Development of a Robust and Combined Controller for On-Orbit Servicing Missions

Abstract

Nowadays, a satellite is considered as out of range forever once it is launched. This may soon no longer hold thanks to on-orbit servicing. However, the complexity of that topic makes it highly challenging on many aspects. On-orbit servicing using a robotic arm is nonetheless the most investigated technology in order to achieve the berthing of two satellites in orbit. This research project aims at developing a robust controller for the deployment of a robotic arm, which is mounted on a servicer satellite, and for the reaching of a defined handle on the target satellite under mission constraints. While operating the space manipulator, the combined control of both the manipulator and the spacecraft base has a great potential in terms of achievable performance and may bring robotic on-orbit servicing one step closer to reality. In order to reveal the potential of this innovative control strategy, a model of the system dynamics was developed, before being used to design a robust controller. The latter was then successfully implemented in different simulators to test its performance and robustness to a variety of constraints including hardware, environment and mission constraints. The simulations proved that combined control can be used for the entire maneuver. Finally, this controller was successfully implemented in the on-board computer of the on-orbit servicing simulator at the German Aerospace Center. From now on, the maneuver can be completed from the ground control room. The implementation of the robust and combined controller has increased the technology readiness level of the reach phase during an on-orbit servicing mission.