Finite-Time Adaptive Sliding Mode Fault-Tolerant Attitude Control for Flexible Spacecraft

This article presents an adaptive fault-tolerant attitude control (FTAC) system designed for flexible spacecraft with minimum computational burden. It offers exceptional energy efficiency and robust anti-unwinding capabilities. First, the spacecraft system dynamics are redefined for the actuator’s performance matrix by considering the flexible appendage’s vibration effects, inertial uncertainties, external disturbances, and faults associated with the actuators (misalignment, bias, and loss of effectiveness). The control scheme is conceived by introducing a modified nonsingular terminal sliding mode (MNTSM) surface with an imposed constraint, and a modal vibration observer (MVO) estimates vibrations induced by flexible appendages. Then, based on the designed sliding manifold, an adaptive law and switching function are employed to estimate and compensate lumped disturbances. Subsequently, an anti-unwinding finite-time adaptive sliding mode (AFASM) fault-tolerant control law is proposed. The remarkable characteristic of the proposed control is its ability to simultaneously handle unwinding and modal vibrations in the presence of actuator faults and demonstrate finite-time precise attitude tracking. The stability and finite-time convergence of the proposed control is established using the Lyapunov and finite-time theory. Finally, numerical simulations illustrate the effectiveness and efficacy of the propounded control for fault-free and faulty actuator scenarios.