Distributed adaptive attitude tracking of multiple spacecraft with a leader of nonzero input

This paper considers the distributed attitude tracking problem of multiple spacecraft with a leader whose control input is possibly nonzero, bounded, and not available to any follower. Based on the relative attitudes and angular velocities of neighboring spacecraft, we design a distributed discontinuous adaptive controller to each follower to guarantee that the attitude errors between the followers and the leader converge to zero for any communication graph containing a directed spanning tree with the leader as the root. To tackle the chattering effect caused by the discontinuous controller, we further propose a distributed continuous adaptive controller, under which both the attitude tracking errors and the adaptive gains are ultimately bounded.