Verification Tests of Carbon-Carbon Composite Grids for Microwave Discharge Ion Thruster

Abstract

Anionbeam opticsfora10-cm-diam 400-W-classmicrowavedischargeion thrusterwasfabricatedanditsapplicabilityto along-termspacemissionwasdemonstrated.Theopticsconsistsofthree1-mm-thick e atcarbon ‐carbon composite panels with approximately 800 holes that were mechanically drilled and positioned with § 0:02-mmaccuracy.Whenmounted onanaluminum ring,spacingforthethreegridswaskeptat0.5 mm bythreesetsofspacers. The thruster produced an ion beam current of 140 mA with a microwave power of 32 W for plasma generation and a total acceleration voltageof 1.8 kV. Although thegrid is sputtered by the impingement of slow ions produced in charge-exchange collisions between fast beam ions and neutral atoms leaking from the engine, the grid showed only slight damage even after an 18,000-h endurance test. Also, other qualie cation tests including a mechanical test under launch conditions as well as a thermal vacuum test simulating the spacecraft thermal environment were successfully completed. Hence, the grid system was qualie ed for spacecraft propulsion.