RM-81 Agena
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The Agena (designated RM-81 by the USAF) was a rocket upper stage developed by Lockheed for the ill-fated WS-117L US reconnaissance satellite program. It lived on to see extensive use as the upper stage/spacecraft for the Corona spy satellite program and as an upper stage on the Thor, Atlas, and Titan boosters. It was also used by the manned Gemini program to practice rendezvous and docking (see Agena Target Vehicle).
It was 5 feet (1.5 m) in diameter, three axis stabilized (for the benefit of the reconnaissance system cameras) and its Bell 8096 engine produced 16,000 lbf (71 kN) thrust using hydrazine (UDMH) and nitrogen tetroxide as propellants. The engine could be restarted multiple times in orbit. The engine was particularly notable for its unusual aluminum construction[1]; the regeneratively cooled channels that cooled the throat and nozzle were formed from straight gun-drill formed channels. The engine started life as the power plant for the canceled rocket-propelled nuclear warhead pod for the Convair B-58 Hustler bomber. Agena was thus known as Hustler early in its development.
There were at least three versions of the Agena:
- A : 69 kN thrust Bell 8048 engine, 120 second burn time, used on Thor and Atlas.
- B : 71 kN thrust Bell 8081 engine, 240 second burn time, used on Thor and Atlas. Launched early SAMOS and MIDAS military satellites and the Ranger lunar probes.
- C : Proposed but never built.
- D : 71 kN thrust Bell 8096 engine, 265 second burn time, used on Thor, Atlas, and Titan. Launched early KH-7 GAMBIT spy satellites and the two Mariner Mars probes.
As a military reconnaissance spacecraft, much information on the project remains classified. The final Agena launch was of an Agena D on 12 February 1987, configured as the upper stage of a Titan 34B. In all, 365 Agena vehicles were launched by NASA and the Air Force [2].
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