CAPE CANAVERAL, Fla. -- A pair of Endeavour astronauts breezed through a second spacewalk Tuesday, completing several key assembly tasks at the International Space Station (ISS) in less time than planned.

STS-111

For complete launch to landing coverage and the most up-to-date news about this assembly mission to the International Space Station click here.

NASA astronaut Franklin Chang-Diaz and French astronaut Philippe Perrin needed only five hours to finish their list of things to do, about 90 fewer minutes than allotted in the timeline.

"It could not have gone any better," said lead ISS flight director Rick LaBrode. "We've added another piece to the ISS city in the sky."

The only hiccup of note came at the end of the spacewalk when a power supply system in the station's airlock didn't work, requiring the spacewalkers to rely on their spacesuit batteries a little longer than planned.

Although engineers don't yet fully understand the trouble, spacewalk officer Tricia Mack said the problem won't have any significant affect on the mission's final spacewalk planned for Thursday, when Chang-Diaz and Perrin are to replace a faulty joint on the station's Canadarm2.

During this 40th spacewalk to assemble the ISS the astronauts:

• Connected power, video and data cables between a work platform and rail car that eventually will allow the station's Canadaian robot arm to move along the outpost's main truss, which still is under construction.

• Positioned a grapple fixture on the platform that will securely hold future station elements while the rail car moves along the truss.

• Permanently bolted the platform to the rail car, allowing a temporary claw that was holding the platform in place to be retracted.

• Relocated a television camera on the platform.

• Attached a bag that holds an emergency power extension chord for the work platform should it be needed some day.

While this was going on outside the complex, crewmembers inside were continuing to unload the Leonardo supply module with its nearly three tons of equipment and supplies.

The unpacking is likely to finish late Tuesday and then repacking will begin in earnest as the crew attempts to fill the Italian "moving van" to 90 percent of capacity.

The plan is to stuff into Leonardo more than two tons of garbage and other equipment no longer wanted on the station, and then return the module to Earth riding in Endeavour's cargo bay.

Meanwhile, the U.S. record for the longest spaceflight is set to be broken Tuesday at 10:19 p.m. EDT (0219 GMT Wednesday).

NASA astronaut Shannon Lucid has held the distinction since her 188-day and four-hour stay aboard the Russian space station Mir in 1986.

But as a result of delays in Endeavour's launch, Expedition Four crewmembers Dan Bursch and Carl Walz -- who were launched to orbit in December -- will surpass that mark and take the record.