Unexpected Collision Detection, Estimation, and Reaction for a Free-Flying Orbital Robot

This paper addresses the unexpected contact handling problem for a free-flying orbital robot. A nonlinear observer is developed to detect, isolate, and estimate a collision. Then, a reaction control strategy is proposed, which aims at avoiding the buildup of the contact force and possible instabilities. It is proved that the controlled system is input-to-state stable. The performance of the observer and the controller is assessed through a numerical example featuring a 7-degree-of-freedom arm mounted on a spacecraft and a realistic measurement model. The spacecraft is equipped with thrusters and variable-speed control moment gyros.