Thor 304 had been erected on the pad a few weeks before launch, and during this step, a connecting pin in the erector broke and sent the rocket falling back down to ground level.

The booster passed routine preflight systems checks and liftoff took place at 6:22 PM PST on July 14, 1980.

Shortly after liftoff, the Thor's telemetry system failed, but weather conditions and visibility were excellent, and the booster could be tracked visually for over two minutes.

However, radar tracking showed that the third stage motor continued operating as it drove the DMSP into the Pacific Ocean.

The investigation board concluded that connectors in the electrical interface between the second and third stage had been jolted loose by the erector mishap several weeks earlier.