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A hypergolic propellant is a rocket propellant combination used in a
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 ...
, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...
and an
oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...
. The main advantages of hypergolic propellants are that they can be stored as liquids at room temperature and that engines which are powered by them are easy to ignite reliably and repeatedly. Common hypergolic propellants are extremely
toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
or
corrosive Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
, making them difficult to handle. In contemporary usage, the terms "hypergol" and "hypergolic propellant" usually mean the most common such propellant combination:
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 ...
plus
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 hazardous unless handled in solution as, for example, hydraz ...
.


History

The fact that
turpentine Turpentine (which is also called spirit of turpentine, oil of turpentine, terebenthine, terebenthene, terebinthine and, colloquially, turps) is a fluid obtainable by the distillation of resin harvested from living trees, mainly pines. Principall ...
may spontaneously combust when mixed with
nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
was discovered as early as the late 17th century by Frederick Slare, but it remained a scientific curiosity for centuries until it was proposed to use it for rocket-assisted take off during WWII. In 1935,
Hellmuth Walter Hellmuth Walter (26 August 1900 – 16 December 1980) was a German engineer who pioneered research into rocket engines and gas turbines. His most noteworthy contributions were rocket motors for the Messerschmitt Me 163 and Bachem Ba 349 interce ...
discovered that hydrazine hydrate was hypergolic with
high-test peroxide High-test peroxide (HTP) is a highly concentrated (85 to 98%) solution of hydrogen peroxide, with the remainder consisting predominantly of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with n ...
of 80–83%. He was probably the first to discover this phenomenon, and set to work developing a fuel. Prof. Otto Lutz assisted the Walter Company with the development of ''
C-Stoff C-Stoff (; "substance C") was a Redox, reductant used in bipropellant rocket fuels (as a fuel itself) developed by Hellmuth Walter Kommanditgesellschaft in Germany during World War II. It was developed for use with T-Stoff (a high-test peroxide) ...
'', which contained 30% hydrazine hydrate, 57%
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...
, and 13% water, and spontaneously ignited with high-strength
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
. BMW developed engines burning a hypergolic mix of nitric acid with various combinations of amines, xylidines, and
aniline Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...
s. Hypergolic propellants were discovered independently, for the second time, in the U.S. by GALCIT and Navy Annapolis researchers in 1940. They developed engines powered by aniline and red fuming nitric acid. Robert Goddard,
Reaction Motors Reaction Motors, Inc. (RMI) was an early American maker of liquid-fueled rocket engines, located in New Jersey. RMI engines with thrust powered the Bell X-1 rocket aircraft that first broke the sound barrier in 1947, and later aircraft such ...
, and
Curtiss-Wright The Curtiss-Wright Corporation is an American manufacturer and services provider headquartered in Davidson, North Carolina, with factories and operations in and outside the United States. Created in 1929 from the consolidation (business), consoli ...
worked on aniline/nitric acid engines in the early 1940s, for small missiles and jet assisted take-off (
JATO JATO (acronym for jet-assisted take-off) is a type of assisted take-off for helping overloaded aircraft into the air by providing additional thrust in the form of small rockets. The term ''JATO'' is used interchangeably with the (more specific ...
). The project resulted in the successful JATO of several Martin PBM and PBY bombers, but the project was disliked because of the toxic properties of both fuel and oxidizer, as well as the high
freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...
of aniline. The second problem was eventually solved by the addition of small quantities of
furfuryl alcohol Furfuryl alcohol is an organic compound containing a furan substituted with a hydroxymethyl group. It is a colorless liquid, but aged samples appear amber. It possesses a faint odor of burning and a bitter taste. It is miscible with but unstabl ...
to the aniline. In Germany from the mid-1930s through
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, rocket propellants were broadly classed as monergols, hypergols, nonhypergols and lithergols. The ending ''ergol'' is a combination of
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
''ergon'' or work, and Latin ''oleum'' or oil, later influenced by the chemical suffix ''-ol'' from
alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...
."-ergol", ''Oxford English Dictionary'' Monergols were
monopropellant Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with biprop ...
s, while nonhypergols were bipropellants that required external ignition, and lithergols were solid/liquid hybrids. Hypergolic propellants (or at least hypergolic ignition) were far less prone to hard starts than electric or pyrotechnic ignition. The "hypergole" terminology was coined by Dr. Wolfgang Nöggerath, at the Technical University of
Braunschweig Braunschweig () or Brunswick ( ; from Low German , local dialect: ) is a List of cities and towns in Germany, city in Lower Saxony, Germany, north of the Harz Mountains at the farthest navigable point of the river Oker, which connects it to the ...
(Brunswick), Germany. The only rocket-powered fighter ever deployed was the
Messerschmitt Me 163 The Messerschmitt Me 163 Komet is a rocket-powered interceptor aircraft primarily designed and produced by the German aircraft manufacturer Messerschmitt. It is the only operational rocket-powered fighter aircraft in history as well as ...
B ''Komet'', which had an HWK 109-509, a rocket motor which consumed methanol/hydrazine as fuel and high-test peroxide ''
T-Stoff T-Stoff (; 'substance T') was a stabilised high test peroxide used in Nazi Germany, Germany during World War II. T-Stoff was specified to contain 80% (occasionally 85%) hydrogen peroxide (H2O2), remainder water, with traces (<0.1%) of stabiliser ...
'' as oxidizer. The hypergolic rocket motor had the advantage of fast climb and quick-hitting tactics at the cost of being very volatile and capable of exploding with any degree of inattention. Other proposed combat rocket fighters such as the Heinkel ''Julia'' and reconnaissance aircraft like the DFS 228 were meant to use the Walter 509 series of rocket motors, but besides the Me 163, only the
Bachem Ba 349 The Bachem Ba 349 Natter () is a World War II German point-defence rocket-powered interceptor aircraft, interceptor, which was to be used in a very similar way to a manned surface-to-air missile. After a vertical take-off, which eliminated the n ...
''Natter'' vertical launch expendable fighter was ever flight-tested with the Walter rocket propulsion system as its primary sustaining thrust system for military-purpose aircraft. The earliest ballistic missiles, such as the Soviet R-7 that launched
Sputnik 1 Sputnik 1 (, , ''Satellite 1''), sometimes referred to as simply Sputnik, was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program ...
and the U.S.
Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...
and Titan-1, used
kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...
and
liquid oxygen Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear cyan liquid form of dioxygen . It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing. Physical ...
. Although they are preferred in space launchers, the difficulties of storing a cryogen such as liquid oxygen in a missile that had to be kept launch ready for months or years at a time led to a switch to hypergolic propellants in the U.S.
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 ...
and in most Soviet ICBMs such as the R-36, but the difficulties of such corrosive and toxic materials, including injury-causing leaks and the explosion of a Titan-II in its silo, led to their near universal replacement with solid-fuel boosters, first in Western
submarine-launched ballistic missiles A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which carries a nuclear warhead ...
and then in land-based U.S. and Soviet ICBMs. In the 1960s, late variants of French Véronique
sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are often ...
and the Vesta rocket, as well as the first stage of the first orbital SLV
Diamant The Diamant rocket (French for "diamond") was the first exclusively French expendable launch system and at the same time the first satellite launcher not built by either the United States or USSR. As such, it has been referred to as being a key ...
used the combination of nitric acid and turpentine discovered by Slare. It may also be used in amateur rocketry. The
Apollo Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed sp ...
, used in the Moon landings, employed hypergolic fuels in both the descent and ascent rocket engines. The
Apollo spacecraft The Apollo spacecraft was composed of three parts designed to accomplish the American Apollo program's goal of landing astronauts on the Moon by the end of the 1960s and returning them safely to Earth. The expendable (single-use) spacecraft ...
used the same combination for the Service Propulsion System. Those spacecraft and the
Space Shuttle The Space Shuttle is a retired, partially reusable launch system, 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. ...
(among others) used hypergolic propellants for their
reaction control system A reaction control system (RCS) is a spacecraft system that uses Thrusters (spacecraft), thrusters to provide Spacecraft attitude control, attitude control and translation (physics), translation. Alternatively, reaction wheels can be used for at ...
s. The trend among Western space-launch agencies is away from large hypergolic rocket engines and toward hydrogen/oxygen engines or methane/oxygen and
RP-1 RP-1 (Rocket Propellant-1 or Refined Petroleum-1) and similar fuels like RG-1 and T-1 are highly refined kerosene formulations used as rocket fuel. Liquid-fueled rockets that use RP-1 as fuel are known as kerolox rockets. In their engines, RP- ...
/oxygen engines for various advantages and disadvantages. Arianes 1 through 4, with their hypergolic first and second stages (and optional hypergolic boosters on the Ariane 3 and 4) have been retired and replaced with the Ariane 5, which uses a first stage fueled by liquid hydrogen and liquid oxygen. The Titan II, III, and IV, with their hypergolic first and second stages, have also been retired for the Atlas V (RP-1/oxygen) and Delta IV (hydrogen/oxygen). Hypergolic propellants are still used in upper stages, when multiple burn-coast periods are required, and in
launch escape system A launch escape system (LES) or launch abort system (LAS) is a crew-safety system connected to a space capsule. It is used in the event of a critical emergency to quickly separate the capsule from its launch vehicle in case of an emergency requiri ...
s.


Characteristics


Advantages

Hypergolically fueled rocket engines are usually simple and reliable because they need no ignition system. Although larger hypergolic engines in some launch vehicles use turbopumps, most hypergolic engines are pressure fed. A gas, usually
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
, is fed to the propellant tanks under pressure through a series of check and
safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds ...
s. The propellants, in turn, flow through control valves into the combustion chamber; there, their instant contact ignition prevents a mixture of unreacted propellants from accumulating and then igniting in a potentially catastrophic hard start. As hypergolic rockets do not need an ignition system, they can fire any number of times by simply opening and closing the propellant valves until the propellants are exhausted, so are uniquely suited for spacecraft maneuvering and well-suited, though not uniquely so, as upper stages of such space launchers as the
Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...
and
Ariane 5 Ariane 5 is a retired European heavy-lift space launch vehicle operated by Arianespace for the European Space Agency (ESA). It was launched from the Guiana Space Centre (CSG) in French Guiana. It was used to deliver payloads into geostationar ...
, which must perform more than one burn. Restartable nonhypergolic rocket engines nevertheless exist, notably the cryogenic (oxygen/hydrogen) RL-10 on the
Centaur A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...
and the J-2 on the
Saturn V The Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, had multistage rocket, three stages, and was powered by liquid-propel ...
. The
RP-1 RP-1 (Rocket Propellant-1 or Refined Petroleum-1) and similar fuels like RG-1 and T-1 are highly refined kerosene formulations used as rocket fuel. Liquid-fueled rockets that use RP-1 as fuel are known as kerolox rockets. In their engines, RP- ...
/LOX
Merlin The Multi-Element Radio Linked Interferometer Network (MERLIN) is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of UK Re ...
on the
Falcon 9 Falcon 9 is a Reusable launch system#Partial reusable launch systems, partially reusable, two-stage-to-orbit, medium-lift launch vehicle designed and manufactured in the United States by SpaceX. The first Falcon 9 launch was on June 4, 2010, an ...
can also be restarted. The most common hypergolic fuels,
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 hazardous unless handled in solution as, for example, hydraz ...
, monomethylhydrazine, and
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), and oxidizer, nitrogen tetroxide, are all liquid at ordinary temperatures and pressures. They are therefore sometimes called "storable liquid propellants". They are suitable for use in spacecraft missions lasting many years. The cryogenity of
liquid hydrogen Liquid hydrogen () is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecule, molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point (thermodynamics), critical point of 33 Kelvins, ...
and
liquid oxygen Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear cyan liquid form of dioxygen . It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing. Physical ...
has so far limited their practical use to space launch vehicles where they need to be stored only briefly. As the largest issue with the usage of cryogenic propellants in interplanetary space is boil-off, which is largely dependent on the scale of spacecraft, for larger craft such as
Starship A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for interstellar travel, traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1 ...
this is less of an issue. Another advantage of hypergolic propellants is their high density compared to cryogenic propellants. LO2 has a density of 1.14 g/ml, while hypergolic oxidizers such as
nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
or nitrogen tetroxide have a density of 1.55 g/ml and 1.45 g/ml, respectively. LH2 fuel offers extremely high performance, yet its density only warrants its use in the largest of rocket stages, while mixtures of hydrazine and UDMH have a density at least 10 times greater. This is of great importance in space probes, as the higher propellant density allows the size of their propellant tanks to be reduced significantly, which in turn allows the probes to fit within a smaller
payload fairing A payload fairing or nose fairing is a nose cone used to protect a launch vehicle, spacecraft payload (air and space craft), payload against the impact of dynamic pressure and aerodynamic heating during launch through an atmosphere. An additiona ...
.


Disadvantages

Relative to their mass, traditional hypergolic propellants possess a lower calorific value than cryogenic propellant combinations like LH2/LO2 or LCH4/LO2. A launch vehicle that uses hypergolic propellant must therefore carry a greater mass of fuel than one that uses these cryogenic fuels. The corrosivity,
toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...
, and
carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...
icity of traditional hypergolics necessitate expensive safety precautions. Failure to follow adequate safety procedures with an exceptionally dangerous UDMH-nitric acid propellant mixture nicknamed "devil's venom", for example, resulted in the deadliest rocketry accident in history, the
Nedelin catastrophe The Nedelin catastrophe or Nedelin disaster, known in Russia as the Catastrophe at Baikonur Cosmodrome (), was a launch pad accident that occurred on 24 October 1960 at the Baikonur Cosmodrome in Soviet Kazakhstan. As a prototype of the R- ...
.


Hypergolic combinations


Common

Common hypergolic propellant combinations include: *
Aerozine 50 __NOTOC__ Aerozine 50 is a 50:50 mix by weight of hydrazine and unsymmetrical dimethylhydrazine (UDMH), developed in the late 1950s by Aerojet General Corporation as a storable, high-energy, hypergolic fuel for the Titan II ICBM rocket engines ...
+ nitrogen tetroxide (NTO) is widely used in historical American rockets, including the Titan II and all engines in the
Apollo Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed sp ...
. Aerozine 50 is a mixture of 50% UDMH and 50% straight hydrazine (N2H4). * Monomethylhydrazine (MMH) + NTO is used in smaller engines and reaction control thrusters:
Apollo command and service module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo (spacecraft), Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functi ...
RCS, Space Shuttle OMS and RCS;
Ariane 5 Ariane 5 is a retired European heavy-lift space launch vehicle operated by Arianespace for the European Space Agency (ESA). It was launched from the Guiana Space Centre (CSG) in French Guiana. It was used to deliver payloads into geostationar ...
EPS; Draco thrusters used by the
SpaceX Dragon Dragon is a family of spacecraft developed and produced by American private space transportation company SpaceX. The first variant, later named SpaceX Dragon 1, Dragon 1, flew 23 cargo missions to the International Space Station (ISS) between ...
spacecraft. * Triethylborane/
triethylaluminium Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important comp ...
(TEA-TEB) +
liquid oxygen Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear cyan liquid form of dioxygen . It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing. Physical ...
is used during the ignition process of some rocket engines that use liquid oxygen, used by the SpaceX Merlin Engine Family and Rocketdyne F-1. * UDMH + NTO is frequently used by
Roscosmos The State Corporation for Space Activities "Roscosmos", commonly known simply as Roscosmos (), is a State corporation (Russia), state corporation of the Russian Federation responsible for space science, space flights, List of space agencies, c ...
, such as in the
Proton (rocket family) Proton (, formal designation: UR-500) is an expendable launch system used for both commercial and Russian government space launches. The first Proton rocket was launched in 1965. Modern versions of the launch system are still in use , making it ...
, and supplied by them to France for the Ariane 1 first and second stages (replaced with UH 25) and
ISRO The Indian Space Research Organisation (ISRO ) is India's national space agency, headquartered in Bengaluru, Karnataka. It serves as the principal research and development arm of the Department of Space (DoS), overseen by the Prime Minister o ...
rockets using Vikas engine.


Less common or obsolete

Less-common or obsolete hypergolic propellants include: * Aniline + nitric acid (unstable, explosive) is used in the
WAC Corporal The WAC Corporal was the first operational sounding rocket developed in the United States. It was an offshoot of the Corporal program, that was started by a partnership between the United States Army Ordnance Corps and the California Institut ...
. * Aniline + hydrogen peroxide (dust-sensitive, explosive) *
Furfuryl alcohol Furfuryl alcohol is an organic compound containing a furan substituted with a hydroxymethyl group. It is a colorless liquid, but aged samples appear amber. It possesses a faint odor of burning and a bitter taste. It is miscible with but unstabl ...
+ red fuming nitric acidCopenhagen Suborbitals SPECTRA Engine * Furfuryl alcohol +
white fuming nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into oxides of nitrogen. Most commercially avail ...
* Hydrazine + nitric acid (toxic but stable) was abandoned due to lack of reliable ignition. No engine with this combination ever went into mass production. * Kerosene + (high-test peroxide + catalyst) is used in
Gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...
, with the peroxide first decomposed by a catalyst. Cold hydrogen peroxide and kerosene are not hypergolic, but concentrated hydrogen peroxide (referred to as high-test peroxide or HTP) run over a catalyst produces free oxygen and steam at over , which is hypergolic with kerosene. *
Tonka Tonka is an American brand and former manufacturer of toy trucks. The company was founded in 1946 and operated as an independent manufacturer of popular steel toy construction type trucks and machinery, until its sale to Hasbro in 1991. Histor ...
(TG-02, about 50%
triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. Like triethanolamine and the tetraethylammonium ion, it is often abbreviated TEA. It is a colourless volatile liquid with a strong fishy odor remini ...
and 50% xylidine) typically oxidized with nitric acid or its anhydrous nitric oxide derivatives (AK-2x group in the Soviet Union) e.g. AK-20F (80% HNO3 and 20% N2O4 with
inhibitor Inhibitor or inhibition may refer to: Biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotransmi ...
). * ''
T-Stoff T-Stoff (; 'substance T') was a stabilised high test peroxide used in Nazi Germany, Germany during World War II. T-Stoff was specified to contain 80% (occasionally 85%) hydrogen peroxide (H2O2), remainder water, with traces (<0.1%) of stabiliser ...
'' (stabilized >80% peroxide) + ''
C-Stoff C-Stoff (; "substance C") was a Redox, reductant used in bipropellant rocket fuels (as a fuel itself) developed by Hellmuth Walter Kommanditgesellschaft in Germany during World War II. It was developed for use with T-Stoff (a high-test peroxide) ...
'' (methanol, hydrazine, water, catalyst) was used in
Messerschmitt Me 163 The Messerschmitt Me 163 Komet is a rocket-powered interceptor aircraft primarily designed and produced by the German aircraft manufacturer Messerschmitt. It is the only operational rocket-powered fighter aircraft in history as well as ...
World War II German rocket fighter aircraft, for its Walter 109-509A engine. * Turpentine + red fuming nitric acid (flown in French Diamant A first-stage) * UDMH + red fuming nitric acid is used in the
MGM-52 Lance The MGM-52 Lance was a mobile field artillery tactical surface-to-surface missile (tactical ballistic missile) system used to provide both W70, nuclear and conventional fire support to the United States Army. The missile's warhead was developed ...
missile system, Agena and Able Upper Stages, and Isayev-built maneuvering engines.


Proposed, remain unflown

* Chlorine trifluoride (ClF3) + all known fuels – Briefly considered as an oxidizer given its high hypergolicity with all standard fuels, it was ultimately abandoned in the 1970s due to the difficulty of handling the substance safely. ClF3 is known to burn concrete and gravel. Chlorine pentafluoride (ClF5) presents the same hazards, but offers higher
specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), ...
than ClF3. * Pentaborane(9) and diborane + nitrogen tetroxide – Pentaborane(9), a so-called zip fuel, was studied by Soviet rocket scientist V. P. Glushko for use in combination with nitrogen tetroxide in the RD-270M rocket engine. This propellant combination would have yielded a significant increase in performance, but was ultimately given up due to toxicity concerns.Astronautix: RD-270
.
* Tetramethylethylenediamine +red fuming nitric acid is a sightly less-toxic alternative to hydrazine and its derivatives.


Related technology

Pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...
substances, which ignite spontaneously in the presence of air, are also sometimes used as rocket fuels themselves or to ignite other fuels. For example, a mixture of triethylborane and
triethylaluminium Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important comp ...
(which are both separately and even more so together pyrophoric), was used for engine starts in the SR-71 Blackbird and in the F-1 engines on the
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
Saturn V The Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, had multistage rocket, three stages, and was powered by liquid-propel ...
rocket, and is used in the
Merlin The Multi-Element Radio Linked Interferometer Network (MERLIN) is an interferometer array of radio telescopes spread across England. The array is run from Jodrell Bank Observatory in Cheshire by the University of Manchester on behalf of UK Re ...
engines on the
SpaceX Space Exploration Technologies Corp., commonly referred to as SpaceX, is an America, American space technology company headquartered at the SpaceX Starbase, Starbase development site in Starbase, Texas. Since its founding in 2002, the compa ...
Falcon 9 Falcon 9 is a Reusable launch system#Partial reusable launch systems, partially reusable, two-stage-to-orbit, medium-lift launch vehicle designed and manufactured in the United States by SpaceX. The first Falcon 9 launch was on June 4, 2010, an ...
rockets.


Notes


References


Further reading

* * ''Modern Engineering for Design of Liquid-Propellant Rocket Engines'', Huzel & Huang, pub. AIAA, 1992. . * ''History of Liquid Propellant Rocket Engines'', G. Sutton, pub. AIAA 2005. .


External links

* {{spacecraft propulsion Rocket propellants Soviet inventions