AS-104 was the fourth orbital test of a boilerplate Apollo spacecraft, and the second flight of the Pegasus micrometeoroid detection satellite.

The primary mission objective was to demonstrate the launch vehicle's iterative guidance mode and to evaluate system accuracy.

The Saturn launch vehicle SA-8 and payload were similar to those of mission AS-103, except that a single reaction control engine assembly was mounted on the boilerplate service module (BP-26).

The total mass placed in orbit, including the spacecraft, Pegasus B, adapter, instrument unit, and S-IV stage, was 34,113 pounds (15,473 kg).

The 1397 kilogram (3080-pound) Pegasus 2 satellite was also carried to orbit by SA-8, being stowed inside the boilerplate's service module, and remaining attached to the S-IV stage.