Bernhard Rebele

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 geo-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

ROKVISS - robotics component verification on ISS current experimental results on parameter identification

ROKVISS, the German new space robotics technology experiment, 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 a 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. A main goal of the experiment is the evaluation of the dynamical parameters (especially friction, motor constant and stiffness), as well as the monitoring of their evolution over the duration of the mission, in order to validate the long term performance of the system. The paper gives first a short overview of the experiment and in particular a description of the applied control structures. The main focus of the paper is on the joint parameter identification results obtained so far, during one year of operation

Planetary rover mobility simulation on soft and uneven terrain

Rovers on Mars or the Moon for planetary exploration are obtaining increased importance within the spaceflight nations. To achieve full mission success, drivability and mobility in all kinds of complex motion scenarios have to be guaranteed. Here, proper modelling and understanding of the complex wheel–soil interaction, i.e. the terramechanics for flexible and rigid wheels interacting with hard, soft and loose soil, are a major driver for supporting reliable rover design and assisting in testing of the flight model. This paper deals with the terramechanical characteristics for wheel–soil contact dynamics modelling and simulation and its experimental validation on the basis of the future European Mars rover mission ExoMars. The physical contact models are integrated by a multi-body system approach and the performance of the rover mobility will be shown for various driving scenarios on hard and soft soil.

Robot Mobility Concepts for Extraterrestrial Surface Exploration

Future space missions are directed to robotic precursor missions to nearby celestial objects. Various science experiments are meant to be performed by autonomous robotic vehicles including detection of widely speculated polar-ice in lunar craters and detect signs of past life on Mars. The locomotion subsystem plays a key role in moving a robot on a surface with high performance capabilities, irrespective of the nature of the terrain. Locomotion on extraterrestrial surfaces can be achieved by a wheeled rover, tracked rover, legged walker or a hybrid vehicle. The first three modes can be classified based on the number of wheels, tracks, or legs the robot possesses. Hybrids can be either a wheeled-leg or a legged-track combination. A survey of different locomotion concepts available for lunar, planetary, and other space exploration missions has been performed and discussed. Choosing the right locomotion mode is a difficult task for a particular mission with each having its own pros and cons. Therefore, a comparative assessment of the various modes which could be used as a quick reference tool is also provided.

ROKVISS - Space Robotics Dynamics and Control Performance Experiments at the ISS

Abstract To guarantee for mission success, already during the design phase, confidence in the robotic dynamics and control models has to be ensured. For validation purposes of the underlying models and design characteristics, the need to have in-orbit testbeds is addressed, especially for the novel robotic electro-mechanical components, such as DLR‘s intelligent robotic joints of the 3 rd generation light-weight robot arms. An ISS-based twojoint robotic configuration experiment, ROKVISS is presented that focuses on the inorbit demonstration of the robot dynamics and control performance by making use of parameter identification techniques for both robotic joint and contact dynamics.