Robust adaptive relative position tracking and attitude synchronization for spacecraft rendezvous

This paper studies the relative position tracking and attitude synchronization of non-cooperative spacecraft rendezvous with model uncertainty and external disturbance. The relative position vector between the chaser spacecraft and the non-cooperative target is required to direct towards the docking port of the target, while the attitude of the two spacecrafts must be synchronized. The coupled six degrees-of-freedom (6DOF) dynamics are modeled for spacecraft relative motion, where the modified Rodrigues attitude parameters are employed to describe relative attitude dynamics. In view of the thrust misalignment of the chaser spacecraft, an integrated robust adaptive controller for 6DOF relative motion is designed, where parametric uncertainties of the chaser spacecraft are estimated online by using gradient adaptive method, and dynamic coupling effect resulting from unknown inertial parameters of the target is handled with a norm-estimation-based adaptive method. It is proved via the Lyapunov theory that the closed-loop system errors asymptotically converge to zero. Numerical simulation example demonstrates theoretical results.