Unsymmetrical dimethylhydrazine (UDMH; 1,1-dimethylhydrazine, НДМГ or codenamed Geptil) is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula H₂NN(CH₃)₂ that is used as a

rocket propellant Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propuls ...

. It is a colorless liquid, with a sharp, fishy, ammonia-like smell typical for organic

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

s. Samples turn yellowish on exposure to air and absorb

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

and

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

. It is

miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies ...

with water,

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

, and

kerosene Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regi ...

. In concentration between 2.5% and 95% in air, its vapors are flammable. It is not sensitive to shock. Symmetrical dimethylhydrazine, 1,2-dimethylhydrazine is also known but is not as useful.

Production

UDMH is produced industrially by two routes. Based on the Olin Raschig process, one method involves reaction of

monochloramine Monochloramine, often called chloramine, is the chemical compound with the formula NH2Cl. Together with dichloramine (NHCl2) and nitrogen trichloride (NCl3), it is one of the three chloramines of ammonia. It is a colorless liquid at its melting p ...

with

dimethylamine Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to aroun ...

giving 1,1-dimethylhydrazinium chloride: :(CH₃)₂NH + NH₂Cl → (CH₃)₂NNH₂ ⋅ HCl In the presence of suitable catalysts, acetylhydrazine can be N-dimethylated using

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

and hydrogen to give the N,N-dimethyl-N'-acetylhydrazine, which can subsequently be hydrolyzed: :CH₃C(O)NHNH₂ + 2CH₂O + 2H₂ → CH₃C(O)NHN(CH₃)₂ + 2H₂O :CH₃C(O)NHN(CH₃)₂ + H₂O → CH₃COOH + H₂NN(CH₃)₂

Uses

UDMH is often used in

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 ...

rocket fuel Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical ...

s as a

bipropellant The highest specific impulse chemical rockets use liquid propellants (liquid-propellant rockets). They can consist of a single chemical (a monopropellant) or a mix of two chemicals, called bipropellants. Bipropellants can further be divided into ...

in combination with the oxidizer

nitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russia rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...

and less frequently with

IRFNA Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists of 84% nitric acid (), 13% dinitrogen tetroxide and 1–2% water. The color of red fuming nitric acid is due to the dinitrogen tetroxide, which breaks ...

(inhibited red fuming nitric acid) or

liquid oxygen 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 applica ...

. UDMH is a derivative of

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

and is sometimes referred to as a hydrazine. As a fuel, it is described in specification MIL-PRF-25604 in the United States. UDMH is stable and can be kept loaded in rocket fuel systems for long periods, which makes it appealing for use in many

liquid rocket A liquid-propellant rocket or liquid rocket utilizes a rocket engine that uses liquid propellants. Liquids are desirable because they have a reasonably high density and high specific impulse (''I''sp). This allows the volume of the propellant ta ...

engines, despite its cost. In some applications, such as the OMS in the

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...

or maneuvering engines,

monomethylhydrazine Monomethylhydrazine (mono-methyl hydrazine, MMH) is a highly toxic, volatile hydrazine derivative with the chemical formula . It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as ...

is used instead due to its slightly higher

specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...

. In some kerosene-fueled rockets, UDMH functions as a starter fuel to start combustion and warm the rocket engine prior to switching to kerosene. UDMH has higher stability than hydrazine, especially at elevated temperatures, and can be used as its replacement or together in a mixture. UDMH is used in many European, Russian, Indian, and Chinese rocket designs. The Russian SS-11 Sego (aka 8K84) ICBM,

SS-19 Stiletto The UR-100N, also known as RS-18A is an intercontinental ballistic missile in service with Soviet Union, Soviet and Russian Strategic Missile Troops. The missile was given the NATO reporting name SS-19 Stiletto and carries the industry designatio ...

(aka 15A30) ICBM,

Proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

Kosmos-3M The Kosmos-3M (russian: Космос-3М meaning "''Cosmos''", GRAU index 11K65M) was a Russian space launch vehicle, member of the Kosmos rocket family. It was a liquid-fueled two-stage launch vehicle, first launched in 1967 and with over 42 ...

R-29RMU2 Layner The R-29RMU2.1 Layner (russian: Р-29РМУ2.1 "Лайнер" meaning ''Liner'') is a Russian liquid-fuelled submarine-launched ballistic missile (SLBM) and the newest member of the R-29 missile family, developed by the Makeyev Rocket Design Bu ...

R-36M The R-36 (russian: Р-36) is a family of intercontinental ballistic missiles (ICBMs) and space launch vehicles (Tsyklon) designed by the Soviet Union during the Cold War. The original R-36 was deployed under the GRAU index 8K67 and was given the ...

Rokot Rokot (russian: Рокот meaning ''Rumble'' or ''Boom''), also transliterated Rockot, was a Russian space launch vehicle that was capable of launching a payload of into a Earth orbit with 63° inclination. It was based on the UR-100N (SS- ...

(based on 15A30) and the Chinese

Long March 2F The Long March 2F ( ''Changzheng 2F''), also known as the CZ-2F, LM-2F and Shenjian (, "Divine Arrow"), is a Chinese orbital carrier rocket, part of the Long March 2 rocket family. Designed to launch crewed Shenzhou spacecraft, the Long Mar ...

are the most notable users of UDMH (which is referred to as "heptyl"

Soviet era The history of Soviet Russia and the Soviet Union (USSR) reflects a period of change for both Russia and the world. Though the terms "Soviet Russia" and "Soviet Union" often are synonymous in everyday speech (either acknowledging the dominance ...

] by Russian engineers). The Titan (rocket family), Titan, Geosynchronous Satellite Launch Vehicle, GSLV, and Delta rocket families use a mixture of 50% hydrazine and 50% UDMH, called

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 ...

, in different stages. There is speculation that it is the fuel used in the ballistic missiles that North Korea has developed and tested in 2017.

Safety

Hydrazines and its methyl derivatives are toxic but

LD50 In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...

values have not been reported. It is a precursor to dimethylnitrosamine, which is carcinogenic. According to scientific data, usage of UDMH in rockets at

Baikonur Cosmodrome The Baikonur Cosmodrome ( kk, Байқоңыр ғарыш айлағы, translit=Baiqoñyr ğaryş ailağy, ; russian: Космодром Байконур, translit=Kosmodrom Baykonur, ) is a spaceport in an area of southern Kazakhstan leased to R ...

has had adverse effects on the environment and local population.

References

External links

Encyclopedia Astronautica

{{hydrazines Rocket fuels Hydrazines

Production

Uses

Safety

See also

References

External links