Hydrogen gas began leaking Friday morning, midway through the fueling process. NASA says it's the same type of problem that delayed two shuttle missions last year. It's considered a serious problem because of the flammability of hydrogen gas.
NASA says the next launch attempt will be no earlier than Sunday. It's possible, though, the flight may be off until December.
If Discovery isn't flying by Sunday, its trip to the International Space Station will have to wait until the beginning of next month because of unacceptable solar angles.
It's the final mission for Discovery as NASA closes down the shuttle program.
NASA: " target="_blank"> http://www.nasa.gov/mission_pages/shuttle/main/index.html