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The Forefront of Space Science

High Hopes for the Age of Epic Space Voyages- Asteroid Explorer “HAYABUSA” and Ion-Engine Technology
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HAYABUSA cruising smoothly

Directing its course toward earth, the asteroid explorer “HAYABUSA” is cruising with its three purple lights shining in the raven black space. Feeling unsatisfied with just looking at the numbers passing over the screens at ground control station, I have an urge to fly to HAYABUSA in order to check the ion engine’s grid holes and touch the engine to check the temperature of the parts with no temperature sensors attached.

On May 9, 2003, the M-V-5 rocket carrying the MUSES-C explorer roared into the blue sky and disappeared. When its radio signal was received at Kagoshima station after the earth had rotated beneath it, the explorer was given the new name “HAYABUSA.” It marked the moment that _-10, a microwave-discharge-type ion engine developed over 15 years, finally became “space-borne.” From end May 2003, we carefully ignited the engines’ plasma one by one to begin ion acceleration. To our unexpected delight, we were able to confirm in real time the velocity change of HAYABUSA’s ion engine acceleration by measuring the Doppler shift of communication signal wave. From July, when the engine tests and adjustments were completed, it began cruising operation, continuous acceleration for 24 hours without real-time monitoring from the earth. By end February 2004, the four ion engines had attained 10,000 hours in accumulated operation though the engines did not operate during year-end and new-year holidays.

HAYABUSA successfully entered a trajectory that will bring it nearby the earth in early May 2004. When flying nearby the earth, its accumulated velocity vector by ion-engine acceleration will be diverted in the direction of the target celestial body, the asteroid Itokawa. HAYABUSA will be accelerated continuously after that and is expected to arrive at Itokawa around the fall of 2005.

Figure 1.
Fig.1 Simultaneous actuation of two microwave-discharge-type ion engines (terrestrial test)
Top: Development model Bottom: Prototype model

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