On Impact De-orbiting for Satellites Using a Prescribed Impedance Behavior *

In a number of on-orbit applications, such as de-orbiting, continuous contact between a servicing robot (chaser) and a serviced satellite (target) is needed. The task includes chaser free-space motion and subsequent contact interaction with a floating target. To achieve this, usually grasping of the satellite is proposed. However, most of the existing satellites on orbit have no dedicated grapple fixtures. In this paper, the problem of continuous contact between two bodies lacking a rigid grasp and fixed bases is studied. It is shown that continuous contact can be achieved by setting an appropriate chaser velocity at the moment of contact, accompanied by an impedance controller. The same controller is applied in both phases without switching, avoiding loss of contact and instabilities, due to unavoidable transition delays and unknown properties. A methodology is developed for selecting the same controller parameters and a suitable trajectory during both phases. The method is valid for spatial systems and illustrated by a planar example.