Performance analysis and gains tuning procedure for a controlled space manipulator used for non-cooperative target capture operations

In the near future robotic systems will be playing an increasingly important role in space applications such as repairing, refuelling, re-orbiting spacecraft and cleaning up the increasing amount of space debris. Space Manipulator Systems (SMSs) are robotic systems made of a bus (which has its own actuators such as thrusters and reaction wheels) equipped with one or more deployable arms. The present paper focuses on the issue of maintaining a stable first contact between the arms terminal parts (i.e. the end-effectors) and a non-cooperative target satellite, before the actual grasp is performed. The selected approach is a modified version of the Impedance Control algorithm, in which the end-effector is controlled in order to make it behave like a mass-spring-damper system regardless of the reaction motion of the base, so to absorb the impact energy. A very important aspect in the analysis of the control performance is the evaluation of the field of applicability of the controller itself. In the present work the influence of this issue on the effectiveness of the proposed control architecture will be analysed, together with the control gains tuning which allows for a robust achievement of the mission requirements. Several numerical results will be presented and discussed.