RD-855
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The RD-855 (,
GRAU index The Main Missile and Artillery Directorate of the Ministry of Defense of the Russian Federation (), commonly referred to by its transliterated acronym GRAU (), is a department of the Russian Ministry of Defense. It is subordinate to the Chief of ...
: 8D68M), also known as the RD-68M, is a liquid-fueled
rocket engine A rocket engine is a reaction engine, producing thrust in accordance with Newton's third law by ejecting reaction mass rearward, usually a high-speed Jet (fluid), jet of high-temperature gas produced by the combustion of rocket propellants stor ...
with four
nozzles A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, ...
. As a vernier engine, it provides fine steering adjustments for rockets. It is powered by a
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. The ...
mixture of
unsymmetrical dimethylhydrazine Unsymmetrical dimethylhydrazine (abbreviated as UDMH; also known as 1,1-dimethylhydrazine, heptyl or Geptil) is a chemical compound with the formula H2NN(CH3)2 that is primarily used as a rocket propellant. At room temperature, UDMH is a colorle ...
(UDMH) fuel with
dinitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russian rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...
() oxidizer. This combination is hypergolic, meaning the two substances ignite on contact, eliminating the need for an external ignition source. The RD-855 can orient its chambers within a range of ±42° using hydraulic cylinders. Each chamber on the Tsyklon rockets is protected by an aerodynamic cover, and these covers are equipped with small retro-rockets allowing for separation from the second stage. The RD-855 utilizes the gas generator cycle, in which a portion of the propellant is burned in a pre-burner to produce hot gases that drive the engine's turbopumps, and then the gases are discarded without passing through the main combustion chamber. It played a key role in rockets such as the R-36,
Tsyklon-2 The Tsyklon-2 (), also known as Tsiklon-2 and Tsyklon-M (known as SL-11 by the United States United States Department of Defense, DoD), GRAU index 11K69, was a Soviet Union, Soviet, later Ukraine, Ukrainian, orbital carrier rocket used from the ...
, and
Tsyklon-3 The Tsyklon-3, also known as Tsiklon-3 and Cyclone-3 (known as SL-14 by the United States DoD), GRAU index 11K68, was a Soviet, and subsequently Ukrainian orbital carrier rocket. Overview Tsyklon-3 launching a Meteor-3 satellite at left A ...
, steering these rockets by adjusting its nozzles. The engine is housed in a cylindrical structure that surrounds the primary
RD-251 The RD-250 (, GRAU index: 8D518) is the base version of a dual-nozzle family of liquid-fuel rocket engines, burning a hypergolic mixture of unsymmetrical dimethylhydrazine (UDMH) fuel with dinitrogen tetroxide () oxidizer in a gas-generator ope ...
engine. This arrangement provides protection for the nozzles and ensures the successful detachment of the rocket's first stage. The RD-855 is activated two seconds before the main RD-251 engine. Manufactured from 1965 to 1992, the RD-855's inaugural flight was on December 16, 1965, aboard the R-36 missile. Its most recent known flight was on January 30, 2009, with the
Tsyklon-3 The Tsyklon-3, also known as Tsiklon-3 and Cyclone-3 (known as SL-14 by the United States DoD), GRAU index 11K68, was a Soviet, and subsequently Ukrainian orbital carrier rocket. Overview Tsyklon-3 launching a Meteor-3 satellite at left A ...
. Although there were plans to restart its production for the
Tsyklon-4 The Tsyklon-4, also known as Tsiklon-4 and Cyclone-4, was a Ukrainian carrier rocket which was being developed for commercial satellite launches. Derived from the Tsyklon-3, it had a new third stage, a larger payload fairing, and a modernised fl ...
, the engine remains out of production following the potential discontinuation of the program.


See also

* R-36 – The
Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
ICBM An intercontinental ballistic missile (ICBM) is a ballistic missile with a range (aeronautics), range greater than , primarily designed for nuclear weapons delivery (delivering one or more Thermonuclear weapon, thermonuclear warheads). Conven ...
for which the RD-855 was created. *
Tsyklon-2 The Tsyklon-2 (), also known as Tsiklon-2 and Tsyklon-M (known as SL-11 by the United States United States Department of Defense, DoD), GRAU index 11K69, was a Soviet Union, Soviet, later Ukraine, Ukrainian, orbital carrier rocket used from the ...
– A
Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
small rocket that uses the RD-855. *
Tsyklon-3 The Tsyklon-3, also known as Tsiklon-3 and Cyclone-3 (known as SL-14 by the United States DoD), GRAU index 11K68, was a Soviet, and subsequently Ukrainian orbital carrier rocket. Overview Tsyklon-3 launching a Meteor-3 satellite at left A ...
– A
Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
small rocket that uses the RD-855. *
Tsyklon-4 The Tsyklon-4, also known as Tsiklon-4 and Cyclone-4, was a Ukrainian carrier rocket which was being developed for commercial satellite launches. Derived from the Tsyklon-3, it had a new third stage, a larger payload fairing, and a modernised fl ...
– A Ukrainian small rocket project that would have used the RD-855. *
Yuzhnoe Design Bureau The ''Pivdenne'' Design Office (), located in Dnipro, Ukraine, is a designer of satellites and rockets, and formerly of Soviet intercontinental ballistic missiles (ICBMs), established by Mikhail Yangel. During the Soviet era, the bureau's OKB des ...
– The RD-855 designer bureau.


References


External links


Yuzhnoye Design Bureau English-language home page

Yuzhmash Home Page
Rocket engines of the Soviet Union Rocket engines using hypergolic propellant Rocket engines using the gas-generator cycle Yuzhmash rocket engines Rocket engines of Ukraine {{rocket-stub