In space, small defects can have big consequences. In an article to appear on November 8, the New Scientist tells us that the $2 billion NASA's Chandra X-Ray Observatory is affected by vision problems. EurekAlert! has released a preview of this article, "Heavens are dimmed for Chandra space telescope."
Apparently, and for an unknown reason, some grease has appeared on an optical filter of one of the cameras of the telescope, "blocking almost half the light at some frequencies." This level of contanimation has never been expected.
"There is ten times as much contamination as we expected at launch," says Herman Marshall, an astrophysicist with the Center for Space Research at MIT. In the three years since the launch, a layer of grease 0.37 micrometres thick has built up on the filter. That's thicker than the filter itself, he says.
Before the grease alters definitively Chandra's sight, let's look at what would lose. Here is a picture of a composite Chandra X-ray and optical image of the massive star HD 192163 (Credit: NASA and SDSU).
[Note: You can see larger versions on this Marshall Space Flight Center page.]
Scientists are not yet sure what is causing the build-up. Analysis of the contamination shows that it contains carbon and fluorine, which points to a problem with a fluorocarbon lubricant called Braycote used on the spacecraft or with other sources of fluorine such as Teflon-coated screws.
Braycote was chosen because it does not normally evaporate at low temperatures. But Marshall thinks the contamination may have occurred when molecules in the lubricant were broken down by mechanical stresses and then bombarded with radiation.
So, what to do to clean the filter? Engineers are thinking about cooking the grease.
A "bakeout" has its own risks, because too much heat could damage the camera or the filter. Or the contamination could settle somewhere worse, says Chandra programme manager Keith Hefner. So far, the other instruments on board are unaffected. "The vehicle is still performing well," says Hefner.
Please note that this story doesn't appear on the official Chandra X-ray Observatory website.
Source: Emily Singer, New Scientist, via EurekAlert!, November 6, 2003
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