MUSES-C Passes Tests
25 Feb 2003
(Source: Institute of Space and Astronautical Science)
MUSES-C Monthly Report No. 3
February 25, 2003
From January to early February, MUSES-C underwent a thermal vacuum test for its flight model, the final important checkpoint before launch. As the main feature of the explorer is that it uses ion engine propulsion, the test focused on the large-output power equipment that is needed to run the ion engine. The test was separated into two rounds. In the first round, we verified the temperatures of and the validity of thermal control for the individual on-board instruments by connecting the ion engine's acceleration power to a simulated load. Verification of the temperature rise in the bottom equipment, another main target of the test, was also made successful by simulating approaching and landing sequences to the asteroid surface, where the temperature is estimated to be about 100??. In the second round, the first such experiment in the world, the flight model's ion engine was actually activated and run up to ion acceleration. It was different from the first round of the test in that the real engine itself was the load to the acceleration power. MUSES-C employs the cluster-type ion engine configuration. Fortunately, we could also confirm that each engine head ran normally.
Although attracting little attention, power-constrained thermal control is one of the new technologies applied to MUSES-C. In conventional satellites and explorers, there is no guarantee that the heaters will not all start at once, with power consumption consequently shooting up to maximum when the temperature falls below the lower limit. In MUSES-C, since a constant amount of power must be secured for the ion engine, a new control logic has been defined for the computer to limit the maximum power consumption by the heaters. Even when the electromagnetic valve for chemical propulsion causes a momentary peak-power hike, the power-constrained thermal control system responds by shutting down the heater power source for an instant. This is a good example of new technologies used not only for major demonstration but also for minor refinement. MUSES-C will be transported to the launch site in Uchinoura in mid-March after pre-launch alignment, inertia data measurement, and the final function test finishing by the end of February.