Adaptive Fixed-Time Disturbance Observer-Based Proximity Control for Spacecrafts With Dynamic Obstacle Constraints

The high-precision and fast-response safety proximity control for servicing spacecrafts is affected by dynamic obstacle constraints and multiple disturbances, such as actuator deviations and flexible vibration. To address this challenge, an adaptive fixed-time disturbance observer (AFTDO)-based composite proximity control scheme is proposed for the servicing spacecrafts to achieve effective obstacle avoidance and high-precision position tracking. Because the multiple disturbances are coupled with the system physical variables (e.g., control input and relative position) and exhibit complicated dynamics, an AFTDO is proposed to estimate the disturbances in fixed time by adaptively learning the bound information of disturbance derivative. For the dynamic obstacle constraints, an artificial potential function-based terminal sliding mode manifold is designed to convert the obstacle constraints to a path planning problem, which effectively provides the repulsion effect of the servicing spacecraft on obstacles and the attractive effect on the target position. Through the designed finite-time composite proximity controller, the antidisturbance ability of the servicing spacecraft can be effectively improved, and the coordinated performance optimization under the obstacle constraints can be also ensured. Simulation results verify the effectiveness of the proposed scheme.