[meteorite-list] After 3 Billion Miles, Stardust Returns Sunday Bearing Cosmic Dust Older Than The Sun

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jan 10 12:15:20 2006
Message-ID: <200601101712.k0AHCAq11177_at_zagami.jpl.nasa.gov>

http://www.nytimes.com/2006/01/10/science/space/10star.html

After 3 Billion Miles, Craft Returns Sunday Bearing Cosmic Dust Older
Than the Sun

By WARREN E. LEARY
New York Times
January 10, 2006

In a blaze across the night sky, it should be a spectacular homecoming
at the end of a very, very long journey.

After covering 2.88 billion miles over seven years, the Stardust
spacecraft is nearing home with its minute but precious cargo: samples
of what are believed to be the oldest materials in the solar system.

Tucked away in what looks like a giant fly swatter of a collector is
dust swooped up from a close encounter with the comet Wild 2 and an
accumulation of particles picked up in three circuits of the Sun.

"This has been a fantastic opportunity to collect the most primitive
material in the solar system," said Donald Brownlee of the University of
Washington, the principal investigator for the mission. "We fully expect
some of the comet particles to be older than the Sun."

Comets, icy bodies that normally inhabit a region near Pluto's orbit,
are made of material many scientists believe is virtually unchanged
since the Sun and the planets formed about 4.6 billion years ago.

Studying comets not only provides clues to how the solar system was
created but could also help explain how certain materials and conditions
combined to form life, researchers said.

"Comets are a library of our history," said Thomas Duxbury, project
manager at the National Aeronautics and Space Administration's Jet
Propulsion Laboratory in Pasadena, Calif., which is supervising the mission.

After its launching in 1999, the Stardust circled the Sun and flew by
Earth for a gravity boost to rendezvous with Wild 2 (pronounced vilt 2)
near Jupiter. On Jan. 2, 2004, the Stardust came within 149 miles of the
comet, deploying shields to protect itself from cometary dust while
extending a 160-square-inch collector filled with a material called
aerogel.

This low-density silicon material, composed of 99.8 percent air, gently
slowed and trapped particles without significantly altering or damaging
them. Stardust also spent 195 days collecting interstellar particles
that flow through the solar system.

The challenge now is to bring them home safely. If all goes as planned,
a capsule bearing the space dust will dive into the atmosphere early
Sunday morning and gently parachute the samples to the Utah desert.

But bringing the Stardust home will require an orchestrated sequence of
events, many of them performed autonomously by the spacecraft. Adding to
the tension is the fact that the Stardust return capsule is similar to
one released by an earlier NASA probe called Genesis, which crashed to
Earth in 2004 when its parachutes failed.

Collector plates that trapped solar particles during Genesis' two-year
mission were shattered and contaminated, but scientists are trying to
recover some of the science.

"We are convinced that this is not going to happen on Stardust," said
Edward Hirst, the mission's systems manager. "We took the lessons
learned on Genesis and looked at Stardust."

Both craft were built by Lockheed Martin and share some systems. But
engineers said that the faulty switch believed to have failed in
deploying parachutes on the more complex Genesis capsule passed testing
on Stardust before launching.

Nonetheless, Mr. Duxbury said, NASA has prepared contingency plans to
recover the samples in case the mission, which cost $212 million, ends
in a crash landing. "If we have an accident and land hard, we still
think we can get the science out," he said.

Stardust has begun its final preparations to come home. On Nov. 16, it
performed the first of three trajectory correction maneuvers aiming it
at a target area southwest of Salt Lake City. The second, Hirst said,
was performed Thursday and was a textbook maneuver. "After sifting
through all the post-burn data, I expect we will find ourselves right on
the money," he said.

The last adjustment, scheduled for Friday, will place the craft in a
re-entry corridor for a landing point within an ellipse measuring 47 by
27 miles.

Plans call for Stardust to release its 101-pound sample return capsule
on Sunday at 12:57 a.m. Eastern time, when the spacecraft is 68,805
miles from Earth. About 15 minutes later, the main spacecraft is to fire
thrusters that divert it from Earth into an orbit around the Sun.

Four hours after release, the three-foot-wide return capsule is to enter
the Earth's atmosphere at 410,000 feet above the Pacific. At 28,860
miles an hour, this will be the fastest a human-made object has ever
entered the atmosphere. At 200,000 feet, the capsule's heat shield will
reach a peak temperature of 365 degrees Fahrenheit, followed 10 seconds
later by peak deceleration as the capsule experiences 38 times the force
of gravity.

The fireball of the descent should be visible from areas in Northern
California, Southern Oregon, Northern Nevada, Southern Idaho and Western
Utah, depending upon clouds and the brightness of the Moon, NASA
officials said.

At about 100,000 feet, a small pilot parachute is to deploy, and the
capsule will begin a vertical descent to 10,000 feet, when the large
main parachute will unfurl to lower the craft to the ground at less than
10 m.p.h..

Specialists aboard helicopters or all-terrain vehicles are to converge
on the capsule to secure it and document its landing area. From there
the space cargo is to be transferred to a temporary, special "clean
room" in a hangar at Michael Army Air Field to avoid contamination and
then moved to a special laboratory at the Johnson Space Center in Houston.

Dr. Brownlee said Stardust's cargo should contain more than a million
particles weighing in total less than a small fraction of an ounce, with
only about 2,000 being as large as the diameter of a human hair. But
because scientists will be examining them on a molecular scale, he said,
they will look like "huge, giant rocks."

There should be enough samples to occupy scientists for decades without
consuming them all, he said.
Received on Tue 10 Jan 2006 12:12:09 PM PST