An Ion Machined Accelerator Grid for the ECR Ion Thruster µ20

Abstract

The “µ20” ion thruster, which successor to a microwave discharge ion thruster “µ10” mounted on “Hayabusa” asteroid explorer, is under research and development. A substantial improvement in performance of the “µ20” thruster has been achieved by equipping with unique magnet geometry and gas injector layout. The next goal has been an improvement in the propellant utilization efficiency. In order to increase the propellant utilization efficiency, new accelerator grid that aperture diameter were much reduced so aggressively from the conventional accelerator grid was designed and fabricated. Excessive accelerator grid impingement currents, however, were expected. In order to reduce accelerator current and decide the optimum aperture diameter distribution, this grid was ion machined for over 1,000hours. As a result of the ion machining process, accelerator current was like it had been before. The propellant utilization efficiency increased from 66.7% to 82.4%.