On Sunday, Dec. 22, NASA astronaut Mike Hopkins tweeted this photo of Saturday's spacewalk, saying, "Wow... can't believe that is me yesterday. Wish I could find the words to describe the experience, truly amazing." Expedition 38 Flight Engineers Rick Mastracchio and Mike Hopkins wrapped up a 5-hour, 28-minute spacewalk outside the International Space Station at 12:29 p.m. EST Saturday, completing the first in a series of excursions aimed at replacing a degraded ammonia pump module associated with one of the station's two external cooling loops that keeps both internal and external equipment cool. A second spacewalk to install a replacement pump module is scheduled for Tuesday, Dec. 24 at 7:10 a.m. EST, with NASA TV coverage beginning at 6:15 a.m. EST.