U.S. astronauts Michael Hopkins and Richard Mastracchio are back to the Quest airlock chamber after having replaced a degraded pump module on the truss of the International Space Station (ISS) U.S. segment, NASA said.

The pump was connected to the U.S. segment's thermal regulation system. The NASA Johnson Space Center in Houston tested the system and said it was in order.

The astronauts had some problems in clipping four fluid lines and three cables into place onto the pump amid a snowstorm of ammonia flakes from the thermal regulation system. They had to decontaminate their spacesuits before returning to the station.

The spacewalk lasted for nearly seven hours.

Japanese astronaut Koichi Wakata assisted in the spacewalk at the robotic arm's controls.

The ISS is being operated by Oleg Kotov, Sergei Ryazansky and Mikhail Tyurin (Russia), Michael Hopkins and Richard Mastracchio (NASA) and Koichi Wakata (JAXA).

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