Atlas (familia) Atlas-Agena

Agena began as an Air Force upper stage and found its natural partner in the Atlas. Its propellants ignited on contact, so no ignition system was needed, and from the second generation onwards it could be restarted in flight. Stacked on a stage-and-a-half Atlas, the combination made a two-and-a-half stage vehicle able to reach high orbits, lunar trajectories and escape velocity.

The early models came and went quickly. Agena A could not restart and flew only a handful of Atlas missions; Agena B arrived late in 1960 with longer tanks and restart capability, but proved unreliable, missing its objective on seven of twenty-eight flights.

After the Ranger 5 booster anomaly, NASA convened a review board that looked at the whole vehicle and reached an awkward conclusion: dozens of configurations existed because every military and civil programme demanded its own modifications, and that variety made real quality control impossible. The board asked for one standard launcher. The result was the Agena D, identical on every flight as far as the Atlas was concerned, which ran off fifteen consecutive successes.

The booster was standardised too. Adapted Atlas D missiles gave way to the SLV-3 and its stretched-tank derivatives, and the very last Atlas-Agena, in 1978, flew on a refurbished Atlas F.

Agena carried the Ranger probes that returned the first close-up pictures of the lunar surface, the Lunar Orbiters that mapped it, and Mariner 2, the first spacecraft to fly past another planet. Every Gemini target vehicle used for rendezvous and docking practice also rode an Atlas.

That public record sits alongside one that is still only partly known: the Air Force, the NRO and the CIA used Atlas-Agena to orbit signals intelligence satellites, and a large share of its one hundred and nine flights carried classified payloads.