Agena Configuration

The Agena was a series of upper stages used with Thor, Atlas, and even Titan boosters (although I am unaware of any current museum display consisting of a Titan with an Agena).

The Agena came in three variants, the Agena A, Agena B, and Agena D (the Agena C, a proposed up-rating of the Agena B, was never built). The A and B variants were used to launch a number of "Discoverer" satellites, which were a cover story for the Corona reconnaissance satellite program, although Atlas/Agena B boosters also launched several Ranger probes to the moon and launched Mariner 2 to Venus.

An improvement in the Agena B was that its engine, which used unsymmetrical dimethyl hydrazine (UDMH) as the fuel and inhibited red fuming nitric acid (IRFNA) as the oxidizer, could be restarted in orbit.

In addition to being used as a satellite launcher, the Agena D was used in NASA's Gemini program as a docking target. Gemini 8 became the first spacecraft to dock with another spacecraft.

Agena A internal configuration schematic inboard profile

Agena A configuration
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Taken from p. 14/15 (p. 17/18 in the PDF) of the Agena
Extraction, reconstruction, and clean-up by

Agena B internal configuration schematic outboard profile

Agena B schematic
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Taken from p. 237 (p. 248 in the PDF) of the Technology and the Air Force: A Retrospective Assessment
Extraction and clean-up by