These launched the SAMOS-E, SAMOS-F (ELINT Ferret), and MIDAS (Missile Defense Alarm System) military early-warning satellites, Ranger lunar probes, Mariner planetary probes, OGO, and Nimbus satellites. The stage carried enough propellant for the engine to burn for a total of four minutes. It was equipped with a Bell 8081 engine, which could generate 71 kilonewtons of thrust, and be restarted in orbit. Versions īell 8096 ( Bell 8247 on Agena Target Vehicle )ĭuring 1960, Lockheed introduced the improved Agena B, which could be restarted in orbit and had longer propellant tanks for increased burn time.

An S-band transponder enabled the Agena to receive ground command sequences (image motion compensation, altered attitude, etc.), which could be stored for later execution. 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. Īs the Agena was designed to hold a fixed orientation in space while orbiting Earth, a passive thermal control system was devised. This enabled the Agena to accommodate the higher pointing stability required for better ground resolution imaging with the improved Corona cameras. Pitch and roll gyro errors were corrected from the horizon sensors, which were later supplemented by Sun and star trackers. A rate gyro unit determined yaw error by sensing orbital rate. Pitch and roll were sensed by two hermetic integrating gyro units. Īttitude 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. Until 1959, the Agena was also known as the Discoverer Vehicle or Bell Hustler. 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. The parabolic shape of the chamber throat made for a difficult gun-drilling problem, which Bell Aerosystems engineers solved by arranging the cooling channels in a 'One-Sheeted Circular Hyperboloid' shape, allowing machinists to gun-drill straight cooling channels through the curved surfaces of the combustion chamber. The regeneratively-cooled channels that cooled the throat and nozzle were formed from straight gun drill formed channels. The engine was notable for its unusual aluminum construction.

This rocket engine could be restarted multiple times in orbit, by radio command, and it frequently was. This is a hypergolic fuel/oxidizer combination, and as such, it does not need an ignition system. 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 Aircraft XLR81 engine produced 16,000 lbs (71 kN) of thrust using unsymmetrical dimethylhydrazine (UDMH) as the fuel, and inhibited red fuming nitric acid (IRFNA) as the oxidizer. In all, 365 Agena vehicles were launched by NASA and the US Air Force. The final launch was of an Agena D on February 12, 1987, configured as the upper stage of a Titan 34B. This followed Lockheed's tradition of naming products for stellar phenomena. 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'. 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. On missions where the payload was not built into the Agena, and instead separated after launch, the Agena was known as an Ascent Agena. Payload components were usually located ahead of the Agena's standard bulkhead. On some missions, the payload was built directly into the Agena, which provided it with electric power, communications and three-axis stabilization. Only 33 Agenas carried NASA payloads and the vast majority were for DoD programs. A total of 365 Agena rockets were launched between Febru and February 1987. 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. 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. The RM-81 Agena (ədʒiːnə) was an American rocket upper stage and satellite bus which was developed by Lockheed Corporation initially for the canceled WS-117L reconnaissance satellite program.

Atlas agena payload