Figure 1. The Jerico arm and end effector.
Résumé
L'ESA et l'Agence Spatiale Italienne développent un système robotique appelé Jerico qui sera installé sur le module russe Spektr fin 1998. Jerico permettra d'évaluer en orbite le système robotique complet tout en permettant après une phase d'évaluation, une exploitation du système pour des besoins scientifiques ou technologiques. Le projet Jerico sera développé en suivant l'approche de l'ESA pour les projets pilote et intégrera des développements issus de différentes sources.
ESA Contractors:
Trasys (B), Verhaert (B),
K. Univ. Leuven / PMA (B),
Krypton (B), SAS (B)
ASI Contractors:
Tecnospazio (I)
Funding:
Jointly funded by ESA's Technology Development Programme 2 and General System Technology Programme 2 and by Italian national funding managed by ASI.
The use of a robot in a space project requires special measures to ensure that it is safe and reliable. One of these is the need to calibrate the robot and its operating environment to compensate for unavoidable a priori modelling errors and to ensure the intrinsically safe operation of the calibrated system. Safe operation can be enhanced by limiting the operations performed by the robot to pre-programmed sequences of movements which require only infrequent interaction with an operator on the ground.
ESA and the Italian Space Agency (ASI) are collaborating in the development of a space robot system called Jerico, with the object of:
Jerico is planned to be installed in the Spektr module of the Russian space station Mir. It will be integrated into the Russian Pelikan system, which includes a small airlock through which a payload can be taken outside the Spektr, a number of standard payload attachment points outside the spacecraft, and a manipulator arm (manually operated by an astronaut inside Spektr) which can transport a payload between the airlock and an attachment point. It is intended that the robot arm of Pelikan be used to install and remove the payload and that time-consuming routine payload-servicing operations be performed automatically by the Jerico robot-arm. This avoids expensive and risky spacewalks and offers a low-cost, flexible and rapid turn-around payload deployment capability.
Installation of the Jerico system should be completed in late 1998. After a proof period of several weeks in-orbit, the arm can be used on a full operational basis for the lifetime of Mir.
The manipulation subsystem of Jerico is derived from work carried out under the Spider Programme, funded by ASI. (Figure 1). It includes a dexterous 7-axis robot arm whose outstretched length is about two metres, a parallel jaw gripper fitted with force-torque and distance sensors, a hand camera, sensors for calibration, and an on-board controller.
Figure 1. The Jerico arm and end effector.
Also on board will be a small, carefully selected, collection of devices (a task board), for exercising and evaluating the robot and a science payload for a real-life demonstration of robotic servicing.
Figure 2 shows how the Jerico arm will be mounted onto a support bridge close to the end of the Spektr module cone. The task board and science payload will be installed on an adapted instrument platform called the European Space Exposure Facility (ESEF), onto which they can be loaded with the longer Pelikan manipulator arm.
Figure 2. A computer-generated scale drawing of Jerico operating on the Spektr module of the Space Station Mir.
Jerico will also be equipped with a video and data handling system (comprising on-ground and on-board parts) which it will share with the Pelikan system. The core of the communications unit has performed well in space during the German Mir'97 mission, flown on the Russian space station.
The ground system of Jerico comprises:
The core of the ground system will be installed at the Mir mission and control centre in Russia, but additional payload monitoring and command stations may be located at "user home bases" distributed over Europe.
Jerico will be operated from the ground. Complex motion sequences can be synthesised by combining lower-level elementary tasks and actions, and their safe execution will be verified by comprehensive simulation before being up-linked to the robot controller.
During normal operation, the sequences will be automatically executed and their progress monitored. Calibration and advanced robot control allow the robot to deal with positional inaccuracies encountered in the real world. Motion is inherently safe, and intrusion into forbidden areas is prevented by ultra-reliable means implemented deep inside the system.
Communication with the ground occurs only a few times per day, and during these contacts, the operator on-ground can up-link new programs or modify the parameters of an existing program to adjust to new situations. Scientists located at a user home base will receive telemetered data needed to monitor their payload, and will have the capability to issue high-level commands to their experiments, using the robot as a transparent tool.
The Jerico robotic system on the Mir Space Station will provide ESA and ASI with the means to evaluate, in-orbit, key technologies for future space robotics missions. Moreover, in combination with the Russian Pelikan system, it will provide a unique infrastructure for automatic servicing of science payloads external to a spacecraft.
Jerico is a new type of "pilot project", which integrates, into a single relatively low-cost system, various building blocks developed under different contracts sponsored by several of ESA's technology research programmes and the Italian national programmes carried out by ASI. This approach has supported a speedy reaction to emerging flight opportunities. The same building blocks may, in principle, be copied and re-used in similar follow-on applications, such as tending external payloads on the International Space Station.
Preparing for the Future Vol. 7 No. 2