Japan is counting down to the homecoming of a space hero next week: not an astronaut but a battered machine limping back from a seven-year odyssey to a distant space rock.

It is hoped the small probe Hayabusa ("Falcon") may have beaten bigger US and European projects to become the first spacecraft to bring home raw material from an asteroid, part of the primeval rubble left over from the making of the solar system.

Hayabusa, which cost 12.7 billion yen (138 million dollars) to develop, is approaching the end of a five-billion-kilometre (three-billion-mile) trek with broken engines, failed posture-adjusting devices and disfunctional batteries.

The spacecraft is due to release a canister expected to contain asteroid dust as it approaches Earth, aiming to land it at the Woomera Test Range in the Australian outback on June 13 -- if all goes well.

Hayabusa itself will be incinerated as it smashes into the atmosphere, prompting devout fans to declare that the falcon will be reborn as a "Phoenix" -- a mythical firebird.

The journey has captured the public imagination, with a computer-graphics movie "Hayabusa back to the Earth" drawing some 150,000 people at planetariums across the nation and proposals that the spacecraft be given a National Honour Award.

The Japan Aerospace Exploration Agency (JAXA), on a special website (http://hayabusa.jaxa.jp/), has received nearly 1,000 messages treating the probe as a human boy and cheering him on in the lonely, difficult journey.

"What's special to Hayabusa is it has enthusiastic fans. I believe ordinary people love it because it tried what is unprecedented," JAXA associate professor Makoto Yoshikawa, told AFP.

The car-size probe with solar paddles has already become the world's first spacecraft to land on and lift off a celestial body other than the moon after it made a rendezvous with the potato-shaped asteroid Itokawa.

Launched on May 9 2003, Hayabusa approached the 540-metre-wide (1,782-foot) asteroid in September 2005.

The probe made a pinpoint landing at a smooth spot on the bumpy, revolving asteroid, which is 300 million kilometres away from Earth -- about twice as far as the sun.

Hayabusa left on Itokawa a metal ball wrapped in a thin plastic film that bears the names of 880,000 people from 149 countries, among them US filmmaker Steven Spielberg and British science fiction author Arthur C. Clarke. All had responded to JAXA's public invitation to be listed.

-- Like firing a grain of sand through the hole of a needle --

The moon and planets like Mars pull a spacecraft in once it gets close to them, but Hayabusa needed to land in near zero gravity.

The task was difficult, Yoshikawa said. "It was like putting up a needle on the top of Mount Fuji and firing a grain of sand through its hole," he said in Sagamihara, west of Tokyo, where ground control is based.

Scientists expect Hayabusa managed to collect dust that floated up when the probe bounced on Itokawa, although data show the probe failed to fire a bullet as planned to crush the surface or raise a curl of sand.

They hope raw samples, unlike scorched remains such as meteorites, will give them clues on how the solar system has developed.

The United States and Europe have both launched big projects to analyse primitive phenomena.

They include Rosetta, a one-billion-euro (1.2-billion-dollar) mission by the European Space Agency due to climax in 2014, which aims to deploy a robot lab on a comet, analyse its soil and transmit the data back home.

In its 2005 Deep Impact mission, the United States smashed a metal mass into a comet to analyse the gas and dust spewed out by the impact. Another US craft, Stardust, returned in 2006 with material scooped up by flying through the wake of a comet.

Scientists say Hayabusa did a great job even if it turns out there is nothing in the sampling capsule, as the spacecraft took pictures and analysed the density, composition of surface elements and other features of the asteroid by using infrared and X-rays.

Hayabusa was hit by a series of technical troubles. It went out of control because of fuel leakage in December 2005 and then lost communication with Earth for seven weeks to January 2006.

When ground control restored communication it was too late for Hayabusa to enter the planned orbit for its return. It needed to wait for three years until the positions of the Earth and Itokawa became ideal.

As ground engineers patched up damaged functions to control Hayabusa, the probe left the asteroid for Earth in April 2007.

It is currently flying on a combination of two partially broken ion engines, with one compensating for the other's disfunctional operation.

"It was an adventure, indeed," Yoshikawa said.

-- New age of exploration in the solar system --

The first era of space exploration is already over "but we'll see an age of going to and returning from small celestial bodies in the solar system," he said. "Hayabusa is the first step of it."

Only the spacecraft, the sun, Earth and the asteroid appear in the film "Hayabusa Back to the Earth", but many children watch the final scene with tears as the probe is burned up, director Hiromitsu Kohsaka said.

"It is important to show reality as it is. It's also symbolic of a life being passed on to the next generation that Hayabusa delivers that previous capsule to Earth and then ends its life," he said.

The JAXA website carries messages from Hayabusa fans ranging from engineers to housewives.

"You will go into flames and will continue to live like a Phoenix in our heart," one message to the probe reads.

Another says: "We'll never forget you no matter how you end up... Can you hear us, Can you see us, Hayabusa?"