A Ground Experiment to Simulate a Free-floating Robot Capturing a Spacecraft

Kurzfassung

The dynamic coupling between the manipulator and its base, considered to be free-floating in the microgravity environment, could lead to a different position of its end-effector compared to that of a structurally similar fixed-based robot, for the same joint input command. Therefore, to ensure the successful completion of a challenging in-orbit task, such as the capture maneuver of a target spacecraft, the verification on ground of the planning and control algorithms of the robotic system proves to be necessary. In this respect, the following thesis presents the ground simulation facility developed at the DLR Institute of Robotics and Mechatronics able to simulate the motion of a robot in space relative to a tumbling target spacecraft. The system was particularly designed having in mind the requirements of the Deutsche Orbitale Servicing Mission (DEOS). The laboratory setup is based on a hybrid method which combines the virtual model of the free-floating system with the real hardware, composed of two Light-Weight Robots (LWRs) fixed to a rigid platform. This way, the dynamical behavior of the whole system is simulated using appropriate dynamic models, while the physical motions of the space manipulator and client satellite are accomplished by two LWRs. The emulation of the free-floating base is performed through the motion of the target spacecraft based on its relative position with respect to the servicer satellite. This way, the developed laboratory simulator provides, on ground, an environment similar to what an astronaut or a remote operator would observe form the servicer spacecraft during the capture maneuver. Moreover, the system proves to be extendible by small hardware and software modifications and to be relatively simple and cheap in contrast to laboratory setups currently being developed around the world for the same task.