Space shuttle Discovery atop pad 39A for the STS-92 mission. Photo: NASA-KSC

With Discovery scheduled for liftoff Thursday night on the 100th shuttle flight, NASA managers are assessing the progress of Hurricane Keith and its possible impact on operations at both the Kennedy Space Center in Florida and the Johnson Space Center south of Houston.

Discovery's countdown to launch on a complex space station assembly mission is scheduled to begin at 12 a.m. Tuesday, leading to a liftoff at 9:38 p.m. Thursday.

Meteorologists with the 45th Space Wing at the Cape Canaveral Air Force Station predict a 60 percent chance of acceptable weather Thursday night and Friday.

But Hurricane Keith is a wildcard.

NASA managers are concerned the storm, now loitering over Belize in Central America, could strengthen as it moves back out over open water and ultimately threaten the Texas coast, including the Johnson Space Center south of Houston.

The projected path of Keith as of 1500 GMT Monday. Photo: NOAA

NASA now operates two manned spaceflight control centers at Johnson, one for the shuttle and another for the international space station. In addition, the controls rooms are linked via phone lines and satellites to Russia's primary mission control center near Moscow.

All three control centers work together during space station assembly missions and NASA has no backup control site that could handle the load if a hurricane shut down the Johnson Space Center during a mission.

As a result, shuttle program manager Ronald Dittemore could be forced to delay Discovery's launching if Keith ends up threatening the Texas coast.

No such decision has been made and Discovery's countdown remains on track to begin on schedule at midnight.

But agency officials say shuttle managers could elect to re-order or delay some countdown tasks and to utilize built-in holds to allow more time to determine Keith's path and whether it might pose any threat to the Johnson Space Center.

As for Hurricane Keith's impact on the Kennedy Space Center, NASA said in a weather advisory today "it currently appears that Keith will re-emerge over the Gulf of Mexico and move toward the central Gulf Coast."

"The heaviest rainfall and cloudiness will be north of the Cape Canaveral vicinity by Thursday evening," the advisory said. "A significant cold front will move into central Florida by late Friday evening. The primary concerns for launch day on Thursday will be showers and cloudiness associated with Hurricane Keith.

"The primary concern on Friday will be weather associated with the cold front," the advisory continued. "If the front moves through the local area by Saturday the primary concern will be strong post-frontal wind on Saturday evening. Heavy seas may be a concern in the solid rocket booster recovery area if delays bring the launch into the weekend."