Chilling out at Hubble

Grunsfeld first struggled to bolt down the 300-pound (135-kilogram) cooler in the telescope's lower instrument bay, working in tight confines next to the super-delicate NICMOS instrument.

Astronauts Rick Linnehan (left) and John Grunsfeld send a tribute of thanks during their final spacewalk on March 8, 2002, to the people who helped plan and execute the STS-109 mission. For complete launch to landing coverage and the most up-to-date news about this mission click here.

"Number One of our scary moments is over," he said after finishing that chore. "We only have Numbers Two and Three to go."

The next harrowing job called for Grunsfeld to anchor himself to the end of the shuttle's robot arm and then haul the cooling system's radiator up to the observatory, a move made possible by crane operator Nancy Currie.

Live images beamed back to Earth via satellite showed Grunsfeld holding the 13-foot-long (3.94-meter-long) radiator at arm's length, the northern edge of South America serving as a backdrop.

"Looks like a big surf board," said Linnehan.

Taking great care not to bang it into a fragile Hubble solar wing, Grunsfeld slowly twirled the radiator to position it for installation on the aft shroud of the telescope -- a work site Linnehan already had scaled up to.

"You're looking great, Rick -- hanging on the side of Hubble," Grunsfeld said.

"Like a Hubble bug," Linnehan replied.

Fixing the radiator to Hubble's hull proved to be even more difficult. The two spacewalkers had trouble lining up its two ends, which were latched down on metal handrails that looked like bronze bathroom towel racks.

No matter, ground engineers said.

"We like the alignment. It's a little bit -- about an inch (2.54 centimeters) in our estimation -- to the right of where it should be, but we feel that's good enough," astronaut Mario Runco radioed up from NASA's Mission Control Center in Houston. "We're ready to leave well enough alone."

The trickiest part of the installation came next. Grunsfeld and Linnehan had to route thick electrical cabling and coolant lines between the radiator and the cooler.

Linnehan likened one of the conduits to "a boa constrictor" as the spacewalkers snaked the lines through the vent hole in the bottom of the telescope. But the two men got the difficult work done nonetheless.

"Good job you guys," Currie said.

Whether the new NICMOS cooling system actually works remains to be seen.

An initial functional test confirmed that the new cooler had been wired up properly. But the system's miniature turbines won't be spun up until after the six-man, one-woman shuttle crew sets Hubble free Saturday.

It will take a month to chill down the instrument's infrared detectors, and the first test images from the refurbished NICMOS won't be taken until early May.

Hubble project officials, meanwhile, consider the cooling system experimental and know full well that the fix might not work.

If it doesn't, "we'll be disappointed," said David Leckrone, chief Hubble scientist. "And I don't want to say we'll be surprised because we did call it an experiment and that's what it is."

The seven-hour, 20-minute excursion represented the crew's last spacewalking hurrah with Hubble. The astronauts are scheduled to cast the $3 billion observatory back into space around 5 a.m. EST (1000 GMT) Saturday.

Columbia remains scheduled to land here at Kennedy Space Center at 4:30 a.m. EST (0930 GMT) next Tuesday.