Japanese spacecraft will plunge back to Earth Sunday
BY STEPHEN CLARK
Posted: June 12, 2010
Japan's Hayabusa probe is set to release a small drum-shaped capsule Sunday for a blazing re-entry and landing in the Australian outback, completing an improbable first round-trip journey to the surface of an asteroid.
"We're excited and very much impatient for the re-entry," said Junichiro Kawaguchi, Hayabusa's project manager at the Japan Aerospace Exploration Agency. "We're also nervous and uneasy since years of operations will end quite suddenly on Sunday."
The mission's homecoming has captured the attention of Japan, where the spacecraft has been immortalized in cartoons and front-page accounts of its heroics.
"We have seen a much bigger reaction from the public than we anticipated before," Kawaguchi said.
Hayabusa, which means peregrine falcon in Japanese, blasted off from Japan's southern coast in May 2003 and spent 30 minutes on the surface of asteroid Itokawa in November 2005, becoming the first spacecraft to ever take off from an asteroid.
But the probe's sample collection device was not activated, meaning Hayabusa probably gathered only small bits of dust from Itokawa, if anything at all.
Hayabusa spent three months exploring Itokawa in late 2005. The probe took 1,600 pictures and collected about 120,000 pieces of near-infrared spectral data and 15,000 data points with its X-ray spectrometer to investigate the small potato-shaped asteroid's surface composition.
During a failed sampling attempt in November 2005, Hayabusa made an unplanned landing and spent up to a half-hour on Itokawa.
Although telemetry showed Hayabusa likely did not fire its projectile while on the surface, scientists were hopeful bits of dust or pebbles found their way through the funnel and into the sample retrieval system.
Although most scientists are not optimistic, some researchers are holding onto hope that pieces of Itokawa made their way into the sample collection chamber.
"Even though a bullet was not fired during the first touchdown, Hayabusa sat with its sampler against the asteroid surface for 30 minutes, which was an unexpectedly long time. This gives us a reason to be hopeful," said Hajime Yano, a Hayabusa team member.
Since its launch, Hayabusa has lost three of its four ion engines, leaked out all of its chemical propellant and is down to a single attitude-controlling reaction wheel. Hayabusa has also run into battery problems, and controllers lost communications with the spacecraft for nearly two months in late 2005 and early 2006, causing the mission to miss its opportunity to come home for landing in June 2007.
The 16-inch-wide capsule will streak into the Earth's atmosphere at 1351 GMT (9:51 a.m. EDT) Sunday, approaching its landing site at the Woomera Prohibited Area in South Australia.
The blunt capsule, which may contain bits of asteroid rock and dust, should settle to a gentle touchdown at Woomera about 20 minutes later.
Officials will not be able to command or communicate with the capsule after it is released.
The spin-up will also heat up the capsule to ensure its battery is operating at peak efficiency. Engineers are concerned about the battery's health after seven years in the harsh conditions of space.
"We need to heat up the interior of the capsule so the battery is conditioned, so the other instruments can be ready," Kawaguchi said. "No heat or control is available once the capsule is separated, and the charge is going down gradually after that. We need to heat it up before the capsule is separated."
The battery provides power for the return craft's systems, including a beacon transmitter that will broadcast its location to recovery teams.
The Hayabusa spacecraft's ion engine fired for the final time Tuesday to fine-tune the probe's trajectory toward the landing site.
Hayabusa is aiming for a 100-kilometer, or 62-mile-long, ellipse at Woomera, an Australian defense facility about the size of England. But Kawaguchi said the ellipse is based on conservative estimates, and the capsule's exact landing point will likely be accurate within a few kilometers.
The capsule will plummet into the atmosphere at 27,000 mph, faster than the re-entry speed of Apollo command modules returning from the moon. NASA's Stardust mission holds the record for the fastest atmospheric entry of a manmade object, but Hayabusa will come a close second.
The heat shield is made of carbon fiber material that was tested in an arcjet facility at NASA's Ames Research Center.
After braving temperatures of nearly 5,000 degrees Fahrenheit, the capsule will jettison part of its heat shield to make way for the deployment of a parachute.
Touchdown is expected around 1411 GMT (10:11 a.m. EDT), according to JAXA. It will be 11:41 p.m. at Woomera.
The forecast at Woomera calls for mostly clear skies, cold temperatures and light to moderate winds, according to the Australia Bureau of Meteorology.
The Hayabusa mothership will also plunge back to Earth, but it will burn up during the fiery re-entry because it is not protected by a heat shield. Kawaguchi said ground controllers hope to use its camera in the final hours of the mission to take snapshots of Japan and other parts of Asia.
The Japanese space agency dispatched more than 50 researchers to Woomera to join Australian defense forces and NASA officials in the recovery effort, according to Kawaguchi.
Teams at Woomera will attempt to optically track the capsule under its parachute, but the nighttime conditions may force the recovery crews to rely on its beacon signal to converge on the landing site.
If researchers retrieve the capsule within a few hours of touchdown, Japanese officials plan to fly the craft back to Tokyo aboard a charter plane as early as Tuesday, according to Kawaguchi.
"That is the ideal scenario. In an off-nominal scenario, recovery itself may take several days or more, so accordingly the return to Japan may be delayed," Kawaguchi said.
After the capsule clears customs, it will be trucked to the Hayabusa control center in Sagamihara, a suburb of Tokyo, where JAXA scientists will begin analyzing the spacecraft in a curation facility.
"Opening the capsule will take place within a few weeks of arrival here," Kawaguchi said in an interview from Sagamihara. "We must take the utmost care to open the capsule. It takes a lot of time to study the samples because they will probably be in fine particles."
Determining whether Hayabusa was shepherding priceless asteroid samples will take even longer.
"We have to distinguish from the asteroid-borne samples from the ground particles," Kawaguchi said. "It isn't an easy task, and it will take a lot of time, at least one month and probably several months."
"That also comes with navigation data to be provided to JAXA, so that we can combine it with ground observation to determine the actual landing point," Kawaguchi said.
NASA is partnering with the SETI Institute, JAXA, and external researchers from the United States, Australia, Germany and the Netherlands for the re-entry campaign.
"Hayabusa will be the first space mission to have made physical contact with an asteroid and returned to Earth," said Tommy Thompson, NASA's Hayabusa project manager from the Jet Propulsion Laboratory in Pasadena, Calif. "The mission and its team have faced and overcome several challenges over the past seven years. This round-trip journey is a significant space achievement and one which NASA is proud to be part of."
Scientists hope to measure the intensity of super-heated plasma from the capsule's bow shock, detect the loss of ablative carbon material and observe the break-up of the Hayabusa main spacecraft.
The DC-8 also gathered data on the re-entry of the Stardust capsule in 2006 and the demise of the European Space Agency's first Automated Transfer Vehicle in 2008.
Engineers could use the data to develop better heat shield designs for future interplanetary missions, including a capsule that might eventually return samples to Earth from Mars.
Tracking stations from NASA's Deep Space Network, along with Japanese ground sites, have provided communications links between Hayabusa's control center and the spacecraft, plus crucial navigation information to keep the probe on course.