| CAPE CANAVERAL, Florida
CAPE CANAVERAL, Florida Two NASA astronauts, their spacesuits rigged with snorkels in case of a water leak, floated outside the International Space Station for 5-1/2 hours on Saturday, successfully completing the first steps to fix the outpost's cooling system.
The spacewalk, which was broadcast live on NASA Television, was the first for NASA since July when the spacesuit helmet worn by Italian astronaut Luca Parmitano began filling with water, a situation that could have caused him to drown.
No such leaks were detected in Saturday's spacewalk, the first of two or possibly three that will be needed to complete the cooling system repair.
The operation was prompted by the December 11 shutdown of one of the station's two U.S. ammonia cooling systems, which forced the crew to turn off non-essential equipment and shut down dozens of science experiments.
While the six-member crew is not in danger, the remaining cooling system cannot support the three laboratories and other modules on the U.S. side of the $100 billion station, a project of 15 nations. The Russian side of the station has a separate cooling system.
Engineers at the Johnson Space Center in Houston tried devising ways to bypass a suspected faulty pump valve, but with time running short, managers decided to have astronauts replace the pump, located outside the station, with a spare.
The work, which began shortly after 7 a.m. EST (1200 GMT), went smoothly, with station flight engineers Rick Mastracchio and Mike Hopkins finishing up an hour earlier than expected.
They were able to not only disconnect the old pump, but also remove it from its pallet on the station's exterior truss, a task originally slated for a second spacewalk on Monday. A third spacewalk, if needed, is scheduled for Wednesday.
"Beautiful day. Awesome view," Mastracchio, a veteran of six previous spacewalks, said as opened the airlock's hatch and saw the view from 260 miles above the southern Atlantic Ocean.
He and Hopkins wore spacesuits that were modified to protect them from another possible water leak. The problem in July was traced to contamination in piece of equipment called a fan pump separator that circulates water and air in the spacesuit and removes moisture from air.
How the water-separator portion of the device became clogged remains under investigation.
Hopkins, who was making his first spacewalk, wore Parmitano's spacesuit, but it had been outfitted with a new fan pump separator.
In addition, both Hopkins and Mastracchio rigged their helmets with homemade snorkels, fabricated out of pieces of plastic tubing and Velcro, which they could have used for breathing in case of another water leak.
The helmets also included water-absorbent pads.
During Saturday's spacewalk, Mastracchio and Hopkins disconnected electrical and fluid lines and removed the 780-pound (354 kg), 5-foot (1.5 meter) wide cooling system pump.
The failed pump, which was then anchored in a temporary storage site, will remain on the station for possible future repair and reuse.
It was installed in 2010 during an unexpectedly difficult series of spacewalks by astronauts Doug Wheelock and Tracy Caldwell Dyson.
"What makes this pump very difficult (to work on) are (the) fluid disconnects because they are so large and they are pressurized and they contain liquid ammonia, so that's a hazard for us if it were to come in contact with us or our suits," Caldwell Dyson said in an interview with a NASA TV mission commentator.
Maintaining focus also can be a challenge, she added. "When you're on one of those pallets, you really have that sensation that you are sticking out on the edge of a skyscraper. Especially when you look down, you see your feet and then you see the Earth going 17,500 mph beneath you, it really does get your attention," she said.
Mastracchio and Hopkins encountered no major problems during Saturday's outing.
"These guys really went out there and were so efficient," Caldwell Dyson said. "It may be more difficult to remove the pump because you don't know exactly what to expect," she added.
(Fixes spelling of Mastracchio on last reference)
(Reporting by Irene Klotz; Editing by Vicki Allen)