Expedition 38 astronauts Rick Mastracchio and Mike Hopkins began the first of three planned spacewalks Dec. 21 to remove and replace a faulty coolant pump module on the international space station (ISS). The pump is associated with one of the station’s two external cooling loops, which circulate ammonia outside the station to keep the internal and external equipment cool. The first contracted Orbital Sciences cargo run has been postponed to no earlier than January. Credit: NASA TV