The countdown reached all the way to practically zero for the SpaceX Falcon 9 rocket. The engine ignition sequence started, but there was an automatic shutdown by onboard computers.
So instead of blasting off from Cape Canaveral on a delivery mission, the rocket remained on its launch pad amid a plume of engine exhaust.
"This is not a failure. We aborted with purpose. It would have been a failure if we were to have lifted off with an engine trending in this direction," said Gwynne Shotwell, president of SpaceX.
Shotwell said that the high combustion chamber pressure in engine No. 5 was to blame and that technicians would conduct an inspection later in the day. If the engine needs to be replaced, a spare is available.
The next launch attempt will be Tuesday if the engine problem can be resolved in time.
This was the first launch attempt by the several private U.S. companies hoping to take over the job of delivering cargo and eventually astronauts to the space station for /*NASA*/. Only governments have accomplished that to date: the United States, Russia, Europe and Japan.
An estimated 1,000 SpaceX and NASA guests poured into the launching area in the wee hours of Saturday, hoping to see firsthand the start of this new commercial era. They left disappointed. The abort was especially disheartening given the perfect weather and the absence of any earlier countdown problems.
The Associated Press contributed to this report.
