山田 和彦

The Japanese balloon base was moved from the Sanriku Balloon Center (SBC) to the Taiki Aerospace Research Field (TARF). The SBC was closed in September 2007, and the new base at the TARF became operational in May 2008. In 2008, the first series of balloon flights at the TARF was carried out. By the success of these flights, we verified that the whole system of the new balloon base is well established. From FY 2009, regular balloon operations with science payloads started at the TARF. In May/June 2009, flight operations of three science experiments were carried out successfully. Five more science flights are planned at the TARF in August/September 2009.

A zero-pressure balloon used for scientific observation in the stratosphere has an unmanageable limitation that its floating altitude decreases during a nighttime because of temperature drop of the lifting gas. Since a super-pressure balloon may not change its volume, the lifetime can extend very long. We had introduced so called the 'lobed-pumpkin' type of super-pressure balloon that can realize a full-scale long-duration balloon and it will be in practical use in the very near future. As for larger super-pressure balloons, however, we still have some potential difficulties to be resolved. We here propose a new design suitable for a larger super-pressure balloon, which is roughly 'lobed pumpkin with lobed cylinder' and can adapt a single design for balloons of a wide range of volumes. Indoor inflation tests were successfully carried out with balloons designed and made by the method. It has been shown that the limit of the resisting pressure differential for a new designed balloon is same as that of a normal lobed-pumpkin balloon.

An aeroshell made from membrane material have an advantage of reduction in the aerodynamic heating, because its small mass and large area enable us to make the low-ballistic-coefficient flight, in which the vehicle decelerates at very high altitude with low atmospheric density. In this paper, we propose a new concept of mini re-entry system for small satellites. This vehicle is called "FEATHER" (Flexible Expanded Aeroshell with Tiny payload Harness for Entry and Recovery). "FEATHER" is a novel re-entry and recovery system, featuring the autonomous aeroshell deployment, the low-ballistic-coefficient re-entry with less severe aerodynamicc heating and so on. FEATHER is composed of the membrane aeroshell made from the high-temperature cloth called ZYLON®, an outer frame made of Shape Memory Alloy (SMA) and a payload. When the aeroshell receives the aerodynamic heating, the temperature of SMA frame rises and restores the circular shape as memorized beforehand. Then the membrane aeroshell is automatically deployed. Therefore the vehicle can achieve the low-ballistic-coefficient flight with a drastic reduction in the aerodynamic heating without any additional sensors, controllers and actuators. The preliminary studies made on FEATHER system so far including the hypersonic wind tunnel experiments are presented in this paper.

A Low-ballistic-coefficient atmospheric-entry technology using a flexible aeroshell is promising for a space transportation system in next generation because it can reduce the maximum aerodynamic heating during a re-entry and the terminal velocity dramatically. Its technology will lead to realize a safer, cheaper and more universal space transportation system. Our group has researched various important subjects in order to apply the flexible aeroshell to actual atmospheric-entry missions. In this paper, the innovative re-entry system from LEO which was defined as the nominal mission by our group is introduced and our current research and development are reported.

A low ballistic coefficient vehicle can drastically reduce peak aerodynamic heating during atmospheric entry. We are developing the new atmospheric entry system using an inflatable flexible aeroshell. A fight test of the system, which is aiming to verify the design method of the inflatable flexible aeroshell, is planned for late August, FY2008. The flight test is performed by stratospheric balloon-drop from altitude of about 30 km. In this paper, the system configuration and the operation sequence of this experiment system are overviewed.

The development of the airtight and heat-resistant membrane is an important factor to realize the low ballistic coefficient reentry spacecraft with flexible aeroshell. The air tightness is necessary for the inflatable structure and the heat-resistance against aerodynamic heating is also demanded. The candidate of the membrane is Zylon[○!R] (Toyobo. Co. Ltd.) and it can endure more than 600 degree Celsius. Authors tried to give Zylon airtight property with coating on it, but the coated sample was not airtight. If polyethylene is used as an inside layer of Zylon, the two layers system have the airtight property. As outer layer should be a heat shield in this case, radiative heat transmission test of membrane is also tested. Thicker Zylon and Zyron with Kapton[○!R] film show less transmission rate than Zylon.