Robotic Capture and De-Orbit of a Heavy, Uncooperative and Tumbling Target in Low Earth Orbit

Abstract

This paper presents a robotic capture concept for large spacecraft in low Earth orbit (LEO) that was developed as part of the the e.Deorbit feasibility study within the scope of the clean space initiative of the European Space Agency (ESA). The defective and tumbling satellite ENVISAT has been chosen as potential target to be captured, stabilized, and subsequently de-orbited in a controlled manner. Following a thorough target analysis including potential grasping points, a robotic capture concept was developed that is based on a 7-DoF dexterous robotic manipulator, a linear two-bracket gripper, and a clamping mechanism for achieving stiff fixation between target and chaser satellites prior to the de-tumbling and execution of the de-orbit maneuver.
\nThe robotic grasp concept includes a stereo-vision
\ncamera system featuring a visual servoing algorithm for
\ncamera-in-the-loop error correction. In addition, a
\nplatform-mounted camera system is utilized for target
\nmodel building as well as relative motion and pose
\nestimation. For concept validation, visual servoing,
\nhaptic grasp and capture simulations were performed.
\nThe task-specific kinematics of the manipulator and
\npotential joint locks as contingency events were
\nvalidated and analyzed using the method of capability
\nmaps. For the complete robotic capture maneuver, an
\nerror budget was created and evaluated. Geometric
\nanalysis and haptic grasp simulations showed that the
\ngripper design and connected grasp approach is feasible
\nand robust. In addition, the kinematics analysis yielded
\na sufficient reachability, even in the case of an
\nimprobable joint lock. FE-analyses were performed to
\nshow that a high compound stiffness can be achieved by
\nthe clamping device and that all required forces can be
\ntransmitted without damaging the target’s structure.
\nOverall, the study showed that the capture and deorbiting
\nof ENVISAT is feasible and robust using the
\ndeveloped robotic concept.