Nasa astronauts Rick Mastracchio and Mike Hopkins have completed the first of three emergency spacewalks to replace a broken cooling pump at the International Space Station.
As the ISS orbited Earth at a speed of five miles per second, veteran spacewalker Mr Mastracchio led the way, followed by Mr Hopkins, who was making his first venture outside the global research lab.
From the inside, Japanese astronaut Koichi Wakata operated the station’s 50ft (15m) robotic arm, hoisting Mr Mastracchio and hefty equipment from one section of the lab to another.
“There are quite a bit of arm manoeuvres throughout all of these EVAs so I’m sure Koichi will be getting a workout,” said lead spacewalk officer Allison Bolinger, using the Nasa acronym for spacewalk: extravehicular activity (EVA).
While flight engineer Mr Mastracchio, 53, soared around with his boots attached to a foot-plate on the robotic arm, Mr Hopkins, 44, was the designated free-floating astronaut of the day.
The men’s first task was to disconnect the ammonia pump, which is about the size of a refrigerator.
On the second spacewalk, set for Monday, the astronauts are to remove the pump so it can be replaced with a spare that was already stowed at the ISS.
A third spacewalk is planned for Christmas Day, when the failed pump will be shuttled away and final installations made on its replacement.
However, there is a chance the astronauts will be able to complete all their work in two spacewalks, Nasa has said.
If not, the Christmas Day outing would be the first since 1974, when a pair of Nasa astronauts “stepped outside the Skylab space station to retrieve film from a telescope and photograph Comet Kohoutek”, the US space agency said.
The urgent spacewalks were called for this week due to a faulty valve that caused a partial shutdown in the system that regulates equipment temperature at the space station.