Hayabusa hovered over its target asteroid but couldn’t land.

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主要内容是讲日本探索小行星失败

Asteroid lander misses its mark
Hayabusa spacecraft fails on its first attempt to take a bite out of an asteroid.
Ichiko Fuyuno

The Japanese craft that was aiming to be the first to land on an asteroid, collect a sample and bring it back to Earth, has apparently failed on its initial attempt.

Japan's space agency said on 20 November that the Hayabusa spacecraft experienced problems when it was less than 17 metres away from its target, forcing it to back off. Mission officials are not yet sure whether the craft should try again later this week, as originally planned.

Hayabusa was supposed to touch down on the 540-metre-long Itokawa asteroid for just a second, shoot a tiny metal ball into the surface at a high speed and capture fragments of the surface.

Long road

Hayabusa arrived at Itokawa in September 2005, after a journey of 300 million kilometres that took two years to complete. Since then it has been hovering around the asteroid, conducting observations in preparation for touchdown.

But things have not gone smoothly. In July and October, two of Hyabusa's three reaction wheels - spinning discs that help to keep the probe in position - stopped functioning. This left the probe relying on its chemical engines, which guide its manoeuvres with reduced accuracy.

On 4 November, a practice touchdown was cancelled as Hyabusa appeared to be slightly off-course. Then, when a practice landing was finally conducted on 12 November, the craft accidentally lost contact with a robot probe called Minerva. This probe was meant to be deposited on the asteroid's surface to take further pictures and collect more data.

Going down

But mission commanders decided to go ahead with the attempt to land the craft and collect material. On the night of 19 November, scientists slowly guided Hayabusa's descent. From 40 metres above the surface it successfully dropped a small ball onto the asteroid, which was supposed to act as a landing target.

"As all the difficult procedures were then over, we felt certain that Hayabusa could definitely land," says project manager Jun'ichiro Kawaguchi. "But then something inexplicable happened."

A few hours after the successful target drop, Hayabusa appeared to stop descending. Scientists at the Japan Aerospace Exploration Agency (JAXA) say it seemed instead to be sliding sideways along the asteroid, at a height of about 10 metres for more than 30 minutes. The agency also temporarily lost contact with the craft.

Mission scientists decided that keeping Hayabusa so close to the hot asteroid surface for any longer might damage its equipment, and sent a signal for the craft to ascend. At that point Hayabusa's autonomous position-adjusting sensor caused the craft to skyrocket upwards, sending it as far as 100 kilometres from the asteroid.

No more time

Hayabusa's team members are now investigating problems and checking the safety of equipment. They have yet to decide when it will conduct the second attempt, which was initially scheduled for 25 November. Concerns are growing as time is running short and little fuel is left.

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"There's still hope that [sampling] can be achieved," says Andrew Cheng, a member of Hayabusa's science team and supervisor of the planetary exploration group at the Johns Hopkins University Applied Physics Laboratory in Maryland. But with "almost no more time and very little fuel left, it is getting worrisome," he adds. If it is to return to Earth, Hayabusa will have to leave Itokawa by early December.

"There'll be very good science return regardless," says Cheng. Hayabusa has proved that Japanese-made ion-propulsion engines work, for example, and has sent some very high-quality photos back to Earth. "But if we cannot get samples, it will be a disappointment, no doubt," he adds.