Microwave ion engine prototype model achieved 18000 hrs of autonomous endurance
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.
