秋山 茉莉子

令和元年度宇宙輸送シンポジウム（2020年1月16日-17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: SA6000147035レポート番号: STCP-2019-035

The combustion of aluminum and magnesium is an attractive power source. Many practical tests have been conducted as a composite propellant of metal powder and water. However, because the safety and the ease of handling are required to be launched into space, it is desirable that nonpowder metal is used as fuel and stored separately from oxidizer. Heat loss has a significant impact on the combustion of bulk metals. Though combustion behavior of bulk metals differs from that of powders, little has been reported on the combustion of bulk metal with water. This study, first, considered two types of ignition method: Joule heating and induction heating and investigated their feasibility in the scale of small spacecraft. Then, two types of experiments were carried out. The former is the wire combustion experiment using Joule heating. This experiment revealed that the characteristics of millimeter scale bulk metal combustion with water vapor. The latter experiment is the induction heating of a magnesium rod as an initial test of the ignition system for centimeter scale fuel. This test demonstrated the heating of the metal and identified the rooms for improvement to ignite the fuel.

Water is one of the most suitable propellants for small spacecraft because it can be stored at low pressure, is safe and abundant on earth. Although propulsion systems using water as a propellant were already operated in space, but the desired thrust was not obtained because the gas-liquid separation was not successful, The University of Tokyo has developed a propulsion system with a vaporization chamber for gas-liquid separation, AQUARIUS. In this research, it was demonstrated whether the required performance could be obtained by changing the method of supplying the propellant to the propulsion system provided with the vaporization chamber.

For the realization of the complicating missions by small spacecrafts, it is necessary to establish the micro-propulsion technology. AQUARIUS (AQUA ResIstojet propUlsion System) is a micro-propulsion system which is going to be installed on a 6U CubeSat EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) and launched in 2020. AQUARIUS uses water as a propellant. The advantages of using water mainly come from two points. First, it exits as a liquid in standard state. Second, it is non-toxic substance. These advantages lead to the easier handling, which results in the cost reduction and the period shortening of the development. However, one of the major disadvantages is that its latent heat 2400 J/g is large compared to the other propellants used in resistojet thrusters. In AQUARIUS, the waste heat of the high temperature devices was reutilized to compensate the latent heat. AQUARIUS is composed of mainly three components: a tank for containing water, a vaporization chamber for vaporization of water, and a thruster head for thrust generation. Up to now, AQUARIUS Flight Model was assembled, and the several kinds of experiments were conducted. In this study, the latest development status of it was shown, mainly focusing on the two types of thrust measurement because the thermal environment was different between AQUARIUS alone and that installed on the spacecraft. From the results, it was estimated that the operational parameters were appropriately chosen, and that the reutilization of the waste heat was successfully conducted in the spacecraft.

Flight model of a micro-water resistojet propulsion system, named AQUARIUS (AQUA ResIstojet propUlsion System) was designed for a deep space exploration by 6U Cubesat. Ultra green propellant: water was used as propellant, which allowed for low pressure feeding system and a safe and easy handling. In addition, water has been arousing interest as a potential resource for future deep space exploration. AQUARIUS has a gas-liquid separation device, named vaporization chamber, where liquid water evaporates at a standard temperature. Waste heat of transponders is reused at the vaporization chamber. MEOP (Maximum Expected Operating Pressure) was designed to be approximately 60 kPa. Flight model was assembled, and operation test was conducted in a vacuum chamber. Thrust performance was measured by using thrust balance. Averaged thrust of more than 4 mN was achieved in a first operation.