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. During an inspection later in the day, engineers discovered a faulty valve and worked into the evening to replace it.
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.