Two spacewalking astronauts, including a German who fell ill at the start of the shuttle Atlantis mission, successfully replaced a nitrogen tank on the orbiting International Space Station on Wednesday, NASA said.
After spending the night in a decompression chamber on the ISS, the two astronauts, American Rex Walheim and his German colleague Hans Schlegel, walked out into space at 1427 GMT for a six hour and 45 minute mission.
Schlegel was unable to take part in the first spacewalk when he fell ill on Saturday just as Atlantis docked with the space station. His illness had delayed the first spacewalk by 24 hours until Monday.
The Atlantis team is helping to install a European laboratory, called Columbus, which they brought with them from Earth. The research facility gives Europe a key foothold for the deeper exploration of the cosmos.
The two billion dollar lab was brought up to the station on the Atlantis shuttle and attached Monday by Walheim and US astronaut Stanley Love in a spacewalk lasting more than six hours.
Wednesday's second spacewalk was to replace a nitrogen tank on the space station, with the two astronauts first having to remove the old tank, before installing the new one.
The new one, also flown to the space station on Atlantis, will be maneuvered into place with the aid of a robotic arm, and the old tank will be flown back to Earth on the shuttle.
A third spacewalk is planned for Friday when Walheim and Love are due to install a solar observatory on the outside of the Columbus lab, as well as another external facility known as an EuTEF which will contain eight experiments measuring the properties of materials in space.
