Near optimal sliding mode attitude control for spacecraft with faults and uncertainties: A learning and observer...

Spacecraft are widely utilized in diverse space missions due to their high maneuverability, where mission success is contingent upon accurate attitude control. However, inertia uncertainty, external disturbances, and actuator faults pose persistent challenges to achieving high robustness and tracking precision with low control effort. This paper investigates near optimal spacecraft attitude control in the presence of lumped uncertainties. First, a fixed-time disturbance observer is developed to rapidly estimate the lumped uncertainties and construct a feedforward compensation term. Then, a concise fixed-time nonsingular terminal sliding surface is designed using the attitude tracking error, such that once the error reaches the sliding manifold, the attitude error converges to the origin within a fixed time, thereby improving tracking accuracy for dynamic attitude tracking tasks. To attain near optimal control performance with reduced tuning burden, an adaptive learning scheme is employed to design the sliding mode controller. Rigorous stability is established via Lyapunov analysis, and simulations demonstrate the effectiveness and superior performance of the proposed method.