Event-driven prescribed-time control with flexible performance for 6-DOF spacecraft flying around a non-cooperative target under input constraints

This paper presents an event-driven prescribed-time control scheme with flexible performance for non-cooperative spacecraft fly-around missions under input constraints. First, an improved integrated model for relative attitude and position control is introduced, accounting for exogenous disturbances, model uncertainties of the non-cooperative target, actuator faults, and input saturation. In practice, the output of actuators is limited, particularly in the case of actuator failure, where the actual thrust or torque generated may not satisfy the requirements of the nominal performance function. To address this, a novel auxiliary system is proposed, which generates a series of modified signals. By incorporating these auxiliary signals, a flexible prescribed-time performance function is designed, allowing the performance to be adaptively relaxed during actuator saturation, and returning to its nominal level once saturation is resolved. Subsequently, an event-triggered robust adaptive controller is developed based on the performance function. This controller updates the control signal aperiodically, thereby conserving communication resources and reducing energy consumption. It guarantees that the relative attitude and position of the spacecraft strictly evolve within the bounds of the designed performance function and converge to the prescribed performance boundary within a specified time frame. Moreover, all closed-loop system states are ultimately uniformly bounded, and the design ensures the avoidance of Zeno behavior. Finally, the effectiveness of the proposed scheme is demonstrated through comparisons with advanced control schemes.