Shuttle Discovery's final flight delayed

The final launch of space shuttle Discovery has been delayed again, this time because of an electrical problem.

NASA decided early Tuesday evening to bump the liftoff until at least Thursday. The decision came less than 24 hours before the scheduled launch time.

NASA has until Sunday, or possibly Monday, to launch Discovery to the International Space Station. Otherwise, it will have to wait until December because of unacceptable sun angles.

Gas leaks had already forced a two-day postponement.

"Discovery is not going out easy," launch director Mike Leinbach said. "She's giving us a little bit of trouble, but that's fine. She'll fly perfectly when she does."

The weather may keep Discovery grounded even longer. Forecasters said there is a 70 per cent chance Thursday afternoon that rain and perhaps even thunderstorms will stall what's officially NASA's next-to-last shuttle flight.

The electrical problem cropped up aboard Discovery early Tuesday. A backup controller for one of the shuttle's three main engines was sluggish in turning on. Voltage irregularities then were noted. Mission managers wanted more time to figure out what was wrong and put the countdown on hold.

Each of the main shuttle engines has both a primary and backup computerized controller that serve as electronic brains. They are critical parts that must work perfectly before going ahead with a launch.

Mike Moses, chairman of the prelaunch mission management team, said a bit of dust or other debris might have prevented the circuit breaker for the controller from making a solid contact. NASA engineers want to make certain that's the reason for the slight voltage irregularities, and that the problem will not worsen and consequently pose an increased risk to launch.

Moses and his team will reconvene Wednesday afternoon to determine whether it's safe to launch Discovery on Thursday or whether repairs might be needed. The latter case would likely push the launch into December.

"We like to say we don't fly with unknown risk and, right now, this risk is a little bit still unknown to us," Moses told reporters. "We're going to take another day to get to know it better."