The craft was due to be tested at Mach 7, which would mark the first time a non-rocket engine has powered vehicles at hypersonic speeds.

But the trial must be run under ideal weather conditions to increase chances for success a flight official told AFP. A first trial back in 2001 saw the loss of the prototype.

"At this point, we have some squally weather conditions for Saturday," said Alan Brown, NASA Public Affairs Officer at Dryden Flight Research Center in California. The trial had been set for 2000 GMT Saturday.

"There's no rainfall predicted but we are expecting some very high level turbulence and we don't want to hazard this vehicule," said Brown. "We are talking turbulences above 110 knots. So we will probably scrub the launch for Saturday if we still have that high turbulence. However, Sunday is looking very good."

The X-43 will be hitched beneath the wing of a B-52 bomber. Once released by the B-52, a rocket will power the prototype to an altitude of 30,000 meters (98,400 feet). Then the craft will separate from the rocket and fly on its own at seven times the speed of sound, around 7,700 kilometers (4,780 miles) per hour.

The solo flight of the X-43 was scheduled to start at 2100 GMT and last about six minutes during which it will do a series of maneuvers before plunging into the ocean.

NASA will be filming the trial.

"You'll see the takeoff of the B-52 from Edwards Air Force Base and its climb out, and there will be a chase plane with a television camera on it," Brown said.

"When the launch actually occurs, we'll have a camera view from one of the chase planes that is flying alongside and slightly to the rear. And they will get the dropping, the X-43 and the booster rocket that will drop away from the B-52. We should get the ignition of the rocket and its acceleration forward and its pitching up. At that point, we are probably going to lose it, because it will outrun the chase planes, seriously," he explained.

"We are trying to arrange to utilize some other aircraft that are not NASA aircraft, that have some very specialized type of camera equipment, visual and infrared, to be able to track the vehicule as it is flying at very high altitude. We don't know if we'll be able to release that footage publicly. It's an army aircraft, it's not from a satellite."

The X-43 on paper has a top speed of 10,000 km/h but it will not be trying to reach that speed during the trial flight.

SPACE.WIRE