Yesterday, Expedition 38 astronauts Rick Mastracchio and Mike Hopkins completed the second spacewalk, in technical terms extravehicular activity (EVA), that was needed to repair the cooling system of the International Space Station. It followed the spacewalk performed on Saturday. Yesterday, in about 7 and a half hours the two astronauts installed a new pump that seems to work regularly.

The module containing the pump is about the size of a refrigerator and on Earth weighs about 350 kg (about 780 pounds). In microgravity conditions there’s no weight anymore but the mass remains so to move it Rick Mastracchio and Mike Hopkins were helped by the robotic arm Canadarm2, operated by Koichi Wakata from inside the International Space Station.

The faulty module was moved to a temporary location, again outside of the Station, where it can stay for a few months. It’s not yet been decided what to do with it: given the size and mass of these modules, sending a new one to the Station is really expensive so they could try to repair it.

After the new module was connected to the cooling system it was switched on while Rick Mastracchio and Mike Hopkins were still out of the Station, so that they were ready to intervene in case of problems. The first work test gave a positive result and the two astronauts completed their spacewalk.

The cooling system of the International Space Station is a bit more complex than a normal home air conditioner on Earth so the tests went on for some more hours. The flow of ammonia used as a refrigerant was successfully restored in the system, one of the two on the Station, that was shut down following the fault.

The new pump was declared operational by mission control so they decided that it was possible to begin the steps to slowly restore the Station’s cooling system. As a Christmas gift, the crew should have a fully working system again.

Originally, three spacewalks were scheduled to perform all the operations necessary to repair the cooling system. Luckily, Rick Mastracchio and Mike Hopkins managed to accomplish quickly especially the removing of the faulty module on Saturday. The consequence is that yesterday’s spacewalk was enough to complete the job.

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