Engineers at the Kennedy Space Center are preparing the shuttle Atlantis for fueling and launch Thursday on a long-awaited mission to deliver Europe's Columbus research lab to the international space station.

With forecasters continuing to predict a 90 percent chance of good weather, NASA Test Director Jeff Spaulding told reporters today there are no technical problems at pad 39A that would delay the start of fueling at 7:06 a.m. Thursday. Launch is targeted for around 4:31:44 p.m. v"After lots of hard work and preparation, I'm pleased to report Atlantis and her crew are finally ready to fly with the Columbus module," Spaulding said. "The countdown is going very smoothly, really no issues to report."

Engineers loaded the shuttle's fuel cell system with hydrogen and oxygen late Tuesday, permitting up to three launch attempts in a row, if necessary, while still preserving the option to extend the mission two days to add a fourth spacewalk. The additional spacewalk is wanted for a detailed inspection of a contaminated solar array rotary joint in the space station's main power truss.

But the launch window closes Dec. 13. If Atlantis isn't off the ground by Friday or Saturday, the team will stand down to reload the shuttle's fuel cell system before a final attempt or two at the end of the window.

Spaulding said the fuel cell loading operation went well, but engineers are troubleshooting a small leak in a ground vent system. The issue will have no impact on launch, but if Atlantis is delayed long enough to require a fuel cell "top off" with fresh hydrogen or oxygen, the leak might require repairs.

Earlier, the ground team repaired three small areas of damage to the external tank's protective foam insulation.

The only other problems involve post-Columbia improvements to monitor foam loss from the external tank and to measure possible debris impacts on the ship's critical wing leading edge panels.

Two issues are affecting external tank documentation. The tank will separate from Atlantis in orbital darkness but even if good lighting was available, a software problem would hinder the crew's ability to downlink whatever pictures might be snapped by a camera mounted in the shuttle's belly. The pictures will be stored on board, however, for post-flight analysis.

A troublesome firmware upgrade to the ship's wing leading edge impact sensor system apparently will prevent any data collection during the climb to space and throughout the mission.

LeRoy Cain, director of shuttle integration at the Kennedy Space Center, said Tuesday it was safe to proceed with launch because the external tank umbilical camera photography and the wing leading edge sensor system are used primarily as backup methods for detecting critical damage to the shuttle's heat shield and foam loss from the external tank.

As always, he said, the crew will carry out detailed heat shield inspections using laser scanners and high-resolution cameras the day after launch and again, after the shuttle undocks from the space station. In addition, the station crew will photograph the shuttle's underbelly during final approach to look for signs of damage, a now-standard part of every post-Columbia mission.

Atlantis commander Steve Frick and his crewmates were briefed on the progress of the countdown early today.

"At this point, I'm pleased to report that all of our launch systems and the launch teams are ready and more importantly, Atlantis and her crew are ready to open a gateway for this newest voyage of Columbus," Spaulding said.

Forecasters, meanwhile, are predicting near ideal weather for Thursday's launch attempt, calling for only a 10 percent chance of low clouds in the area. The odds are 80 percent "go" Friday and 60 percent favorable on Saturday.

"The vehicle's looking good and the weather's looking good, too, both here at Kennedy Space Center and at the TAL (trans-Atlantic landing) sites," said weather officer Kathy WInters.

"We'll have a cold front that's going to be moving through tomorrow morning but it's going to be dry and so we're not expecting any weather with it. So the only thing we have just a slight concern for is if we get any cold air, strato-cumulus clouds that come in from off the water, that would be a low-cloud/ceiling issue. But really, overall we have just a 10 percent chance of KSC weather prohibiting launch."

At least one of NASA's three emergency runways in Spain and France should be acceptable all three days, but the weather at emergency runways in New Mexico and California could be a problem Friday and Saturday, with a chance of showers at both sites.