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Comet Wild 2
Team Stardust, NASA's first dedicated sample-return mission to a comet, passed a huge milestone January 2, 2003 by successfully navigating through the particle- and gas-laden coma around comet Wild 2 (pronounced "Vilt-2"). During the hazardous traverse, the spacecraft flew within 240 kilometers (149 miles) of the comet, catching samples of comet particles and scoring detailed pictures of Wild 2's pockmarked surface. The comet is about 5 km (3 miles) in diameter.
"Things couldn't have worked better in a fairy tale," said Tom Duxbury, Stardust project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "These are the best pictures ever taken of a comet," said Principal Investigator Dr. Don Brownlee of the University of Washington, Seattle. "Although Stardust was designed to be a comet sample-return mission, the fantastic details shown in these images greatly exceed our expectations."
The collected particles, stowed in a sample-return capsule onboard Stardust, will be returned to Earth for in-depth analysis. That will occur on January 15, 2006, when the capsule makes a soft landing at the U.S. Air Force Utah Test and Training Range. The microscopic particle samples of comet and interstellar dust collected by Stardust will be taken to the planetary material curatorial facility at NASA's Johnson Space Center, Houston, Texas, for analysis.
Stardust has traveled about 3.22 billion kilometers (2 billion miles) since its launch on February 7, 1999. As it closed the final gap with its cometary quarry, it endured a bombardment of particles surrounding the nucleus of comet Wild 2. To protect Stardust against the blast of expected cometary particles and rocks, the spacecraft rotated so it was flying in the shadow of its "Whipple Shields." The shields are named for American astronomer Dr. Fred L. Whipple, who, in the 1950s, came up with the idea of shielding spacecraft from high-speed collisions with the bits and pieces ejected from comets. The system includes two bumpers at the front of the spacecraft—which protect Stardust's solar panels—and another shield protecting the main spacecraft body (see image below). Each shield is built around composite panels designed to disperse particles as they impact, augmented by blankets of a ceramic cloth called Nextel that further dissipate and spread particle debris.
The STARDUST Navigation Camera (NC), built by the Jet Propulsion Laboratory (JPL) and flying on a spacecraft built by Lockheed Martin Astronautics (LMA), experienced contamination of its optical surfaces after launch. This contamination took energy that normally would be deposited on one picture element (pixel) and spreading it over tens of pixels, lowering the central brightness and blurring the image. The source of the contamination is not known, but may have occurred during the launch phase when any warm contaminant would come to rest on the coldest surface around, in this case the camera optics and detector. Studies indicated that this contamination could probably be sublimated, i.e., boiled away, by heating the optics. Sources of such heat included electric heaters on the spacecraft, other subsystems that produce heat when powered on, and the Sun. The NC Charged Couple Device (CCD) heater was turned on for a week and small improvement was shown. Therefore, as the spacecraft approached nearer to the Sun, the NC's charge coupled device and mirror motor heaters were turned on for about one month. Also during a recent trajectory correction maneuver, the Sun fortuitously illuminated the NC radiator, which normally keeps the CCD cold, thus increasing the temperature even further. This combined heating effect brought the CCD, primary optics and mirror temperatures from –35 degrees C (–31 degrees F) to over +20 degrees C (68 degrees F). The image quality improved significantly.
