Event‐triggered prescribed performance robust collision‐free capturing control for drag‐free spacecraft system

This paper addresses the capturing control problem of a plug-and-play modularized drag-free spacecraft system, including two spherical proof masses, where the performance constraints, collision risk, uncertain model parameters, unknown external disturbances, and limited communication are considered simultaneously. First, a nonlinear relative dynamics of spherical proof masses with respect to spacecraft is formulated for the capture process. Second, two different prescribed performance event-triggered robust collision-free capturing control strategies are developed to capture the free-floating proof masses successfully. Suppose only the performance metrics on the relative position are considered, and an event-triggered adaptive terminal sliding mode capturing controller is implemented to achieve the capture process within a finite time. Suppose more performance constraints, such as the user predefined capture duration and the performance bounds on both the relative position and the relative velocity, are taken into account, and an event-triggered appointed-time prescribed performance capturing controller is proposed to solve the above issues. In particular, an artificial potential function is utilized to avoid the collision, and a relative threshold event-triggered rule is employed to save the communication source between the controller and the actuator without any Zeno behaviour. The simulation results demonstrate the efficacy and superiority of the proposed method.