400-V Bus-Direct Driven High-Power Arcjet Thruster Using Dimethyl Ether as Additive for Extending Lifetime

Today, high-power electric propulsion devices are attracted for the next generation spacecraft; an arcjet thruster is regarded as a promising option because it produces higher thrust to power ratio among electric propulsion. Moreover, the next generation spacecraft would have 400-V bus, and hence, the 400-V bus direct drive of arcjet thrusters would simplify the thruster systems by eliminating voltage converters, and using lower-current cables. However, high-power arcjet operation possibly aggravates cathode erosion, to shorten lifetime. Hence, we propose to use dimethyl ether (DME) as life-extending agent. DME has various preferable characteristics for additives: DME is not toxic nor reactive, and through the thermal decomposition, generates carbon, which would form the layer on the cathode so as to prevent erosion. In this study, we prototyped a 3-kW class water-cooled arcjet thruster to evaluate the effect of DME addition. Cathode erosion rate per power were 0.210 μg/kJ, 0.192 μg/kJ, 0.154 μg/kJ, at mass ratio of DME of 0%, 3%, and 5%, respectively, and hence, DME addition reduced cathode erosion. However, the arc discharge was more frequently unstabilized with increasing DME mass ratio in the range of 0–5%.