澤井 秀次郎

Hydrazine is used for most conventional monopropellant thrusters for spacecraft propulsion systems. Due to its toxicity, considering environmental pollution and safe handling, it has been suggested to apply "green propellants" to spacecraft propulsion systems. Among green propellants, HAN (Hydroxyl Ammonium Nitrate)-based liquid propellant has promising characteristics of lower toxicity, higher performance (higher density and specific impulse) and longer storability. Therefore, this attractive propellant is considered as a promising candidate of monopropellant for replacing hydrazine propellant. Though it has some advantages shown above, it is very difficult to control its combustion because of sometimes unpredictable reactivity under high pressure conditions. In recent research, it was found that the reactivity of HAN-based propellants can be somewhat reduced by the addition of methanol as a fuel.In our previous study, reactivity of HAN-based propellant with methanol and some catalysts was investigated. In the measurement, oxidizer-rich propellant shows higher reactivity with S-405, which is used commonly for hydrazine monopropellant thrusters. Then, firing tests with a thruster were conducted to understand the effects of methanol additive amount. Although stable combustion was observed, thruster performance was much lower than predicted.In this study, more firing tests were conducted with changes of methanol additive ratio and thruster configuration (combustion chamber length and catalyst bed layer length) to obtain fundamental combustion characteristics of HAN-based thruster for higher thruster performance. As a result, some valuable data as well as development problems for higher-performance thruster design

A new composition of the hydroxyl ammonium nitrate (HAN)-based solution containing ammonium nitrate, methanol, and water had been developed for monopropellant in a reaction control system (RCS) as an alternative to conventional hydrazine. Comparing this solution with hydrazine, Isp is 20% higher, density is 1.4 times, the freezing point is much lower, and the toxicity is low, which makes this solution promising as a RCS propellant. The linear burning rate of the solution is moderate at the operating pressures of an RCS thruster. However, it was found that the linear burning rate had some characteristics whose mechanisms had not been understood. The combustion mechanism of this solution was investigated, the burning behavior was observed using a medium speed camera, and a temperature profile for the combustion wave was measured with a fine 2.5 mu m-diameter thermocouple. From these results, the instability of the liquid interface may trigger a sudden increase in the burning rate to a violently high region, and methanol was found to be effective in reducing the bubble growth rate in the solution. For RCS thruster use, reactivity with several catalysts was evaluated in an open-cup test. Consequently, the S405 catalyst for hydrazine showed the best performance among Pt-based, Pd-based, Ru-based, Ir-based, and S405 catalysts. Thruster tests were conducted successfully using S405 in both the pulsing and continuous modes. As a result, it was found that S405 has little effect in activation of the reaction of methanol contained in the propellant. High-concentration Pd catalyst was found to improve the decomposition characteristic of the solution.

ドラッグフリー技術に基づいた新しい自由落下カプセルを,2006年5月に高高度気球B200を用いて高度40km から投下し,微小重力実験が行われた。今回の最初の試験飛行により,三陸大気球観測所の制御室とカプセルとの間での無線通信,ドラッグフリー制御,そして飛行シーケンスを分析するための基本的データを得ることに成功した.