Robot Explorers: US Unmanned Space Missions

Robot Explorers: US Unmanned Space Missions: page 24

Stardust is the first US space mission whose only mission is to explore a comet, and the first robotic mission designed to return extraterrestrial material from outside the orbit of the Moon. Comets are leftover materials that formed of the planets and the Sun more than 4.5 billion years ago, and contain many of the organic materials thought to be essential for the origin of life.

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Stardust was launched on February 7, 1999 from Cape Canaveral aboard a Delta II rocket. The image at left was taken with a camera attached to the outside of the spacecraft as it climbed above the launchpad.

Stardust's mission is to collect dust and carbon-based samples during its close encounter with Comet Wild 2 (pronounced Vilt 2), named after its discoverer. In order to meet up with Comet Wild 2, Stardust will make three loops around the Sun. On the second loop, its trajectory intersected the comet. During this meeting, which took place earlier year, Stardust performed a variety of tasks including making counts of comet particle encountered by the spacecraft, and real-time analyses of the compositions of these particles.

Stardust passed by Comet Wild 2 on January 2, 2004, and successfully captured thousands of particles of cometary dust released from the surface of the comet. The spacecraft is now on its way back home to Earth, where it is expected to return on January 15, 2006.

During the flyby, the highest resolution images of a comet ever taken were obtained. The image at right is a composite of a long exposure image showing the jets of material streaming from the comet's nucleus and a short exposure image showing detail of the nucleus itself.

"This spectacular composite image shows a surface feature unlike any other planetary surface see to date in our solar system", says Professor Donald Brownlee, the Stardust Principal Investigator from the University of Washington. "Other than our sun, this is currently the most active planetary surface in our solar system, jetting dust and gas streams into space and leaving a trail millions of miles long."

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To collect particles without damaging them, Stardust uses an extraordinary substance called aerogel. This is a silicon-based solid with a porous, sponge-like structure in which 99.8 percent of the volume is empty space. By comparison, aerogel is 1,000 times less dense than glass, which is another silicon-based solid. When a particle hits the aerogel, it buries itself in the material, creating a carrot-shaped track up to 200 times its own length. This slows it down and brings the sample to a relatively gradual stop. Since aerogel is mostly transparent - with a distinctive smoky blue cast - scientists will use these tracks to find the tiny particles.

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The primary objective of the Stardust mission is to capture both cometary samples and interstellar dust. Main challenges to accomplishing this successfully involve slowing down the particles from their high velocity with minimal heating or other effects that would cause their physical alteration. When the Stardust Spacecraft encounters the Comet Wild 2, the impact velocity of the particles will be up to 6 times the speed of a rifle bullet. Although the captured particles will each be smaller than a grain of sand, high-speed capture could alter their shape and chemical composition - or even vaporize them entirely.

The aerogel aboard the Stardust Spacecraft is fitted into a "tennis racket" shaped collector. This is unfolded from the protective Sample Return Capsule to expose it to space during flight. One side of the collector will be faced towards the particles in Comet Wild 2, while the reverse, or B side, will be turned to face the streams of interstellar dust encountered during its journey.

After the encounter with Comet Wild 2, the aerogel collector was retracted into the Sample Return Capsule (SRC) and will be returned to Earth for detailed analysis by scientists at the NASA's Johnson Space Center.

The capsule successfully touched down in Utah in January of this year.
For more information on Stardust visit http://stardust.jpl.nasa.gov/

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	Copyright ©2004 Colleen Gino	Images and content courtesy JPL and NASA.