Astronauts David Wolf and Piers Sellers completed a six-hour four-minute spacewalk today, the second of three required to install, outfit and activate a 14.5-ton solar array truss segment on the international space station.

The 45th station assembly spacewalk began at 10:31 a.m. EDT and ended at 4:35 p.m. EDT when Wolf and Sellers began repressurizing the Quest airlock module. The two astronauts have now logged 13 hours and five minutes of spacewalk time through two extravehicular excursions, pushing the total station assembly EVA time to 278 hours and 49 minutes.

"Thanks a lot everybody in Houston," Wolf called from the airlock. "It was a good day."

"Houston concurs," replied astronaut Stan Love from mission control. "You guys were hot."

During today's spacewalk, Sellers and Wolf installed clamp-like devices to prevent ammonia coolant leaks in quick-disconnect fittings; deployed a second television camera platform; completed unlatching numerous locks that secured critical systems during launch; and completed initial activation of an astronaut rail car mounted on the forward face of the S1 truss. The work was completed 25 minutes ahead of schedule.

However, the spacewalkers were not able to install two of the two dozen ammonia quick-disconnect clamps today as they originally planned.

During a mission status briefing, lead spacewalk planner Oscar Koehler said the two spool positioning devices, or SPDs, in question, located on the station's interim P6 solar array truss, were not equipped with the metal locking collars needed to anchor the SPDs.

The collars were added to other ammonia line fittings at the Kennedy Space Center after engineers decided to attach the SPDs to prevent potential leaks. Engineers were unable to gain access to the two QDs in question at the Kennedy Space Center and somehow, that word never made it to Houston. There is no immediate problem with the two fittings in question and engineers will be looking into alternative fixes.

It's not clear exactly how many SPDs were, in fact, installed today. Koehler said 22 of 24 were installed while a NASA spokesman said earlier today a total of 25 SPDs were to be installed.

Finally, mission operations representative Robert Castle, said shuttle commander Jeffrey Ashby fired Atlantis' maneuvering jets this morning to boost the station's altitude by 3.98 statute miles. Another reboost maneuver is planned later to add an additional 2.4 miles of altitude. The station's current average altitude is 241.7 miles.

"Everything in the EVA that needed to get done got done, we're on track for finishing the mission and finishing it on time," Castle said.