NASA: "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, originally planned for Monday, is now scheduled for Tuesday."

More at SpaceFlightNow and NYT.

[Image: NASA TV]