Klaus Landzettel

DLR's robotics technologies for on-orbit servicing

The paper outlines the long-term space robotics projects as well as recent results in DLRs robotics laboratory. The driving force behind all the efforts made in hardware and software development is to design highly integrated robot systems which can be utilized in space, especially for extravehicular activities. Our envisaged field of application reaches from servicing satellites in low Earth and geostationary orbit to space stations as well as planetary exploration robots, all of them fully ground controlled from Earth. The ground control concept is based on the MARCO architecture, which was verified in a few space robotics projects over recent years. It includes taskoriented programming capabilities for autonomous robot control at the remote site as well as methods for direct telemanipulation by means of virtual reality and telepresence techniques, which allows a realistic feeling for the ground operator via visual and haptic feedback devices. In addition to the control techniques, a new generation of ultra-lightweight robot arms with articulated hands is required to give the space robot systems the necessary dexterity. A number of experiments will verify and consolidate the usage of space robots. First, the ROKVISS experiment aims at the verification of DLRs lightweight robotics components under realistic mission conditions. Second, the TECSAS experiment will show the feasibility of autonomous as well as telepresence methods for further satellite servicing tasks. Third, a strong cooperation with industry will create the first business case in on-orbit-servicing: by attaching a tugboat to a satellite, whose propellant is declining, the lifetime of valuable telecommunication satellites could be prolonged for several years.

Predictive and knowledge-based telerobotic control concepts

The problems that arise when sensor-controlled robots in space are teleoperated from ground stations are discussed. A supervisory control concept is described that makes it possible to realize shared control between teleoperator and sensor-controlled robot in a variety of configurations. Predictive 3D computer graphics currently seems to be the only way to cope successfully with the problem of transmission-time delays of several seconds. Appropriate estimation schemes in combination with knowledge-based world modeling are outlined, which include models of the delay lines, the robot, moving objects, etc., and which derive the necessary updates from sensory data as they are sent down from the spacecraft to earth (e.g. via real-time stereo vision). The space robot technology experiment Rotex scheduled for the next German Spacelab mission (2D) is taken as a basis for the problem description.<<ETX>>

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

Space Robotics—DLR's Telerobotic Concepts, Lightweight Arms and Articulated Hands

The paper briefly outlines DLRs experience with real space robot missions (ROTEX and ETS VII). It then discusses forthcoming projects, e.g., free-flying systems in low or geostationary orbit and robot systems around the space station ISS, where the telerobotic system MARCO might represent a common baseline. Finally it describes our efforts in developing a new generation of “mechatronic” ultra-light weight arms with multifingered hands. The third arm generation is operable now (approaching present-day technical limits). In a similar way DLRs four-fingered hand II was a big step towards higher reliability and yet better performance. Artificial robonauts for space are a central goal now for the Europeans as well as for NASA, and the first verification tests of DLRs joint components are supposed to fly already end of 93 on the space station.

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

A new laboratory simulator for study of motion of free-floating robots relative to space targets

This paper presents detailed description of a laboratory simulator that uses two robots fixed on earth to simulate the motion of a robot in space relative to a free-flying target. This simulator is appealing because it creates an environment on earth similar to what an astronaut observes watching from the space shuttle. Therefore, it could be a valuable tool for training of astronauts on earth. Also, this simulator uses off-the-shelf industrial robots in contrast to laboratory facilities today that use special designs of robots to achieve this same task. The proposed simulator can be valuable for studying real-time motion in space and in evaluating the effectiveness of onboard sensors and control systems. The objectives of this paper are to: i) describe the laboratory setup, ii) present the computational details of this simulator, iii) estimate the computation needs of this simulator, and iv) present a computer implementation of this simulator using two KUKA robots.

DLR’s Advanced Telerobotic Concepts and Experiments for On-Orbit Servicing

Space robotics will become a key technology for the exploration of outer space and the operation and maintenance of space stations, satellites and other platforms, saving costs and relieving man from dangerous tasks. But we do not have to wait until robots are really autonomous or intelligent, since by modern teleoperation and telepresence we are able to remotely control robot systems from the ground in the sense of “prolonging man’s arm into space”. Humans, with their several hundred thousand years of evolution, will not adapt themselves to the hostile space environment, whilst robots, which have only been developed for just over 40 years, can be much more easily adapted to such an environment. As presented within this work, few pioneering telerobotic experiments like ROTEX, the first remotely controlled space robot system, ETS-VII, the first free-floating space robot experiment, or ROKVISS, Germany’s recent advanced space robot experiment on the International Space Station, have been proposed and conducted on the way towards a space robot assistant system for the usage as an artificial astronaut to perform On-Orbit Servicing (OOS) tasks.

Advances in orbital robotics

Outlines the situation in orbital space robotics with special reference to what DLR (German Aerospace Center) has contributed to the field. After our ROTEX experiment, the first remotely controlled space robot inside the space shuttle, the Japanese ETS VII has now been the first remotely controlled free-flying space robot. We had the opportunity to control this arm from the ground, too, including the use of the robot arm as a satellite attitude controller. It is outlined how it is now time to take the next steps towards operational ground-controlled space robot systems, presumably first on the International Space Station, but later on as free flying robonauts assisting or even replacing extra vehicular activities.

Robotics Component Verification on ISS ROKVISS - Preliminary Results for Telepresence

ROKVISS, Germanys newest 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 is 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 will be operated for at least one year in free space to evaluate and qualify intelligent light weight robotics components under realistic circumstances for maintenance and repair tasks as foreseen in upcoming manned and unmanned space applications in near future. This paper focuses in the telepresence control mode, its technology and first results from the space experiment ROKVISS

Dexhand: A Space qualified multi-fingered robotic hand

Despite the progress since the first attempts of mankind to explore space, it appears that sending man in space remains challenging. While robotic systems are not yet ready to replace human presence, they provide an excellent support for astronauts during maintenance and hazardous tasks. This paper presents the development of a space qualified multi-fingered robotic hand and highlights the most interesting challenges. The design concept, the mechanical structure, the electronics architecture and the control system are presented throughout this overview paper.