CAPE CANAVERAL, Fla. (AP) _ Astronauts working to bring to life a new 17 1/2-ton addition to the international space station lost another bolt to the void during a spacewalk early Wednesday.
The bolt was similar to one that popped off Tuesday and floated free during an earlier spacewalk.
Steve MacLean of the Canadian Space Agency told Mission Control on Wednesday that he was removing a cover on a crucial rotary joint when one of the four bolts he needed disappeared.
``I did not see it go,'' MacLean said. ``I'm looking to see if anything is floating.''
Space debris can be dangerous if it punctures space station walls or spacesuits and can jam crucial mechanisms. However, spacewalkers have a long history of losing things in space. In July, Discovery spacewalkers lost a 14-inch spatula that floated away.
There was no indication that the latest missing bolt went into the rotary joint or any other space station mechanisms, and the assumption is it floated away, NASA spokesman Grey Hautaluoma said. He said that the astronauts simply used three bolts for the task instead of four, and that there shouldn't be a problem with that.
MacLean ran into another small problem a short time later when an extension on his pistol-grip power tool broke while he was trying to remove a restraint on the rotary joint.
``Son of a gun,'' he muttered, then gathered the pieces in a trash bag so they wouldn't float away and went to a toolbox to retrieve another.
During Wednesday's six-hour spacewalk, MacLean and astronaut Dan Burbank needed to release and remove 16 locks and six restraints that kept the rotary joint in place during Saturday's launch from the Kennedy Space Center. The ferris-wheel-like rotary joint will allow two solar arrays, once unfurled, to always face the sun as the space station circles Earth.
Those solar arrays will eventually supply a quarter of the space lab's power when it is completed by 2010.
The astronauts had to remove more than a dozen insulation covers and scores of bolts wearing bulky spacesuit gloves.
On Tuesday, astronaut Joe Tanner lost another bolt during a spacewalk with astronaut Heidemarie Stefanyshyn-Piper. He asked MacLean to be on the lookout for it Wednesday.
``I've been looking for that bolt all along but I haven't seen it,'' MacLean said.
Tanner and Piper planned to return for a third spacewalk on Friday.
Before the mission, NASA managers and the astronauts had warned that the spacewalks could be difficult. The spacewalk was the second of three spacewalks to hook up the new $372 million addition to the space station during Atlantis' 11-day mission.
``For the outside observer, it's going to look boring since the guys aren't going to be moving around a whole lot,'' Tanner said before the mission. ``What they're doing is so extremely critical, but very repetitive. We will work hard at not getting lulled into boredom or complacency.''
Both Burbank and MacLean made their spacewalk debuts this week.
``I just don't want to be real clumsy,'' Burbank said before the mission. ``The first thing I'm going to do is go slow and ease my way into it.''
To pump them up for the hard work ahead, Mission Control played ``Taking' Care of Business'' as their wake-up song.
Engineers have determined that Atlantis' heat shield is in such good shape _ free from the type of the damage that led to Columbia's disintegration _ that it is clear for landing at the end of its scheduled mission next Wednesday.
MacLean got a chance to informally inspect the shuttle's underside when he posed for a spacewalking photo.
``That's about as photogenic as I get,'' he said.