Endurance Test of Microwave Engine

A low-power, microwave-discharge type electrostatic thruster has been developed for applications to 50 kg- class satellites at Advanced Technology Institute Ltd. (ATI) in Hokkaido, Japan. A prototype of the engine was manufactured, and its endurance test has been performed since October, 2002. The result in the first 2100 hours of the test was reported previously. After 1534 hours of operation, the neutralizer was change from a filament cathode to a microwave cathode. Also after 1854 hours of operation, a graphite shield has been installed on the inner surface of the magnetic nozzle to protect the Sm-Co magnets and to reduce sputtering. Thus, the endurance test of magnetic nozzle and the cathode had to start over. The discharge chamber and antenna for the main discharge are the only parts that have been used since the beginning of the endurance test in October 2002. After nearly 7200 hours of operation, the microwave engine operation became unstable, and the endurance test was stopped. The microwave cathode has logged over 5500 hours of operation, the magnetic nozzle with graphite shield has logged over 5200 hours of operation, and the other parts of the microwave engine has logged over 7100 hours of operation at the end of the endurance test. Therefore, it is successfully demonstrated that the microwave engine has a lifetime of over 5000 hours. The magnetic flux density of the discharge chamber magnets has decreased by 250 gauss over 7100 hours. The magnetic flux density of the magnetic nozzle magnets and the cathode chamber magnets has not decreased because of the graphite shield and the aluminum shield, respectively. The engine performance was affected not only by daily air temperature change but also seasonal change of the surrounding air. During the period when surrounding air condition was most stable, the acceleration current varied ± 0.6 mA. Various kinds of sputtering have shown that the most sputtering occurs at magnetic cusps. The cathode orifice, which is made of aluminum, had no sputtering damage, but there was some deposition on the plasma side of the surface.