RENDEZVOUS and docking maneuvers represent operational key technologies in many spacecraft missions and consist of a series of orbital maneuvers and controlled trajectories during which an active spacecraft (chaser) tries to capture a passive target vehicle. The goal of the mission is that the chaser vehicle has to safely and efficiently approach, up to few centimeters (surface-to-surface), the target vehicle, satisfying the strict requirements of docking in terms of relative position, speed, and with zero angular velocities. Once the target is reached, the chaser has to remain stationary until the hold mechanism captures and docks the target vehicle. The faced problem requires control of both the relative position and the relative attitude of the vehicles.

Our focus is on the final approaching phase of the rendezvous maneuver, which is considered to start when the chaser is 500 m far from the target. The aim of the control strategy is twofold: 1) the controller must guarantee that the chaser tracks the specified position of the target while 2) the attitude stability is maintained. These goals must be reached despite the environmental disturbances acting on the spacecraft and taking into account the uncertainties affecting the actuators: the performances of which are subject to physical constraints related to their feasible switching frequency and intensity of the thrusts.