RoboGrav - Towards Force Sensitive Space Manipulators

Abstract

This paper introduces RoboGrav, a mission focused on the testing of a fully torque sensorized robotic arm under zero gravity conditions performed during the 42nd DLR parabolic flight campaign. Conducted in collaboration with the German Aerospace Center (DLR), KINETIK Space, iBOSS, the Technical University of Munich (TUM), and Novespace, RoboGrav aims to advance the development and testing of torque-controlled robotic manipulators for On-Orbit-Servicing (OOS) and space assembly tasks. The paper highlights the significant role of torque sensing, enhancing manipulation tasks under zero gravity conditions. Experimental tests were performed to ensure controller stability during free-space motions in zero gravity, using a pin shaped end effector for environmental interactions. External force sensing was employed to assess the robot's accuracy and performance across various controllers. This also enabled a comparison of the robot's behavior in both zero gravity and full-gravity environments, providing valuable insights into the transfer of Earth-developed algorithms to space applications. A simulated satellite docking task, using the iBOSS "iSSi" interface, demonstrated the robot's capability to manage position inaccuracies through impedance control, thus improving operational robustness. Technology developed for this project, such as the integration of torque sensors, the presented FPGA-based joint control algorithms and communication interfaces, high-level controllers and decision-making algorithms, can be transferred to future space missions. RoboGrav's torque-sensorized robotic arm offers valuable lessons and methodologies for future space servicing and space assembly missions.