Coupled orbital and attitude control in spacecraft rendezvous and soft docking

This paper discusses coupled orbital and attitude control in spacecraft rendezvous and soft docking. The target spacecraft orbit can be either circular or elliptic. The high-fidelity model for this problem is intrinsically a nonlinear system but can be viewed as a linear time-varying system. Therefore, a model predictive control-based design is proposed to deal with the time-varying feature of the problem. A robust pole assignment method is used in the model predictive control-based design because of the following merits and/or considerations: (a) no oscillation crossing the horizontal line for the relative position and relative attitude (between the target and the chaser spacecraft) to achieve soft docking by placing all closed-loop poles in the negative real axis of the complex plan, which will avoid collision between the target and the chaser in the docking stage, (b) fast online computation, (c) measurement and control error tolerance, and (d) disturbance rejection. This paper will discuss these considerations and merits and use some design examples to demonstrate that the desired performance is indeed achieved.