The OV1 (Orbiting Vehicle 1) were small research satellite to be launched piggy back on Atlas ICBM test flights. They consisted in general of the OV1 satellite and the OV1-PM propulsion module (or upper stage) to reach orbit.
The SM-65D Atlas, or Atlas D, was the first operational version of the U.S. Atlas missile. Atlas D was first used as an intercontinental ballistic missile (ICBM) to deliver a nuclear weapon payload on a suborbital trajectory. It was later developed as a launch vehicle to carry a payload to low Earth orbit on its own, and later to geosynchronous orbit, to the Moon, Venus, or Mars with the Agena or Centaur upper stage.
