Coupled orientation and orbit maintenance in formation flight via sliding mode control

The concept of the formation flight has been in existence for more than 15 years. In the literature, most of proposed control strategies considered the uncoupled orbit and orientation model and controller. In this paper, the desired attitudes of the follower satellites are coupled with the relative positions, due to the mission requirements (e.g., stereoscopic imagery). A generalized full nonlinear orbit dynamic model is adopted, in which, the leader and follower satellites can be in any closed orbit (i.e., circular or elliptic). To obtain high accuracy position and attitude control, a sliding mode controller combined with a boundary layer controller is developed. The proposed controller is capable of maintaining the desired orientation continuously. Furthermore, the relative position of these two vehicles is also maintained on a continuous basis, instead of one or twice per day.