Image: Spacewalk
NASA astronauts Tracy Caldwell Dyson and Douglas Wheelock work to install a new cooling pump module on the the International Space Station during a Monday spacewalk.
updated 8/16/2010 8:30:42 PM ET 2010-08-17T00:30:42

Spacewalking astronauts installed a new coolant pump for the International Space Station on Monday, accomplishing urgent cooling-system repairs after more than two weeks of impaired operations in orbit.

Initial tests showed that the ammonia pump was operating well, though flight controllers still have more checks to make. If everything goes well, NASA expects to have the space station's disabled cooling loop back in action and everything working normally within a few days.

"Hopefully, we'll have a pump up and running, be back in business at the space station, astronaut Douglas Wheelock said at the conclusion of spacewalk No. 3.

"We're going to have a lot cooler station here shortly," promised Mission Control.

The orbiting lab has been operating on half its normal cooling capability since the pump failed July 31, forcing the six-person crew to shut down science projects and turn off unnecessary equipment to avoid overtaxing the single functioning cooling line. But living conditions never deteriorated.

Wheelock and Tracy Caldwell Dyson spent nearly 23 hours on emergency spacewalking repairs, conducting three outings in just 10 days.

Unlike the first two spacewalks, Wednesday's seven-hour, 20-minute excursion unfolded almost perfectly.

Wheelock deftly slid the bathtub-size pump into place, then bolted it down as Caldwell Dyson hooked up power cables. The spacewalkers then connected all the ammonia fluid lines.

To everyone's relief, the work went smoothly, with no apparent leakage of the toxic substance. On the first spacewalk, ammonia streamed out and forced NASA to add an extra outing to get the job done.

"We did not see any ammonia come out today, amazingly," Mission Control radioed. Wheelock said a couple of frozen flakes may have drifted out, but nothing more.

Wheelock proudly showed off the checklist on his arm cuff to the TV cameras. Printed in black ink were the words, "Game over!!"

Getting the pump installed was "a huge relief for a whole lot of people," said flight director Courtenay McMillan. A special team of engineers numbering in the hundreds had been working practically nonstop ever since the trouble struck.

NASA said a fourth spacewalk eventually will be needed to move the failed pump into a better storage location, but managers are uncertain whether this crew or another will carry out the work.

"The first thing is to give folks a break," deputy program manager Kirk Shireman said.

The pumps — weighing 780 pounds (355 kilograms) apiece — are needed to drive ammonia through cooling loops and keep electronics equipment from overheating. Four spare pumps were on board; the one installed Monday was the oldest of the bunch. It flew up in 2006.

Engineers are uncertain how and why an electrical short knocked out one of the two original ammonia pumps.

As the spacewalk drew to a close, Wheelock asked Mission Control how the new pump was doing. Good, he was told. "Ah, sweet!" he replied.

NASA said the repair effort was one of the most challenging ever undertaken at the 12-year-old space station. Indeed, the astronauts' work was hampered by the large ammonia leak that erupted during the first spacewalk on Aug. 7. It took two spacewalks for Wheelock and Caldwell Dyson to remove the broken pump; they finally succeeded last Wednesday.

Monday's outing was the 150th spacewalk in support of construction and maintenance at the 220-mile-high (350-kilometer-high) complex.

The space station is home to three Americans and three Russians. It's supposed to continue working until 2020, but that will become increasingly difficult to accomplish once NASA's shuttles stop flying next year. Two shuttle missions remain, with a third possible if the White House and Congress sign off on it. NASA would use that third mission to bring the broken pump back to Earth for analysis; otherwise, it will have to be discarded, ultimately, as garbage.

Once the three remaining shuttles are retired, the Russian, European and Japanese space agencies will take over all crew and cargo shipments until U.S. commercial launch providers have new rockets ready for NASA.

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