The Stardust space probe was first proposed as part of NASA’s series of low cost Discovery probes in 1995. Its goal was to capture material from a comet and interstellar dust from beyond the Earth-Moon system and return it to Earth. Stardust was launched on its nearly seven year mission on February 7th, 1999 on a Delta II rocket
Since even with careful maneuvering, particles would strike the space craft at about six times the velocity of a bullet, a means had to be found to capture the material without heating or impact effects that would alter it. To collect the particles without damaging them, Stardust employs a substance called aerogel. Aerogel 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 cone-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 translucent, with a distinctive smoky blue cast. Scientists will use these tracks to find the tiny particles.
The aerogel aboard the Stardust Spacecraft is fitted into a “tennis racket” shaped collector. The collector was unfolded from the protective Sample Return Capsule to expose it to space during flight. One side of the collector was faced towards the particles in Comet Wild 2, while the reverse, or B side, was turned to face the streams of interstellar dust encountered during its voyage. The collector was retracted back into the space craft after the encounter with Wild 2.
The first collection of interstellar dust took place from February to May in 2000. After an Earth gravity assist maneuver, the space craft soared beyond the orbit of Mars to the furthest away it traveled beyond the sun. From August to December of 2002, Stardust collected more interstellar dust.
On November 2nd, 2002, Stardust flew within 1900 miles of asteroid Anne Frank. The probe used the opportunity of this encounter to test its tracking camera in preparation of its main encounter with Comet Wild 2. The asteroid, discovered in 1942, is about two and a half miles across and is named after the famous Jewish diarist who was murdered in a concentration camp during the Second World War.
On January 2nd, 2004, Stardust, NASA successfully navigated through the particle and gas-laden coma around comet Wild 2. During the traverse, the spacecraft flew within 149 miles of the comet, catching samples of comet particles and taking detailed pictures of Wild 2’s pockmarked surface. Even though Stardust’s camera was designed for navigation and not science, the images taken of Wild 2 have provided scientists with a great deal of data about comets. It beamed back 72 black-and-white pictures showing broad mesas, craters, pinnacles and canyons with flat floors on the surface of Wild 2, Stardust also successfully captured a great deal of material from the comet.
As the Stardust probe approached Earth, a small sample capsule detached and entered the Earth’s atmosphere at a record 29,000 miles per hour in the early hours of January 15th. Slowed by it’s heat shield, the capsule opened a parachute at 100,000 feet. It touched down safely at the Dugway Proviing grounds in Utah, bouncing three times. A helicopter retrieved the capsule and took it to a clean room at nearby Michael Army Air Field. Seven years and three billion miles later, Stardust had successfully returned to Earth.
In the coming months, the material gathered by Stardust will be examined at the Johnson Space Flight Center. It is hoped that the material, the first delivered from outer space in thirty years, will yield data about the origins of the universe.
The public with be invited to participate in the examining of the one and a half million particles thought to be gathered in Stardust’s aerogel collector. The Stardust@home project, slated to begin in March, will permit computer users to an image from a virtual microscope that will be the size of a single grain of salt. Those who discover a microscopic sample of either the comet or interstellar dust will get to name it.
Volunteers will be required to pass close attention to the aerogel images to pick out the dust trails and distinguish them from false images. They will be required to pass a simple test using sample pictures.
If two our of four volunteers pick out a dust trail from an image, the image will be sent to a hundred more volunteers for verification. If at least twenty verify the dust trail, the image will be examined by a team of University of California at Berkley undergraduates who are trained to pick up the dust trails. Researchers at the Johnson Space Flight Center will then remove the grains once they are identified using specially developed microtweezers and micro-pickle forks.