We developed the Advanced Space Robot Testbed with Redundant Arms (ASTRA) for studying the autonomous control of a space robot. Berthing a satellite that is moving in space is the kind of difficult and dangerous task expected of space robots. This paper describes a robot which berthes a mockup satellite that is moving and rotating in zero gravity. The features of the robot include the capability for an autonomous approach to a moving target satellite on the base of a visual estimation of satellite motion, real-time visual tracking control for tracking satellite handles with two robot arms, and the capability to grasp the satellite handles while exerting minimum mechanical shock because of flexible wrist mechanisms and impedance control. We ran a satellite berthing experiment with ASTRA to check its performance.
