Image: NASA astronauts Tracy Caldwell Dyson and Doug Wheelock
NASA TV
NASA astronauts Tracy Caldwell Dyson, left, and Doug Wheelock work to set up the ammonia spare pump module after it was installed on the S1 Truss during an Aug. 16, 2010 spacewalk outside the International Space Station. It was the third spacewalk dedicated to the repair.
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updated 8/19/2010 4:55:03 PM ET 2010-08-19T20:55:03

Astronauts living on the International Space Station said Thursday that their orbiting lab is finally back in action after a series of tricky spacewalks to replace a broken coolant pump.

American astronauts Douglas Wheelock, Tracy Caldwell Dyson and Shannon Walker lauded the efforts of engineers on Earth to help them restore the station's cooling system to full strength after a vital pump module failed July 31. The astronauts performed three challenging spacewalks this month to make the repairs.

"As far as we can tell, things are coming back up nominally," Caldwell Dyson said, adding that the station's U.S, Japanese and European labs are up and running. "We've got most of our lab back so, to us here on orbit, things are looking better than normal."

The space station is home to six astronauts; three Americans and three Russians.

Emergency space station repairs
During three spacewalks, Wheelock and Caldwell Dyson removed the faulty ammonia pump and replaced it with one of four spares stored on the exterior of the International Space Station. Walker operated the robotic arm from inside the space station. (Graphic: The International Space Station Explained)

"It demonstrates how we can respond in an emergency," Walker said during the interview with CBS News broadcast on NASA TV. "I think it was really NASA at its finest to get this repair done in short order."

And while these types of major repairs could become more complicated following the retirement of NASA's space shuttle fleet, the ability for the ground controllers and station astronauts to mobilize and complete such a task in a short timeframe highlights the strong cooperative effort of those involved, the astronauts said.

"It was a validation of our teamwork, our training and everyone involved," Wheelock said. "The way everything came together was a great lesson in teamwork. I think the confidence is real high on the team as we press forward."

Practice makes space perfect
To plan and practice the spacewalks ahead of missions, astronauts rehearse the skills and maneuvers in the Neutral Buoyancy Laboratory (NBL), a huge underwater tank at Johnson Space Center in Houston.

"Our training in the NBL back in Houston is skills-based," Wheelock explained. "And those skills came in very handy. But when you get outside with the temperature changes and the pure vacuum out there, things don't behave as they do on Earth. We have to be ready for those things."

For Walker, that meant remaining confident in her expertise at operating the station's robotic arm.

"Just like with the spacewalk operations, I was trained sort of generically," Walker said. "With the final EVA, I didn't get the procedures until the day of."

During the first spacewalk, a stuck ammonia hose, and later an ammonia leak, gave Wheelock and Caldwell Dyson some trouble when it refused to budge.

"I think the greatest thing that I learned on my earlier EVAs (extravehicular activities) is just to expect that," Wheelock said. "Just take a deep breath, think of the different ways that you can finesse the piece of hardware, and listen to what the trainers are telling you on the ground. And don't give up trying."

For the spacewalkers, the stubborn hose acted as their nemesis, said Wheelock.

"We needed a villain to fight against when we were out there," he said. "But we were able to rise to the challenge as a team."

Unforgettable spacewalks
The set of three EVAs will likely resonate with Caldwell Dyson, as they were her first spacewalks. Amid the demanding tasks, she took time to reflect on the significance of the situation, and described the experience as "awe-inspiring."

"The first EVA was a culmination of 12 years of training," Caldwell Dyson said. "It was a culmination of so much desire and years of training that it's a feeling I'll never forget.

The station is slated to keep flying through at least 2020, so spare parts will be a major concern once NASA's space shuttles stop flying next year.

NASA currently plans to fly two final shuttle missions (in November of this year and February 2011) before retiring its three-shuttle fleet for good. The possible addition of a third shuttle flight is being discussed by lawmakers.

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