ADELAIDE, Australia (AP) -- Scientists will be eagerly scanning the night sky over the Australian Outback this weekend for the long-delayed return of the first spacecraft to complete a round-trip journey to an asteroid.
The Hayabusa capsule has traveled 2.5 billion miles (4 billion kilometers) in seven years and is expected to land in the desert of South Australia state Sunday night.
Launched by Japan in 2003, Hayabusa is expected to be carrying space material collected during its two brief landings on the asteroid, which will offer insights into the creation and makeup of the solar system.
"There's absolutely nothing like going to the source," said Trevor Ireland, associate director for Earth Chemistry at Australian National University and the only Australian on the Hayabusa team. "Hayabusa has sampled an asteroid in situ and soon we will have in hand an actual asteroid. Any sample coming back from (the asteroid) will be a major scientific prize for us."
He said scientists will learn more from studying the asteroid sample than from meteorites that are burned during their fall on Earth and become contaminated by materials here.
Hayabusa, which means 'falcon,' will re-enter Earth's atmosphere late Sunday night above the Woomera Prohibited Area, a remote military zone 300 miles (485 kilometers) northwest of the South Australian state capital of Adelaide.
The main body of the spacecraft will burn up on re-entry - expected to create a spectacular burst in the midnight sky - but a small container carrying the samples retrieved from the asteroid should parachute to the desert floor. Scientists who gathered this week in the small town of Woomera outside the military area will then collect the 40-pound (18-kilogram) container, seal it in an airtight vessel and take it to Japan for study.
The Woomera Prohibited Area takes up 49,000-square miles (127,000-square kilometers) but the capsule is targeted to land within a 150-kilometer long stretch already triangulated by scientists guiding its course.
The Japan Aerospace Exploration Agency built and launched the asteroid explorer, which landed on its target in late 2005. Hayabusa took photo images from all angles of the 1,640-foot (500-meter) -long asteroid called Itokawa before landing. It was designed to shoot a bullet into the surface of the asteroid that would crush it and propel any material through a long tube into the sample collection container.
There is no certainty that the bullet actually fired, scientists say, but they believe that the impact of the tube's landing would have forced some material upward and into the collection chamber.
"Just the process of landing would have coated the inside with dust," said Michael Zolensky, one of two NASA scientists involved in the project. "It has the capacity to hold one-tenth of a kilogram (3.53 ounces), but we really only need less than a gram (0.04 ounce) of material. One microscopic grain can be sliced into more than 100 pieces and farmed around the world for testing and research."
The scientists hope to study how and when the asteroid was formed, its physical properties, what other bodies it may have been in contact with and how the solar wind and radiation have affected it.
The Japanese space agency said the aim of the $200 million project was to understand the origin and evolution of the solar system, as well as paving the way for future sample return missions.
Hayabusa was originally due to return to Earth in 2007 but a series of technical glitches - including a deterioration of its ion engines, broken control wheels and the malfunctioning of electricity-storing batteries - forced it to miss its window to maneuver into the Earth's orbit until this year.
If Hayabusa is indeed carrying samples from the asteroid, it would be only the fourth sample return of space material in history - including the moon matter collected by the Apollo missions, comet matter by Stardust and solar matter in the Genesis mission.
Preliminary analysis of the samples will be carried out by the team of Japanese, American and Australian scientists in Japan, but after one year scientists around the world can apply for access to bits of the asteroid material for research.
For now, though, the Hayabusa scientists admitted to some sleepless nights as the arrival hour finally nears. Zolensky said the years out of sight have not erased Hayabusa from his mind.
"I have a model of it hanging in my office," he said. "We have worked 20 years on this mission. For something to go all the way out to an asteroid and come back is extremely exciting."