( dpa ) - A German astronaut embarked on a space walk Wednesday after recovering from a bout of illness that thwarted a previous attempt.
Hans Schlegel and his US associate Rex Waldheim passed through the airlock of the International Space Station to replace a nitrogen tank on its external cooling system.
It was the first spacewalk for the 56-year-old German since he was forced to pull out of Monday's spacewalk to hook up the space station's new European laboratory, Columbus.
During the six-hour operation, the two astronauts will replace the station's empty nitrogen tank with a new one lifted into position from the shuttle Atlantis with the help of a robotic arm.
The Atlantis, carrying a crew of seven and the European Space Agency's Columbus module, docked with the ISS at 17.17 GMT on Saturday after a two-day journey.
The laboratory was successfully hooked up Monday, a day later than planned because of Schlegel's "unspecified" illness. Frenchman Leopold Eyharts Tuesday became the first astronaut to inspect the inside of the laboratory.
With the one-day delay in the first spacewalk, NASA extended the Atlantis mission by a further day, with the shuttle now scheduled to return to earth on February 19.
NASA had declined to specify what Schlegel's "health issues" were, with a NASA official only commenting that they were not life- threatening.
But US media reports spoke of the well-known phenomenon of "space adaptation sickness" in which astronauts suffer nausea and orientation problems. The TV network CNN, citing space experts, said 50 per cent of astronauts suffer from it and the problems usually go away after two to three days.
Schlegel was given a clean bill of health at the start of the week.