CAPE CANAVERAL -- NASA began moving the scaffolding that protects the space shuttle for bad weather early Thursday, despite lingering clouds and other weather woes that cast doubt on whether Discovery will blast off this week.

Discovery was scheduled to blast off Thursday evening and streak by a nearly full moon, taking seven astronauts on a mission to rewire the International Space Station.

As NASA resolved technical concerns Wednesday, two lurking weather problems gave NASA less than an even chance of launching Thursday. The official likelihood of good weather Thursday is only 40 percent and that drops to 30 percent Friday and nudges back up to 40 percent Saturday.

The biggest problem is a bank of low clouds that are sticking around because of a cold front coming through. NASA rules prohibit launching in low clouds because engineers need clear skies to observe the shuttle during ascent and in case of emergency, the shuttle commander needs to be able to see clearly enough to guide Discovery on a difficult back-flip maneuver to land back at Kennedy Space Center.

On top of that, all three overseas emergency landing sites in Spain and France are forecast to have bad weather and NASA won't launch unless one emergency landing site has clear weather.

If Discovery doesn't launch Thursday, Friday looks even worse because the forecast calls for winds that far exceed NASA's rules about safety for launch and emergency landings. On Saturday the winds still look too strong, but not quite as bad. The next best weather for launch really doesn't come until next Tuesday, shuttle weather officer Kathy Winters said.

NASA usually sloshes through weather problems for daytime summer launch tries and has easier times later in the year. Weather officer Tech. Sgt. Matt Timmerman said when he was assigned to Discovery's December night launch he figured the skies would be more cooperative.

"This is just a timing factor," Timmerman said. "It's more unfortunate than unusual."

NASA has through Dec. 17 to launch the shuttle on its mission so Discovery won't be in orbit when the new year starts because NASA worries about a computer change-of-date problem. But if Discovery is still grounded by Dec. 18, NASA may decide to keep trying anyway through the day after Christmas.

NASA wrestled with two technical concerns before resolving them Wednesday.

The first concern was a split-second power surge that occurred early Tuesday when power was about to be switched from the shuttle's launch platform to Discovery itself. Tests found no problems with the shuttle, main engines, boosters and external fuel tank.

The second involved a booster-seal glue that helps connect segments of the solid rocket boosters. A recent test by the manufacturer raised questions about whether the glue was as strong as it should be. After evaluating data, NASA managers concluded that the adhesive passed all the acceptable criteria and was good to fly.

Along with spacewalking astronauts rewiring the space station, Discovery will deliver a 2-ton addition and replace one of the space station's three crew members.

This is the first planned night launch in four years. NASA required daylight liftoffs for the three flights after the 2003 Columbia accident to make sure the agency could get good photos of the external fuel tank. Foam breaking off the tank at liftoff caused the damage that killed Columbia's seven astronauts.

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