Event-triggered fault-tolerant tracking control for 6-DOF spacecraft rendezvous with predefined-time strategy under input saturation

This article investigates autonomous rendezvous control (ARC) problem of 6-DOF spacecraft using sliding mode control (SMC) technique, emphasizing predefined-time disturbance observer and controller, despite input constraints and restricted communication. Unlike traditional event-driven methods that solely transmit asynchronous control signals, the proposed method can also facilitate non-periodic data transmission to the controller, significantly enhancing communication resource utilization. Furthermore, a self-triggered (ST) mechanism is proposed to diminish the reliance on supplementary monitoring devices. A predefined-time disturbance observer is developed, which can estimate and compensate for lumped disturbances including parameter uncertainty, external disturbance, actuator fault, and input saturation under restricted communication. Based on a novel derivable nonsingular predefined time sliding mode surface, a robust fault-tolerant controller is proposed. It is proved that the relative position and attitude of the spacecraft can converge to a small bounded region around the origin within a predefined time. Additionally, the closed-loop states remain ultimately uniformly bounded and Zeno-free behavior is guaranteed. A series of digital simulations are performed to validate the key characteristics of the proposed scheme.