Discovery's seven-member crew was being strapped in when they heard the news. Problems with two fuel sensors caused NASA to pull the plug less than three hours before America's first shuttle flight in two and a half years.
William Harwood says, "This is a critical system. They have four of these systems and they require all four to be operating at launch. Right now it looks like they've got problems with two of those."
Despite the fuel sensor problems, weather was also a wild card all day. As the countdown continued, the rain came down and storm clouds hung over the horizon. Prior to liftoff, a window cover blew off and damaged some shuttle tiles, and crews were late fueling because of minor launch pad heater problems.
NASA was able to fix those problems and characterized them as typical last minute glitches. The fuel sensor problem is not, and it's not clear how long it will take to fix
NASA has not announced a new launch date.