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Collecting Solar-Wind Data Will Be Delicate Endeavor

Posted on: Monday, 3 May 2004, 06:00 CDT

When NASA's Genesis probe returns solar wind samples to Dugway Proving Ground in the western Utah desert, the achievement will be a combination of extreme science and down-to-earth concern about breaking glass.

The probe, launched in 2001, has been gathering samples of the solar wind most of the time since. Solar wind is a river of high- speed particles blowing off the sun. The particles embedded themselves on delicate glass-like collectors.

Collection ended in April, and the collectors were tucked away on the probe. The probe is now on its way back to Earth.

When a canister containing the samples re-enters the atmosphere, it is to be captured by a helicopter above Dugway's mud flats.

A practice recovery of a squat cylinder weighing the same as the canister, 420 pounds, went smoothly last week despite a brisk, cold wind and a dense cloud cover. A helicopter lofted the target above the clouds and released it. A radar controller at Hill Air Force Base, 100 miles away, directed a second chopper to head toward the descending target.

As the cylinder drifted toward earth below a parafoil wing, the second helicopter swooped in. An 18-foot boom extended from the bottom of the helicopter. A hook at the end of the rod snagged the parafoil, then detached from the boom as its line played out from the helicopter.

The drag on the line slowed the capsule to a halt, allowing the helicopter crew to gently lower it to scientists at a drop zone.

Inside the Genesis probe, solar wind collectors are made of ultra- pure material. According to NASA, they are coated with gold/ platinum, diamond, germanium and pure silicon. Also, a concentrator will focus solar particles on a surface made of diamond and silicon carbide deposits.

These bits of the sun, flying onto the collectors, presumably were embedded in its surfaces. NASA scientifically characterized the collector plates before they were launched so the agency knows the exact makeup of each.

"When we bring it back, everything that's not what we launched is solar wind," said Don Sevilla, payload recover lead engineer from the Jet Propulsion Laboratory, Pasadena, Calif. Then he laughed, "Unless they can identify that it's not."

NASA predicts some of the plates will have pitting from the impacts of micrometeoroids, and some will be penetrated by fast- moving space dust. Probably two plates per array will have holes drilled through them.

"We don't want them to break," Sevilla said.

The helicopter is supposed to snag the capsule gently, preventing it from slamming into the desert and shattering collector plates.

Without the midair catch, when the capsule lands it will hit the ground with a force up to 25 or 30 times normal gravity. It would tumble. If some plates are already broken by micrometeoroids, the bouncing could let their pieces break more plates.

No contamination could reach the plates in the vacuum of space. But once the capsule enters the atmosphere above Utah, air will flow in.

The inflow will be filtered to remove as many contaminants as possible. But atmospheric oxygen could cause chemical reactions.

"It compromises the science because you have allowed something other than solar wind to bathe the collectors for a length of time," he said. "And we want them just washed with something that's innocuous, like pure nitrogen."

NASA scientists plan to purge the atmosphere from the probe soon after the landing.

What can understanding the solar wind teach us?

"Essentially, the sun is a representative of what the solar system was like when it formed," Sevilla said. "The materials that are coming off the sun are going to help scientists figure out some real questions about how the solar system formed."

E-mail: bau@desnews.com

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