Robotic on-orbit servicing - DLR's experience and perspective

The increasing number of launched satellites per year, calls for solutions to keep free operational space for telecommunication systems in gee-synchronized orbit, as well as to avoid the endangering of space systems in LEO (Low-Earth Orbit) and of the public living in the habited parts on Earth. Examples for such dangerous stranded space systems in the past are Skylab and MIR. In the future, the uncontrolled and accidental de-orbiting of other huge satellites is expected, where parts of these will hit the surface of the Earth. A feasible way to handle such problems might be to enforce the operational requirement to use some dedicated residual fuel for a controlled de-orbiting, or in case of GEO (Geostationary Orbit), to lift the satellites at their end of life into the graveyard orbit. Despite these measures, malfunctions of solar generators, control systems or thrusters cannot be avoided. Therefore, on-orbit servicing (OOS) will be a mandatory and challenging topic for space robotics in the near future. The outcome of national German projects like ROTEX, ESS and GETEX/ETS-VII represent a know-how which can be directly applied for the development of OOS-Robotic systems. Control structures and several possible operational modes are discussed within this paper. The recently started national project ROKVISS already provides the necessary space-qualified hardware as well as the very powerful telepresence operational mode. The paper will concentrate on a description of the ROKVISS mission The space robotic mission TECSAS (Technology Satellite for Demonstration and Verification of Space Systems), is a veiy good opportunity to demonstrate and verify satellite capturing, for various degrees of interaction between the robot and the satellite controllers and for various degrees of target cooperation. The first business case for on-orbit servicing will hopefully become reality within the next few years. DLR's industrial partner, Orbital Recovery Corp.' has initiated its so-called Orbital Life Extension System (CX-OLEV™). The CX-OLEV will operate as an orbital tugboat, supplying the propulsion, navigation and guidance to keep a telecommunications satellite in its dedicated orbital slot for several additional years (station keeping). A short SLES mission description will be given afterwards. The purpose of ROKVISS, Germans new space robotics technology experiment is to provide robotic hardware components as well as tele-robotic control methods to be applied in the near future for on orbit servicing (OOS). ROVISS was successfully installed outside at the Russian Service Module of the International Space Station (ISS) during an extravehicular space walk at the end of January 2005. Since February 2005 the two-joint manipulator can be operated from ground via a direct radio link. The aim of ROKVISS is the in flight verification of highly integrated modular robotic joints as well as the demonstration of different control modes, reaching from high system autonomy to force feedback teleoperation (telepresence mode). The experiment was already operated for one year in free space and evaluated and qualified the intelligent light weight robotics components under realistic circumstances.