"Right now we think we have eliminated all possible causes" related to the glitch, shuttle program director Bill Parson said in a televised press conference from Kennedy Space Center, near Cape Canaveral, Florida.

One of the four fuel sensors in the Discovery's huge exterior fuel tank was faulty during launch preparations, leading the National Aeronautics and Space Administration to abort the launch just hours from deadline.

"We have done everything we possibly could on the vehicule," Parsons said after announcing that a tentative launch date had been set for the Discovery at 10:39 am (1439 GMT), Tuesday, weather permitting.

The planned July 26 launch would be the first US shuttle launch since Columbia tore apart in February 2003, killing all seven astronauts aboard.

Parson acknowledged that the agency had not determined its exact cause of the glitch, but that it was confident all would go well.

"We have a great amount of work to do to get us through this but we all agree that this work is doable to take us to a launch on the 26th (of July)," Parson said.

"We believe the best way to go through this is to do a countdown" and fuel up the shuttle for launch, he said.

"If the sensors work like we think they will, then we'll launch on that day. If anything goes not according to the plan we have in front of us then we will have a scrub," Parsons added.

NASA engineers will attempt to repair an electrical problem in the shuttle they believe contributed to the fuel sensor's intermittent fault.

"Then workers will swap circuits for two of the sensors to provide a means to isolate the problem to the wiring or the point sensor box, should the problem recur during the countdown," the space agency said in a statement.

Parsons said NASA could still go ahead with the launch even if the problem recurs during countdown.

"If it was a known failure, we might very well be willing to fly with three of the four sensors," he said, explaining that two sensors are needed to cut power to the three shuttle engines during liftoff if hydrogen level is too low.

The other two sensors, Parsons said, merely serve as backup.

Should the engines shut off during liftoff, the Discovery would glide to an emergency landing at several sites around the world.

NASA said the launch window of opportunity for the Discovery to properly rendezvous with the orbiting International Space Station, extends to July 31.

If the shuttle fails to lift-off in July, NASA will have to wait for the next launch window, September 9 to 24.

The delay has been a major disappointment for the agency, which is seeking to recover its prestige after Columbia broke up as it re-entered Earth's atmosphere on February 1, 2003.

Following an independent probe, the agency was forced to rethink the shuttle program and has made changes to the shuttles to reduce the risk of a new accident.

The new delays were compounded by NASA's desire to launch during daylight hours. That reduces the window during which Discovery can lift off for its ISS rendezvous.

Hundreds of engineers were mobilized to study as many as 200 potential causes for the malfunctioning fuel gauge system, and how to fix it.

The faulty sensor was one of four that sends data on the levels of hydrogen in the spacecraft's massive external fuel tank, to determine when the three engines should be shut off during the ascent into orbit.

NASA had a similar problem in April but never found the cause. The problem disappeared after technicians replaced cables and electronic boxes attached to the gauges.

During their 12-day mission, seven astronauts aboard Discovery will test changes made since Columbia tragedy, which caused NASA to ground its space shuttle fleet.

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