Coupled Control of Chaser Platform and Robot Arm for the e.Deorbit Mission

Abstract

The e.Deorbit mission is devoted to safely remove Envisat from its orbit by robotic capture means. The major challenges in the close range are the motion synchronisation between the Chaser and the Target satellite Envisat and the coupled control during capture employing the robot arm. This paper is devoted to the coupled control phase, during which the Chaser performs station keeping at the Capture Point, which is a point relative to the Target in the Target body frame, while the robot is grasping the Target. The robot arm has to place the end-effector at the Grasping Point, a well-defined position at the Target's launch adapter ring, while compensating the station keeping errors of the Chaser platform. The impedance controlled robot operates in operational space coordinates defining the pose of the robot end-effector with respect to the Grasping Point and also directly controls the robot joint configuration. The bandwidths of the two controllers considered in this study differ by more than two orders of magnitude, allowing independent control design of the two. The overall performance of the coupled control in terms of station keeping performance for the Chaser and positioning performance of the end-effector is demonstrated in Monte Carlo simulations.