Two astronauts floated out of space shuttle Atlantis to install a 164 million dollar passageway for spacewalkers on the international space station. Michael Gernhardt and James Reilly got started an hour late on their spacewalk late Saturday, which followed a successful dress rehearsal of the big event. There we go, Gernhardt said, popping open the hatch. Everyone in orbit and mission control was relieved to see the space station robot arm step through all its paces earlier in the day without any of the problems exhibited in recent months. The dry run, conducted soon after the two spacecraft docked late Friday night, cleared the way for Saturday night's lengthy spacewalk to hook up the new air lock.
Paul Hill, the lead flight director, expected space station alpha's arm to work just fine.
Atlantis carried up the 6 1/2-ton air lock in its cargo bay. Because the shuttle's 15-meter robot arm cannot reach the attachment point on the international space station, the station's 17-meter robot arm was assigned the lifting.

The Canadian-built station arm had a variety of start-up problems after it was installed during the last shuttle flight in April. Hundreds of engineers in the US and Canada spent weeks trying to understand and solve the difficulties.
A bad computer card was to blame for the most serious and persistent trouble, involving the shoulder joint, and ended up delaying Atlantis' flight one month.
Bureau Report