This December 24, 2013 NASA TV still image shows astronaut Mike Hopkins(L) on the robotic arm holding a spare pump and Rick Mastracchio position a spare pump as they slide it into the truss during a spacewalk outside the Ineternational Space Station(ISS). Two NASA astronauts stepped out Tuesday on a rare Christmas Eve spacewalk to complete repairs at the International Space Station. “The 10th spacewalk of the year at the International Space Station is now officially under way,” a NASA commentator said at 6:53 am (1153 GMT), as astronauts made a second outing to replace an ammonia pump module whose internal control valve failed December 11.The main task of the day is to retrieve a spare pump module from an external stowage platform and install it. NASA astronauts Rick Mastracchio, 53, and Mike Hopkins, 44, made swift work of their first spacewalk on Saturday, disconnecting and pulling out the old cooling pump that regulates the temperature of equipment at the orbiting space lab. AFP PHOTO / HO / NASA TV == RESTRICTED TO EDITORIAL USE / MANDATORY CREDIT: “AFP PHOTO / NASA TV / NO SALES / NO MARKETING / NO ADVERTISING CAMPAIGNS / DISTRIBUTED AS A SERVICE TO CLIENTS ==