The LR91 was an American liquid-propellant

rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accorda ...

, which was used on the second stages of Titan intercontinental ballistic missiles and

launch vehicles A launch vehicle or carrier rocket is a rocket designed to carry a payload (spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and syste ...

. While the original version - the LR91-3 - ran on

RP-1 RP-1 (alternatively, Rocket Propellant-1 or Refined Petroleum-1) is a highly refined form of kerosene outwardly similar to jet fuel, used as rocket fuel. RP-1 provides a lower specific impulse than liquid hydrogen (LH2), but is cheaper, is s ...

LOX Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an appli ...

(as did the companion LR87-3) on the

Titan I The Martin Marietta SM-68A/HGM-25A Titan I was the United States' first multistage intercontinental ballistic missile (ICBM), in use from 1959 until 1962. Though the SM-68A was operational for only three years, it spawned numerous follow-on mode ...

, the models that propelled the

Titan II The Titan II was an intercontinental ballistic missile (ICBM) developed by the Glenn L. Martin Company from the earlier Titan I missile. Titan II was originally designed and used as an ICBM, but was later adapted as a medium-lift space l ...

and later were switched to

Aerozine 50 __NOTOC__ Aerozine 50 is a 50:50 mix by weight of hydrazine and unsymmetrical dimethylhydrazine (UDMH), originally developed in the late 1950s by Aerojet General Corporation as a storable, high-energy, hypergolic fuel for the Titan II ICBM rocket e ...

/ N₂O₄. This engine was vacuum optimized and ran the gas-generator cycle. The thrust chamber used fuel for regenerative cooling, with separate

ablative In grammar, the ablative case (pronounced ; sometimes abbreviated ) is a grammatical case for nouns, pronouns, and adjectives in the grammars of various languages; it is sometimes used to express motion away from something, among other uses. ...

skirt. The

LR87 The LR87 was an American liquid-propellant rocket engine used on the first stages of Titan intercontinental ballistic missiles and launch vehicles. Composed of twin motors with separate combustion chambers and turbopump machinery, it is cons ...

, which was used for the Titan first stage, was used as a template for the LR91. Early LR91 engines used on the

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

, the engine was converted to use Aerozine-50 and nitrogen tetroxide, which are

hypergolic A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. T ...

and storable at room temperature. This allowed Titan II missiles to be kept fully fueled and ready to launch on short notice.

Versions

* LR91-3: Titan I version. Run on RP-1/LOX. * LR91-5: Titan II version. Propellant was switched to Aerozine50, N₂O₄. * LR91-7: Similar to LR91-5, it was used on Stage 2 of Gemini Titan II. This version was human rated. * LR91-9: Used in earlier versions of Titan III upper stage. * LR91-11: Version used on the Titan III and Titan IV.

References

External links

Encyclopedia Astronautica

National Museum of the USAF, Ohio

Rocket engines using kerosene propellant Rocket engines using hypergolic propellant Rocket engines using the gas-generator cycle {{rocket-stub

Versions

See also

References

External links