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Upgraded Hubble Runs Into Trouble
26 March 1997 7:00 pm
NASA engineers are unable to focus a camera on an instrument installed last month on the Hubble Space Telescope. The blurred vision is expected to delay a number of studies, including observations of young galaxies and of Pluto's moon Charon.
Although three of the Hubble's four instruments have passed their postupgrade checkups so far with flying colors, scientists have run into snags trying to focus the third of three cameras on the new Near Infrared Camera and Multi-Object Spectrometer (NICMOS), installed during a space walk in mid-February. Camera 3 has NICMOS's only spectrograph--an instrument that separates light into discrete wavelengths. Such information can tell scientists about the chemical composition and movements of planets, stars, and galaxies.
Engineers suspect the problem with NICMOS may be a glitch in its cooling system. The instrument must be kept extremely cold to keep it from giving off infrared heat that would obscure the infrared waves from space that it's supposed to observe. Thus, NICMOS sits in a cryogenic Dewar--essentially a giant thermos filled with solid nitrogen and aluminum foam cooled to -215 degrees Celsius. Troubleshooters suspect that two internal components of the Dewar that were not supposed to touch have come in contact, creating a heat leak that has warmed the nitrogen and expanded the Dewar. Such a scenario may have nudged camera 3's light detector out of range of its focusing mechanisms. Although the fuzzy camera is not completely blind, the problem could prevent scientists from collecting as much data as they had planned.
The heat leak may also shorten the entire instrument's lifetime. The Dewar contained enough nitrogen to last 4.5 years, but that could be cut to 2 or 3 years, says Hubble program scientist David Lecrone of the Goddard Space Flight Center in Greenbelt, Maryland. However, he says, there is a silver lining: The higher temperature will make the detectors for all three cameras 25% more sensitive, so they will collect more data per observation. And the heat leak could heal itself. As the solid nitrogen warms, it will slowly sublimate off into space, which may ease the pressure enough to bring camera 3's detector back into focus. If the problem fails to correct itself, NASA engineers may be able to use Hubble's master focusing system to sharpen camera 3's images.
The problem has forced project scientists to postpone observations requiring camera 3, such as a look at the dusty interior of young galaxies, says Richard Terrile of NASA's Jet Propulsion Laboratory in Pasadena, California. But he's not worried. "There is plenty to keep us busy with cameras 1 and 2," he says. "NICMOS will still turbocharge the time machine that is Hubble. It will just rev up more slowly than we originally planned."