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The RM-81 Agena was an American rocket upper stage and satellite support bus which was developed by Lockheed initially for the canceled WS-117L reconnaissance satellite program. Following the split-up of WS-117L into SAMOS and Corona for image intelligence, and MIDAS for early warning, the Agena was later used as an upper stage, and an integrated component, for several programs, including Corona reconnaissance satellites and the Agena Target Vehicle used to demonstrate rendezvous and docking during Project Gemini. It was used as an upper stage on the Atlas, Thor, Thorad and Titan IIIB rockets, and considered for others including the Space Shuttle and Atlas V. A total of 365 Agena rockets were launched between February 28, 1959〔 and February 1987. On some missions, the payload was built directly into the Agena, which provided it with electric power, communications and three-axis stabilization. Payload components were usually located ahead of the Agena's standard bulkhead. On missions where the payload was not built into the Agena, and instead separated after launch, the Agena was known as an ''Ascent Agena''. The Agena was upgraded twice from the original Agena-A in order to support heavier and more sophisticated satellites, such as Corona spacecraft with multiple and more powerful cameras. The Agena name was suggested by the Department of Defense's Advanced Research Projects Agency for the star Beta Centauri, also known as Agena, because this upper stage would "ignite in the sky". This followed Lockheed's tradition of naming products for stellar phenomena. The final Agena launch was of an Agena-D on February 12, 1987, configured as the upper stage of a Titan 34B. In all, 365 Agena vehicles were launched by NASA and the US Air Force.〔http://www.designation-systems.net/dusrm/app1/rm-81.html〕 == Characteristics == 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 was derived from the XLR-81 propulsion unit for the canceled rocket-propelled nuclear warhead pod of the Convair B-58 Hustler bomber. Until 1959, the Agena was also known as the Discoverer Vehicle or Bell Hustler.〔(【引用サイトリンク】title=HISTORY - AGENA AS OF 31 DEC67, VOLUME I )〕 The manned Project Apollo Lunar Module Ascent Propulsion System was modeled closely on the Agena engine. Attitude control of the horizontal flying Agena was provided by an inertial reference package with three gyroscopes, two horizon sensors, and micro-jets using a nitrogen-freon mixture of cold gas. Pitch and roll were sensed by two hermetic integrating gyro units. A rate gyro unit determined yaw error by sensing orbital rate. Pitch and roll gyro errors were corrected from the horizon sensors, which were later supplemented by Sun and star trackers. This enabled the Agena to accommodate the higher pointing stability required for better ground resolution imaging with the improved Corona cameras.〔 As the Agena was designed to hold a fixed orientation in space while orbiting Earth, a passive thermal control system was devised.〔 The main source of the Agena's electrical power was silver peroxide-zinc batteries, which from the early 1960s on were supplemented by solar arrays. An S-band beacon enabled the Agena to receive ground command sequences (image motion compensation, altered attitude, etc.), which could be stored for later execution.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「RM-81 Agena」の詳細全文を読む スポンサード リンク
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