Performance characterization of a miniature microwave discharge ion thruster operated with water

Abstract

Fundamental characteristics of a microwave-discharge miniature ion thruster using water as a propellant, instead of the conventional xenon, are presented in this paper intended for future applications for CubeSats. Water has advantages in terms of safety, handling ability, and availability compared to any other propellant, and these features are especially important for CubeSats. The ion thruster consists of an ion source and a neutralizer, and both use an electron cyclotron resonance heating to generate the plasma. Water was fed to the ion thruster or the neutralizer as a vapor and the direct thrust measurement was conducted. As a result, the thrust correction factor of the ion source was 0.92 ± 0.074 with a beam acceleration voltage of over 0.80 kV, which was similar to the typical values for xenon ion thruster. The ion beam was extracted at the lower mass flow rate, the highest thrust was 164 ± 13.4 μN, and the highest specific impulse was 665 ± 59 s while neglecting the neutralizer. The electron emission current from the neutralizer was 9.5 ± 0.08 mA, which is sufficient to neutralize the ion beam. These experiments demonstrated the basic features of the miniature ion thruster using water and a future possibility of water propellant utilization for CubeSats.