In a piece of aerial razzle-dazzle worthy of a James Bond movie, a NASA spacecraft is scheduled to drop a capsule into Earth's atmosphere Wednesday, and a helicopter waiting in the skies over Utah will try to pluck it in midair and bring home its precious cargo -- a few micrograms of the stuff that makes up the sun.

Fittingly, a Hollywood stunt pilot has been given the task of tracking down the Genesis capsule after two parachutes have slowed its 25,000 mph descent, snatching it with a hook and then lowering it oh-so-gently to scientists who will accept delivery of the first material from space to be brought back to Earth in nearly three decades.

"On a scale of 10, [the difficulty] is between an eight and a nine," said helicopter pilot Dan Rudert of South Coast Helicopter in Santa Ana, Calif. "From where we'll be above it, a five-foot[-diameter] disk looks like a Frisbee." But, he added, in practice runs "we've caught them with a hundred percent success rate."

The snatch-and-grab finale may be the mission's showiest moment, but Genesis also carries high scientific hopes. The precious particles of solar wind embedded in its ceramic plates weigh little more than a few grains of salt, but they are expected to contain all of nature's known elements and isotopes in the same mix they had in the young sun's disk-like "solar nebula" 4.5 billion years ago. The particles are a potential treasure trove for scientists endeavoring to figure out the original composition of the solar system.

"Processes on Earth and elsewhere have changed the starting material," said Carlton Allen, NASA's astromaterials curator, who will take eventual custody of the Genesis samples at the Johnson Space Center's Lunar Sample Laboratory Facility. "But the ratios [of elements and isotopes] in the outer layers of the sun haven't changed since the beginning."

The best way to maintain the samples' integrity is to keep the 420-pound capsule from being jarred by an uncontrolled landing. This is where the helicopter comes in. It will grab the capsule's parachute with a hook at the end of an 181/2 -foot boom, then pay out as much as 450 feet of Kevlar cable to gradually slow the capsule until it hangs over the Utah Test and Training Range of the Army's Dugway Proving Ground.

If the first helicopter fails to make the grab, a second chopper flying 1,000 feet behind will make a second attempt. "We want to capture it about 4,500 feet above the ground," Rudert said at a recent NASA television news conference. "But we're cleared to capture it as low as 500 feet." Planners estimate the helicopters will have time for five attempts to hook the capsule.

The helicopter that does not snag the capsule will land, and the hovering helicopter will lower the capsule so the second crew can strip the parachute from it and attach a new line. Then the hovering helicopter will fly it to nearby Michael Army Air Field, where NASA has set up a portable "clean room." There, engineers will purge the inside of the capsule with nitrogen gas to remove any contamination from Earth's atmosphere.

"If it parachutes to the ground, it will only be traveling nine miles per hour, but several things will be compromised," said California Institute of Technology nuclear geochemist Don Burnett, lead scientist for the mission. The project could survive a hard landing, he said, but research would be delayed, and "we are very concerned about the time it takes to get the nitrogen purge."

Genesis was launched from Florida's Cape Canaveral Air Force Station on Aug. 8, 2001, as the fifth of NASA's low-cost Discovery missions of solar system exploration. It has cost $264 million.

The spacecraft took a bit more than three months to fly to Lagrange 1, a point about a million miles from Earth where the gravities of Earth and the sun cancel each other out. There Genesis had uninterrupted exposure to the sun and was well beyond Earth's magnetic field, which shields the planet from the solar wind.

Genesis went into a "halo orbit" around Lagrange 1, holding its position with periodic thruster corrections as it accompanied Earth on its journey around the sun. On Dec. 3, 2001, the spacecraft opened its five arrays to begin 850 days of collecting samples of the solar wind.

The circular collectors are about a yard wide, each with 55 hexagonal tiles mounted inside. The tiles -- about four inches across -- are made of a variety of ceramic materials, including silicon, germanium, sapphire, artificial diamond and metallic glass. They "look like pizzas with pepperoni," project scientist David Lindstrom said.

Charged particles spewed out by the sun embedded themselves in the tiles. "You'll get the entire periodic table" of elements, Allen said earlier this year in his Houston offices. The collection plates are made of different materials because no one substance absorbs the various types of particles equally well.

On April 1, Genesis finished its experiments, closed its arrays and began the flight home. The bits of matter it carries are the first samples brought from space since the U.S. and Soviet moon missions ended in 1976.

While Genesis made its long trip back to Earth, flight operations director Roy Haggard picked the three-member helicopter teams.

"Every avenue we explored, people referred us to stunt pilots," Haggard said at the news conference. "Stunts, for pilots, are the most exciting and challenging work they can find."

Also, Rudert added, stunt pilots are used to flying high and dangling things on long lines.

The capsule needs to hit a "keyhole" in Earth's atmosphere about 410,000 feet above the Pacific at 11:55 a.m. Eastern time Wednesday. It will be traveling at 24,861 mph and will enter U.S. airspace over northern Oregon.

If the approach looks bad, engineers can abort reentry as many as three hours before landing, put the spacecraft into orbit around Earth and try again in six months.

A bit over two minutes after the capsule pierces Earth's atmosphere, the capsule will deploy a drogue parachute, slowing the spacecraft as it plunges from an altitude of 108,000 feet to 22,000 feet in six minutes. The drogue will then break away, deploying the main parachute, known as a parafoil. Tracking the spacecraft on radar, the recovery helicopters will move in and make the interception as soon as they spot the target.

After the nitrogen purge, the capsule will travel to Houston's Sample Laboratory, whose clean rooms still house more than 790 pounds of the 800 pounds of moon rocks brought back by Apollo astronauts in the 1970s.

Allen said the lab has prepared a special facility to handle the Genesis capsule and its cargo. "We open the space capsule, take out the plates, cut them up and mail them out" to researchers, he said.

Beyond the protective blanket of Earth's magnetic field, Genesis collected pristine particles from the sun's solar wind.A stunt pilot maneuvers above the Test and Training Range of the Army's Dugway Proving Ground in Utah on a test flight to capture a dummy disk. Pilots have snagged the chute in all 11 practice drops.