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While many people may spend Christmas Eve doing last-minute gift shopping, two American astronauts have a more challenging matter to attend to Tuesday. In orbit more than 200 miles above the planet, Flight Engineers Rick Mastracchio and Mike Hopkins are set to embark on a spacewalk to repair part of the International Space Station's cooling system. It will be the second Christmas Eve spacewalk in history, according to NASA. The two engineers will be carrying out the second in a series of expeditions needed to replace a malfunctioning pump, which circulates ammonia through loops outside the station to keep equipment cool. The pump developed problems December 11, when an internal valve stuck in an incorrect position. The space station's life support system remains up and running, but operations were cut back as a result of the failure, NASA said. The two astronauts spent about five and half hours outside the space station on Saturday working to remove the problematic pump. They are scheduled step out again Tuesday at 7:10 a.m. ET to install a new one. If everything goes according to plan, the repair job will be completed Tuesday. Spacesuit problem Mastracchio will be using a different spacesuit after a small amount of water leaked into the cooling system of the one he wore on Saturday. NASA said the issue with the suit, which happened at the end of the spacewalk, was unrelated to a problem experienced in July, when water pooled in an Italian astronaut's helmet, causing a spacewalk to be cut short. "Both Mastracchio and Hopkins reported dry conditions repeatedly throughout Saturday's activities and the two were never in danger," the agency said. NASA had installed new safeguards, including snorkels inside the spacesuits that would allow astronauts to take breaths if water formed and they had to return to the space station. Tuesday's spacewalk will be the 176th to support the space station's assembly and maintenance, according to NASA. The previous Christmas Eve spacewalk took place in 1999, the agency said, when Discovery astronauts Steve Smith and John Grunsfeld spent more than eight hours refitting parts of the Hubble Space Telescope. The other people in the International Space Station at the moment include Russian cosmonauts Mikhail Tyurin, Sergey Ryazanskiy and Oleg Kotov and Japanese astronaut Koichi Wakata.