In December, Stardust, the mission to Comet Wild 2 to capture dust particles and return them to Earth, cleared a coating that was clouding its camera optics by applying heat. Today, team members are investigating the reappearance of the coating, which is similar to the frost on a car windshield, and they plan to use the same heating technique again to clean up the optics.
The camera is designed to guide Stardust to its encounter with Comet Wild 2 in 2004 and is still capable of meeting its objectives. As Stardust passed by Earth last January, it snapped pictures of the Moon with excellent resolution and similar pictures will be acquired of the comet during the Wild 2 flyby. Engineers deduced that the clouding of the lens might be due to a substance that evaporates and settles, clinging to the coldest parts of the camera.
"We believe that the heating option will give us back our improved sensitivity performance and reduced scattered light, thereby providing excellent images at Comet Wild 2," said Stardust project manager Tom Duxbury of NASA's Jet Propulsion Laboratory, Pasadena, Calif. A longer period of heating may clean the optics permanently. If not, heat will be applied again as the spacecraft gets closer to the comet.
The mission will bring back more than 1,000 dust particles from the coma, the cloud of dust and gas that surrounds a comet. Stardust's Cometary and Interstellar Dust Analyzer (CIDA), provided by the Max-Planck-Institut fur extraterrestrische Physik of Garching, Germany, will capture comet dust, study its composition, and transmit the data back as the spacecraft flies through space. A dust flux monitor, provided by the University of Chicago, will measure the comet particle count and size during the encounter.
During the latest imaging sessions, the filter wheel, which allows imaging in different colors of light, was found to be stuck in one position, the optical navigation position, which uses a clear filter. This could be due to any of several possible situations, such as a faulty power supply, a shorted coil or a locked wheel. The imaging at the comet will only be minimally affected since the camera will continue to take black and white pictures of an object that probably has very little color. The primary objectives of the camera, which guide the spacecraft to the comet and take images of the comet nucleus, will still be carried out in full.
Stardust, a part of NASA's Discovery Program of low-cost, highly focused science missions, was built by Lockheed Martin Astronautics and Operations, Denver, Colo. is managed by the Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology, Pasadena, Calif. The Principal Investigator is astronomy professor Donald E. Brownlee of the University of Washington in Seattle. More information on the Stardust mission is available at http://stardust.jpl.nasa.gov.