Two astronauts from the US space shuttle Atlantis stepped out into space on Monday on the first walk of the current mission, to prepare the European research laboratory Columbus for hooking up to the International Space Station, NASA said.
Astronauts Rex Walheim and Stanley Love emerged from the decompression chamber of the International Space Station at 1413 GMT, 22 minutes before the planned time, for the walk slated to last nearly seven hours.
The walk comes a day later than originally scheduled, after German astronaut Hans Schlegel, who was to accompany Love on the walk, fell ill.
The National Aeronautics and Space Administration has not revealed the cause of Schlegel's illness or commented on his status. On Sunday, European Space Agency spokesman Markus Bauer, said Schlegel, 56, appears to have recuperated and was doing "very well."
"We are assuming that he will take part in the second spacewalk," said Bauer.
Asked Sunday about the spacewalk adjustments, Sarafin said "the change won't have any impact on the mission; we accelerated some activities including inspection," while making it understood that things could change.
He said Schlegel, a space veteran who flew on a 1993 shuttle mission, and Atlantis co-pilot Alan Poindexter would supervise the spacewalk as internal procedure experts.
The two billion dollar, 10-tonne Columbus laboratory represents a milestone in Europe's role in space. Paid for mostly by Germany, Italy and France, it is the first ISS addition not made in the United States or Russia.
The laboratory will be used for biotechnology and medicine experiments involving microgravity.
Love and Walheim spent the night before the walk in a decompression chamber to purge nitrogen from their bodies, NASA said.
During their walk, planned to last six hours and 50 minutes, the two are to prepare the cylindrical, 4,5 meters in diameter Columbus lab, for attachment to the Harmony module, which will be its permanent place on the ISS.
During the walk they first must set up the system to allow the ISS's powerful robotic arm to move the Columbus module into position for attachment to Harmony.
After that is done, they have a number of small jobs related to the hook-up to perform, such as installing panels to protect it from the impact of micro-meteorites.
According to NASA plans, in March 2008 another laboratory, the Japanese module Kibo, is also to be attached to Harmony.
Clearing up concerns that launch debris may have damaged the shuttle, on Sunday mission chief John Shannon said that the thermal shield on Atlantis's nose and wing forward edges were in perfect condition.
He also said the mission could be prolonged a second day, a decision to be taken on Tuesday.