Sub-Milli-Newton Class Miniature Microwave Ion Thruster

Abstract

A miniaturized microwave ion source with a 1.6-cm beam diameter grid system was designed and then evaluated experimentally. Based on the HAYABUSA μ10 neutralizer, we fabricated a small 18-nun-diam discharge chamber, into which 4.2 GHz microwaves were launched through an L-shaped antenna that was located in a magnetic field created by permanent magnets and iron yokes. Ion beams were emitted from the small discharge chamber when operated with a grid system whose respective hole diameters of the screen grid and acceleration grid were 0.72 and 0.43 mm, and the total number of grid holes was 211. For a beam voltage of 1500 V and a microwave input power of 10 W, the typical thruster performance was thrust of 0.34 mN, a thrust/power ratio of 16 mN/kW, propellant utilization efficiency of 68%, and a specific impulse of 3200 s. If we were able to further reduce the ion production cost (circa 3000 W/A in the current experiment), this thruster would be a candidate for main propulsion of a small satellite or precise attitude control of various sizes of satellites.