Agena in orbit - Credit: NASA. 30,272 bytes. 435 x 280 pixels.

One of the real workhorses of U. S. space exploration, Agena was an 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 manoeuvres 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 2 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 had played important roles in such military and NASA programs as Discoverer, Samos, Mariner, OGO, Lunar Orbiter, Ranger and Orbiting Astronomical Observatory.