Astronaut Rick Mastracchio works to remove the Ammonia Pump. Credit NASA TV.
This is not the first time that the ISS has had a problem with the coolant system. And this time, NASA has been prepared. A spare ammonia coolant pump was previously placed in storage outside the station just for this type of situation. On Saturday Dec. 21, astronauts Rick Mastracchio and Mike Hopkins donned their american-designed spacewalk suits and exited the station through the Quest airlock. Both astronauts are veterans of the space program, and both have made EVAs before. For Mastracchio this was his 7th spacewalk and the 2nd for Hopkins. The EVA was the 175th spacewalk for ISS maintenance and assembly.
Astronaut Mastracchio and the ammonia pump are moved at the end of the robotic arm.
The astronauts quickly moved ahead of schedule and after detaching the hoses and wires from the defective unit, reconnected the station coolant system hoses so that the coolant in the system could remain liquid. WIth time to spare, they moved on to the first task scheduled for the next EVA, and while attached to the robotic arm and guided by astronaut Koichi Wakata, Mastrachio attached the defective pump to a storage location on the Truss segment.
Since the recent suit malfunction in which astronaut Parmitano experienced a water leak in his EVA helmet, NASA has been concerned that the same event coould occur again. In preparation for the EVA, astronauts on the station "McGuyvered" an extra breathing tube in the helmet for the two spacewalkers. In this spacewalk, however, both suits remained dry and the astronauts returned to the station on time. Two more EVA's are planned to complete the repair to the station coolant system.
You can read an excellent detailed account of the EEVA at NASA Spaceflight.com: http://www.nasaspaceflight.com/2013/12/spacewalkers-first-pump-module-replacement-evas/