Comet Mission Set for Return to Earth Second Time NASA Has Tried to Retrieve Material From Space By NED POTTER Dec. 21, 2005 b - For seven years now, the little ship has wandered the inner solar system, working flawlessly despite the extremes of outer space. Its makers have called it Stardust -- inspired partly by a Joni Mitchell song, partly by its mission. Two years ago, it passed through the tail of a comet called Wild 2, gathering the tiny particles of ice and dust that pelted it at thousands of miles an hour.

Now comes the final challenge: It must return safely home.

In the early hours of Sunday, January 15, Stardust's sample-return capsule will come tearing into Earth's atmosphere at 28,800 miles an hour. Slowed by friction with the air, and then by parachute, it will land on the floor of the Utah desert, at the Dugway Proving Grounds, west of Salt Lake City.

Helicopters will follow it in the dark, carefully landing upwind of the little ship. They will carry it to a clean room, where it will be disassembled forshipment to a sealed laboratory in Houston.

That's what will happen if all goes well. But as often happens in space exploration, "if" is the key word.

This is only the second time since the Apollo moon landings that NASA has tried to bring anything back from deep space. The first time, in 2004, ended in near-disaster.

Genesis

That probe, called Genesis, also featured a capsule returning to the Utah desert. But instead of wafting down under a parachute, the Genesis sample capsule came tumbling toward the ground at 400 miles an hour.

"We do not see a drogue chute. Negative drogue," reported a waiting controller, referring to the parachute that was supposed to slow the craft's reentry. v As mission scientists watched helplessly, the capsule crashed in the sand --the whole event perfectly framed by an automatic long-range tracking camera.

"Do you have an altitude?" asked a controller who could not see the pictures.

"That's impact, sir," came the irritated reply. "Ground level."

After months of painstaking work, scientists could finally identify cosmic particles collected in space and extract them from the wrecked capsule. An investigation concluded that small servos that controlled parachute release had been installed backward, years before when Genesis was assembled.

"I think the space business has humbled us occasionally," said Firouz Naderi of NASA's Jet Propulsion Laboratory.

Managers of the Stardust mission felt humble too; their ship, while designed differently, was already in space -- and if it was flawed, there might be no way to fix it.

"We went through a very rigorous and extensive process," said Ed Hirst, Stardust's mission system manager, "digging up the blueprints, going through all the testing that was done prelaunch." Hirst and his colleagues were at a news conference to preview the landing. "We're convinced that is not going to happen on Stardust."

But, he said, the 100-pound landing capsule is a complicated machine. "Bringing it home for the first time is the only way to test a system like this."

Older Than the Sun

What can get overlooked, amid the drama of the return, is why Stardust was sent into space in the first place.

"Our mission is called Stardust, in part because we believe some of the particles in the comet will, in fact, be older than the sun," said Don Brownlee of the University of Washington, the Principal Investigator for the mission.

"Comets may be responsible for bringing the oceans and atmosphere to early Earth," said Andrew Dantzler, who directs Solar System exploration for NASA.It is believed that after the sun and planets formed, the solar system was crowded with comets and other leftover debris, crashing frequently to Earth -- and perhaps carrying the chemical building blocks for life as it exists today.

Stardust came within 150 miles of its target comet, passing through its "coma," the cloud of dust and ice that surrounds it. As Brownlee pointed out, the comet has probably been spewing the same material for more than four and a half billion years. Having this material in the lab, scientists say, is well worth the $168 million the mission cost.

They will be out in the cold Utah night waiting for their ship, and Tom Duxbury, the project manager, said the streak of the re-entering capsule will be visible up and down the West Coast.

"We are coming in," he said, "faster than any man-made object has ever come in before."

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(Contributed by Julius Mills)