Yusuke Maru

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 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.

Space Transportation Symposium FY2020 (January 14-15, 2021. Online Meeting)

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.

During the touchdowns of the "Hayabusa2" spacecraft on the asteroid Ryugu, some of the ejected surface materials were scattered toward the spacecraft. Apart from impact sampling by firing a metallic projectile, another mechanism of this phenomenon is surface material ejecta from formation of a crater by RCS thrusts of the spacecraft during its ascent from the asteroid surface after the touchdown. We conducted ground experiments of gas injection into simulated soil under vacuum in order to investigate the interaction between thruster plume and asteroidal regolith.

This paper presents a hydrogen ignition experiment conducted to establish safety standards for high-pressure hydrogen handled at the hydrogen stations for fuel cell vehicles (FCV). In the experiment, cryogenic hydrogen pressurized to over 80 MPa was leaked from a pinhole nozzle, and the blast pressure at the ignition and the flame length during steady combustion were measured. The hydrogen supply equipment used in the experiment has a maximum flow rate of 100 kg/h, a maximum discharge pressure of 90 MPa, and a temperature adjustment range of 50 K-300 K. Four types of pinhole nozzles with different outlet diameters, viz. 0.2 mm, 0.4 mm, 0.7 mm, and 1.0 mm were used to leak the hydrogen. In the experiment, the effects of the pinhole nozzle diameter, hydrogen supply pressure and temperature, and an igniter location on the blast pressure and flame length were evaluated. The igniter being appropriately positioned, once a steady flame was formed, combustion continued even if the ignition source was turned off, which necessitated the stopping of hydrogen supply to extinguish the fire. As a result of the experiment, it was found that the blast pressure and the flame length can be expressed as the correlation equations of the hydrogen leakage flow rate. However, even if the leakage flow rate was the same, we found that the flame length increases with decreasing the hydrogen supply temperature. We presented a correlation equation for the cryo-compressed hydrogen flame length that is about 30% longer than the previously presented equations for 300 K hydrogen flame. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

At bipropellant chemical propulsion systems, iron in oxidizer is one of the topics to be noted and controlled. Actually, to avoid the influence of the iron ingredient, several long term mission spacecraft such as interplanetary probes flush the oxidizer piping periodically. The major influence of steel contaminated oxidizer is known to be flow decay. Still, operation data of the HAYABUSA2 spacecraft indicates possibility of other drawbacks. This paper discusses its impact to the reactivity of the hypergolic propellant, especially for the propellant combination of N₂H₄/MON3, which is the case of HAYABUSA2. A series of open cup firing tests show that the reactivity deteriorates when the oxidizer is contaminated with iron.

Balloon Symposium 2019 (November 7-8, 2019. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan

第2回観測ロケットシンポジウム（2019年8月5日-6日. 宇宙航空研究開発機構宇宙科学研究所（JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000142004レポート番号: Ⅰ-4

2nd Sounding Rocket Symposium (August 5-6, 2019. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan

The 29th Workshop on JAXA Astrodynamics and Flight Mechanics 2019 (July 22-23, 2019. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan

<p>To develop a loading arm for ship-to-shore transfer of liquefied hydrogen, an emergency release system (ERS) for liquefied hydrogen has been designed and manufactured. In order to estimate its mechanical and thermal behaviors, we have developed a calculation model for temperature and stress distribution of the ERS at low temperatures during the transfer of liquefied hydrogen. The calculation has revealed that the surface temperature would exceed the boiling point of oxygen. A prototype model of the designed ERS has been manufactured and tested by filling liquid hydrogen in the model. The temperature and strain on the surface have been measured during the test and compared with the calculation results. The results have shown that the calculation can predict the temperature on the surface of ERS and that the designed ERS can avoid generating liquefied oxygen. It has also been shown that the measured strains are well consistent with the predicted strain on the surface of ERS. It has been demonstrated that the developed ERS exhibits performance good enough to be utilized for the loading arm for transfer of liquefied hydrogen. </p>

<p>In this paper, we evaluate a mobility system using skids for a small lander. The small lander named Smart Lander for Investigating Moon (SLIM) has been developed by ISAS/JAXA. In the small lander mission such as SLIM, planetary surface exploration after the landing will become difficult due to the restriction of the lander's payload weight for a rover and observation equipment. To solve this problem, we propose the mobility system using skid-sliding to improve exploration capability of the small lander mission. We confirmed the skids' sliding potential of the small lander using numerical simulation. The simulation showed that the small lander can travel to the desired direction using skids and thruster control.</p>

Multiobjective design optimization of the engine of the atmosphere-assisted reusable sounding rocket is performed for maximizing the maximum altitude and the payload weight. The result shows that a trade-off between maximization of maximum altitude and payload weight maximization.

第34回宇宙構造・材料シンポジウム（2018年12月4日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)), 相模原市, 神奈川県資料番号: SA6000137026レポート番号: B04

The exploration of energization and radiation in geospace (ERG) satellite, nicknamed "Arase," is the second satellite in a series of small scientific satellites created by the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency. It was launched on December 20, 2016, by the Epsilon launch vehicle. The purpose of the ERG project is to investigate how high-energy (over MeV) electrons in the radiation belts surrounding Earth are generated and lost by monitoring the interactions between plasma waves and electrically charged particles. To measure these physical processes in situ, the ERG satellite traverses the heart of the radiation belts. The orbit of the ERG is highly elliptical and varies due to the perturbation force: the apogee altitude is approximately 32,200-32,300 km, and the perigee altitude is 340-440 km. In this study, we introduce the scientific background for this project and four major challenges that need to be addressed to effectively carry out this scientific mission with a small satellite: (1) dealing with harsh environmental conditions in orbit and electromagnetic compatibility issues, (2) spin attitude stabilization and avoiding excitation of the libration by flexible structures, (3) attaining an appropriate balance between the mission requirements and the limited resources of the small satellite, and (4) the adaptation and use of a flexible standardized bus. In this context, we describe the development process and the flight operations for the satellite, which is currently working as designed and obtaining excellent data in its mission.