The primary payload, the Galileo spacecraft with its attached Inertial Upper Stage (IUS), was successfully deployed on its journey to Jupiter. STS-34 was only the second shuttle flight to deploy a planetary spacecraft, the first being STS-30, which deployed the Magellan spacecraft.

Besides the Galileo spacecraft, Atlantis' payload bay held two canisters containing the Shuttle Solar Backscatter Ultraviolet (SSBUV) experiment. SSBUV, which made its first flight on STS-34, was developed by NASA to check the calibration of the ozone sounders on free-flying satellites, and to verify the accuracy of atmospheric ozone and solar irradiance data. The experiment operated successfully.

STS-34 carried a further five mid-deck experiments, all of which were deemed successful, including the Polymer Morphology (PM) experiment, sponsored by the 3M Company under a joint endeavor agreement with NASA. The PM experiment was designed to observe the melting and resolidifying of different types of polymers while in orbit. The Mesoscale Lightning Experiment, which had been flown on previous shuttle missions, observed the visual characteristics of large-scale lightning in the upper atmosphere.