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The LR-91 was an American liquid-propellant rocket engine, which was used on the second stages of Titan intercontinental ballistic missiles and launch vehicles. While the original version - the LR-91-3 - run on RP-1/LOX (as did the companion LR-87-3) on the Titan I, the models that propelled the Titan II and later were switched to Aerozine 50/N2O4.〔 This engine was a vacuum optimized and run the gas generator cycle. The thrust chamber used fuel for regenerative cooling, with separate ablative skirt.〔 The LR-87, which was used for the Titan first stage, was used as a template for the LR-91. Early LR-91 engines used on the Titan I burned RP-1 and liquid oxygen. Because liquid oxygen is cryogenic, it could not be stored in the missile for long periods of time, and had to be loaded before the missile could be launched. For the Titan II, the engine was converted to use Aerozine-50 and nitrogen tetroxide, which are hypergolic and storable at room temperature. This allowed Titan II missiles to be kept fully fueled and ready to launch on short notice.〔 == Versions == Improvement and modifications required to comply with the man rating of the RD-0105 led it to have two versions: * LR-91-3: Titan I version. Run on RP-1/LOX.〔 * LR-91-5: Titan II version. Propellant was switched to Aerozine-5/N2O4.〔 * LR-91-7: Similar to LR-91-5, it was used on Stage 2 of Gemini Titan 2. This version was human rated.〔 * LR-91-9: Used in earlier versions of Titan 3 upper stage.〔 * LR-91-11: Version used on the Titan III and Titan IV.〔 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「LR-91」の詳細全文を読む スポンサード リンク
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