OV4-1T included a small rocket motor to maximize orbital separation (180°) from OV4-1R. Both satellites were cylindrical, in diameter, with domed upper ends. Total length was . Silver oxide/zinc batteries provided for a 50-day lifespan. Two sets of OV4 "whispering gallery" satellites were built. OV4-2T and OV4-2R were never flown. Operations OV4-1T and OV4-1R were scheduled for launch on the MOL Heat Shield Qualification flight, with a Titan IIIC rocket. The dummy MOL (a Titan first-stage oxidizer tank) was equipped with a variety of experiments and dubbed OV4-3. OV1-6 was also mounted on the Titan III. The rocket took off from Cape Canaveral Launch Complex 40 on 3 November 1966 at 13:50:42 UTC. OV4 Missions OV5 Background The OV5 program was a continuation of the Environmental Research Satellite (ERS) series developed by Space Technology Laboratories, a subdivision of TRW Inc. These were very small satellites launched pick-a-back with primary payloads since 1962—a natural fit under the Orbiting Vehicle umbrella. The primary innovation over the earlier ERS series was a command receiver, allowing instructions to be sent from the ground, and a Pulse-code modulation digital telemetry system, versus the analog transmitters used on prior ERS missions. Like prior ERS, the OV5s were spin-stabilized and heat was passively controlled. All of the OV5 series were built by TRW with the exception of OV5-6, built by AFCRL, and OV5-9, built by Northrop Corporation. OV5 Missions Program conclusion The OV program was phased out in the late 1960s, the last of the series (an OV1) flying in 1971. The program orbited 184 experiments at extremely low launch costs and with very short proposal-to-orbit times. OV was succeeded by the Space Test Program, managed by the Space Missile Organization's Space Experiments Support Program, which had absorbed the ARSP in 1968. The Space Test Program followed the new trend in satellites, which preferred custom-built one-offs with specific payloads to vehicles built on standardized plans. References Satellites orbiting Earth Military space program of the United States Satellite series