Autonomous trajectory planning for rendezvous and proximity operations by conic optimization

Autonomous rendezvous and proximity operations of spacecraft require the capability of onboard planning and executing highly constrained trajectories without ground support. This paper presents a general and rigorous methodology and algorithmic procedure toward this goal with a target vehicle that can be in an arbitrary orbit. The rendezvous and proximity operations problem is formulated as a nonlinear optimal control problem, subject to various state and control inequality constraints and equality constraints on interior points and terminal conditions. By a lossless relaxation technique, a relaxed problem is formed, the solution of which is proven to be equivalent to that of the original rendezvous and proximity operations problem. The relaxed problem is then solved by a novel successive solution process, in which the solutions of a sequence of constrained subproblems with linear, time-varying dynamics are sought. After discretization, each of these problems becomes a second-order cone programming problem. Their solutions, if they exist, are guaranteed to be found by a primal-dual interior-point algorithm. The efficacy of the proposed methodology is strongly supported by numerical experiments.