Coupled Attitude and Orbit Dynamics and Control in Formation Flying Systems

In this paper, generalized equations of motion for a leader/follower satellite pair are derived. The equations are generalized to include non-circular reference orbits by regularizing the governing equations to be true-anomaly dependent rather than time dependent. In addition, the vehicles are considered to have finite dimensions and are pointed to a specific location on the Earth (i.e., their attitude and orbit dynamics are coupled). An Euler angle attitude representation was chosen and each vehicle is assumed gravity gradient stabilized (i.e., each satellite's z-axis points to its own nadir). Finally, an attitude controller based on the sliding mode concept was developed and implemented to control the attitude of the follower relative to the leader. For the close-loop scenario, both vehicles are required to point to the same position on the surface of the earth (i.e., the nadir of the leader). Simulation results illustrate the capability/performance of the controller developed.