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RM-81 Agena: Wikis


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An Agena outfitted as a Gemini program Agena Target Vehicle.

The Agena (designated RM-81 by the USAF) was a rocket upper stage developed by Lockheed for the canceled WS-117L American reconnaissance satellite program. The Agena rocket itself lived on to experience extensive use as the upper stage/spacecraft for the CORONA reconnaissance satellite program and as an upper stage on the Thor, Atlas, and Titan I and II boosters. It was also used by the manned Gemini program to practice rendezvous and docking (see Agena target vehicle). 365 Agena rockets were launched between January 1959 and February 1987, when the last Agena D was launched.

The Agena not only served as a docking target for the Gemini spacecraft (first successful on the Gemini 8 mission), but the rocket was also fired on several Gemini missions in order to boost the combination to a higher orbit, and to bring it back again. In the Gemini 11 mission, an elliptical orbit with an apogee of 1375 kilometer (860 mile) altitude above the surface of the Earth. This set a manned space mission record altitude record that held until the Apollo 8 mission left Earth orbit and went to orbit the Moon, 238,000 miles away.

In many cases, such as in the MIDAS, CORONA, and Discoverer satellite systems, the working parts of the satellite - the cameras, sensors, telemetry system, etc., - were built into the Agena rocket frame, usually ahead of the Standard Agena bulkhead, and so the rocket and the satellite became one.



The Agena was 5.0 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 lbs. (71 kN) of thrust using unsymmetrical dimethyl hydrazine (UDMH) as the fuel, and inhibited red fuming nitric acid (IRFNA) as the oxidizer. This is a hypergolic fuel/oxidizer combination, and as such, it does not need an ignition system. This rocket engine could be restarted multiple times in orbit, by radio command, and it frequently was. The engine was notable for its unusual aluminum construction. 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. The Agena was thus known as the Hustler early in its development. The manned Project Apollo Lunar Module ascent stage engine was modeled closely on the Agena engine.


There were at least three versions of the Agena:

  • A : 69 kilonewton thrust Bell 8048 engine, 120 second burn time, used on the Thor and Atlas rockets as an upper stage.
  • B : 71 kilonewton thrust Bell 8081 engine, 240 second burn time, used on the Thor and Atlas rockets as an upper stage. These launched the SAMOS and MIDAS (Missile Defense Alarm System) military early-warning satellites and the Ranger and Lunar Orbiter lunar probes.
  • C : Proposed but never built.
  • D : 71 kilonewton thrust Bell 8096 engine, 265 second burn time, used on the Thor, Atlas, and Titan rockets. These launched the KH-7 GAMBIT spy satellites, three Mariner probes to Venus and the two Mariner space probes to Mars.

As a military reconnaissance spacecraft, some information on the project might remain classified, but during the Administration of President Bill Clinton during the 1990s, the existence of the CORONA and its results were declassified and revealed, as was the fact that the long Discoverer series of purported scientific satellites was just disinformation to cover up for the CORONA program. 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 [1].

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