The spacewalk was broadcast live by Nasa
Two US astronauts have successfully repaired a critical cooling system pump at the International Space Station, the US space agency Nasa says.
Rick Mastracchio and Mike Hopkins completed a spacewalk of 7.5 hours 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 now says all the systems should be back up and running by the weekend.
“It’s the best Christmas ever,” Mission Control radioed the astronauts.
In reply, Mr Hopkins said: “Merry Christmas to everybody. It took a couple (of) weeks to get her done, but we got it.”
It was the two astronauts’ second spacewalk in three days to replace the pump, which is about the size of a refrigerator.
Nasa has said that the station’s six-member crew was never in danger.
It was only the second Christmas Eve spacewalk in the history of the space programme. The only previous spacewalk on 24 December was in 1999 during a Hubble Space Telescope repair mission.
Tuesday’s repair mission came on the 45th anniversary of the now iconic Earthrise photograph, taken by the crew of Apollo 8 as they orbited the Moon in 1968