By Brendan McGarry - 2012-05-20T04:00:07Z

Roger Gilbertson/SpaceX via Bloomberg

The SpaceX Falcon 9 rocket stands in Cape Canaveral, Florida.

The SpaceX Falcon 9 rocket stands in Cape Canaveral, Florida. Photographer: Roger Gilbertson/SpaceX via Bloomberg

A U.S. mission to send the first unmanned commercial spacecraft to the International Space Station was aborted with a half second left in the countdown.

Space Exploration Technologies Corp.s Falcon 9 rocket, carrying the companys Dragon capsule, attempted to lift off at 4:55 a.m. yesterday from Cape Canaveral, Florida. A computer detected an engine pressure problem, grounding the rocket and delaying the flight for a new attempt May 22.

The closely held company, known as SpaceX and led by billionaire Elon Musk, was trying to make history by docking its vehicle with the station. The U.S. government retired its own shuttle fleet last year and relies on other countries for rides to space. The U.S. wants the private sector to take over the job of ferrying supplies to and from the lab.

This is not a failure, Gwynne Shotwell, president of Hawthorne, California-based SpaceX, said during a National Aeronautics and Space Administration press conference after the scrubbed attempt. We aborted with purpose. It would be a failure if we were to have lifted off with an engine trending in this direction.

The engines ignited and rumbled momentarily before going silent. An on-board computer aborted the launch a half-second before liftoff after detecting high pressure in engine five, possibly caused by a fuel valve malfunction, Shotwell said. An inspection later yesterday found a faulty valve on the engine, and it was to be replaced last night.

The software did what it was supposed to do -- aborted engine five, and it went through the remaining engine shutdown, she said. The Falcon 9 rocket needs all nine engines for liftoff and at least seven to achieve orbit.

More here:

SpaceX’s Commercial Launch to Space Station Aborted at Liftoff