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The microwave discharge ion engine generates plasmas of the main ion source as well as the neutralizer using 4 GHz microwave without discharge electrodes and hollow cathodes, so that long life and durability against oxygen and air are expected. MUSES-C "HAYABUSA" spacecraft installing four microwave discharge ion engines was launched into deep space by M-V rocket on May 9, 2003. After vacuum exposure and several runs of baking for reduction of residual gas the ion engine system established the continuous acceleration of the spacecraft toward an asteroid. The Doppler shift measurement of the communication microwave revealed the performance of ion engines, which is 8 mN thrust force for a single unit with 3,200 sec specific impulse at 23 mN/kW thrust power ratio. At the beginning of December 2003 the accumulated operational time exceeded 7,000 hours and units.

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