Fractional-Order Sliding Mode Control for Free-Floating Space Manipulator With Disturbance and Input Saturation

This paper proposes a fractional-order sliding mode control scheme for the tracking control of free-floating space manipulators (FFSM), addressing system uncertainties, external disturbances, and input saturation. First, a new fractional-order non-singular terminal sliding mode is designed, incorporating a fractional-order integral term into the traditional non-singular terminal sliding mode surface to ensure finite-time convergence of the tracking error across all phases. To mitigate chattering, a finite-time disturbance observer is utilized to estimate and compensate for the system uncertainties and unknown disturbances. Subsequently, a new fixed-time anti-saturation compensator is presented to suppress the influences of input saturation. With an innovative fixed-time sliding surface and adaptive gain, the compensator ensures the auxiliary variables vanish in fixed time when the saturation disappears, thereby enhancing the convergence characteristics of the tracking error effectively. Finally, a fractional-order non-singular terminal sliding mode controller is established by integrating the proposed fractional-order non-singular terminal sliding mode, finite-time disturbance observer, and fixed-time anti-saturation compensator. The presented controller significantly improves the transient response and tracking precision of the FFSM. The theoretical stability of the closed-loop system is proved, and simulation results confirm the effectiveness and superiority of the proposed methods compared to existing approaches.