Control system of new micro-gravity experimental system "BOV" from high altitude balloon

This paper proposes control system for a new micro gravity experimental system called BOV (Balloon-based Operation Vehicle). BOV uses a free-fall capsule with doubleshell structure to prevent influence of aerodynamic disturbance. Additionally, BOV is raised to 40km by a high altitude balloon to extend micro gravity duration to 30(or possibly 60) seconds. Thus we realize a medium duration micro gravity experimental system with good micro gravity environment. In this system, the most characteristic point is double-shell Structure. The inner shell can fall freely since the outer shell is controlled not to collide with the inner shell. To realize this non-contact control, BOV's body is controlled by translational control and attitude control. For translational control, there are four laser displacement sensors in the middle of BOV to measure clearance between the inner shell and the outer shell. The center position of the inner shell is estimated by the Newton-Raphson method with four laser displacement sensors. Using this estimation, force commands are calculated with PD controller. Attitude control is also necessary to maintain stable micro gravity experiments. BOV has three fiber optical gyros to measure the body rates. Torque commands are also calculated with PD controller. The rolling angle is controlled by only D controller since the initial error angle is possible to exert a bad influence for that the balloon is rotated in the upper air. BOV is separated from the high altitude balloon after the balloon arrives at 40km altitude. For 35 seconds the micro gravity experiment is carried out. After the experiment, the pilot-chute is opened for speed reduction. In addition, main-chute is opened at 7.5km altitude for safety descent. In this paper, control system for the new micro gravity experimental system is proposed. This system has double shell structure and the inner shell can fall freely. In the experiment, we realize good-quality micro gravity and realize to continue moderate micro gravity duration. This system is now improving and near future we can utilize BOV's system for moderate micro gravity duration with low-cost easily.