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Spacecraft Stardust's Blurry Vision Persists
By Andrew Bridges
Pasadena BureauChief
posted: 06:00 pm ET
07 September 2000
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stardust_update_000907 PASADENA, Calif. An attempt to boil off an unknown substance blurring the camera on NASAs Stardust spacecraft has proved inconclusive, delaying a resolution to a problem that has dogged the comet mission team for nearly a year.Should it persist, the fogging on the spacecrafts navigational camera will not jeopardize its prime objective: the collection of dust particles from the comet Wild-2 for return to Earth in 2006. However, it will thin the missions gravy, permitting the spacecraft at most a blurry-eyed view of Wild-2s nucleus as it cruises by the comet in 2004. 
An artist's rendering of Stardust with its Dust Collector deployed, using Aerogel to capture interstellar grains. This week, engineers at NASAs Jet Propulsion Laboratory (JPL) received the last of a series of test images taken by the probes navigational camera after heating for a full week a protective window covering its electronic sensor. Engineers hoped the heat would boil off the unknown contaminant.Fuzzy blur The latest images, which should have crisply shown the cameras small calibration lamp located in front of the camera lens including its zigzag filament instead showed a fuzzy blur. "Unfortunately, since we didnt resolve the filament, the results were inconclusive," said Thomas Duxbury, the missions project manager at JPL.Engineers will now point the camera to the stars, and snap a half-dozen images on Sept. 12. Those star field images will give the mission team a better shot at understanding how the heating might have helped or hindered the problem. Normally, each star appears as a sharp pinprick of light, perhaps just three picture elements, or pixels, across, to the camera. With the blurring, the stars could be a smeared mess hundreds of pixels in size. However, when mission members have those images in hand, perhaps as early as Sept. 21, they will be able to better discern even small improvements in the cameras vision. "We are going to see how many pixels are they spread over," Duxbury said of the stars. Warming things up The mission team will then likely switch on a heater by the cameras protective window, as well as one near the cameras mirror, for a month or more. The two heaters would warm the cameras sensor, or charge-coupled device, its mirror and main optics, or nearly all the imagers components. Should future images fail to show any improvement, engineers could then command the spacecraft to turn the camera toward the Sun for as much as a full minute, allowing its rays to burn off the substance. However, the Suns ultraviolet rays could alter the contaminant, perhaps turning it even darker and compounding the problem.The origin of the contaminant remains a mystery. Duxbury said there are two possible sources for the volatile materials: contaminants vented from the upper stage of the Delta 2 rocket that hoisted the probe into space or moisture absorbed by the spacecrafts carbon structure while sitting on the launch pad in humid Florida in February 1999.Since the camera is kept cooler than the remainder of the spacecraft, it would have acted almost like flypaper for any volatiles escaping it during the normal outgassing period immediately following launch. Even a thin, splotchy veneer of the unknown substance would suffice to skew the cameras vision. As it stands at present, the blurred camera will still allow the missions navigational team to maneuver close enough to Wild-2 to collect comet dust and volatile samples in 2004. Those samples, as well as particles of interstellar dust, will then be returned to Earth for study two years later.Earlier this summer, mission members had feared a solar flare might have damaged the spacecrafts camera. However, subsequent tests ruled out any damage. Work on the blurring problem may drag on another year or more.
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