ROBERT SIEGEL, HOST:
Flying above the Earth today other Christmas Eve mission, surfing the globe of thousands of miles an hour, were two astronauts. In a spacewalk today, they replaced a pump that is crucial for normal operations aboard the International Space Station.
NPR's Joe Palca has more.
JOE PALCA, BYLINE: The pump circulates ammonia coolant around the station in one of two independent cooling systems. Having two systems is essential for removing the heat generated by all the station's electrical equipment.
ROB NAVIAS: This pump module is considered one of the more critical components on the space station.
PALCA: Rob Navias was the Voice of Mission Control during today's activities. So when the pump failed earlier this month, NASA mission managers didn't waste any time scheduling the space walks needed to make repairs. This was the second space walk in four days for Flight Engineers Rick Mastracchio and Mike Hopkins. On Saturday, the pair removed the failed pump. Today's job was to install the new one. Navias says the pump is huge, about the size of the large commercial refrigerator.
NAVIAS: Each pump module weighs 780 pounds on Earth. Of course, in space it's weightless but has a mass of 780 pounds.
PALCA: And moving that much mass requires precision movements, so slow and steady is the name of the game. In fact, nearly every step in today's space walk was carefully choreographed. You don't just put the pump in place and start tightening the bolts. You do it in the order ground controllers in Houston tell you to.
Doug Wheelock was today's spacecraft communicator.
DOUG WHEELOCK: We're going to install the pump module in this order. Bolt One, Four, Three, Two expecting 17 turns.
PALCA: The spacewalk went fairly smoothly. The astronauts had a hard time with one of the four ammonia lines they had to connect. And some frozen flakes of ammonia leaked into space giving the appearance of a totally impossible snow storm 260 miles above the Earth. After the astronauts had spent about six hours tightening bolts, connecting ammonia lines, connecting electrical lines, Navias says ground controller were able to perform an initial check on the replacement pump.
NAVIAS: Good news, from the flight control team. We have a pump that is alive and well.
PALCA: A test later this evening should tell whether the pump is ready for regular operations.
This was the second space time NASA had to schedule a spacewalk on Christmas Eve - not that there was much mention of that holiday during the mission, except maybe one.
NAVIAS: This is Mission Control, Houston. So the flight control team here in Mission Control is looking at their list and checking it twice. And...
PALCA: Well, maybe that was just a coincidence.
Joe Palca, NPR News.
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