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.
The robotic grasp concept includes a stereo-vision
camera system featuring a visual servoing algorithm for
camera-in-the-loop error correction. In addition, a
platform-mounted camera system is utilized for target
model building as well as relative motion and pose
estimation. For concept validation, visual servoing,
haptic grasp and capture simulations were performed.
The task-specific kinematics of the manipulator and
potential joint locks as contingency events were
validated and analyzed using the method of capability
maps. For the complete robotic capture maneuver, an
error budget was created and evaluated. Geometric
analysis and haptic grasp simulations showed that the
gripper design and connected grasp approach is feasible
and robust. In addition, the kinematics analysis yielded
a sufficient reachability, even in the case of an
improbable joint lock. FE-analyses were performed to
show that a high compound stiffness can be achieved by
the clamping device and that all required forces can be
transmitted without damaging the target’s structure.
Overall, the study showed that the capture and deorbiting
of ENVISAT is feasible and robust using the
developed robotic concept.