Fixed-time adaptive prescribed-performance sliding-mode control for space manipulators with actuator uncertainties

This study investigates a fixed-time adaptive tracking control scheme with prescribed performance for space manipulators subjected to bounded external disturbances, parametric uncertainties, and actuator faults. An enhanced prescribed performance function is introduced, and a non-singular fast terminal sliding-mode surface is constructed based on the tracking error to ensure transient, steady-state performance. A model-based fixed-time control strategy is first designed under the assumption that all disturbances and uncertainties are known. To relax this assumption, an adaptive control law is developed to estimate and compensate for lumped uncertainties, without requiring prior system knowledge. Subsequently, a fixed-time adaptive prescribed-performance control method is proposed to achieve rapid convergence, high tracking accuracy, and robustness. The fixed-time stability and prescribed-performance compliance of the closed-loop system are rigorously established using the Lyapunov theory. Numerical simulations and experimental results, based on a space-manipulator case study, confirm the effectiveness and superiority of the proposed control approach.