Abort-Safe Spacecraft Rendezvous in case of Partial Thrust Failure

In this paper a spacecraft rendezvous policy is developed that yields safe rendezvous trajectories under various thruster failure scenarios. The policy makes use of polytopic robust backwards reachable sets to characterize the state-space that under a given thruster failure scenario would lead to collision between a deputy and a chief spacecraft no matter the remaining available thrust. That is, this region of state-space is such that no feasible evasive abort maneuver exists for the given failure scenario. Abort-safety constraints are formulated as local hyperplanes separating the deputy spacecraft and the unsafe state-space. These constraints are incorporated in a model predictive control-based online trajectory generation scheme in order to guide the deputy to rendezvous with its chief through an inherently safe approach. Simulations demonstrate the effectiveness of the safety constraints in altering a nominally unsafe rendezvous to one that is abort-safe.