Scientists await return of Japanese asteroid probe

A "welcome home" team of eager scientists is anxiously awaiting this month's return of a Japanese asteroid probe and its planned nosedive into Australia because — just maybe — it is toting a tiny, but prized, piece of space rock.

If all goes well, the sample return capsule of Japan's Hayabusa spacecraft will parachute down on June 13 over a sparsely populated land within Woomera Test Range in South Australia.

Blazing through the sky, the capsule's re-entry would be both a triumph of stick-to-it-ness and a tribute to scientific curiosity.

That's the view of Peter Jenniskens, the principal investigator of the NASA-sponsored Hayabusa Re-Entry Airborne Observing Campaign from the SETI Institute in Mountain View, Calif.

Jenniskens detailed the nail-biting role of airborne sky watchers at Meteoroids 2010 — an international conference on minor bodies in the solar system held here May 24-28.

First, a little history

The Japan Aerospace Exploration Agency (JAXA) launched Hayabusa on May 9, 2003. The probe was lofted to try out new engineering technologies including a shakeout of ion propulsion, as well as autonomous navigation, sampler and re-entry capsule concepts.

In late 2005, Hayabusa loitered around and surveyed asteroid 25143 Itokawa for some three months, relaying impressive imagery and science data about the celestial rock of ages. Two surface sample runs were carried out, but whether or not the asteroid collecting equipment worked as planned is not clear. However, a specimen of dust and pebbles from Itokawa may have been snared.

After Hayabusa departed the S-class asteroid, it had to overcome numerous engineering difficulties en route back to Earth, such as ion engine woes, broken reaction wheels, a leaking thruster, even a lengthy loss of communication with ground controllers.

"Fortunately, they were terrific in tackling these issues," Jenniskens told SPACE.com. "They found a solution every time and that's really very impressive. It is a really big achievement when the object actually comes into the atmosphere and is brought back to Earth...an incredible achievement."

Importing asteroid bits

Jenniskens said Hayabusa's troubles spurred worry at times that the re-entry would have to be scrapped.

But now the spacecraft is being maneuvered for its re-entry into Australia. A critical trajectory correction maneuver of the spacecraft is set for June 4, followed five days later with a fine-tuning tweak that refines the return capsule's landing spot.

Also in order is the legal paperwork for the foreign-made hardware to touch down in Australia. Hayabusa is truly an import, not only from Japan but from outer space too. Japan obtained import consent via the Authorized Return of Overseas Launch Space Object from the Space Licensing and Safety Office of the Australian Government.

Hayabusa will be the third re-entry event directly from interplanetary transfer orbit to the Earth, following in the wake trail of NASA's Genesis and Stardust entries, said Masa-yuki Yamamoto of Kochi University of Technology in Japan.

At the meeting, Yamamoto detailed the ground observation equipment being set up to record Hayabusa's fiery plunge.

Three optical stations are being installed near the Woomera Prohibited Area in Australia to profile the capsule's ablating thermal protection system. Additionally, infrasound and seismic sensors will be installed on four stations to detect atmospheric shock waves emitted from the incoming capsule, Yamamoto said.

The return capsule is outfitted with a parachute that provides high reflectivity for radar signals and a radio responder to locate it within desert brush. After recovery, the sample return capsule will be taken to Tokyo, opened there to assess if it indeed holds treasured bits of asteroid Itokawa.

Winging it

The Hayabusa Re-Entry Multi-instrument Aircraft Campaign makes use of NASA's DC-8 Airborne Laboratory. On the spacecraft's re-entry day, the instrument-packed aircraft will be flying at 39,000 feet in a race-track pattern at some distance from the landing site.

An international lineup of scientists will be onboard, Jenniskens noted, at the ready to flip the switches on an array of equipment, from high definition TV cameras, intensified cameras, high frame-rate cameras, near-infrared sensitive cameras and spectrographs. Mounted to numbers of aircraft windows, this gear will attempt to snare the light from the capsule during its speedy and heated entry.

Jenniskens is no stranger to eyeing human-made meteors. He ran a similar airborne campaign for the Stardust sample return capsule entry in January of 2006 and took part in observing the September 2004 Genesis spacecraft re-entry.

He was also a principal investigator for the joint European Space Agency/NASA multi-instrument aircraft campaign that monitored the controlled destructive re-entry over the South Pacific of Europe's 13-ton Automated Transfer Vehicle, the Jules Verne, in September 2008.

"Every one of these so far has had its unique challenges," Jenniskens said. "For Hayabusa we're basically getting two experiments at the same time," he said, pointing out that the spacecraft bus itself will reenter and bust up into pieces right behind the sample return capsule.

It is not clear how well the 16-inch (40-cm) diameter capsule will stand out from the debris of the main spacecraft, Jenniskens said.

Spike of adrenaline

The Hayabusa return capsule is unlike the shape of the Stardust capsule. It also makes use of a different heat shield material to thwart torrid temperatures similar to those seen by a craft zooming in from Mars and akin to the speed of natural meteors.

The 40-pound (18-kg) capsule's entry, ejection of its heat shield, parachute system deployment and landing will occur in the middle of the night in dark-sky conditions.

As for the airborne observing campaign, "to do all the coordination takes a while," Jenniskens stated. "This has been in the works for a year-and-a-half."

Hayabusa will hot-foot its way toward terra firma at well over 26,000 mph (12 kilometers per second). As it plows into Earth's atmosphere and turns into an artificial fireball, that event will last all of a minute.

"It's very brief. Just leading up to the event is a spike of adrenaline," Jenniskens said. "There are second thoughts and worries. When you push the button on your instrument, will it really do what you set out to do? Is the lens cap off?"

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Leonard David has been reporting on the space industry for more than five decades. He is past editor-in-chief of the National Space Society's Ad Astra and Space World magazines and has written for SPACE.com since 1999.