DEVELOPMENT OF HAN-BASED LIQUID PROPELLANT THRUSTER

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