WISE, which is to lift off from Vandenberg Air Force Base Dec. 7, is designed to map the entire sky in infrared light.
"To see infrared light from the cosmos, WISE must be chilled to out-of-this-world cold temperatures," NASA said. "This prevents the telescope from picking up its own infrared glow, or heat. A bottle-like chamber, called a cryostat, surrounds and cools the telescope and detectors. The cryostat will be filled with frozen hydrogen, which slowly evaporates away over a period of about 10 months -- enough time for WISE to scan the sky one-and-a-half times."
NASA engineers are pumping hydrogen gas into the cryostat's two tanks, one after the other. Surrounding pipes filled with liquid helium are used to cool and condense the hydrogen gas to a liquid, officials explained. Once a tank is filled with liquid hydrogen, the liquid helium flow is increased, freezing the hydrogen.
Ultimately, the hydrogen will be cooled to minus 447 degrees Fahrenheit -- the coldest temperature theoretically attainable. Scientists said the coldest of the spacecraft's detectors will operate at about minus 445 degrees Fahrenheit.
Liquid helium will continue to be piped around the cryostat until 19 hours before launch. At that point, NASA said, WISE will be perfectly chilled.
Copyright 2009 by United Press International.
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