Continually worsening weather forecasts and two late-breaking technical worries created uncertainty Wednesday about the planned night launch of the space shuttle Discovery.
NASA meteorologists downgraded the chance for good weather at the scheduled 9:35 p.m. EST Thursday launch time to only 40 percent with low, lingering clouds more likely than not to prevent liftoff.
"The forecast has trended toward the worse," NASA shuttle weather officer Kathy Winters said Wednesday morning.
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Along with concern about the weather, engineers planned to spend much of Wednesday trying to decide whether the two technical problems — a brief power surge and concerns about a glue that helps protect seals in the solid-fuel rocket boosters — were minor or major.
It was too early to tell if these would postpone Discovery's launch, launch integration manager LeRoy Cain said at a Tuesday evening news conference.
Shuttle Test Director Jeff Spaulding said in a Wednesday morning news conference that he expected the power surge issue to be cleared as not a problem later in the day.
The split-second power surge occurred early Tuesday when power was about to be switched from the shuttle's launch platform to Discovery itself.
Early tests found that the shuttle's main engines, boosters and external fuel tank were OK after the power burst, but NASA was not saying the same about Discovery, Cain said.
Concern about booster-seal glue involved adhesive that helps connect segments of the solid rocket boosters.
Routine tests found that the adhesive used on some of the joints in the booster segments might not be as strong as it should be, but the problem seemed to be minor, NASA spokeswoman June Malone said.
The adhesive is primarily designed as a thermal barrier to protect the seal but is one of many systems that keep hot gas from escaping and is not one of the main ones, she said.
"The adhesive does not produce the seals," Malone said.
The seal is produced mostly by the pressure of the segments themselves, she said.
As NASA wrestled with the technical issues, the weather outlook continued to get gloomier.
Each time meteorologists updated their weather forecasts this week, the chance for clear enough weather for a launch dropped, going from 80 percent to 70 percent to 60 percent and, on Wednesday, 40 percent.
Winters said the main concern was low-hanging clouds associated with a slowly moving weather front.
If the clouds block Thursday's attempt, the weather will get only worse on Friday and Saturday. Because of projected high wind, forecasters gave NASA only a 30 percent chance on Friday and a 40 percent chance for Saturday. The weather gets more promising after that with Tuesday being the best day, Winters said.
NASA has four launch opportunities over five days, if need be, to start the 12-day mission.
Aside from those potential problems and the concern about worsening weather, NASA was marching toward its first nighttime launch in four years.
"We're on track and on target for Thursday," Cain said.