Agena D

Nitric acid/UDMH propellant restartable rocket stage. 205 launches, 1963 to 1987. Often integrated with the functional payload. Launched by Atlas Agena D; Thor Agena D; Titan 3B; Titan 34B.

One of the real workhorses of U. S. space exploration, the Agena upper stage which was also employed as a spacecraft, the whole vehicle going into orbit. Agena played a key role in manned space flight; it was the target vehicle for rendezvous and docking maneuvers in NASA's Gemini project. Agena had a main rocket engine capable of multiple re-starts in space; in the modified target vehicle version it also had two secondary engines to provide small changes in velocity and position in orbit. In the Gemini Agena, a control system could handle 96 commands from the astronauts or from ground stations. Agena was used as an upper stage with the Thor, augmented Thor, Atlas and Titan boosters; it played important roles in such military and NASA programs as Corona, Keyhole, Discoverer, Samos, Mariner, OGO, Lunar Orbiter, Ranger and Orbiting Astronomical Observatory.

The Agena D was essentially a standardized version of the Agena B. The restartable Agena D could accept a range of payloads and be fitted to Atlas, Thor, or Titan boosters without modification. Its outstanding dry weight fraction, resulting in it being selected for use in preference to the heavier Transtage for many Titan missions.

Cost $ : 8.700 million.