Microgravity Experiment for Attitude Control of a Tethered body by Arm Link Motion

A tethered space robot, which is connected to a mother spacecraft through a piece of tether, is a new space system proposed in the previous work. The tethered subsystem is envisioned to be a multi-body system for a robot, whose attitude can be controlled under tether tension by its own link motion. This paper discusses about microgravity experiment for attitude control of a tethered space robot. Design and mechanism of the experimental device, required for the proposed attitude control, were explained. Also, link motion control algorithm was designed considering structure of the experimental device. Link motion is controlled for obtaining: (i) torque acting in direction to stable attitude; and (ii) torque damping rotational motion. The proposed control approach was confirmed by two kinds of microgravity experiment. One is by capsule dropping, which can provide high quality microgravity condition during 4.5 seconds. The other is by parabolic flight by an airplane, which can provide 0.01G level condition during 20 seconds. Characteristics of the proposed control approach mounted on the hardware device have been clarified.