CAPE CANAVERAL, Fla., March 8 (UPI) -- In a bid to revive a dormant infrared camera aboard the Hubble Space Telescope, space-walking astronauts left shuttle Columbia's crew cabin for a fifth and final outing Friday before the observatory is returned to orbit.
John Grunsfeld and Richard Linnehan tackled the technically challenging job of installing a prototype supercooling refrigerator inside the telescope to plunge the temperature of Hubble's Near Infrared Camera and Multi-Object Spectrometer, or NICMOS, to just 75 degrees above absolute zero so it can detect the faint cool glow of distant stars and galaxies.
NICMOS was installed in the second Hubble servicing mission in 1997, but ran out of its nitrogen ice coolant two years later due to an equipment problem. Working with the Air Force, NASA engineers devised what is believed to be the first mechanical cooler to be used in a spacecraft: a 300-pound, neon gas cryogenic refrigerator equipped with three small turbines designed to spin at 400,000 revolutions per minute.
The astronauts also installed a 13-foot radiator on the outside of the telescope, then turned to the ammonia cooling lines that will be used to dissipate heat from NICMOS.
"Snaking the various coolant lines and electrical connectors through the bottom of the telescope is a task we have no real data on," Grunsfeld said before launch. "It was never anticipated when Hubble was designed that we'd be hanging radiators on the outside and plumbing them through the bottom."
NICMOS will take about a week to cool down, engineers said, with the first test images slated to be returned to Earth next month.
"In theory, the life of the NICMOS cooling system, operating in the weightless environment, could be indefinite," said Hubble program manager Preston Burch.
While hopeful the cooler will revive the camera, scientists are not holding their breath.
"If we don't get it done, we'll be disappointed," said project scientist David Leckrone. "I don't want to say we'll be surprised."