Active fractional-order sliding mode control of flexible spacecraft under actuators saturation

In this article, a novel multi-objective modified fractional-order nonsingular terminal sliding mode (MFONTSM) controller is designed for the flexible spacecraft attitude control and passive vibration suppression, assuming the control torque saturation in the system dynamics. Then, by considering the effects of flexible components on the appendages modal equation as an external disturbance, an active FONTSM controller is designed separately to suppress any residual vibrations using piezoelectric actuators. The practical fixed-time stability of the closed-loop system is analyzed and proved using the Lyapunov theorem. Finally, the proposed controllers’ performance has been tested in the presence of uncertainties, external disturbances, and the absence of the damping matrix to study the proposed method’s effectiveness. It was observed that the proposed passive and active control strategies were able to achieve fast attitude stabilization while providing substantial vibration suppression under uncertainty and disturbance even in the absence of any damping terms in the system. •Modern spacecraft have large and lightweight appendages with high flexibility.•Spacecraft attitude control with passive/active vibration suppression is imperative.•Actuators in practice have limited capabilities and are often prone to saturation.•Fractional-order control systems offer improvements over integer-order counterparts.•In fixed-time stability, the settling time is upper bounded by a prede- fined constant.