Liftoff is scheduled for Saturday at 3:43 p.m. EST, the National Aeronautics and Space Administration said at a news conference.

NASA scrubbed the scheduled 4:31 p.m. EST liftoff shortly after fueling operations started Thursday morning.

Two fuel tank sensors at the bottom of the liquid hydrogen portion of Atlantis' 15-story external tank appeared to be malfunctioning 16 minutes after fueling operations started, indicating an open circuit, NASA officials said. NASA flight rules allow one sensor to fail without affecting a planned launch, but not two or more, Space.com reported.

Known as engine cut-off sensors, NASA said the instruments measure the amount of liquid hydrogen remaining in the shuttle's fuel tanks to ensure all engines shut down before the fuel supply is exhausted.