NASA engineers readied the space shuttle Discovery for a second launch attempt, scheduled for Tuesday, keeping one eye on Florida's capricious summer weather and another on fuel sensors whose mysterious malfunction scrubbed the first try nearly two weeks ago.
Shuttle weather officer Kathy Winters said Monday that Tropical Storm Franklin appeared to pose no threat to Kennedy Space Center, but she warned that thunderheads drifting in from the Gulf Stream had a 40 percent chance of forcing a postponement of the launch, scheduled for 10:39 a.m. Eastern time.
"They form 20 to 30 miles offshore," Winters said at a news conference. "But the upper-level winds are 30 to 35 miles per hour from the east-northeast," blowing toward the coast of central Florida.
Launch rules require clear skies for a 20-mile radius around the space center's runways to facilitate an emergency landing if the shuttle has to abort the launch after liftoff. If weather causes a scrub, engineers will try again Wednesday, and if necessary they could try at least twice more before the end of the month.
Discovery, pointed skyward at the space center's Launch Pad 39B, will be the first shuttle to lift off since Columbia, which disintegrated during reentry 21/2 years ago. NASA regards Tuesday's flight as a test of the safety improvements made since the disaster.
Mission Commander Eileen Collins and six other astronauts were in quarantine at the space center, waiting to go aboard Discovery early Tuesday. The shuttle will make a 13-day trip to the international space station, returning to the space center, or one of several alternate landing sites in the United States or Europe, on Aug. 7.
The agency suffered a frustrating blow July 13, when the sensor malfunction caused engineers to scrub Discovery's initial launch attempt less than three hours from liftoff, disappointing scores of visiting dignitaries, including more than 60 members of Congress.
Considerably fewer journalists were on hand Monday than the 1,200 who showed up July 13, and Tuesday's launch promised to be a more subdued affair, although first lady Laura Bush was scheduled to attend.
The sensor, in the bottom of the shuttle's external fuel tank, is one of four designed to trigger an emergency main engine shutoff if the tank prematurely runs out of liquid hydrogen fuel during launch.
After the July 13 scrub, NASA assembled 12 teams of troubleshooters who spent 10 days trying to figure out why the sensor failed to respond to a routine pre-launch test and remained locked in the "wet" position.
While their analysis failed to pinpoint the problem, the launch team has adopted a strategy that assumes that only one of the four hydrogen sensor systems -- the sensor itself, its circuitry and its control box hookup -- is susceptible to malfunction.
If the suspect system malfunctions in the way that engineers have predicted, the launch team is prepared to make an exception to its self-imposed rule requiring that all four sensors be functioning and launch, instead, with three. If any other malfunction is detected, the team will scrub.
"Personally, I think we have done an extensive degree of troubleshooting and analysis to understand what we've got. I believe that we're ready," said NASA test director Pete Nickolenko. "We fully expect that it should work as designed."