US astronauts have successfully repaired a critical cooling system pump at the International Space Station.
Space agency NASA said Rick Mastracchio and Mike Hopkins completed a seven-and-a-half hour spacewalk to replace the faulty ammonia pump.
The pump broke down two weeks ago, leaving the US side of the station without half its cooling system. All non-essential equipment had to be switched off and many scientific experiments were halted.
NASA has said that the station's six-member crew was never in danger.
It was the two astronauts' second spacewalk in three days to replace the pump, which is about the size of a refrigerator. NASA said all the systems should be back up and running by the weekend.
It was only the second Christmas Eve spacewalk in the history of the space programme, the BBC reports. The only previous spacewalk on 24 December was in 1999 during a Hubble Space Telescope repair mission.