The spacecraft for asteroid sample return mission, MUSES-C, scheduled for launch in May 2003, will have an ISAS-developed microwave ion engine onboard for interplanetary navigation. The prototype model of this engine has achieved 18000 hours of autonomous endurance running. The ion engine that started the endurance test on March 30, 2000 to verify its performance for the mission requirement of 18000 hours has continued autonomous running over approx. 2 and a half years. It successfully achieved the original goal of 18000 hours at 2:00AM on October 25, 2002, and still keeps running at present. The engine used for the endurance test is a prototype model of MUSES-C and has been produced in complete accordance with the design, material and manufacturing of the flight model.
The figure shows the cumulative time (graduations on the left) from the start of the test up to the achieving point of 18000 hours and the screen current corresponding to thrust (graduations on the right) over calendar time. As shown in the figure, there are some breaks in the sequence of cumulative time. They indicate the engine cutoff due to the following reasons and do not indicate in any way malfunctioning of the engine: use of endurance test facilities for flight model testing and adjusting; legally scheduled power cut and regular maintenance and inspection of the engine; troubles in the ground support equipment such as a cooling system. Moreover, through the entire test period, the engine has successfully maintained the required thrust performance level, which clearly proves its high potential as a reliable engine in the future.
The picture shows the running engine after it has achieved the target 18000 hours. Xenon is used as the propellant, and electrons are emitted from the luminescent point, neutralizer, in front. Some wear due to Xenon sputtering shown around the ion beam acceleration and outlet areas is well within expectation and has no impact on the performance of the engine.