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A liquid-propellant rocket or liquid rocket utilizes a
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 ...
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 tanks to be relatively low. It is also possible to use lightweight centrifugal
turbopump A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpo ...
s to pump the
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 to produce thrust. The energy required can either come from the propellants themselves, as with a chemic ...
from the tanks into the combustion chamber, which means that the propellants can be kept under low pressure. This permits the use of low-mass propellant tanks that do not need to resist the high pressures needed to store significant amounts of gasses, resulting in a low
mass ratio In aerospace engineering, mass ratio is a measure of the efficiency of a rocket. It describes how much more massive the vehicle is with propellant than without; that is, the ratio of the rocket's ''wet mass'' (vehicle plus contents plus propellan ...
for the rocket. An inert gas stored in a tank at a high pressure is sometimes used instead of pumps in simpler small engines to force the propellants into the combustion chamber. These engines may have a higher mass ratio, but are usually more reliable, and are therefore used widely in satellites for orbit maintenance. Liquid rockets can be
monopropellant rocket A monopropellant rocket (or "monochemical rocket") is a rocket that uses a single chemical as its propellant. Chemical-reaction monopropellant rockets For monopropellant rockets that depend on a chemical reaction, the power for the propulsive rea ...
s using a single type of propellant, or bipropellant rockets using two types of propellant.
Tripropellant rocket A tripropellant rocket is a rocket that uses three propellants, as opposed to the more common bipropellant rocket or monopropellant rocket designs, which use two or one propellants, respectively. Tripropellant systems can be designed to have high ...
s using three types of propellant are rare. Some designs are
throttleable A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ...
for variable thrust operation and some may be restarted after a previous in-space shutdown. Liquid propellants are also used in
hybrid rocket A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. The hybrid rocket concept can be traced back to the early 1930s. Hybrid rockets avo ...
s, with some of the advantages of a
solid rocket A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants ( fuel/ oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Arabs, Chinese, ...
.


History


Russia / Soviet Union

The idea of a liquid rocket as understood in the modern context first appeared in 1903 in the book ''Exploration of the Universe with Rocket-Propelled Vehicles'', by the Russian school teacher
Konstantin Tsiolkovsky Konstantin Eduardovich Tsiolkovsky (russian: Константи́н Эдуа́рдович Циолко́вский , , p=kənstɐnʲˈtʲin ɪdʊˈardəvʲɪtɕ tsɨɐlˈkofskʲɪj , a=Ru-Konstantin Tsiolkovsky.oga; – 19 September 1935) ...
.The magnitude of his contribution to
astronautics Astronautics (or cosmonautics) is the theory and practice of travel beyond Earth's atmosphere into outer space. Spaceflight is one of its main applications and space science its overarching field. The term ''astronautics'' (originally ''astron ...
is astounding, including the
Tsiolkovsky rocket equation Konstantin Eduardovich Tsiolkovsky (russian: Константи́н Эдуа́рдович Циолко́вский , , p=kənstɐnʲˈtʲin ɪdʊˈardəvʲɪtɕ tsɨɐlˈkofskʲɪj , a=Ru-Konstantin Tsiolkovsky.oga; – 19 September 1935) ...
, multi staged rockets and using liquid oxygen and liquid hydrogen in liquid propellant rockets. Tsiolkovsky influenced later rocket scientists throughout Europe, like
Wernher von Braun Wernher Magnus Maximilian Freiherr von Braun ( , ; 23 March 191216 June 1977) was a German and American aerospace engineer and space architect. He was a member of the Nazi Party and Allgemeine SS, as well as the leading figure in the develop ...
. Soviet search teams at
Peenemünde Peenemünde (, en, " Peene iverMouth") is a municipality on the Baltic Sea island of Usedom in the Vorpommern-Greifswald district in Mecklenburg-Vorpommern, Germany. It is part of the ''Amt'' (collective municipality) of Usedom-Nord. The commu ...
found a German translation of a book by Tsiolkovsky of which "almost every page...was embellished by von Braun's comments and notes." Leading Soviet rocket-engine designer
Valentin Glushko Valentin Petrovich Glushko (russian: Валенти́н Петро́вич Глушко́; uk, Валентин Петрович Глушко, Valentyn Petrovych Hlushko; born 2 September 1908 – 10 January 1989) was a Soviet engineer and the m ...
and rocket designer
Sergey Korolev Sergei Pavlovich Korolev (russian: Сергей Павлович Королёв, Sergey Pavlovich Korolyov, sʲɪrˈɡʲej ˈpavləvʲɪtɕ kərɐˈlʲɵf, Ru-Sergei Pavlovich Korolev.ogg; ukr, Сергій Павлович Корольов, ...
studied Tsiolkovsky's works as youths, and both sought to turn Tsiolkovsky's theories into reality. From 1929 to 1930 in
Leningrad Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
Glushko pursued rocket research at the
Gas Dynamics Laboratory Gas Dynamics Laboratory (GDL) (russian: Газодинамическая лаборатория) was the first Soviet research and development laboratory to focus on rocket technology. Its activities were initially devoted to the development ...
(GDL), where a new research section was set up for the study of liquid-propellant and electric rocket engines. This resulted in the creation of ORM (from "Experimental Rocket Motor" in Russian) engines to . A total of 100 bench tests of liquid-propellant rockets were conducted using various types of fuel, both low and high-boiling and thrust up to 300 kg was achieved. During this period in
Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 million ...
Fredrich Tsander, a scientist and inventor was designing and building liquid rocket engines which ran on compressed air and gasoline. Tsander used it to investigate high-energy fuels including powdered metals mixed with gasoline. In September 1931 Tsander formed the Moscow based '
Group for the Study of Reactive Motion The Moscow-based Group for the Study of Reactive Motion (also 'Group for the Investigation of Reactive Engines and Reactive Flight' and 'Jet Propulsion Study Group') (russian: Группа изучения реактивного движения, ...
', better known by its Russian acronym “GIRD”. In May 1932, Sergey Korolev replaced Tsander as the head of GIRD.
Mikhail Tikhonravov Mikhail Klavdievich Tikhonravov (July 29, 1900 – March 3, 1974) was a Soviet engineer who was a pioneer of spacecraft design and rocketry. Mikhail Tikhonravov was born in Vladimir, Russia. He attended the Zhukovsky Air Force Academy from 1922 ...
launched the first Soviet liquid propelled rocket, fueled by liquid oxygen and jellied gasoline, the GIRD-9, took place on 17 August 1933, which reached an altitude of . In January 1933 Tsander began development of the GIRD-X rocket. This design burned liquid oxygen and gasoline and was one of the first engines to be regeneratively cooled by the liquid oxygen, which flowed around the inner wall of the combustion chamber before entering it. Problems with burn-through during testing prompted a switch from gasoline to less energetic alcohol. The final missile, long by in diameter, had a mass of , and it was anticipated that it could carry a payload to an altitude of . The GIRD X rocket was launched on 25 November 1933 and flew to a height of 80 meters. In 1933 GDL and GIRD merged and became the
Reactive Scientific Research Institute Reactive Scientific Research Institute (commonly known by the joint initialism RNII; russian: Реактивный научно-исследовательский институт, Reaktivnyy nauchno-issledovatel’skiy institut) was one of the ...
(RNII). At RNII Gushko continued the development of liquid propellant rocket engines ОРМ-53 to ОРМ-102, with powering the RP-318 rocket-powered aircraft. In 1938
Leonid Dushkin Leonid Stepanovich Dushkin (Леонид Степанович Душкин) (August 15, 1910 in the Spirove settlement of the Tver region – April 4, 1990), was a major pioneer of Soviet rocket engine technology. He graduated from Moscow ...
replaced Glushko and continued development of the ORM engines, including the engine for the rocket powered interceptor, the
Bereznyak-Isayev BI-1 The Bereznyak-Isayev BI-1 was a Soviet short-range rocket powered interceptor developed during the Second World War. Early design Soviet research and development of rocket-powered aircraft began with Sergey Korolev's GIRD-6 project in 1932. H ...
. At RNII Tikhonravov worked on developing oxygen/alcohol liquid-propellant rocket engines. Ultimately liquid propellant rocket engines were given a low priority during the late 1930s at RNII, however the research was productive and very important for later achievements of the Soviet rocket program.


France

Pedro Paulet Pedro Eleodoro Paulet Mostajo (2 July 1874 or 4 July 1875 – 30 January 1945) was a Peruvian polymath – variously serving as an architect, diplomat, engineer and journalist. He claimed to have been the first person to build a liquid-propellant ...
wrote a letter to ''El Comercio'' in
Lima Lima ( ; ), originally founded as Ciudad de Los Reyes (City of The Kings) is the capital and the largest city of Peru. It is located in the valleys of the Chillón, Rímac and Lurín Rivers, in the desert zone of the central coastal part of ...
in 1927, claiming he had experimented with a liquid rocket engine while he was a student in Paris three decades earlier. Historians of early rocketry experiments, among them
Max Valier Max Valier (9 February 1895 – 17 May 1930) was an Austrian rocketry pioneer. He was a leading figure in the world's first large-scale rocket program, Opel-RAK, and helped found the German ''Verein für Raumschiffahrt'' (VfR – "Spacefligh ...
,
Willy Ley Willy or Willie is a masculine, male given name, often a diminutive form of William (given name), William or Wilhelm (name), Wilhelm, and occasionally a nickname. It may refer to: People Given name or nickname * Willie Aames (born 1960), American ...
, and John D. Clark, have given differing amounts of credence to Paulet's report. Valier applauded Paulet's liquid-propelled rocket design in the
Verein für Raumschiffahrt ''Verein'' is a German word, sometimes translated as ''union'', ''club'' or ''association'', and may refer to: * '' Eingetragener Verein'' (e. V.), a registered voluntary association under German law * Swiss Verein, a voluntary association under ...
publication ''Die Rakete'', saying the engine had "amazing power" and that his plans were necessary for future rocket development.
Wernher von Braun Wernher Magnus Maximilian Freiherr von Braun ( , ; 23 March 191216 June 1977) was a German and American aerospace engineer and space architect. He was a member of the Nazi Party and Allgemeine SS, as well as the leading figure in the develop ...
would later describe Paulet as "the pioneer of the liquid fuel propulsion motor" and stated that "Paulet helped man reach the Moon". Paulet was approached by
Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
to help develop rocket technology, though he refused to assist and never shared the formula for his propellant.


United States

The first ''flight'' of a liquid-propellant rocket took place on March 16, 1926 at
Auburn, Massachusetts Auburn is a town in Worcester County, Massachusetts, United States. The population was 16,889 at the 2020 census. History The Auburn area was first settled in 1714 as of today outer parts of Worcester, Sutton, Leicester and Oxford, Massachus ...
, when American professor Dr. Robert H. Goddard launched a vehicle using
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 app ...
and gasoline as propellants. The rocket, which was dubbed "Nell", rose just 41 feet during a 2.5-second flight that ended in a cabbage field, but it was an important demonstration that rockets utilizing liquid propulsion were possible. Goddard proposed liquid propellants about fifteen years earlier and began to seriously experiment with them in 1921. The German-Romanian
Hermann Oberth Hermann Julius Oberth (; 25 June 1894 – 28 December 1989) was an Austro-Hungarian-born German physicist and engineer. He is considered one of the founding fathers of rocketry and astronautics, along with Robert Esnault-Pelterie, Konstantin ...
published a book in 1922 suggesting the use of liquid propellants.


Germany

In Germany, engineers and scientists became enthralled with liquid propulsion, building and testing them in the late 1920s within
Opel RAK Opel-RAK were a series of rocket vehicles produced by German automobile manufacturer Fritz von Opel, of the Opel car company, in association with others, including Max Valier, Julius Hatry, and Friedrich Wilhelm Sander. Opel RAK is generally con ...
, the world's first rocket program, in Rüsselsheim. According to
Max Valier Max Valier (9 February 1895 – 17 May 1930) was an Austrian rocketry pioneer. He was a leading figure in the world's first large-scale rocket program, Opel-RAK, and helped found the German ''Verein für Raumschiffahrt'' (VfR – "Spacefligh ...
's account, Opel RAK rocket designer,
Friedrich Wilhelm Sander '' Friedrich Wilhelm Sander (25 August 1885 in Glatz (Kłodzko) – 15 September 1938) was a German pyrotechnics and rocket technology engineer as well as manufacturer remembered for his contributions to rocket-powered flight as key protagonist of ...
launched two liquid-fuel rockets at Opel Rennbahn in Rüsselsheim on April 10 and April 12, 1929. These Opel RAK rockets have been the first European, and after Goddard the world's second, liquid-fuel rockets in history. In his book “Raketenfahrt” Valier describes the size of the rockets as of 21 cm in diameter and with a length of 74 cm, weighing 7 kg empty and 16 kg with fuel. The maximum thrust was 45 to 50 kp, with a total burning time of 132 seconds. These properties indicate a gas pressure pumping. The main purpose of these tests was to develop the liquid rocket-propulsion system for a Gebrüder-Müller-Griessheim aircraft under construction for a planned flight across the English channel. Also spaceflight historian
Frank H. Winter Frank H. Winter (born 1942) is an American historian and writer. He is the retired Curator of Rocketry of the National Air and Space Museum (NASM) of the Smithsonian Institution of Washington, D.C. Winter is also an internationally recognized hist ...
, curator at National Air and Space Museum in Washington, DC, confirms the Opel group was working, in addition to their solid-fuel rockets used for land-speed records and the world's first manned rocket-plane flights with the Opel RAK.1, on liquid-fuel rockets. By May 1929, the engine produced a thrust of 200 kg (440 lb.) "for longer than fifteen minutes and in July 1929, the Opel RAK collaborators were able to attain powered phases of more than thirty minutes for thrusts of 300 kg (660-lb.) at Opel's works in Rüsselsheim," again according to Max Valier's account. The Great Depression brought an end to the Opel RAK activities. After working for the German military in the early 1930s, Sander was arrested by Gestapo in 1935, when private rocket-engineering became forbidden in Germany. He was convicted of treason to 5 years in prison and forced to sell his company, he died in 1938. Max Valier's (via
Arthur Rudolph Arthur Louis Hugo Rudolph (November 9, 1906 – January 1, 1996) was a German rocket engineer who was a leader of the effort to develop the V-2 rocket for Nazi Germany. After World War II, the United States Government's Office of Strategic Ser ...
and Heylandt), who died while experimenting in 1930, and Friedrich Sander's work on liquid-fuel rockets was confiscated by the German military, the
Heereswaffenamt ''Waffenamt'' (WaA) was the German Army Weapons Agency. It was the centre for research and development of the Weimar Republic and later the Third Reich for weapons, ammunition and army equipment to the German Reichswehr and then Wehrmacht ...
and integrated into the activities under General
Walter Dornberger Major-General Dr. Walter Robert Dornberger (6 September 1895 – 26 June 1980) was a German Army artillery officer whose career spanned World War I and World War II. He was a leader of Nazi Germany's V-2 rocket programme and other projects a ...
in the early and mid-1930s in a field near Berlin. Max Valier was a co-founder of an amateur research group, the VfR, working on liquid rockets in the early 1930s, and many of whose members eventually became important rocket technology pioneers, including
Wernher von Braun Wernher Magnus Maximilian Freiherr von Braun ( , ; 23 March 191216 June 1977) was a German and American aerospace engineer and space architect. He was a member of the Nazi Party and Allgemeine SS, as well as the leading figure in the develop ...
. Von Braun served as head of the army research station that designed the
V-2 rocket The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name ''Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was develop ...
weapon for the Nazis. By the late 1930s, use of rocket propulsion for manned flight began to be seriously experimented with, as Germany's Heinkel He 176 made the first manned rocket-powered flight using a liquid rocket engine, designed by German aeronautics engineer
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 ...
on June 20, 1939. The only production rocket-powered combat aircraft ever to see military service, the Me 163 ''Komet'' in 1944-45, also used a Walter-designed liquid rocket engine, the
Walter HWK 109-509 The Walter HWK 109-509 was a German liquid-fuel bipropellant rocket engine that powered the Messerschmitt Me 163 Komet and Bachem Ba 349 aircraft. It was produced by Hellmuth Walter Kommanditgesellschaft (HWK) commencing in 1943, with licen ...
, which produced up to 1,700 kgf (16.7 kN) thrust at full power.


Post World War II

After World War II the American government and military finally seriously considered liquid-propellant rockets as weapons and began to fund work on them. The Soviet Union did likewise, and thus began the
Space Race The Space Race was a 20th-century competition between two Cold War rivals, the United States and the Soviet Union, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the t ...
. In 2010s
3D printed 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
engines started being used for spaceflight. Examples of such engines include SuperDraco used in
launch escape system A launch escape system (LES) or launch abort system (LAS) is a crew-safety system connected to a space capsule that can be used to quickly separate the capsule from its launch vehicle in case of an emergency requiring the abort of the launch, s ...
of the
SpaceX Dragon 2 Dragon 2 is a class of partially reusable spacecraft developed and manufactured by American aerospace manufacturer SpaceX, primarily for flights to the International Space Station (ISS). SpaceX has also launched private missions such as Ins ...
and also engines used for first or second stages in
launch vehicle 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 sys ...
s from Astra,
Orbex Orbital Express Launch Ltd., or Orbex, is a United Kingdom-based aerospace company that is developing a small commercial orbital rocket called Prime. Orbex is headquartered in Forres, Moray, in Scotland and has subsidiaries in Denmark and Germany ...
, Relativity Space, Skyrora, or Launcher.


Types

Liquid rockets have been built as
monopropellant rocket A monopropellant rocket (or "monochemical rocket") is a rocket that uses a single chemical as its propellant. Chemical-reaction monopropellant rockets For monopropellant rockets that depend on a chemical reaction, the power for the propulsive rea ...
s using a single type of propellant,
bipropellant 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 t ...
s using two types of propellant, or more exotic
tripropellant rocket A tripropellant rocket is a rocket that uses three propellants, as opposed to the more common bipropellant rocket or monopropellant rocket designs, which use two or one propellants, respectively. Tripropellant systems can be designed to have high ...
s using three types of propellant. Bipropellant liquid rockets generally use a liquid
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. The concept was originally applied solely to those materials capable of releasing chemical energy b ...
, such as
liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33  K. However, for it to be in a fully l ...
or a hydrocarbon fuel such as
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 ...
, and a liquid
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 ). In other words, an oxi ...
, such as
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 app ...
. The engine may be a
cryogenic rocket engine A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel and oxidizer; that is, both its fuel and oxidizer are gases which have been liquefied and are stored at very low temperatures. These highly efficient engines were first f ...
, where the fuel and oxidizer, such as hydrogen and oxygen, are gases which have been liquefied at very low temperatures. Liquid-propellant rockets can be
throttle A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle' ...
d (thrust varied) in realtime, and have control of mixture ratio (ratio at which oxidizer and fuel are mixed); they can also be shut down, and, with a suitable ignition system or self-igniting propellant, restarted.
Hybrid rocket A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. The hybrid rocket concept can be traced back to the early 1930s. Hybrid rockets avo ...
s apply a liquid or gaseous oxidizer to a solid fuel.


Principle of operation

All liquid rocket engines have tankage and pipes to store and transfer propellant, an injector system, a combustion chamber which is very typically cylindrical, and one (sometimes two or more) rocket nozzles. Liquid systems enable 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 is ...
than solids and hybrid rocket motors and can provide very high tankage efficiency. Unlike gases, a typical liquid propellant has a density similar to water, approximately 0.7–1.4g/cm³ (except
liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33  K. However, for it to be in a fully l ...
which has a much lower density), while requiring only relatively modest pressure to prevent vaporization. This combination of density and low pressure permits very lightweight tankage; approximately 1% of the contents for dense propellants and around 10% for liquid hydrogen (due to its low density and the mass of the required insulation). For injection into the combustion chamber, the propellant pressure at the injectors needs to be greater than the chamber pressure; this can be achieved with a pump. Suitable pumps usually use centrifugal
turbopumps A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpo ...
due to their high power and light weight, although
reciprocating pump A reciprocating pump is a class of positive-displacement pumps that includes the piston pump, plunger pump, and diaphragm pump. Well maintained, reciprocating pumps can last for decades. Unmaintained, however, they can succumb to wear and tear. ...
s have been employed in the past. Turbopumps are usually extremely lightweight and can give excellent performance; with an on-Earth weight well under 1% of the thrust. Indeed, overall
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 ...
thrust to weight ratio Thrust-to-weight ratio is a dimensionless ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine that is an indicator of the performance of the engine or vehicle. The instantaneous thrust-to-w ...
s including a turbopump have been as high as 155:1 with the SpaceX
Merlin 1D Merlin is a family of rocket engines developed by SpaceX for use on its Falcon 1, Falcon 9 and Falcon Heavy launch vehicles. Merlin engines use RP-1 and liquid oxygen as rocket propellants in a gas-generator power cycle. The Merlin eng ...
rocket engine and up to 180:1 with the vacuum version Alternatively, instead of pumps, a heavy tank of a high-pressure inert gas such as helium can be used, and the pump forgone; but the
delta-v Delta-''v'' (more known as " change in velocity"), symbolized as ∆''v'' and pronounced ''delta-vee'', as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such a ...
that the stage can achieve is often much lower due to the extra mass of the tankage, reducing performance; but for high altitude or vacuum use the tankage mass can be acceptable. The major components of a rocket engine are therefore the
combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Intern ...
(thrust chamber),
pyrotechnic igniter In pyrotechnics, a pyrotechnic initiator (also initiator or igniter) is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, such as thermites, gas generators, and solid-fuel rockets. T ...
,
propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the ...
feed system, valves, regulators, the propellant tanks, and the
rocket engine nozzle A rocket engine nozzle is a propelling nozzle (usually of the de Laval Karl Gustaf Patrik de Laval (; 9 May 1845 – 2 February 1913) was a Swedish engineer and inventor who made important contributions to the design of steam turbines and cent ...
. In terms of feeding propellants to the combustion chamber, liquid-propellant engines are either pressure-fed or pump-fed, and pump-fed engines work in either a
gas-generator cycle The gas-generator cycle is a power cycle of a pumped liquid bipropellant rocket engine. Part of the unburned propellant is burned in a gas generator (or preburner) and the resulting hot gas is used to power the propellant pumps before being exha ...
, a staged-combustion cycle, or an
expander cycle The expander cycle is a power cycle of a bipropellant rocket engine. In this cycle, the fuel is used to cool the engine's combustion chamber, picking up heat and changing phase. The now heated and gaseous fuel then powers the turbine that drives ...
. A liquid rocket engine can be tested prior to use, whereas for a solid rocket motor a rigorous
quality management Quality management ensures that an organization, product or service consistently functions well. It has four main components: quality planning, quality assurance, quality control and quality improvement. Quality management is focused not on ...
must be applied during manufacturing to ensure high reliability. A Liquid rocket engine can also usually be reused for several flights, as 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 n ...
and
Falcon 9 Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company SpaceX. The rocket has two stages. The first (booster) stage carries the second stage and pay ...
series rockets, although reuse of solid rocket motors was also effectively demonstrated during the shuttle program. Use of liquid propellants can be associated with a number of issues: * Because the propellant is a very large proportion of the mass of the vehicle, the
center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...
shifts significantly rearward as the propellant is used; one will typically lose control of the vehicle if its center mass gets too close to the center of drag/pressure. * When operated within an atmosphere, pressurization of the typically very thin-walled propellant tanks must guarantee positive
gauge pressure Pressure measurement is the measurement of an applied force by a fluid ( liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pre ...
at all times to avoid catastrophic collapse of the tank. * Liquid propellants are subject to '' slosh'', which has frequently led to loss of control of the vehicle. This can be controlled with slosh baffles in the tanks as well as judicious control laws in the
guidance system A guidance system is a virtual or physical device, or a group of devices implementing a controlling the movement of a ship, aircraft, missile, rocket, satellite, or any other moving object. Guidance is the process of calculating the changes in po ...
. * They can suffer from
pogo oscillation Pogo oscillation is a self-excited vibration in liquid-propellant rocket engines caused by combustion instability. The unstable combustion results in variations of engine thrust, causing variations of acceleration on the vehicle's flexible structu ...
where the rocket suffers from uncommanded cycles of acceleration. * Liquid propellants often need
ullage motor Ullage motors (also known as ullage engines or ullage rockets) are relatively small, independently fueled rocket engines that may be fired prior to main engine ignition, when the vehicle is in a zero-g situation. The resulting acceleration cause ...
s in zero-gravity or during staging to avoid sucking gas into engines at start up. They are also subject to vortexing within the tank, particularly towards the end of the burn, which can also result in gas being sucked into the engine or pump. * Liquid propellants can leak, especially hydrogen, possibly leading to the formation of an explosive mixture. * Turbopumps to pump liquid propellants are complex to design, and can suffer serious failure modes, such as overspeeding if they run dry or shedding fragments at high speed if metal particles from the manufacturing process enter the pump. * Cryogenic propellants, such as liquid oxygen, freeze atmospheric water vapor into ice. This can damage or block seals and valves and can cause leaks and other failures. Avoiding this problem often requires lengthy ''chilldown'' procedures which attempt to remove as much of the vapor from the system as possible. Ice can also form on the outside of the tank, and later fall and damage the vehicle. External foam insulation can cause issues as shown by the Space Shuttle Columbia disaster. Non-cryogenic propellants do not cause such problems. * Non-storable liquid rockets require considerable preparation immediately before launch. This makes them less practical than
solid rocket A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants ( fuel/ oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Arabs, Chinese, ...
s for most weapon systems.


Propellants

Thousands of combinations of fuels and oxidizers have been tried over the years. Some of the more common and practical ones are:


Cryogenic

* Liquid oxygen (LOX, O2) and liquid hydrogen (LH2, LH, H2) –
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 n ...
main engines, Ariane 5 main stage and the Ariane 5 ECA second stage, the BE-3 of Blue Origin's New Shepard, the first and second stage of the Delta IV rocket, Delta IV, the upper stages of the Ares I, Saturn V (rocket), Saturn V's S-II, second and S-IVB, third stages, Saturn IB (rocket), Saturn IB, and Saturn I (rocket), Saturn I as well as Centaur (rocket stage), Centaur rocket stage, the first stage and second stage of the H-II, H-IIA, H-IIB, and the upper stage of the Geosynchronous Satellite Launch Vehicle, GSLV Mk-II and Geosynchronous Satellite Launch Vehicle Mark III, GSLV Mk-III. The main advantages of this mixture are a clean burn (water vapor is the only combustion product) and high performance. * Liquid oxygen (LOX) and liquid methane rocket fuel, liquid methane (CH4, liquefied natural gas, LNG) – the in-development Raptor (rocket engine family), Raptor (SpaceX) and BE-4 (Blue Origin) engines. (See also Propulsion Cryogenics & Advanced Development project of NASA, and Project Morpheus.) One of the most efficient mixtures, oxygen and hydrogen, suffers from the extremely low temperatures required for storing liquid hydrogen (around ) and very low fuel density (, compared to RP-1 at ), necessitating large tanks that must also be lightweight and insulating. Lightweight foam insulation on the Space Shuttle external tank led to the 's Space Shuttle Columbia disaster, destruction, as a piece broke loose, damaged its wing and caused it to break up on atmospheric reentry. Liquid methane/LNG has several advantages over LH. Its performance (max.
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 is ...
) is lower than that of LH but higher than that of RP1 (kerosene) and solid propellants, and its higher density, similarly to other hydrocarbon fuels, provides higher thrust to volume ratios than LH, although its density is not as high as that of RP1. This makes it specially attractive for reusable launch systems because higher density allows for smaller motors, propellant tanks and associated systems. LNG also burns with less or no soot (less or no coking) than RP1, which eases reusability when compared with it, and LNG and RP1 burn cooler than LH so LNG and RP1 do not deform the interior structures of the engine as much. This means that engines that burn LNG can be reused more than those that burn RP1 or LH. Unlike engines that burn LH, both RP1 and LNG engines can be designed with a shared shaft with a single turbine and two turbopumps, one each for LOX and LNG/RP1. In space, LNG does not need heaters to keep it liquid, unlike RP1. LNG is less expensive, being readily available in large quantities. It can be stored for more prolonged periods of time, and is less explosive than LH.


Semi-cryogenic

* Liquid oxygen (LOX) and
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 ...
(kerosene) – Saturn V (rocket), Saturn V's S-IC, first stage, Zenit rocket, R-7 Semyorka, R-7-derived vehicles including Soyuz (rocket family), Soyuz, Delta rocket, Delta, Saturn I (rocket), Saturn I, and Saturn IB (rocket), Saturn IB first stages, Titan (rocket family), Titan I and Atlas rockets, Falcon 1 and
Falcon 9 Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company SpaceX. The rocket has two stages. The first (booster) stage carries the second stage and pay ...
* Liquid oxygen (LOX) and alcohol (ethanol, C2H5OH) – early liquid rockets, like Germany, German (World War II) A4, aka V-2, and Redstone (rocket), Redstone * Liquid oxygen (LOX) and gasoline – Robert Goddard (scientist), Robert Goddard's first liquid rocket * Liquid oxygen (LOX) and carbon monoxide (CO) – proposed for a Mars ''hopper'' vehicle (with a specific impulse of approximately 250s), principally because carbon monoxide and oxygen can be straightforwardly produced by Zirconia electrolysis from the Martian atmosphere without requiring use of any of the Martian water resources to obtain Hydrogen.


Non-cryogenic/storable/hypergolic

Many non-cryogenic bipropellants are hypergolic propellant, hypergolic (self igniting). * T-Stoff (80% hydrogen peroxide, H2O2 as the oxidizer) and C-Stoff (methanol, , and hydrazine hydrate, as the fuel) – used for the Hellmuth-Walter-Werke HWK 109-509A, -B and -C engine family used on the Messerschmitt Me 163B Komet, an operational rocket fighter plane of World War II, and Bachem Ba 349, Ba 349 ''Natter'' manned Takeoff#Vertical takeoff, VTO interceptor prototypes. * Nitric acid (HNO3) and kerosene – Soviet Union, Soviet Bereznyak-Isayev BI-1, BI-1 and Mikoyan-Gurevich I-270, MiG I-270 rocket fighter prototypes, Scud-A, aka SS-1 SRBM * Inhibited red fuming nitric acid (IRFNA, HNO3 + N2O4) and unsymmetric dimethyl hydrazine (UDMH, (CH3)2N2H2) – Soviet Scud-C, aka SS-1-c,-d,-e * Nitric acid 73% with dinitrogen tetroxide 27% (AK27) and kerosene/gasoline mixture (TM-185) – various Russian (USSR) cold-war ballistic missiles (R-12 Dvina, R-12, Scud-B,-D), Iran: Shahab-5, North Korea: Taepodong-2 * High-test peroxide (H2O2) and kerosene – United Kingdom, UK (1970s) Black Arrow, United States, USA Development (or study): BA-3200 * Hydrazine (N2H4) and red fuming nitric acid – MIM-3 Nike Ajax Antiaircraft Rocket * Unsymmetric dimethylhydrazine (UDMH) and dinitrogen tetroxide (N2O4) – Proton rocket, Proton, Rokot, Long March 2 (rocket family), Long March 2 (used to launch Shenzhou (spacecraft), Shenzhou crew vehicles.) * Aerozine 50 (50% UDMH, 50% hydrazine) and dinitrogen tetroxide (N2O4) – Titan (rocket family), Titans 2–4, Apollo lunar module, Apollo service module, interplanetary probes (Such as Voyager 1 and Voyager 2) * Monomethylhydrazine (MMH, (CH3)HN2H2) and dinitrogen tetroxide (N2O4) – Space Shuttle orbiter's orbital maneuvering system (OMS) engines and Reaction control system (RCS) thrusters. SpaceX's Draco (rocket engine), Draco and SuperDraco engines for the Dragon spacecraft. For storable propellant, storable ICBMs and most spacecraft, including crewed vehicles, planetary probes, and satellites, storing cryogenic propellants over extended periods is unfeasible. Because of this, mixtures of hydrazine or its derivatives in combination with nitrogen oxides are generally used for such applications, but are toxic and carcinogenic. Consequently, to improve handling, some crew vehicles such as Dream Chaser and Space Ship Two plan to use
hybrid rocket A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. The hybrid rocket concept can be traced back to the early 1930s. Hybrid rockets avo ...
s with non-toxic fuel and oxidizer combinations.


Injectors

The injector implementation in liquid rockets determines the percentage of the theoretical performance of the Rocket engine nozzle, nozzle that can be achieved. A poor injector performance causes unburnt propellant to leave the engine, giving poor efficiency. Additionally, injectors are also usually key in reducing thermal loads on the nozzle; by increasing the proportion of fuel around the edge of the chamber, this gives much lower temperatures on the walls of the nozzle.


Types of injectors

Injectors can be as simple as a number of small diameter holes arranged in carefully constructed patterns through which the fuel and oxidizer travel. The speed of the flow is determined by the square root of the pressure drop across the injectors, the shape of the hole and other details such as the density of the propellant. The first injectors used on the V-2 created parallel jets of fuel and oxidizer which then combusted in the chamber. This gave quite poor efficiency. Injectors today classically consist of a number of small holes which aim jets of fuel and oxidizer so that they collide at a point in space a short distance away from the injector plate. This helps to break the flow up into small droplets that burn more easily. The main types of injectors are * Shower head * Self-impinging doublet * Cross-impinging triplet * Centripetal or swirling * pintle injector, Pintle The pintle injector permits good mixture control of fuel and oxidizer over a wide range of flow rates. The pintle injector was used in the Apollo Lunar Module engines (Descent Propulsion System) and the Kestrel (rocket engine), Kestrel engine, it is currently used in the Merlin (rocket engine), Merlin engine on
Falcon 9 Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company SpaceX. The rocket has two stages. The first (booster) stage carries the second stage and pay ...
and Falcon Heavy rockets. The RS-25 engine designed for 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 n ...
uses a system of fluted posts, which use heated hydrogen from the preburner to vaporize the liquid oxygen flowing through the center of the posts and this improves the rate and stability of the combustion process; previous engines such as the F-1 used for the Apollo program had significant issues with oscillations that led to destruction of the engines, but this was not a problem in the RS-25 due to this design detail.
Valentin Glushko Valentin Petrovich Glushko (russian: Валенти́н Петро́вич Глушко́; uk, Валентин Петрович Глушко, Valentyn Petrovych Hlushko; born 2 September 1908 – 10 January 1989) was a Soviet engineer and the m ...
invented the centripetal injector in the early 1930s, and it has been almost universally used in Russian engines. Rotational motion is applied to the liquid (and sometimes the two propellants are mixed), then it is expelled through a small hole, where it forms a cone-shaped sheet that rapidly atomizes. Goddard's first liquid engine used a single impinging injector. German scientists in WWII experimented with impinging injectors on flat plates, used successfully in the Wasserfall missile.


Combustion stability

To avoid instabilities such as ''chugging,'' which is a relatively low speed oscillation, the engine must be designed with enough pressure drop across the injectors to render the flow largely independent of the chamber pressure. This pressure drop is normally achieved by using at least 20% of the chamber pressure across the injectors. Nevertheless, particularly in larger engines, a high speed combustion oscillation is easily triggered, and these are not well understood. These high speed oscillations tend to disrupt the gas side boundary layer of the engine, and this can cause the cooling system to rapidly fail, destroying the engine. These kinds of oscillations are much more common on large engines, and plagued the development of the Saturn V, but were finally overcome. Some combustion chambers, such as those of the RS-25 engine, use Helmholtz resonators as damping mechanisms to stop particular resonant frequencies from growing. To prevent these issues the RS-25 injector design instead went to a lot of effort to vaporize the propellant prior to injection into the combustion chamber. Although many other features were used to ensure that instabilities could not occur, later research showed that these other features were unnecessary, and the gas phase combustion worked reliably. Testing for stability often involves the use of small explosives. These are detonated within the chamber during operation, and causes an impulsive excitation. By examining the pressure trace of the chamber to determine how quickly the effects of the disturbance die away, it is possible to estimate the stability and redesign features of the chamber if required.


Engine cycles

For liquid-propellant rockets, four different ways of powering the injection of the propellant into the chamber are in common use. Fuel and oxidizer must be pumped into the combustion chamber against the pressure of the hot gasses being burned, and engine power is limited by the rate at which propellant can be pumped into the combustion chamber. For atmospheric or launcher use, high pressure, and thus high power, engine cycles are desirable to minimize gravity drag. For orbital use, lower power cycles are usually fine. ;Pressure-fed cycle (rocket), Pressure-fed cycle: The propellants are forced in from pressurised (relatively heavy) tanks. The heavy tanks mean that a relatively low pressure is optimal, limiting engine power, but all the fuel is burned, allowing high efficiency. The pressurant used is frequently helium due to its lack of reactivity and low density. Examples: AJ-10, used in the Space Shuttle Orbital Maneuvering System, OMS, Apollo Service Propulsion System, SPS, and the second stage of the Delta II. ;Electric pump-fed engine, Electric pump-fed: An electric motor, generally a brushless DC electric motor, drives the pumps. The electric motor is powered by a battery pack. It is relatively simple to implement and reduces the complexity of the turbomachinery design, but at the expense of the extra dry mass of the battery pack. Example engine is the Rutherford (rocket engine), Rutherford designed and used by Rocket Lab. ;Gas-generator cycle (rocket), Gas-generator cycle: A small percentage of the propellants are burnt in a preburner to power a turbopump and then exhausted through a separate nozzle, or low down on the main one. This results in a reduction in efficiency since the exhaust contributes little or no thrust, but the pump turbines can be very large, allowing for high power engines. Examples: Saturn V's F-1 engine, F-1 and J-2 engine, J-2, Delta IV's RS-68, Ariane 5's HM7B, Falcon 9 v1.1, Falcon 9's Merlin 1D, Merlin. ;Tap-off cycle: Takes hot gases from the main
combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Intern ...
of the rocket engine and routes them through engine
turbopump A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpo ...
turbines to pump propellant, then is exhausted. Since not all propellant flows through the main combustion chamber, the tap-off cycle is considered an open-cycle engine. Examples include the J-2S and BE-3. ;Expander cycle: Cryogenic fuel (hydrogen, or methane) is used to cool the walls of the combustion chamber and nozzle. Absorbed heat vaporizes and expands the fuel which is then used to drive the turbopumps before it enters the combustion chamber, allowing for high efficiency, or is bled overboard, allowing for higher power turbopumps. The limited heat available to vaporize the fuel constrains engine power. Examples: RL10 for Atlas V and Delta IV second stages (closed cycle), H-II's LE-5 (bleed cycle). ;Staged combustion cycle (rocket), Staged combustion cycle: A fuel- or oxidizer-rich mixture is burned in a preburner and then drives turbopumps, and this high-pressure exhaust is fed directly into the main chamber where the remainder of the fuel or oxidizer undergoes combustion, permitting very high pressures and efficiency. Examples: SSME, RD-191, LE-7. ;Staged combustion cycle (rocket)#Full-flow staged combustion cycle, Full-flow staged combustion cycle: Fuel- and oxidizer-rich mixtures are burned in separate preburners and driving the turbopumps, then both high-pressure exhausts, one oxygen rich and the other fuel rich, are fed directly into the main chamber where they combine and combust, permitting very high pressures and incredible efficiency. Example: SpaceX Raptor.


Engine cycle tradeoffs

Selecting an engine cycle is one of the earlier steps to rocket engine design. A number of tradeoffs arise from this selection, some of which include:


Cooling

Injectors are commonly laid out so that a fuel-rich layer is created at the combustion chamber wall. This reduces the temperature there, and downstream to the throat and even into the nozzle and permits the combustion chamber to be run at higher pressure, which permits a higher expansion ratio nozzle to be used which gives a higher ''I'' and better system performance.Rocket Propulsion elements - Sutton Biblarz, section 8.1 A liquid rocket engine often employs regenerative cooling (rocketry), regenerative cooling, which uses the fuel or less commonly the oxidizer to cool the chamber and nozzle.


Ignition

Ignition can be performed in many ways, but perhaps more so with liquid propellants than other rockets a consistent and significant ignitions source is required; a delay of ignition (in some cases as small as a few tens of milliseconds) can cause overpressure of the chamber due to excess propellant. A hard start can even cause an engine to explode. Generally, ignition systems try to apply flames across the injector surface, with a mass flow of approximately 1% of the full mass flow of the chamber. Safety interlocks are sometimes used to ensure the presence of an ignition source before the main valves open; however reliability of the interlocks can in some cases be lower than the ignition system. Thus it depends on whether the system must fail safe, or whether overall mission success is more important. Interlocks are rarely used for upper, unmanned stages where failure of the interlock would cause loss of mission, but are present on the RS-25 engine, to shut the engines down prior to liftoff of the Space Shuttle. In addition, detection of successful ignition of the igniter is surprisingly difficult, some systems use thin wires that are cut by the flames, pressure sensors have also seen some use. Methods of ignition include Pyrotechnic initiator, pyrotechnic, electrical (spark or hot wire), and chemical. Hypergolic propellants have the advantage of self igniting, reliably and with less chance of hard starts. In the 1940s, the Russians began to start engines with hypergols, to then switch over to the primary propellants after ignition. This was also used on the American F-1 rocket engine on the Apollo program. Ignition with a pyrophoric agent: Triethylaluminium ignites on contact with air and will ignite and/or decompose on contact with water, and with any other oxidizer—it is one of the few substances sufficiently pyrophoric to ignite on contact with cryogenic
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 app ...
. The enthalpy of combustion, ΔcH°, is . Its easy ignition makes it particularly desirable as a
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 ...
Pyrotechnic initiator, ignitor. May be used in conjunction with triethylborane to create triethylaluminum-triethylborane, better known as TEA-TEB.


See also

* Comparison of orbital launch systems * Comparison of orbital launchers families * Comparison of orbital rocket engines * Comparison of solid-fuelled orbital launch systems * List of space launch system designs * List of missiles * List of orbital launch systems * List of sounding rockets * List of military rockets


References


Sources cited

* * * *


External links


An online book entitled ''”How to Design, Build, and Test Small Liquid-Fuel Rocket Engines”''

The Heinkel He 176, worlds's first liquid-fuel rocket aircraft
{{DEFAULTSORT:Liquid-Propellant Rocket American inventions Rocket propulsion Rocket engines by propellant