Agena

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The Agena system was an upper rocket stage that used a restartable rocket engine. It could operate as a satellite in its own right or it could be used to launch satellites and space probes in conjunction with more powerful lower rocket stages. Typical first-stage boosters were Thor and Atlas.Agena B, built by Lockheed Aircraft Corporation, was used in a number of early U.S. Air Force satellite projects, including Discoverer, Samos, Midas, and Vela, and a variety of NASA projects, including Echo, Mariner, Nimbus, and Ranger. Agena stages also were used as docking targets in the manned Gemini program. Dimensions of the stage depended on the mission. A typical Agena B stage used in the U.S. Air Force programs of the 1960s was 8 m (26.5 ft) long and 1.5 m (5 ft) in diameter. The stage had a fueled weight of about 7,167 kg (15,800 lb). The propellants were IRFNA and UDMH; the Bell 8096 rocket engine had a thrust of 7,260 kg (16,000 lb).Agena D, the version of the vehicle in use after Agena B, had a lengthÑexcluding payloadÑof 7 m (23.25 ft) and carried more propellant than its predecessors. It could also accept a variety of payloads. It was launched atop Titan 3B, Atlas SLV-3A, and Thor. The last Agena to be manufactured was launched in 1987.