NASA planned three spacewalks to fix the failing cooling system aboard the International Space Station, ISS. The first spacewalk was completed 5 hours and 28 minutes. Space suit issues delayed the second mission until Dec. 24, originally scheduled for Dec. 23.

The ISS cooling system failed earlier in December but the technical glitch did not put the Expedition 38 crew in any danger. The ammonia pump module is associated with two cooling loops that are used to keep internal and external instruments cool. One of the pump modules failed and had to be replaced. The first spacewalk removed the faulty pump module and was completed on Dec. 21 at 12:29 p.m. EST.

NASA astronauts Rick Mastracchio and Mike Hopkins will replace the pump module as part of the second spacewalk on Dec. 24. For Mastracchio, it was his seventh spacewalk and the first for Hopkins. During the first spacewalk, the two astronauts made their way to the Loop A pump module from the Quest airlock. Hopkins positioned himself at the Starboard 1 truss segment while Mastracchio attached himself to the ISS' robotic arm, with JAXA astronaut Koichi Wakata controlling the arm and moving Mastracchio to the different task areas, reports NASA.

The two astronauts detached four ammonia fluid lines, attaching the lines to a pump module jumper box which sends the ammonia to a plumbing system to keep it in a liquid state. A thermal cover was attached to the jumper box and, due to the speedy work by Mastracchio and Hopkins, ground control approved the removal of the pump module, a task that was on the agenda for Monday's spacewalk.

Mastracchio removed the pump module while Hopkins prepared the Payload Orbital Replacement Unit Accommodation, POA, that would serve as the module's storage unit on the ISS' Mobile Base System, described by NASA as a railcar, and a grapple fixutre. Wakata guided the arm, which carried Mastracchio and the pump module, to the grapple fixture.

After completing the spacewalk, the two astronauts entered the airlock and, during that time, water entered Mastracchio's space suit. NASA opted to use a backup suit for the next spacewalk, delaying the second mission to resize Mastracchio's space suit. A video of the successful first spacewalk, courtesy of NASA, can be viewed below.