山田 和彦

<p>In the electrodynamic flow control, weakly-ionized plasma flow behind the strong shock wave could be controlled by the applied magnetic field around a reentry vehicle. To control the flow field, a very strong magnetic field is required and it could be applied by the superconducting magnet, which is too large and heavy for a reentry capsule. Thus, in the present study, to avoid the use of the superconducting magnet, the electrodynamic effect from the combination of multiple weaker magnetic source such as permanent magnets is numerically investigated. According to the MHD simulation, the influence on the drag force caused by the multiple magnetic source, which is placed equiangularly around the body axis, could be diminished by the Hall effect. When the Hall effect is significant, the induced electric current intensity is very small because the electric field is generated much weaker than the one of the single magnet case. Therefore, the present magnetic configuration using multiple magnetic source might not be effective under the high Hall parameter condition such as the reentry flight.</p>

<p>For landing a rover on the Mars ground, supersonic parachute has been developed in JAXA. Key technologies are categorized in aerodynamic performance, mechanical strength, ejection system, and validation method of the design for pre-flight model. So far, we have performed experiments in low-speed, transonic, and supersonic wind tunnels in Chofu aerospace center and ISAS. From these experiments, we have investigated aerodynamic performance such as drag coefficients, opening load factor, and stability of the parachute. We have also evaluated the mechanical strength in these wind tunnel tests. In addition, ejection system with automobile airbag inflator has been developed and a vertical ground test is performed in Noshiro Rocket Testing Center.</p>

A demonstration flight of an advanced reentry vehicle was carried out using a sounding rocket. The vehicle was equipped with a flexible (membrane) aeroshell deployed by an inflatable torus structure. Its most remarkable feature was the low ballistic coefficient that enables reduction in aerodynamic heating and deceleration at a high altitude. During the suborbital reentry, temperatures at several locations on a backside of the flexible aeroshell and inside the capsule were measured by means of embedded thermocouples. The aerodynamic heating behavior of the vehicle was investigated using the measured temperature history, in combination with a numerical prediction in which a flow-field simulation of the heating was conducted. In this flow-field simulation, both laminar flow and turbulent flow were assumed, and the deformation of the flexible aeroshell was considered. A thermal model of the capsule and membrane aeroshell was developed, and the heat flux profiles of the vehicle surface during aerodynamic heating were constructed based on the measured temperatures. The measured temperature data were found to be in reasonable agreement with the predicted data if the flow field near the capsule of the vehicle was assumed to be laminar, with a transition to turbulent flow near the membrane aeroshell.

An inflatable re-entry vehicle is a candidate for future re-entry systems. Owing to the large area and configuration of the vehicle, it can afford a few advantages during the re-entry, descent, and landing approach, such as a decrease of aerodynamic heating and soft landing without requiring a parachute system. To investigate aerodynamic characteristics of inflatable reentry vehicle at low-Mach-number flight, wind tunnel tests were performed in JAXA Low-Speed-Wind tunnel. In this research, we investigated aerodynamic characteristics of 2 types of inflatable reentry vehicle, SMAAC and TITANS, at a low-Mach-number by using numerical simulation. Through the flow field simulation, it was indicated that the computed result of drag coefficient shows reasonable agreement with the experimental one. In the case of TITANS, the computed results showed good agreements compared with experimental results though it was confirmed that a blockage effect was observed.

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.