Space shuttle Discovery was moved to the launch pad at Cape Canaveral, Fla., on Thursday for next month's planned flight, which NASA may bump up by a week to avoid any year-end computer glitches.

The U.S. space agency is considering a launch as early as Dec. 6, with the launch window extending until Dec. 17 or 18. During the 12-day mission, astronauts will perform some rewiring of the International Space Station and drop off a new lab crew member.

NASA wants Discovery back on the ground by Dec. 31 because of concerns that shuttle computers aren't designed to make the change from the 365th day of the old year to the first day of the new year while in flight.

Year-end transition an unknown

"We've just never had the computers up and going when we've transitioned from one year to another," said Discovery astronaut Joan Higginbotham. "We're not really sure how they're going to operate."

The 80,000-kilogram shuttle began its 6½ kilometre trek from the Vehicle Assembly Building shortly before 12:30 a.m. and arrived 7½ hours later.

Even if the shuttle crew finds itself in space on New Year's Day, procedures could be devised to make a transition if necessary, said Steve Oswald, a vice-president for Boeing Co., which has either merged with or acquired the companies that built the space shuttles.

"Under some weird circumstance … if we have an 'Oh my god,' and we have to be up there, I am sure we would figure out a way to operate the vehicle safely," Oswald said. "It just wouldn't be flying in the normal certified mode that we are used to flying."

If Discovery gets off the ground next month, it will be the third shuttle flight of the year, and only the fourth since the 2003 Columbia disaster.

It also will be the first night launch in four years. NASA required daylight launches after Columbia to make sure engineers had clear photos of the shuttle's external tank; falling foam from Columbia's tank had damaged its wing, dooming the shuttle.

NASA managers believe the illumination from the space shuttle's boosters should allow for photos at night, and radar should be able to detect any debris. Astronauts also are able to inspect the shuttle for damage while in flight.

Discovery's astronauts will take three spacewalks to add an $11 million US addition to the space station and rewire the space lab's electrical system. The shuttle will also drop off U.S. astronaut Sunita Williams and bring home German astronaut Thomas Reiter, who has been at the space station since July.