Certificate of Appreciation from JAXA to the Himeno Laboratory for its contribution to the development of the H3 rocket

On 8 May 2024, the Japan Aerospace Exploration Agency (JAXA) presented a letter of appreciation to the Himeno Laboratory of the Department of Aeronautics and Astronauics for its contribution to the development of the H3 rocket and the successful launch of the second test vehicle. Certificate of Appreciation for the development of the H3 rocket and successful launch of the second test vehicle, which was presented by The Japan Aerospace Exploration Agency (JAXA), a letter of appreciation to companies and research institutes that have made significant contributions to the development of the H3 rocket, Japan’s new primary launch vehicle, and the successful launch of the second test flight vehicle.

The ground facilities of a heavy rocket launch (launch pad) have an underground passage (flame trench) to release the engine exhaust gas. Depending on the operating conditions, such as when the countdown is paused and then resumed, it may be possible to start the engine with a large amount of cooling water in the trench. In such cases, there is a concern that the engine exhaust may hit the water pool with great force, and the water blown up may hit the body of launch vehicle and ground equipment, causing damage. For a safe launch, the behaviour of the water in the flame trench must be predicted according to the amount of water. Experiments (test runs) using actual rockets and launch pads could be considered, but this was considered impractical due to the risk of airframe damage and cost.
In response to this problem, Professor Himeno and his laboratory’s graduate students (at the time), consulted by JAXA, devised a model experiment based on the similarity law of fluid mechanics and proposed a method for predicting the behaviour of water in the flame trench. The laboratory conducted an experiment simulating engine exhaust using a high-pressure air source (for wind tunnel facilities) in the Engineering Building No. 7 at the Hongo Campus.
As a result, it was confirmed that the behaviour of the water in the trench observed in the model experiment reproduced the phenomena observed in the past H-IIB rocket ground combustion tests and at the launch of the H3 test vehicle No. 1. On top of that, it was also able to carry out an experiment that imposed a dangerous water level at which the blown-up water would directly hit the body of launch vehicle. The knowledge obtained from the series of experiments has been utilised in determining the operating conditions of the H3 rocket.

Future aspirations and impressions

It is encouraging for both students and staff that our contribution as a laboratory has been recognized alongside companies that possess advanced technology. It is truly a real pleasure of fluid mechanics, the fact that the prediction of real-scale phenomena based on similarity laws and model-scale experiments has been confirmed. We were forced to carry out experiments on a day of heavy snow just after the start of the new year in response to requests for data as soon as possible. It has become a good memory now. We would like to continue to contribute to the development and operation of rockets and space vehicles through experiments and numerical simulations.

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