Endurance test of microwave engine

Abstract

A low-power, microwave-discharge-type electrostatic thruster has been developed for 50 kg-class microsatellites. A breadboard model of the microwave engine was manufactured, and two endurance tests were performed to verify its durability. During the first endurance test of 1200 h, only slight changes in the thruster discharge chamber were observed. However, the stainless-steel magnetic nozzle just downstream of the discharge chamber had sputter damage near the nozzle exit extending to the midsection of the Sm-Co magnets on the inner wall. Although the thruster operation was unaltered by the sputter damage, it was decided to shield the magnetic nozzle surface with graphite to protect it from impinging ions and reduce sputtering. Thus, the magnetic nozzle was replaced by one with a graphite shield for the second endurance test. Also, the filament neutralizer was replaced by a microwave-discharge neutralizer. The thruster discharge chamber, including the antenna, was kept from the first endurance test. After more than 5000 h of operation in the second endurance test, thruster operation became unstable, and the endurance test was stopped. The microwave neutralizer had logged over 5500 h of operation. The magnetic nozzle with a graphite shield had logged over 5200 h of operation. The other parts of the thruster had logged over 7100 h of operation.