CAPE CANAVERAL, Fla. — The launching of a privately owned cargo rocket heading to the International Space Station was aborted at the last second on Saturday morning.

The rocket’s nine engines had ignited, but computers detected a high pressure in the chamber of the center engine and shut them down The rocket is held down during the final engine checks and never left the launching pad.

The rocket and its cargo capsule, both built by the Space Exploration Technologies Corporation of Hawthorne, Calif., represent an important step in NASA’s evolution to rely more heavily on commercial companies for its human spaceflight program.

If the capsule, the Dragon, reaches the space station, it will be first commercial spacecraft to dock there. All previous vehicles, like NASA’s space shuttles and Russia’s Soyuz capsules, were government operated.