New flight control problem for Japan's asteroid probe

All a question of attitude

Doubts were raised yesterday over the future of Japan's asteroid sample and return mission, as the spacecraft lost another part of its attitude control system. The news has prompted concern that the craft won't be able to make its planned landing on an asteroid next month.

The Hayabusa spacecraft, specifically designed to collect a sample from the Itokawa asteroid and return it to Earth, lost the second of its three reaction wheels earlier this week.

With only one functioning wheel left, Hayabusa will have to rely more heavily on its chemical propellant thrusters to keep it oriented in space.

The probe, which is now some 305m kilometres from Earth and just 6.8km from its final target, has completed most of its scans of the asteroid. Mission controllers hope that it will be able to take more high resolution images in the coming weeks.

Conservation of fuel will be paramount, and may lead to alterations of the mission profile. Attitude control will be managed by combining two reaction control systems with the remaining functional reaction wheel.

The original plan involves two touchdowns on the Itokawa asteroid in November. At each touchdown, the craft will fire a pellet at the rock and collect the dust sent up by the impact.

Hayabusa will begin its return journey to Earth this December, and all being well, is expected back on Earth in June 2007. ®

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