The launch of the space shuttle Discovery was pushed back to at least Sunday as engineers continue to troubleshoot a faulty sensor in the spacecraft's eternal fuel tank, a U.S. space agency official was quoted by Reuters as saying. Wayne Hale, the deputy director of the space shuttle programme, said that in order for a launch to take place on Sunday, NASA would have to be "extremely lucky". Discovery was slated to launch Wednesday afternoon from Cape Canaveral, Florida, but the faulty switch forced NASA to scrub the mission just two-and one-half hours before the scheduled liftoff. Discovery's launch would be the first since Columbia burned up while re-entering the earth's atmosphere in February 2003, killing all seven astronauts aboard. Hale had initially hoped to get the shuttle off the ground Saturday, but engineers are still trying to figure out why the sensor does not read that the tank is "dry" when told during tests to do so. NASA drained the tank, which is the orange structure connected to the belly of the shuttle, but after three hours the gauge - one of four - at the bottom of the tank was still showing "wet". --More 2329 Local Time 2029 GMT