Welcome to ETS-7 experiments of Tohoku Univercity Japanese

Academic Experiments Carried Out
on ETS-VII Japanese Flying Space Robot

The Paper Presented at
The 2001 IEEE International Conference on Robotics and Automation
Received the Best Conference Paper Award

The Engineering Test Satellite VII (ETS-VII, Fig. 1), developed and launched by National Space Development Agency of Japan (NASDA, currently JAXA) in November 1997, is the world-first free-flying space robot. A number of exciting orbital robotics experiments, including rendezvous, docking, manipulation, berthing, ORU exchange, fuel transfer, structure assembling, were successfully demonstrated using its autonomous capability and/or teleoperation from the ground station (the round-trip time delay was 5-7 seconds including data relay satellites and computer networks) [1][2]. After it had completed all the scheduled mission prepared by the space agency by the end of May 1999, the opportunity was opened for additional experiments for advanced academic research.

Selected for this unique and precious opportunity, two research groups of Tohoku University conducted exciting flight experiments. The group led by Professor Yoshida demonstrated the manipulator operation to minimize the reaction to the base satellite attitude and also the manipulator operation with respect to the inertial space. The ETS-VII has a 2 meter-long 6 DOF manipulator arm on its 2.5 ton unmanned satellite base. As the inertia of the manipulator arm is relatively large, its reaction to the base is not negligible for a proper attitude control. As a version of coordinated control between the manipulator and the base, Prof. Yoshida et al. proposed special maneuver called "Reactionless Manipulation [3][4]," which was verified to yield almost zero attitude disturbance during the point-to-point operation of the onboard manipulator arm.

Fig.1 The ETS-VII, a Japanese free-flying space robot in orbit

For the capture of a free-floating target, such as a malfunctioning satellite or a piece of space debris, the manipulator has to be operated in the inertial frame, not in the satellite based frame that can be altered due to the manipulator reaction. To cope with this issue, the Generalized Jacobian Matrix (GJM) based inertial manipulation was theoretically proposed in 1987 [5] and 1989 [6], and this technology was also verified by the ETS-VII flight experiments.
A continuous whole sequence to capture a target satellite was not demonstrated although*, key technologies including rendezvous and precise proximity flight control with the target, visual servo-tracking and the GJM based inertial manipulation toward a specific capture point, and berthing operation after the capture, were all tested separately by ETS-VII, which will open a solid way to future satellite servicing (Fig.2).

The above results were published in the International Journal of Robotics Research [7].

The other group of Tohoku University, led by Professor Uchiyama, demonstrated teleoperation with a predictive display using computer graphics and a special haptic device to provide virtual force feeling to an operator [8]. Also a group of Kyoto University, led by Professors Yoshikawa and Yokokoji, demonstrated a bilateral teleoperation under 7-s time delay condition [9].

* Note: a target capture experiment was conducted in the situation that the target satellite (Orihime, left in Fig.2) was freely floating but confined in the space of a half-released docking connector of the chaser satellite (Hikoboshi, right in Fig.2) [2]

Fig.2 Computer graphics simulation for the target capture by the manipulator arm by integrating technologies verified by ETS-VII

[1] M.Oda, et al., "ETS-VII, Space Robot In-Orbit Experiment Satellite", Proc. of 1996 IEEE Int. Conf. on Robotics and Automation, pp. 739-744, 1996.

[2] N. Inaba and M. Oda, "Autonomous Satellite Capture by a Space Robot - world first on-orbit experiment on a Japanese Robot Satellite ETS-VII," Proc. of 2000 IEEE Int. Conf, on Robotics and Automation, pp. 1169-1174, 2000.

[3] K. Yoshida, D. N. Nenchev and M. Uchiyama, "Moving base robotics and reaction management control," Robotics Research: The Seventh International Symposium, Ed. by G. Giralt and G. Hirzinger, Springer Verlag, pp. 101-109, 1996.

[4] D. N. Nenchev, K. Yoshida, P. Vichitkulsawat amd M. Uchiyama, "Reaction null-space control of flexible structure mountedmanipulator systems," IEEE Transactions on Robotics and Automation, Vol.15, No.6, pp.1011-1023, 1999.

[5] Y.Umetani and K.Yoshida, "Continuous Path Control of Space Manipulators Mounted on OMV," Acta Astronautica, Vol.15, No.12, pp.981-986, 1987.

[6] Y.Umetani and K.Yoshida, "Resolved Motion Rate Control of Space Manipulators with Generalized Jacobian Matrix," IEEE Transactions on Robotics and Automation, Vol.5, No.3, pp.303-314, 1989.

[7] K. Yoshida "Engineering Test Satellite VII Flight Experiments For Space Robot Dynamics and Control: Theories on Laboratory Test Beds Ten Years Ago, Now in Orbit," International Journal of Robotics Research, Vol.22, No.5, pp.321-335, 2003.

[8] W-K. Yoon, T. Goshozono, H. Kawabe, M. Kinami, Y. Tsumaki, M. Uchiyama, M. Oda and T. Doi, "Model-Based Space Robot Teleoperation of ETS-VII Manipulator," IEEE Transaction on Robotics and Automation, Vol. 20, No. 3, pp. 602-612, 2004.

[9] T. Imaida, Y. Yokokohji, T. Doi, M. Oda, and T. Yoshikawa, "Ground-Space Bilateral Teleoperation of ETS-VII Robot Arm by Direct Bilateral Coupling Under 7-s Time Delay Condition," IEEE Transaction on Robotics and Automation, Vol. 20, No. 3, pp. 499-511, 2004.

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