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Hayabusa sets sights on planet Earth for June return

Posted: March 13, 2010

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The Japanese Hayabusa spacecraft is homing in on Earth.

The robotic probe shut off its ion engine March 5 to allow engineers to perform a precise determination of the craft's trajectory. From now on, the ion engine will be commanded to operate intermittently to fine tune Hayabusa's path toward Earth.

Current projections indicate Hayabusa will pass about 80,000 miles from Earth, without further propulsion efforts. But subsequent thrusts of the xenon-fueled ion engine will delicately guide the spacecraft on course for re-entry Earth's atmosphere over Australia.

Having survived a series of cataclysms that threatened to bury the mission in a celestial graveyard, the refrigerator-sized probe will release a capsule to streak into Earth's atmosphere in June, if all goes well.

Animation of sample return capsule entering Earth's atmosphere. Credit: JAXA

The 1.3-foot diameter entry container will plummet into the atmosphere at nearly 27,000 mph, descending by parachute to the Woomera Test Facility in South Australia.

Officials with the Japan Aerospace Exploration Agency, or JAXA, aren't providing an exact date for the return yet.

Hayabusa, which means peregrine falcon in Japanese, could be carrying bits of rock or gravel-like material in the return capsule from asteroid Itokawa. The spacecraft spent about two months studying the asteroid in 2005, and even touched down on Itokawa for about 30 minutes in a botched sample collection descent.

The sample gathering system was designed to fire a projectile into the asteroid's surface, breaking loose bits of rock and funneling the material into a chamber.

According to an analysis of telemetry recorded from the spacecraft, Hayabusa never fired a pellet during two sample collection attempts, deflating the hopes of scientists.

Researchers are still hopeful a small amount of asteroid material was collected as the sample funnel struck Itokawa's surface.

The craft's survival and return was put in doubt by a major fuel leak and several serious systems failures as it finished its mission in the vicinity of Itokawa in late 2005.

Artist's concept of Hayabusa at asteroid Itokawa. Credit: JAXA
The Hayabusa spacecraft is now limping through space, propelled by a makeshift ion engine using components from two powerplants previously declared failed. Ground teams rigged the new thrusting technique after Hayabusa's last fully operational engine stopped working in November.

Hayabusa is also down to one reaction wheel to maintain the probe's orientation in space. The craft's other two reaction wheels failed within two years of launch.

Engineers are also worried that residual propellant from a 2005 fuel leak could still coat the spacecraft's outer skin. When Hayabusa travels closer to the sun as it approaches Earth, the fuel could heat up and evaporate, causing an "eruption" that may send the spacecraft in an out-of-control tumble, according to project officials.

Assuming Hayabusa survives those toils, the spacecraft's return capsule must survive a fiery-hot re-entry into the atmosphere with a heat shield two years beyond its design life.

That's because the series of problems after Hayabusa's 2005 reconnaissance of asteroid Itokawa forced managers to postpone the probe's return from 2007 until 2010.