Status Report

NASA’s Stardust Photographs Target Comet – Wild 2

By SpaceRef Editor
December 1, 2003
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NASA’s Stardust Photographs Target Comet – Wild 2
stardust

Forty-nine days before its historic rendezvous with a comet, NASA’s
Stardust spacecraft successfully photographed its quarry, comet Wild 2
(pronounced Vilt-2), from 25 million kilometers (15.5 million miles)
away. The image, the first of many comet portraits it will take over
the next four weeks, will aid Stardust’s navigators and scientists as
they plot their final trajectory toward a Jan. 2, 2004 flyby and
collection of samples from Wild 2.


"Christmas came early this year," said Project Manager Tom Duxbury at
NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "Our job is to aim
a 5 meter (16 foot) long spacecraft at a 5.4 kilometer (3.3 mile) wide
comet that is closing on it at six times the speed of a bullet. We
plan to "miss the comet" by all of 300 kilometers (188 miles), and all
this will be happening 389 million kilometers (242 million miles) away
from home. By finding the comet as early and as far away as we did,
the complexity of our operations leading up to encounter just dropped
drastically."


The ball of dirty ice and rock, about as big as three Brooklyn Bridges
laid end-to-end, was detected on November 13 by the spacecraft’s
optical navigation camera on the very first attempt. The set of images
was stored in Stardust’s onboard computer and downloaded the next day
where mission navigator Dr. Shyam Bhaskaran processed them and noticed
a white blob of light bisecting the base of a triangle made by three
stars Stardust uses for deep space navigation.


"When I first looked at the picture I didn’t believe it," said
Bhaskaran. "We were not expecting to observe the comet for at least
another two weeks. But there it was, very close to where we thought it
would be."


The Wild 2 sighting was verified on November 18 using the second set
of optical navigation images downloaded from Stardust. To make this
detection, the spacecraft’s camera saw stars as dim as 11th visual
magnitude, more than 1,500 times dimmer than a human can see on a
clear night.


The early detection of Wild 2 provides mission navigators critical
information on the comet’s position and orbital path. Future optical
navigation images will allow them to do more fine-tuning. In turn,
these new orbital plots will be used to plan the spacecraft’s approach
trajectory correction maneuver. Stardust’s first such maneuver is
planned for December 3.


Unlike other orbiting bodies, the paths of comets cannot be precisely
predicted because their orbits about the Sun are not solely determined
by gravity. The escape of gas, dust and rock from comets provides a
"rocket effect" that causes them to stray from a predictable orbital
path. The actual orbital path cannot be precisely determined from
Earth-based telescopes because the comet is shrouded in a cloud of
escaping gas and dust. What is seen from Earth is not the actual 5.4
kilometer (3.3 mile) wide body composed of rock and ice, but the cloud
of debris and gas that envelops it.


"With these images we anticipate we will flyby comet Wild 2 at an
altitude of 300 kilometers, give or take about 16 kilometers," added
Bhaskaran. "Without them, we wouldn’t be able to safely get any closer
to the comet than several thousand kilometers."


Stardust will return to Earth in Jan. 2006 to make a soft landing at
the U.S. Air Force Utah Test and Training Range. Its sample return
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, where the samples will be carefully
stored and examined.


Stardust’s cometary and interstellar dust samples will help provide
answers to fundamental questions about the origins of the solar
system. More information on the Stardust mission is available at


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


Stardust, a part of NASA’s Discovery Program of low-cost, highly
focused science missions, was built by Lockheed Martin Astronautics
and Operations, Denver, Colo., and is managed by JPL for NASA’s Office
of Space Science, Washington, D.C. JPL is a division of the California
Institute of Technology in Pasadena. The principal investigator is
astronomy professor Donald E. Brownlee of the University of Washington
in Seattle.

SpaceRef staff editor.