丸 祐介

In order to ensure the safety of hydrogen energy system, a robust and reliable hydrogen sensor device with an optical fiber Bragg grating (FBG) has been developed. The sensing mechanism is based on temperature changes in the device induced by the heat of the catalytic reaction of hydrogen on platinum-loaded fumed silica catalyst powder. Through optimization of the preparation conditions for the catalyst, which is a hydrogen-sensitive substance, a large degree of heat generation in the presence of hydrogen could be obtained, and good stability was also achieved. A sensor device in which a column filled with the obtained catalyst powder was attached to a commercially available robust FBG for tem-perature measurement, and integrated with another FBG as a temperature reference via a heat shielding plate, was fabricated and evaluated. A stable baseline was demonstrated even in an environment where the ambient temperature severely fluctuated, and a sensor output proportional to the hydrogen concentration could be obtained. The detection limit was about 0.2 vol%, and the long-term stability of the device was good.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this chapter, the development procedure and the operation of Hayabusa2 bipropellant chemical propulsion system are described in detail. Lessons learned from the original Hayabusa (sample return mission from the asteroid Itokawa) and Akatsuki (Venus climate orbiter mission) are described, and the countermeasures incorporated into the design of Hayabusa2 chemical propulsion system are detailed. On-orbit data is used to assess the impulse provided by each thruster. In particular, the cause of thrust variability under pulsed operation is investigated, and approaches to ensure stable and reliable thruster operation are proposed. Furthermore, the relation between thrust duration and generated impulse is modeled to enable reliable reproduction of the required ΔV.

In this paper, the authors investigate whether airbreathing engines have useful application to vertical takeoff and vertical landing systems, which currently represent the mainstream for reusable launch vehicles. A theoretical analysis has been performed to determine the net impact of the specific impulse benefits and weight penalties of a vertical takeoff reusable launch vehicle fitted with an airbreathing propulsion system. To maximize the thrust-to-weight ratio of an airbreathing engine, the authors propose using a conventional fan driven by a separate gas generator in lieu of a conventional core airbreathing combustor, as well as combined rocket-airbreathing operation to reduce engine size. The proposed engine system and its propulsive performance are described herein. Furthermore, a new sounding rocket is described as a practical application for the proposed vertical takeoff and vertical landing airbreathing engine. Conventional horizontal takeoff and horizontal landing airbreathing engine concepts tend to focus on maximizing specific impulse and airspeed, which necessitates further development, specifically in the areas of heat-resistant materials and structural technology. By proposing a vertical takeoff and vertical landing airbreather in this study, a different approach is taken and the potential to significantly improve launch capability and reliability is demonstrated in comparison to the current technology level for reusable launch vehicles.

This study experimentally investigated the cause and the scattering mechanism of the phenomenon in which a celestial surface object scattered by a thruster injection has a spacecraft direction component. The phenomenon was first observed by Hayabusa2 touchdown. One of the mechanisms by which objects on the surface of the asteroid are scattered toward the spacecraft is the making crater by the thruster injection. We investigated the trends in the direction and amount of scattering of surface objects by injecting thrusters into a sandbox created in a vacuum chamber.

令和二年度宇宙輸送シンポジウム（2021年1月14日-15日. オンライン開催)資料番号: SA6000160080レポート番号: STEP-2020-044

The supersonic wind tunnel tests using a rigid parachute model were conducted for Mach numbers ranging from 2.0 to 3.0. The rigid model consists of suspension lines and a riser between the forebody and rear body, and the effect of these suspension lines was investigated. Three characteristic flow modes, namely, high-pressure, low-pressure, and attachment modes, were observed. These three modes were classified on the basis of the shape and position of the apex of the shock wave. In addition, the non-dimensional pressure observed at the center of the canopy varied according to the pressure mode produced. The emergence of each pressure mode depended on the parameters, namely, freestream Mach number, trailing distance, and distance between the bundling point and rear body. Pressure-mode transitions were observed when specific conditions and configuration of the parameters were achieved. (C) 2020 Elsevier Masson SAS. All rights reserved.