The countdown had seemed routine and the rocket lifted off as scheduled at 6:22 p.m. EDT, but then burst into a fireball seconds later. The debris crashed down on the launching pad, spreading fiery wreckage around the area.
NASA said all personnel are accounted for and no one was injured.
This was the first catastrophic launch failure since NASA began its commercial spaceflight effort.
The rocket was constructed by Orbital Sciences Corp., which contracts with NASA to supply the ISS. A statement from Orbital said the company has formed an "anomaly investigation board" which will work with government agencies on a probe into the explosion.
"As we begin to gather information, our primary concern lies with the ongoing safety and security of those involved in our response and recovery operations," said Frank Culbertson, Orbital's Executive Vice President. "We will conduct a thorough investigation immediately to determine the cause of this failure and what steps can be taken to avoid a repeat of this incident."
NASA stated on its website that "a mishap occurred shortly after liftoff," and promised to provide more information as soon as possible. It said it was working with Orbital Sciences to gather data on the mission's failure.
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