A new private supply ship for the International Space Station remained stuck on the ground Saturday after rocket engine trouble led to a last-second abort of the historic flight.

All nine engines for the SpaceX Falcon 9 rocket roared to life Saturday morning. But with a mere half-second remaining before liftoff, the onboard computers automatically shut everything down. So instead of blasting off on a delivery mission to the space station, the rocket stayed on its launch pad amid a plume of engine exhaust.

Even NASA's most seasoned launch commentator was taken off-guard.

"Three, two, one, zero and liftoff," announced commentator George Diller, his voice trailing as the rocket failed to budge. "We've had a cutoff. Liftoff did not occur."

SpaceX president Gwynne Shotwell said that 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.

Tuesday is the earliest that SpaceX can try again to send its cargo-laden Dragon capsule to the space station. The California-based company — formally known as Space Exploration Technologies Corp. — is targeting every few days for a launch attempt to save fuel in case of rendezvous problems at the space station. Wednesday also could be a launch option.

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.

NASA is looking to the private sector, in this post-shuttle era, to get American astronauts launching again from U.S. soil. SpaceX officials said that could happen in as little as three years, possibly four. Several other companies are in the running.

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.

'This is not a failure'

Shotwell was asked by a reporter whether she considered Saturday's abort a failure.

"This is not a failure," she said. "We aborted with purpose. It would be a failure if we were to have lifted off with an engine trending in this direction."

She added: "The software did what it was supposed to do" with the engine shutdown.

Everyone around town, at least, is rooting for a successful flight.

"Go SpaceX," read the sign outside Cape Canaveral City Hall. Until NASA's space shuttles retired last summer, the sign had urged on the launches of Discovery, Endeavour and, finally, Atlantis. Those ships are now relegated to museums.

Late last month, SpaceX conducted a test firing of the nine first-stage rocket engines at the pad. Each engine — including No. 5 — was "rock solid," Shotwell said.

The first flight of the Falcon 9 rocket from Cape Canaveral, in June 2010, encountered similar last-second engine trouble, but there was enough time to fix the problem and fly the same day. SpaceX has just a single second each day to launch this time around because of the space station rendezvous.

Six months after the initial Falcon 9 flight, SpaceX launched another rocket with a Dragon capsule that reached orbit. It was the first time a private company put a spacecraft into orbit and then recovered it. The newest Dragon also is meant to splash down into the Pacific, returning space station experiments and equipment.

For Saturday's launch attempt, SpaceX's billionaire founder, Elon Musk, was in the SpaceX Mission Control in Hawthorne, Calif. He helped create PayPal and founded SpaceX 10 years ago. He also runs Tesla Motors, his electric car company.