminal control

In this paper, an adaptive fault tolerant nonlinear control is proposed for attitude tracking problem of satellite with three magnetorquers and one reaction wheel in the presence of inertia uncertainties, external disturbances, and actuator faults. Firstly, sliding surface variable is chosen based on avoiding the singularity of control signal and guaranteeing the convergence of attitude tracking error to zero in a finite-time. Subsequently, modified non-singular fast terminal sliding mode is designed as fault tolerant control approach. Then, the control gain of reaching law is adaptively designed to improve the performance of proposed controller. The adaptive control gain is designed independent of the upper and lower bounds of the actuator effectiveness factors. Stability proof is performed by Lyapunov function candidate to show that attitude tracking errors and angular velocities are converged to zero. To evaluate the performance of proposed method, simulation results are compared with their non-adaptive version. Outcomes show better performance of the proposed controller in tracking the desired attitude, a significant reduction in convergence time, and reduction in the chattering of control torque.