Dynamics, control and impedance matching for robotic capture of a non-cooperative satellite

In this paper, the contact motion between rigid bodies floating in space is formulated and dynamic conditions are investigated in order to capture a non-cooperative target. As for the theoretical investigation, the definition of the virtual mass is recalled to model the inertial property of a space robot for the case of no joint control. By selecting the posture, the virtual mass can be altered, but its variation may be minor. Then the impedance control is introduced to realize a wide range of impedance characteristics. Impedance matching is discussed for the case in which the hand of an impedance-controlled robot approached and collided with a passive target. The specific inertia property, referred to as Virtual-mass for Impedance Matching, is defined as an equivalent virtual mass of the hand that yields impedance matching with a target floating in space. Experiments are carried out using two robot manipulators as a motion simulator of chaser and target. Through the experiments, the concept of the impedance matching is verified and satellite capture is demonstrated using the strategy that an impedance controlled probe is inserted into the thruster nozzle cone of the target. Whether the impedance matching gives a criteria if the target is pushed away by the probe is investigated.