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The Forefront of Space Science

Development and Future of Microgravity Experiment System Using a Balloon
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Beyond microgravity experiments

The vehicle is being developed exclusively for microgravity experiments and, therefore, is designed from the aspect of functions required for the purpose. On second thought, however, the vehicle would reach supersonic speed if we conducted a 40-second microgravity experiment. In case of a one-minute experiment, the vehicle would accelerate to about twice the speed of sound. In other words, as a result of developing a system to enable microgravity experiments more easily for a longer duration, we can obtain a vehicle capable of supersonic flight.

This means that the vehicle’s applications expand to various fields outside microgravity experiments. For example, it can also serve as a tool to develop jet engines for space planes.

Figure 3
Figure 3. ATREX engine under firing test at static state on the ground

Many varied ideas are now proposed for future space transportation systems. Taking into consideration that ordinary people without special training may use the system, one promising candidate is the space plane that is gently accelerated by a jet engine. The idea of a space plane is attractive in the long term. Looking at the current status, however, we are facing the greatest problem, the lack of a good concept to develop jet engines to propel space planes. On this issue, JAXA has actively pursued research on the “ATREX Engine” (Fig. 3) since before its reorganization. To our regret, however, it is not yet demonstrated that the engine operates normally and smoothly at speeds far exceeding the speed of sound. By using the vehicle that we are developing, it is technically possible to perform a demonstration test of the engine. We are aiming to perform the test by all means.

Furthermore, we expect that, by equipping a jet engine with a vehicle to accelerate itself downward to cancel air resistance, we could extend the duration of microgravity experiments or fly the vehicle back to a recovery point on the ground after experiments. In particular, there is a tendency for jet-engine thrust to grow as the density of inlet air increases, which is also true for air resistance. For this reason, the jet engine is especially attractive as a thrust engine to offset air resistance. With an eye toward future space planes as well as future microgravity experiments, it is meaningful to pursue the possible use of jet engines.

Regarding the space plane, we hope that our vehicle will be fully utilized to solve various problems hindering the development of the future plane, not limited to its engine development. Besides engine development, it is thought that there are many other studies that cannot be accomplished by ground tests or analysis alone. We hope that our vehicle will be used for such studies and, conversely, that such studies will help improve our microgravity experiment system.

For the Future

We built the first trial vehicle and tried to float it with a balloon, but unfavorable upper winds prevented it. With further improvements to the vehicle, we expect to launch the vehicle successfully next time.

(Shujiro SAWAI)

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