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ISS back in action after marathon spacewalk series

Everything is up and running again on the International Space Station following a marathon series of spacewalks to replace a critical cooling pump. The pump's failure had forced the US-Russian crew to shut down non-critical systems and put many experiments on hold for nearly three weeks.

The two-loop cooling system relies on the flow of ammonia coolant, but with one loop shut down the astronauts had to install electric power jumpers to transfer current between loops and route additional power to the Russian segment of the station. That allowed much of the station to continue near-normal operations with three of four stabilising gyroscopes, life support systems and critical communications equipment.

But experiments in the Japanese Kibo module and the European Space Agency's Columbus module had to be shut down, along with most of the science racks in the US portion of the station.

The eventual failure of one or both pumps was anticipated long ago. NASA had stored four spare cooling pumps, which weigh 355kg (780lb) on Earth, on an external stowage platform on the station in July 2006.

When a pump failed on 31 July, astronauts set into motion a long-ready plan. However, in attempting to remove the broken pump on the initial spacewalk on 7 August, US astronauts Tracy Caldwell Dyson and Doug Wheelock struggled to disconnect one of its four ammonia lines, spraying ammonia into space. A second spacewalk was needed just to remove the damaged system. Two more walks were required to complete the swap-out mission.

The final 7h 20min spacewalk pushed the total time for time in space to repair the coolant system to 22h 49min, and Wheelock into the record books. His total time over six career spacewalks now stands at 43h 30min, moving him into the number 10 slot on the list of most experienced spacewalkers.

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