The STARDUST Mission, the fourth Discovery Class NASA spacecraft, plans to actually capture stardust. Interstellar particles, the dust of the stars, are formed outside of our solar system, streaming into and through it continually. They were discovered by the Ulysses spacecraft in 1992 and confirmed recently by the Galileo spacecraft now orbiting Jupiter. Although we know that this dust is produced by other stars, the exact nature of these particles is unknown and it will be our challenge to bring them safely into the laboratory for examination. During the same flight, in the most exciting, dangerous and potentially rewarding part of the mission, we will rendezvous with a comet and bring parts of it home to Earth. Comets are interesting to us not only in that they come into our midst in a glorious display of light as they pass by on their way to visit the Sun, but in the fact that they harbor components of the stuff that formed the solar system itself, encapsulated unchanged for upwards of 4.5 billion years. Each time they come close enough to Sol and begin receiving its energy, new material is exposed, ejected from the surface and sent out into space, propelled by the pressure of the solar wind. What makes this mission especially unique is the method that will be used to obtain the samples. Aerogel, a glass crystal structure having the approximate density of air, will be employed to capture particles with the least amount of damage possible to the substance and still be able to stop it. The sample collector is contained in a Sample Reentry Capsule (SRC) similar to the atmospheric entry shell employed on Mars Pathfinder. At three different points during the flight the SRC opens and an arm holding the aerogel in a waffle-like paddle, affectionately called "The Fly Swatter", is extended to capture interstellar dust particles that enter and pass through our solar system. Once the sample has been taken, the arm folds down and the cover closes protecting the sample during the remainder of its journey. At encounter with the comet the SRC opens again, extending the sample collector above the spacecraft's forward protective shield. As the spacecraft passes through the comet's plume, particles of varying sizes will be slowed to a stop and retained in the aerogel, leaving entry tracks in it marking their location. The single sample collector will do double duty by capturing interstellar particles on the aft side and cometary dust on the forward side of the same aerogel. Using the entry tracks as a guide as to which direction the particles have entered, the scientists will be able to identify each type of particle and separate them for analysis. The comet we are visiting is named Wild-2, pronounced "vildt two". It is a short period comet that has only recently been discovered, having been sent into the inner solar system by a pull from the giant planet Jupiter. Prior to its 1974 encounter with Jupiter Wild-2 has remained unchanged, orbiting in cold storage too far from the Sun to become active. Since its orbit change it has only visited the sun five times making it very valuable as a 'fresh' comet. Wild-2 now returns to the Sun every few years making it an excellent candidate for this mission as we are afforded more opportunities to study its activity through successive apparitions, something long period comets do not offer except over extremely long time spans. Its orbit being more circular than most comets is also preferred so as to synchronize the spacecraft's orbit with the comet for rendezvous. |
| On board will be a camera, adapted from a Voyager spare, that will give us the closest, highest resolution images ever obtained of a comet nucleus. On approach, the camera is used for navigation to determine our path across the comet's bow. It will be looking through a periscope that sees around the Whipple Shield protecting the spacecraft from bombardment by material surrounding the comet nucleus. Once we get into the coma the periscope glass will most likely be etched beyond use. At this point the camera mirror will turn, tracking and imaging the comet nucleus directly as we pass over it at a distance of ~50km, obtaining pictures with a resolution ten times that of spacecraft Giotto that imaged comet Halley.
As we near Earth on the return leg, the spacecraft will begin to slowly rotate to stabilize its attitude for accuracy. The SRC will be spun up and released at the proper moment for an unguided entry into Earth's atmosphere and a parachute landing within a predetermined footprint in the Utah desert. We launch February 1999. The STARDUST partnership: NASA/Jet Propulsion Laboratory, Lockheed Martin Astronautics, University of Washington Take a tour of the mission at the |
