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JET PROPULSION LABORATORY
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NASA's Stardust spacecraft, launched in February 1999 on a mission to collect a sample from Comet Wild-2, remains in good health as it travels the solar system. Engineers and scientists have just completed a series of tests to see if mild heating will remove some contamination on the spacecraft's navigation camera optics, which scatters light and blurs the images. The navigation camera's principal function is to help guide the spacecraft on its final approach to the comet, and the obscuration on the camera is not expected to seriously impair the main mission of collecting and returning samples from Comet Wild- 2's dust tail. However, close navigation to the comet may change somewhat depending on the results of further testing.

On Monday, Sept. 4, the final images were received from an onboard test to determine if mild heating alone might clear the camera's view. A few months ago, engineers detected that a small amount of an unknown substance had settled on one or more optical components of the camera. Engineers were trying to clear the debris by turning on a small heater on a window that protects the detector. Images showing the contamination confirm that the camera is "fogged."

The week-long heater test increased the temperature around the window from -35C (-31F) to about 8C (47F). Then the camera took pictures of a small calibration lamp immediately in front of the camera lens, inside the spacecraft. The blurring shown in the recent images changed from image to image as the heating progressed.

Engineers hope to better characterize the nature of the blurring by analyzing navigation camera images of several starfields. Since small points of light, the stars, will provide a more specific target than the general illumination from a light source, the starfield pictures should show how the sharpness of the images has changed after the heating test. Engineers will analyze the images when the camera data are received from the spacecraft in late September. The navigation team may perform additional heating and imaging tests if this seems useful and/or necessary. It is also possible that there may be contamination on the periscope and/or the scan mirror, which are external to the lens.

Project engineers say that since the camera was the coldest part of the spacecraft shortly after launch, it would tend to act almost like flypaper in picking up any volatile materials coming from the spacecraft immediately after launch. Investigations into the origin of the coating are inconclusive.

The camera's main duty is to guide the spacecraft to the exact point of closest approach to the comet, and it is also scheduled to take pictures of the comet. The blurring is not expected to seriously impair the main science mission of collecting and returning samples from Comet Wild-2's dust tail. However, close navigation to the comet may change somewhat depending on the results of further testing.