The Institute of Space and Astronautical Science (ISAS) has been developing a microwave discharge ion engine system applicable to the asteroid sample return mission temporarily designated as "MUSES-C", which will depart from the Earth in 2002 and return to the Earth in 2006. An engineering model of the thruster was assembled into an endurance test set to be dedicated for its lifetime verification since February 1997. The total operational time reached 18,000 hours without any fatal failures attributed to the electrode-less microwave discharge. The carbon-carbon composite grids assembly was proved to meet the requirement of long-term ion acceleration. Prom 1999, prototype models of the engine were fabricated and dedicated to system environment tests such as vibration, shock, thermal-vacuum and electrical interface tests.
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