your connection to The Boston Globe

US astronauts conduct first of three spacewalks

CAPE CANAVERAL, Fla. -- Four or five flakes of toxic ammonia dripped from a cooling line cap yesterday, but apparently didn't touch two US astronauts conducting the first of three spacewalks planned outside the international space station over the next nine days.

The leak occurred late in the spacewalk, 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. Ammonia, which can cause contamination, was a big concern since the toxic substance leaked out of a cooling line onto astronaut Robert Curbeam's spacesuit when he performed a similar task in 2001.

During yesterday's spacewalk, the astronauts 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. The astronauts will perform a second spacewalk, set for Sunday, and a third US spacewalk together to jettison thermal blankets.

US 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.