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YM COLUMN ARCHIVE

February 11, 2009

Here comes “HAYABUSA” time once again

This is about HAYABUSA as you may know well. HAYABUSA that was launched from Uchinoura Space Center in 2003 was “quietly and excursively” on the space journey back to the earth after having finished its mission of extraordinary exploration of the asteroid ITOKAWA. And now HAYABUSA reignited the ion engine at 11:35am on February 4, 2009 to have started powered flight once again for the actual return to the earth after through “dormant mode” since October 18 of the year before last.

HAYABUSA is to continue velocity acceleration by the ion engine until around March next year and to execute the second phase orbital change for coming back home. We just can’t keep our eyes off the vehicle covered with functional troubles all over. I just report to you as of now that the spaceship is cruising in interplanetary space in good shape.

From the ion engine of HAYABUSA, ionized xenon is emitted at the high rate of 30km/s by which reaction the vehicle gains speed. However, its thrust power is so weak that the vehicle travels heading for earth over a year by repeating orbital changes little by little. “Many small make a great”.

I didn’t figure out its orbit myself, but HAYABUSA seems to be in the almost same direction as KAGUYA on lunar orbit as possibly taken in one camera frame. The distances are so different though; three hundred million kilometers for HAYABUSA and four hundred thousand for KAGUYA.

In operating ion engine this time, HAYABUSA team reactivated a reaction wheel of the probe that had been on coasting flight so far and by so doing they regained three axes control, which enabled them to commence powered flight by reigniting ion engine on February 4. On the same day at 11:35am (JST), reignition of ion engine was confirmed.

The schedule projected after March next year is that the mission team is to guide HAYABUSA closing in to the earth to a certain distance as closely as possible onto the earth orbit by radio navigation from around April through to June next year, and then to release the capsule to enter the atmosphere in June 2010.

Although the total operating hours of ion engine in space is 31,000 hours and the effective orbital change (acceleration by ion engine) is 1700m/s so far up to now, thrust performance and residual propellant are left sufficient enough. Residual propellant necessary to make it to earth is 400m/s.

The difficult operation has started. Please give your hot cheers to the HAYABUSA team who are making intense efforts by burning up their youths for the glorious end of the mission.

I welcome your opinions on this column to the following E-mail address.
matogawa@planetary.or.jp

(Translated by The Planetary Society of Japan)