Having trekked 3.2 billion kilometers (2 billion miles) across cold,
radiation-charged and interstellar-dust-swept space in just under five
years, NASA’s Stardust spacecraft is closing in on the main target of
its mission — a comet flyby.

"As the saying goes, ‘We are good to go,’" said project manager Tom
Duxbury at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "There
are significant milestones ahead that we need to achieve before we reach
the comet on Jan. 2, but we have a great team of engineers and
scientists that have trained hard for this moment, and we have a
spacecraft that is in great shape."

All this intense earthly preparation is directed at Wild 2 (pronounced
Vilt 2), a ball of dirty ice and rock, about as big as 20 Titanics
laid end-to-end. Discovered in 1978, Wild 2 orbits the Sun once every
6.39 years on a trajectory that carries it nearly as close to the Sun
as Mars is, and as far away from the Sun as Jupiter.

On Jan. 2 at 11:40:35 am PST, the 5.4-kilometer-wide (3.3-mile) comet
will sail past the 5-meter-long (16-foot) Stardust spacecraft at a
distance of about 300 kilometers (186 miles) and at a relative speed
of 21,960 kilometers per hour (13,650 miles per hour). The plan is
thus because Stardust is a sample return mission.

"In recent decades, spacecraft have passed fairly close to comets and
provided us with excellent data," said Dr. Don Brownlee of the
University of Washington, principal investigator for the Stardust
mission. "Stardust, however, marks the first time that we have ever
collected samples from a comet and brought them back to Earth for

Clad for battle behind specially designed armored shielding, Stardust
will document its passage through the hailstorm of comet debris with
two scientific instruments that will scrutinize the size, number and
composition of dust particles in the coma – the region of dust and gas
surrounding the comet’s nucleus. Along with these instruments, the
spacecraft’s optical navigation camera will be active during the flyby
and should provide images of the dark mass of the comet’s nucleus.
Data from all three will be recorded onboard Stardust and beamed back
to Earth soon after the encounter.

The chain of events began nine days out from the comet when Stardust
deployed its "cometary catcher’s mitt," a tennis-racket-shaped
particle catcher of more than 1,000 square centimeters (160 square
inches) of collection area filled with a material called aerogel. Made
of pure silicon dioxide, like sand and glass, aerogel is a thousand
times less dense than glass because it is 99.8 percent air. The
high-tech material has enough "give" in it to slow and stop particles
without altering them radically.

"The samples we will collect are extremely small, 10 to 300 microns in
diameter, and can only be adequately studied in laboratories with
sophisticated analytical instruments," said Brownlee. "Even if a ton
of sample were returned, the main information in the solids would
still be recorded at the micron level, and the analyses would still be
done a single grain at a time."

After the sample has been collected, the collector will fold down into
a return capsule, which will close like a clamshell to secure the
sample for a soft landing at the U.S. Air Force’s Utah Test and
Training Range in January 2006. The capsule, holding microscopic
particles of comet and interstellar dust, will be taken to the
planetary material curatorial facility at NASA’s Johnson Space Center,
Houston, Texas, where the samples will be carefully stored and

Scientists believe in-depth terrestrial analysis of cometary samples
will reveal a great deal not only about comets but also related to the
earliest history of the solar system. Locked within the cometary
particles is unique chemical and physical information that could
provide a record of the formation of the planets and the materials
from which they were made.

Stardust, a project under NASA’s Discovery Program of low-cost, highly
focused science missions, was built by Lockheed Martin Space Systems,
Denver, and is managed by the Jet Propulsion Laboratory for NASA’s
Office of Space Science, Washington, D.C. JPL is a division of the
California Institute of Technology in Pasadena. More information on
the Stardust mission is available at

http://stardust.jpl.nasa.gov .