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Last Updated: Wednesday, 23 November 2005, 23:50 GMT
Asteroid probe 'did touch down'
By Paul Rincon
BBC News science reporter

Asteroid Itokawa, Jaxa
Apparently, Hayabusa bounced off something on the surface more than once
Dr Andy Cheng
Johns Hopkins University
The Hayabusa space probe landed successfully on its asteroid target despite the initial announcement of a failure, Japan's space agency says.

It apparently failed to drop equipment to collect material from the surface of asteroid Itokawa.

The Japanese spacecraft is on a mission to return surface samples to Earth.

But a team member told the BBC Hayabusa could have disturbed enough surface material for some to have got into its sample collection chamber by accident.

On Sunday, controllers lost contact with the probe for about three hours after it had manoeuvred to within several metres of the space rock.

The Japan Aerospace Exploration Agency (Jaxa) subsequently announced the landing attempt had failed.

But the data now show that the spacecraft touched down on the potato-shaped asteroid located 290 million km (180 million miles) from Earth for about half an hour.

Second attempt

When it "lands", the probe is designed to fire a metal pellet into the surface at 300m/s. After the firings, Hayabusa is supposed to take off to collect the dust ejected by the impact.

"Apparently, Hayabusa bounced off something on the surface more than once and spent some 39 minutes resting on it, but the samplers didn't fire," science team member Andy Cheng of Johns Hopkins University told the BBC News website.

The asteroid is named after Hideo Itokawa, a father of Japan's space programme

"It's possible some asteroidal material has been collected, but the spacecraft has no sensor to confirm that."

Although the body of the probe had not suffered any major damage, some of its sensors needed to be checked, the Japanese space agency said.

Jaxa has said it will decide on Thursday whether to make a second attempt to land Hayabusa, scheduled for Friday 25 November.

Solar System dynamics require that the spacecraft begin its return to Earth in the first week of December - so time is of the essence.

It is also unclear how much fuel Hayabusa has left. Two of the spacecraft's four stabilising reaction wheels have failed.

'Incredibly nasty'

These wheels help the probe maintain its "attitude", or orientation, in space without needlessly expending fuel by using thrusters to do the same job.

Controllers have been forced to use thrusters in addition to the last remaining reaction wheels in order to maintain a stable attitude.

The spacecraft is also understood to have lost two attitude sensors, or inertial measurement units. The combination of these two issues has proved a significant hindrance to the mission.

Neither has it been helped by the unexpectedly jagged terrain of Itokawa.

"The object has not been co-operative at all. It is an incredibly nasty place to land," said Dr Cheng.

"The surface is strewn with very angular, large rocks - much more so than was expected. They've picked the most benign looking spot, but it has not turned out to be very benign."

The only experience in landing on asteroids comes from Nasa's Near Earth Asteroid Rendezvous (Near) mission, which touched down on the asteroid Eros. That "wasn't anywhere as ragged-looking", according to Andy Cheng.

The mission has lost a small robotic "hopper" called Minerva. This was to have performed several 10m-high jumps on the surface, taking pictures and temperature readings.

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