Four or five flakes of toxic ammonia fell from a cooling line cap but apparently did not touch two U.S. astronauts conducting the first of three spacewalks planned outside the international space station over the next nine days.
The leak occurred late in the almost eight-hour spacewalk Wednesday, as astronauts Michael Lopez-Alegria and Sunita Williams disconnected and prepared to stow away two fluid lines that had been connected to an ammonia reservoir outside the space station.
Tests in the airlock later showed no contamination, and the spacewalk officially ended at 6:09 p.m. EST (2309 GMT), seven hours and 55 minutes after it started.
Ammonia was a big concern since it could be an irritant to the crew and cause respiratory problems if it got in the space station in significant amounts. The toxic substance leaked out of a cooling line onto astronaut Robert Curbeam's spacesuit when he performed a similar task in 2001.
Lopez-Alegria and Williams did not face the same problems as Curbeam did with ammonia. Nevertheless, Mission Control told the spacewalkers to remain in their spacesuits for an extra 25 minutes once they entered the station's airlock to make sure there was no ammonia on their suits that could contaminate the orbiting lab.
"We don't think we have contamination, but that's probably for the lawyers," Lopez-Alegria said.
Replied Mission Control: "We're going to follow the path of safety."
The ammonia flakes likely came from residue left by ammonia which had leaked over time and was "nothing approaching a real leak," spacewalk flight director Derek Hassmann said after the spacewalk. "I personally wasn't concerned ... that we would introduce any ammonia."
During Wednesday's spacewalk 220 miles (354 kilometers) above Earth, the astronauts successfully switched coolant lines from a temporary cooling system to a permanent one and secured a thermal cover around an obsolete radiator that Mission Control retracted by remote control. Lopez-Alegria made electrical connections for a new system that will allow power from the station to be shared with a docked shuttle.
The astronauts ran out of time and got only one of two fluid lines stowed, and they did not get to "get-ahead" such tasks as taking photos of a solar array that will be retracted during the next shuttle mission, in March.
The astronauts will perform identical tasks during their second spacewalk, set for Sunday. The astronauts will take a third U.S. spacewalk together on Thursday to jettison thermal blankets, reports AP.
U.S. astronauts have never attempted three spacewalks in such a short time without a space shuttle docked at the station. If the spacewalks go as planned, Lopez-Alegria will have two weeks to rest before going on a fourth spacewalk, set for Feb. 22.