WASHINGTON, DC – Two astronauts of the US space shuttle Endeavor prepared Saturday for a third mission spacewalk outside the orbiting International Space Station to complete repairs on one of the station's three double solar antenna arrays.

Americans Heide Stefanyshyn-Piper, 45, and Steve Bowen, 44, are scheduled for a spacewalk that could last seven hours or more, the longest on the mission that began on November 15.

The two astronauts are tasked with finishing repairs to the ISS's starboard Solar Alpha Rotary Joint race ring and replacing trundle bearing assemblies. The worn-out parts will be taken to Earth for inspection.

By 1630 GMT Stefanyshyn-Piper and Bowen, both US navy captains, had finished putting on their bulky astronaut suits ahead of exiting the craft.

"Everything moves very smoothly, in fact ahead of schedule," said a NASA spokesman. "The preparation runs almost an hour ahead of schedule."

The spacewalk is scheduled to at 1845 GMT, but could begin ahead of schedule, the spokesman said.

The complex work in space will be orchestrated by Shane Kimbrough, 41, who was on a spacewalk along with Stefanyshyn-Piper on Thursday.