Second spacewalk begins to replace degraded pump on ISS

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Astronauts aboard the International Space Station are conducting a second and final spacewalk to fix the outpost's cooling system early on Tuesday (December 24), a NASA official said.

NASA astronauts Rick Mastracchio and Mike Hopkins left the station's Quest airlock on to install a new ammonia pump at 6:53 a.m. EST., according to NASA.

During an initial spacewalk on Saturday, Mastracchio and Hopkins removed a failed pump, accomplishing about half the work planned for the second spacewalk. That prompted the National Aeronautics and Space Administration to drop plans for a third spacewalk, provided that no problems occur on Tuesday.

"It's apparent now that we'll be able to get most of our critical objectives done tomorrow (Tuesday)," space station flight director Judd Frieling said during an interview on NASA Television on Monday.

One of two cooling systems on the U.S. side of the space station, a $100 billion project of 15