Astronauts begin ISS spacewalk to perform urgent repair
21 December 2013 Last updated at 12:37 GMT
Astronauts have begun the first of a series of urgent repair spacewalks at the International Space Station.
The two men will disconnect an ammonia pump that contains a bad valve.
The breakdown has crippled the space station's critical cooling system for the past 1½ weeks.
The work is expected to take Rick Mastracchio and Mike Hopkins three spacewalks to complete.
They wore spacesuits that were modified to protect them from a possible water leak, after the last Nasa spacewalk, in July, had to be aborted.
Luca Parmitano's helmet filled up with so much water that he could not hear or speak as the spacewalk came to an abrupt end.
This time the astronauts have fitted their helmets with helmets with homemade snorkels.