NASA Comet Hunter Closing on Quarry
December 30, 2003
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 study."
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 examined.
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 .
