Astronauts aboard the ISS will celebrate Christmas performing a spacewalk

Christmas fix of space station cooling system

Broken cooling system prompts astronauts to perform the second Christmas Eve spacewalk in the history of human space flight.

American astronauts  Rick Mastracchio and Mike Hopkins will perform a second spacewalk today to replace the broken ammonia pump of one of the stations's cooling systems that went down on 11 December.

Having progressed beyond expectations during the first spacewalk on Saturday, the astronauts are foreseen to wrap up the work today, allowing Nasa to scrap the originally planned third space walk. On Saturday, the astronauts managed to completely remove the broken pump, which will be today replaced with a spare item. During the Christmas Eve spacewalk, Mastracchio and Hopkins will be supported by Japanese astronaut Koichi Wakata operating the robotic Canadarm.

The operation marks the second time in the history when astronauts have had to venture out in open space on the Christmas Eve, with the first occasion having been the 1999 Hubble Space Telescope upgrade mission performed by Space Shuttle Discovery astronauts Steve Smith and John Grunsfeld.

The Saturday space-walk was the first Nasa-organised extra-vehicular activity since European astronaut Luca Parmitano, using an American-made spacesuit, experience problems in July as his helmet was filling with water, possibly putting his life at risk.

For Mastracchio’s and Hopkins’ space-walk, the suspect components were replaced and the helmets fitted with absorbent pads and makeshift snorkels. The astronauts didn’t report any leaks during the Saturday spacewalk, though an unrelated problem occurred after the astronauts returned to the air-lock, when a small amount of water entered the cooling system of Mastracchio’s spacesuit.

For this reason, Nasa rescheduled the second spacewalk from Monday to Tuesday 24 December, allowing the astronauts to resize a spare spacesuit to be used by Mastracchio during the second extra-vehicular activity.

The ISS was running on one out of two cooling systems, since one of the ammonia pumps broke down on 11 December, forcing the crew to switch off several experiments to prevent overheating the station.

The busy Christmas working schedule of the crew 38 aboard the ISS will continue on Friday with Russian astronauts Oleg Kotov and Sergey Ryazanskiy performing a Russia-organised spacewalk to install two high-fidelity cameras on Russia’s Zvezda service module. During the operation, the current space station commander Kotov and flight engineer Ryazanskiy will replace several outdated experiments mounted outside the station.

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