Ground controllers have regained contact with the problem-plagued Hayabusa spacecraft they lost control of in December 2005. But they still do not know whether the asteroid-probing mission will be able to return to Earth as planned.

The Japanese craft was designed to return the first-ever samples from an asteroid to Earth in 2007. But a series of instrument failures and communication glitches have meant it probably did not collect any samples during two landings on the 540-metre-long asteroid Itokawa in November 2005. Nonetheless, mission controllers still wanted to bring the spacecraft back to Earth in case some asteroid dust had slipped into its collection chamber by chance.

But just when it was supposed to leave Itokawa in December 2005, the spacecraft lost all contact with mission controllers after a fuel thruster leak prevented it from pointing its antenna towards Earth.

Now, contact has been re-established. Japan's Aerospace Exploration Agency (JAXA) revealed it began to receive weak signals from the spacecraft at the end of January and that in recent weeks it has received telemetry signals that broadcast the spacecraft's position, orientation and health.

Finding thrust

The data suggest most of the spacecraft's fuel has already been lost to space. In December, mission managers knew that most of the hydrazine fuel had leaked away. But they still hoped to fire the fuel's oxidiser, nitrogen tetroxide, to control the spacecraft's orientation.

"But during the absence of the spacecraft signal, it looks like our oxidiser also leaked out," mission manager Jun'ichiro Kawaguchi told New Scientist. "That was a big shock. We think the chemical propulsion engines are not usable as of today."

That means mission managers will have to rely on the craft's relatively weak ion thrusters to try to point and stabilise the spacecraft. The thrusters, which use electric fields to accelerate a beam of ions, were originally designed only to propel the craft forwards on its 2-billion-kilometre round trip to Itokawa.

Kawaguchi believes the ion thrusters will be able to accomplish both tasks. But he says that they were not designed to be turned on and off repeatedly, so mission managers will try to minimise their use.

Baking operation

To do that, they must try not to lose control of the spacecraft again. So they are turning on every instrument to heat the spacecraft enough to vaporise every last drop of fuel that may still be on board, either frozen on an outside surface or pooled as liquid inside a pipe.

"We are concerned – any further fuel leak may tumble the spacecraft again," Kawaguchi says. This "baking operation" is expected to take until the end of 2006.

At that point, managers will decide whether to try and send the spacecraft on a three-year return journey to Earth in early 2007, when the distance between Earth and the asteroid is once again minimised.

"We will do our best to make the spacecraft return," says Kawaguchi. But given the loss of the mission's fuel thrusters and damage to some wiring and other instruments caused by the leak itself, he adds: "It's probably a miracle we can operate the spacecraft even in this condition."

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