The planned launch of the privately-built SpaceX Falcon 9 from Cape Canaveral was shut down by computers in the last half-second Saturday due to engine trouble. The rocket was bound for the International Space Station. Gwynne Shotwell, president of SpaceX, told reporters that chamber pressure in one of the engines might mean it has to be replaced before a successful launch but that a replacement engine is available. Another launch attempt may be made as early as Tuesday. NASA has been working with SpaceX, as well as other private companies, to develop alternative plans for space exploration after the discontinuation of the shuttle program.