<p>A block of aerogel from the Stardust space probe, on display in the Smithsonian Air and Space Museum in Washington, D.C.
</p><p>Stardust was launched by NASA on February 7, 1999.  Its mission:  Study  asteroid 5535 Annefrank, collect samples from the coma of comet Wild 2, and photograph comet Tempel 1.
</p><p>Stardust returned its cometary samples to Earth on January 15, 2006.
</p><p>There were five experiments aboard Stardust.  The first was a cometary and interstellar dust analyzer that used a mass spectrometer to determine the content of such dust.  The dust flux monitor instrument determined how much dust was in space or a comet's coma, and how fast it was traveling.  The dynamic science experiment used radio waves and radar to analyze the surface and mass of comets and asteroids.
</p><p>But the most important experiment was the Stardust Sample Collector.
</p><p>The tennis racket-sized collector was filled with 90 blocks of "aerogel" -- an inert, porous, silica-based substance designed to capture dust grains.  More than 99 percent of aerogel is empty space.  When a particle hits the aerogel, it becomes buried. It also leaves behind it a tunnel, which helps determine how fast the dust grain was moving when it hit.  Each aerogel block was fitted into an aluminum grid.  When the experiment ended, the collected folded down and into the capsule.  When Stardust came close to Earth in 2006, the capsule was ejected and re-entered the Earth's atmosphere.  Parachutes gave it a soft landing.
</p><p>A million photographs will be taken to image all the aerogel and find all the dust grains.
</p>
After its pass by Earth, the main Stardust satellite kept on flying out toward the edge of the solar system.  On March 24, 2011, Stardust was told to burn its remaining fuel. This helped scientists determine how to more accurately measure fuel on spacecraft.  With Stardust out of gas, the satellite was switched off and allowed to head into the galaxy.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/23165290@N00">Tim Evanson</a> from Cleveland Heights, Ohio, USA
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/timevanson/7276434220/">Stardust aerogel - Smithsonian Air and Space Museum - 2012-05-15</a>