The first test on a fuel sensor system on Discovery's external tank has been successfully carried out early Thursday.
Discovery and a crew of seven were set to blast off for the international space station at 10:39 a.m. EDT (1439GMT). The threat of storm clouds put the odds of good launch weather at 60 percent.
NASA had the paperwork ready to go in case the equipment trouble reappeared and the space agency's managers decided to press ahead with the launch with just three of the four sensors working, a deviation from a rule instituted after the 1986 Challenger explosion.
"All the sensors are performing as expected," NASA commentator Jessica Rye was quoted as saying be the AP.
Stephanie S. Stilson, NASA's vehicle manager for the Discovery, said in an interview on Monday that the four-sensor requirement was outdated and would probably be changed for the next shuttle mission. NASA has rewired the sensor network so that failure of more than one at a time is less likely, Ms. Stilson said, according to New York Times.
Discovery has only until the beginning of August to fly to the space station on a 12-day supply and repair mission; the next launch opportunity will not come until Sept. 9.
While in orbit, Discovery's crew will inspect the most vulnerable areas of the spacecraft, using a new 15-meter (50-foot), laser-tipped boom. They also will practice repairing samples of deliberately damaged thermal tile and panels, the AP informs.