On the coordinated attitude alignment of a group of spacecraft without velocity measurements

We consider the coordinated attitude control problem for a group of spacecraft without velocity measurements. Our approach is based on the introduction of an auxiliary dynamical system for each spacecraft (playing the role of velocity observers in a certain sense) to generate the individual and relative damping terms in the absence of the actual angular velocities and relative angular velocities. Our main interest is to provide new design methodologies to minimize the order of the controllers as well as the information flow requirement between spacecraft in the team. We will address the following two problems: (1) Design a velocity-free attitude tracking and synchronization control scheme, that allows the team members to align their attitudes and track a time-varying reference trajectory (simultaneously). (2) Design a velocity-free synchronization control scheme, in the case where no reference attitude is specified, and all spacecraft are required to synchronize their attitudes to the same final time-varying attitude. Throughout this paper, the communication flow between spacecraft is assumed to be fixed and undirected. Simulation results are provided to show the effectiveness of the proposed control schemes.