View source for Liquid rocket propellant

{{Short description|Liquid form of rocket propellants}}
{{Main|Liquid-propellant rocket}}

The highest [[specific impulse]] chemical rockets use liquid propellants ([[liquid-propellant rocket]]s). They can consist of a single chemical (a '''monopropellant''') or a mix of two chemicals, called [[bipropellants]]. Bipropellants can further be divided into two categories; [[hypergolic propellant]]s, which ignite when the fuel and [[Oxidizing agent|oxidizer]] make contact, and non-hypergolic propellants which require an ignition source.<ref>{{cite book|title=Space Mission Analysis and Design|last1=Larson|first1=W.J.|last2=Wertz|first2=J.R.|date=1992|publisher=Kluver Academic Publishers|location=Boston}}</ref>

About 170 different [[propellants]] made of [[liquid fuel]] have been tested, excluding minor changes to a specific propellant such as propellant additives, corrosion inhibitors, or stabilizers. In the U.S. alone at least 25 different propellant combinations have been flown.<ref>{{cite journal|last=Sutton|first=G. P.|title=History of liquid propellant rocket engines in the united states|journal=Journal of Propulsion and Power|date=2003|volume=19 |issue=6 |pages=978–1007|doi=10.2514/2.6942}}</ref>

Many factors go into choosing a propellant for a liquid-propellant rocket engine. The primary factors include ease of operation, cost, hazards/environment and performance.<ref>{{Cite journal |last=Romantsova |first=O. V. |last2=Ulybin |first2=V. B. |date=2015-04-01 |title=Safety issues of high-concentrated hydrogen peroxide production used as rocket propellant |url=https://www.sciencedirect.com/science/article/abs/pii/S0094576514004007 |journal=Acta Astronautica |volume=109 |pages=231–234 |doi=10.1016/j.actaastro.2014.10.022 |issn=0094-5765|url-access=subscription }}</ref>

== History ==

=== Development in early 20th century ===
[[File:Goddard and Rocket.jpg|thumb|200px|right|[[Robert H. Goddard]] on March 16, 1926, holding the launching frame of the first liquid-fueled rocket]]

[[Konstantin Tsiolkovsky]] proposed the use of liquid propellants in 1903, in his article ''Exploration of Outer Space by Means of Rocket Devices.''<ref>Tsiolkovsky, Konstantin E. (1903), "The Exploration of Cosmic Space by Means of Reaction Devices (Исследование мировых пространств реактивными приборами)", The Science Review (in Russian) (5), archived from the original on 19 October 2008, retrieved 22 September 2008</ref><ref>{{Cite book|title=Macmillan encyclopedia of energy|url=https://archive.org/details/macmillanencyclo00zume|url-access=registration|date=2001|publisher=Macmillan Reference USA|isbn=0028650212|editor-last=Zumerchik|editor-first=John|location=New York|oclc=44774933}}</ref>

On March 16, 1926, [[Robert H. Goddard]] used [[liquid oxygen]] (''LOX'') and [[gasoline]] as [[Rocket propellant |propellant]]s for his first partially successful [[liquid-propellant rocket]] launch. Both propellants are readily available, cheap and highly energetic. Oxygen is a moderate [[cryogen]] as air will not liquefy against a liquid oxygen tank, so it is possible to store LOX briefly in a rocket without excessive insulation. {{clarify|date=July 2023}}

In Germany, engineers and scientists began building and testing liquid propulsion rockets in the late 1920s.<ref>{{cite web |url=https://repository.si.edu/bitstream/handle/10088/30573/Weimar%20Rocket%20Fad.pdf |title=The Rocketry and Spaceflight Fad in Germany, 1923-1933 |author=MJ Neufeld}}</ref> According to [[Max Valier]], two liquid-propellant [[Opel RAK]] rockets were launched in [[Rüsselsheim]] on April 10 and April 12, 1929.<ref>{{Cite book |last=Valier |first=Max |title=Raketenfahrt |pages=209–232 |language=de |doi=10.1515/9783486761955-006 |isbn=978-3-486-76195-5}}</ref>

=== World War II era ===
Germany had very active rocket development before and during [[World War II]], both for the strategic [[V-2 rocket]] and other missiles. The V-2 used an alcohol/LOX [[liquid-propellant engine]], with [[hydrogen peroxide]] to drive the fuel pumps.<ref name=Clark2018>{{cite book |isbn = 978-0-8135-9918-2 |title = Ignition!: An Informal History of Liquid Rocket Propellants |last1 = Clark |first1 = John Drury |author-link=John Drury Clark |date = 23 May 2018 |publisher = Rutgers University Press |url=https://books.google.com/books?id=BdU4DwAAQBAJ  |pages=302}}</ref>{{rp|9}} The alcohol was mixed with water for engine cooling. Both Germany and the United States developed reusable liquid-propellant rocket engines that used a storeable liquid oxidizer with much greater density than LOX and a liquid fuel that [[Hypergolic propellant|ignited spontaneously on contact]] with the high density oxidizer.{{citation needed|date=May 2025}} 

The major manufacturer of German rocket engines for military use, the [[Hellmuth Walter Kommanditgesellschaft|HWK firm]],<ref>[http://www.walterwerke.co.uk/walter/index.htm British site on the HWK firm]</ref> manufactured the [[Ministry of Aviation (Nazi Germany)|RLM]]-numbered '''109-500'''-designation series of rocket engine systems, and either used [[T-Stoff|hydrogen peroxide]] as a monopropellant for [[Walter HWK 109-500|''Starthilfe'']] rocket-propulsive assisted takeoff needs;<ref>[http://www.walterwerke.co.uk/ato/109500.htm Walter site-page on the ''Starthilfe'' system]</ref> or as a [[Walter HWK 109-507|form of thrust]] for [[Henschel Hs 293|MCLOS-guided air-sea glide bombs]];<ref>[http://www.walterwerke.co.uk/missiles/hs293.htm Wlater site-page on the Henschel air-sea glide bomb]</ref> and used in a bipropellant combination of the same oxidizer with a [[C-Stoff|fuel mixture of hydrazine hydrate and methyl alcohol]] for [[Walter HWK 109-509|rocket engine systems intended for manned combat aircraft propulsion]] purposes.<ref>[http://www.walterwerke.co.uk/walter/motors.htm List of 109-509 series Walter rocket motors]</ref> 

The U.S. engine designs were fueled with the bipropellant combination of [[nitric acid]] as the oxidizer; and [[aniline]] as the fuel. Both engines were used to power aircraft, the [[Me 163 Komet]] interceptor in the case of the Walter 509-series German engine designs, and [[RATO]] units from both nations (as with the ''Starthilfe'' system for the Luftwaffe) to assist take-off of aircraft, which comprised the primary purpose for the case of the U.S. liquid-fueled rocket engine technology - much of it coming from the mind of U.S. Navy officer [[Robert Truax]].<ref>{{cite book|last=Braun|first=Wernher von (Estate of)|author-link=Wernher von Braun|author2=Ordway III |author3=Frederick I | others=& David Dooling, Jr.|title=Space Travel: A History|year=1985|publisher=Harper & Row|location=New York|isbn=0-06-181898-4|pages=83, 101|orig-year=1975}}</ref>

=== 1950s and 1960s ===
{{unreferenced section|date=March 2017}}
During the 1950s and 1960s there was a great burst of activity by propellant chemists to find high-energy liquid and solid propellants better suited to the military. Large strategic missiles need to sit in land-based or submarine-based silos for many years, able to launch at a moment's notice. Propellants requiring continuous refrigeration, which cause their rockets to grow ever-thicker blankets of ice, were not practical. As the military was willing to handle and use hazardous materials, a great number of dangerous chemicals were brewed up in large batches, most of which wound up being deemed unsuitable for operational systems.{{citation needed|date=May 2025}}  In the case of [[nitric acid]], the acid itself ({{chem|H|N|O|3}}) was unstable, and corroded most metals, making it difficult to store. The addition of a modest amount of [[dinitrogen tetroxide|nitrogen tetroxide]], {{chem|N|2|O|4}}, turned the mixture red and kept it from changing composition, but left the problem that nitric acid corrodes containers it is placed in, releasing gases that can build up pressure in the process. The breakthrough was the addition of a little [[hydrogen fluoride]] (HF), which forms a self-sealing metal fluoride on the interior of tank walls that ''Inhibited'' Red Fuming Nitric Acid. This made "IRFNA" storeable.<ref name="Clark2018" /> 

Propellant combinations based on IRFNA or pure {{chem|N|2|O|4}} as oxidizer and kerosene or [[hypergolic]] (self igniting) [[aniline]], [[hydrazine]] or [[unsymmetrical dimethylhydrazine]] (UDMH) as fuel were then adopted in the United States and the Soviet Union for use in strategic and tactical missiles. The self-igniting storeable liquid bi-propellants have somewhat lower specific impulse than LOX/kerosene but have higher density so a greater mass of propellant can be placed in the same sized tanks. Gasoline was replaced by different [[hydrocarbon]] fuels,<ref name=Clark2018 /> for example [[RP-1]]{{snd}} a highly refined grade of [[kerosene]]. This combination is quite practical for rockets that need not be stored.

== Kerosene ==
{{unreferenced section|date=December 2017}}
The V-2 rockets developed by Nazi Germany used LOX and ethyl alcohol. One of the main advantages of alcohol was its water content, which provided cooling in larger rocket engines. Petroleum-based fuels offered more power than alcohol, but standard gasoline and kerosene left too much soot and combustion by-products that could clog engine plumbing. In addition, they lacked the cooling properties of ethyl alcohol.

During the early 1950s, the chemical industry in the U.S. was assigned the task of formulating an improved petroleum-based rocket propellant which would not leave residue behind and also ensure that the engines would remain cool. The result was [[RP-1]], the specifications of which were finalized by 1954.<ref name="Clark2018" /> A highly refined form of jet fuel, RP-1 burned much more cleanly than conventional petroleum fuels and also posed less of a danger to ground personnel from explosive vapours. It became the propellant for most of the early American rockets and ballistic missiles such as the Atlas, Titan I, and Thor. The Soviets quickly adopted RP-1 for their R-7 missile, but the majority of Soviet launch vehicles ultimately used storable hypergolic propellants. {{As of|2017}}, it is used in the [[multistage rocket|first stage]]s of many orbital launchers.

== Hydrogen ==
Many early rocket theorists believed that [[Hydrogen gas|hydrogen]] would be a marvelous propellant, since it gives the highest [[specific impulse]]. It is also considered the cleanest when oxidized with [[oxygen]] because the only by-product is water. Steam reforming of [[natural gas]] is the most common method of producing commercial bulk hydrogen at about 95% of the world production<ref name="Ogden 1999">{{cite journal |last=Ogden |first=J.M. |year=1999 |title=Prospects for building a hydrogen energy infrastructure |journal=[[Annual Review of Energy and the Environment]] |volume=24 |pages=227–279 |doi=10.1146/annurev.energy.24.1.227 |doi-access=}}</ref><ref>{{cite report |title=Hydrogen production: Natural gas reforming |publisher=U.S. [[Department of Energy]] |url=https://energy.gov/eere/fuelcells/hydrogen-production-natural-gas-reforming |access-date=6 April 2017}}</ref> of {{nobr|500 billion m<sup>3</sup>}} in 1998.<ref>{{cite report |last1=Rostrup-Nielsen |first1=Jens R. |last2=Rostrup-Nielsen |first2=Thomas |date=2007-03-23 |df=dmy-all |title=Large-scale Hydrogen Production |page=3 |publisher=[[Haldor Topsøe (company)|Haldor Topsøe]] |url=http://www.topsoe.com/sites/default/files/topsoe_large_scale_hydrogen_produc.pdf |url-status=dead |access-date=2023-07-16 |archive-url=https://web.archive.org/web/20160208011417/http://www.topsoe.com/sites/default/files/topsoe_large_scale_hydrogen_produc.pdf |archive-date=2016-02-08 |quote=The total hydrogen market in 1998 was 390×{{10^|9}}&nbsp;Nm³/y + 110×{{10^|9}}&nbsp;Nm³/y co-production.}}</ref> At high temperatures (700–1100&nbsp;°C) and in the presence of a [[metal]]-based [[catalyst]] ([[nickel]]), steam reacts with methane to yield [[carbon monoxide]] and hydrogen.

Hydrogen is very bulky compared to other fuels; it is typically stored as a cryogenic liquid, a technique mastered in the early 1950s as part of the [[Thermonuclear weapon#United States|hydrogen bomb development program]] at [[Los Alamos National Laboratory|Los Alamos]]. [[Liquid hydrogen]] can be stored and transported without boil-off, by using [[helium]] as a cooling refrigerant, since helium has an even lower boiling point than hydrogen. Hydrogen is lost via venting to the atmosphere only after it is loaded onto a launch vehicle, where there is no refrigeration.<ref>{{cite book |first=Richard |last=Rhodes |author-link=Richard Rhodes |year=1995 |title=Dark Sun: The making of the hydrogen bomb |pages=483–504 |publisher=[[Simon & Schuster]] |place=New York, NY |isbn=978-0-684-82414-7 }}</ref>

In the late 1950s and early 1960s it was adopted for hydrogen-fuelled stages such as [[Centaur (rocket stage)|Centaur]] and [[Saturn I|Saturn]] upper stages.{{citation needed|date=March 2017}} Hydrogen has low density even as a liquid, requiring large tanks and pumps; maintaining the necessary extreme cold requires tank insulation. This extra weight reduces the mass fraction of the stage or requires extraordinary measures such as pressure stabilization of the tanks to reduce weight. (Pressure stabilized tanks support most of the loads with internal pressure rather than with solid structures, employing primarily the [[tensile strength]] of the tank material.{{citation needed|date=March 2017}})

The Soviet rocket programme, in part due to a lack of technical capability, did not use liquid hydrogen as a propellant until the [[Energia (rocket)|Energia]] core stage in the 1980s.{{citation needed|date=March 2017}}

=== Upper stage use ===
The liquid-rocket engine bipropellant [[liquid oxygen]] and hydrogen offers the highest specific impulse for conventional rockets. This extra performance largely offsets the disadvantage of low density, which requires larger fuel tanks. However, a small increase in specific impulse in an upper stage application can give a significant increase in payload-to-orbit mass.<ref name="Sutton 2010">{{cite book |last1=Sutton |first1=E.P. |last2=Biblarz |first2=O. |year=2010 |title=Rocket Propulsion Elements |edition=8th |publisher=Wiley |location=New York |isbn=9780470080245 |url=https://archive.org/details/Rocket_Propulsion_Elements_8th_Edition_by_Oscar_Biblarz_George_P._Sutton |via=Internet Archive}}</ref>

=== Comparison to kerosene ===
{{unreferenced section|date=March 2017}}
Launch pad fires due to spilled kerosene are more damaging than hydrogen fires, for two main reasons:
*Kerosene burns about 20% hotter in absolute temperature than hydrogen.
*Hydrogen's buoyancy. Since hydrogen is a deep cryogen it boils quickly and rises, due to its very low density as a gas. Even when hydrogen burns, the [[Steam|gaseous {{chem|H|2|O}}]] that is formed has a molecular weight of only {{val|18|ul=Da}} compared to {{val|29.9|ul=Da}} for air, so it also rises quickly. Spilled kerosene fuel, on the other hand, falls to the ground and if ignited can burn for hours when spilled in large quantities.
Kerosene fires unavoidably cause extensive heat damage that requires time-consuming repairs and rebuilding. This is most frequently experienced by test stand crews involved with firings of large, unproven rocket engines.

Hydrogen-fuelled engines require special design, such as running propellant lines horizontally, so that no "traps" form in the lines, which would cause pipe ruptures due to boiling in confined spaces. (The same caution applies to other cryogens such as liquid oxygen and [[liquid natural gas]] (LNG).) Liquid hydrogen fuel has an excellent safety record and performance that is well above all other practical chemical rocket propellants.

== Lithium and fluorine ==
The highest-specific-impulse chemistry ever test-fired in a rocket engine was [[lithium]] and [[fluorine]], with hydrogen added to improve the exhaust thermodynamics (all propellants had to be kept in their own tanks, making this a [[tripropellant rocket|tripropellant]]). The combination delivered 542&nbsp;s specific impulse in vacuum,<ref>{{Cite book |last=Clark |first=John D. |title=Ignition! An informal history of liquid rocket propellants |date=1972 |publisher=Rutgers University Press |isbn=978-0-8135-0725-5 |location=New Brunswick, N.J |page=189}}</ref> equivalent to an exhaust velocity of 5320&nbsp;m/s. The impracticality of this chemistry highlights why exotic propellants are not actually used: to make all three components liquids, the hydrogen must be kept below −252&nbsp;°C (just 21&nbsp;K), and the lithium must be kept above 180&nbsp;°C (453&nbsp;K). Lithium and fluorine are both extremely corrosive. Lithium ignites on contact with air, and fluorine ignites most fuels on contact, including hydrogen. Fluorine and the [[hydrogen fluoride]] (HF) in the exhaust are very toxic, which makes working around the launch pad difficult, damages the environment, and makes getting a [[launch license]] more difficult. Both lithium and fluorine are expensive compared to most rocket propellants. This combination has therefore never flown.<ref>{{cite web |title=Current Evaluation of the Tripropellant Concept |first=Robert |last=Zurawski |date=June 1986 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860018652.pdf }}</ref>

== Methane ==
Liquid [[methane]] and liquid oxygen used together as rocket propellants are known as '''methalox''' propulsion.<ref>{{cite web |url=https://www.fastcompany.com/91027604/intuitive-machines-how-this-houston-start-up-is-making-space-history |title=Intuitive Machines: How this Houston startup is making space history |publisher=Fast Company}}</ref> Methane is the primary component of [[natural gas]], and in its liquid form it offers several operational properties useful for rocket propulsion. Compared with liquid hydrogen, liquid methane provides lower specific impulse but is easier to store, transport and handle due to its higher boiling point, higher density, and resistance to [[hydrogen embrittlement]]. Methane also produces less carbon-based residue than kerosene, which can reduce cleaning and inspection requirements for reusable engines.<ref name=pbt20140219>{{cite news |title=SpaceX propulsion chief elevates crowd in Santa Barbara |url=http://www.pacbiztimes.com/2014/02/19/spacexs-propulsion-chief-elevates-crowd-in-santa-barbara/ |date=2014-02-19 |publisher=Pacific Business Times |access-date=2014-02-22}}</ref><ref name=nsf20140307>{{cite web |last=Belluscio|first=Alejandro G. |title=SpaceX advances drive for Mars rocket via Raptor power |work=NASAspaceflight.com |date=2014-03-07 |url=http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/ |access-date=2014-03-07}}</ref>

The potential to synthesize methane and oxygen on Mars via the [[Sabatier reaction]] has also made the combination attractive for long-duration mission planning. In NASA’s [[Mars Design Reference Mission]] 5.0 studies (2009–2012), methalox was baselined for the crewed lander stage.

During the 2010s and 2020s, multiple launch providers began developing methane-fueled engines and vehicles. Several news outlets described the period as a "methalox race" to achieve the first orbital launch using methane propulsion.<ref name="nsf-20230712">{{cite web |last=Beil |first=Adrian |url=https://www.nasaspaceflight.com/2023/07/zhuque-2-launch2/ |title=LandSpace claims win in the methane race to orbit via second ZhuQue-2 launch |work=NASASpaceFlight |date=12 July 2023 |access-date=16 July 2023}}</ref><ref>{{cite web|url=https://www.reuters.com/technology/space/china-beats-rivals-successfully-launch-first-methane-liquid-rocket-2023-07-12/ |title=China beats rivals to successfully launch first methane-liquid rocket |work=Reuters |date=12 July 2023 }}</ref>

{{As of|2025|December}}, five methalox launch vehicles have reached orbit:
* [[Zhuque-2]] — Reached orbit on its second flight on 12 July 2023, becoming the first methane-fueled rocket to do so.<ref>{{cite web |last=Bell |first=Adrian |date=12 July 2023 |title=LandSpace claims win in the methane race to orbit via second ZhuQue-2 launch |url=https://www.nasaspaceflight.com/2023/07/zhuque-2-launch2/ |access-date=12 July 2023 |website=NASASpaceFlight.com}}</ref> Developed by [[LandSpace]], the vehicle uses the [[TQ-12]] and associated methalox engines.
* [[Vulcan Centaur]] — Reached orbit on its first launch (Cert-1) on 8 January 2024.<ref>{{cite web |author1=Josh Dinner |date=2024-01-08 |title=ULA's Vulcan rocket launches private US moon lander, 1st since Apollo, and human remains in debut flight |url=https://www.space.com/ula-vulcan-centaur-first-launch-peregrine-celestis-moon-mission |access-date=2024-01-08 |website=Space.com}}</ref> Its first stage uses [[Blue Origin]]’s methalox [[BE-4]] engine; the second stage uses the hydrolox [[RL10]].
* [[New Glenn]] — Reached orbit on its first flight on 16 January 2025. The rocket is powered by methalox [[BE-4]] engines on the first stage and hydrolox [[BE-3U]] engines on the second stage.
* [[Zhuque-3]] — Reached orbit on its first flight on 3 December 2025. Developed by [[LandSpace]], the vehicle uses nine TQ-12A engines on the first stage and one [[TQ-15]]A engine on the second stage.
* [[Long March 12A]] — Reached orbit on its first flight on 23 December 2025. Developed by [[Shanghai Academy of Spaceflight Technology]], the vehicle uses seven [[Longyun]]-70 engines on the first stage and one [[YF-209]]V engine on the second stage.

Other methalox vehicles and engines in testing or development include:

* [[SpaceX Starship|Starship]] — Achieved a [[transatmospheric orbit]] on its [[IFT-3|third test flight]] on 14 March 2024.<ref>{{cite web |title=Starship's Third Flight Test |url=https://www.spacex.com/launches/mission/?missionId=starship-flight-3 |access-date=2024-05-07 |website=SpaceX }}</ref> It uses the methalox [[SpaceX Raptor|Raptor]] engine.<ref name=fg20121120>{{cite web |last=Todd |first=David |title=Musk goes for methane-burning reusable rockets as step to colonise Mars |url=http://www.flightglobal.com/blogs/hyperbola/2012/11/musk-goes-for-methane-burning.html |access-date=2012-11-22 |website=FlightGlobal/Blogs Hyperbola |date=2012-11-20 |url-status=dead |archive-date=2012-11-28 |archive-url=https://web.archive.org/web/20121128070948/http://www.flightglobal.com/blogs/hyperbola/2012/11/musk-goes-for-methane-burning.html }}</ref>
* [[Rocket Lab Neutron|Neutron]] — In development, uses nine methalox [[Archimedes (rocket engine)|Archimedes]] engines on the first stage and Archimedes Vacuum on the second stage.
* [[Stoke Space Nova|Nova]] — In development, using a methalox Zenith engine on the first stage and a hydrolox engine on the second stage.
* [[Terran R]] — In development, uses 13 methalox [[Aeon R]] engines on the first stage and one Aeon Vac on the second stage.
* [[Hyperbola-3]] — In development, uses nine methalox JD-2 engines.
* [[Long March 9]] — In development, uses 30 [[YF-215]] engines on the first stage and two on the second.
* [[Yuanxingzhe-1]] — In development.
* [[Prometheus (rocket engine)|Prometheus engine]] — In development, {{cvt|980|kN}} methalox engine being developed by the  [[European Space Agency]]. Completed hot-fire tests in 2023.<ref name=NSF-2023>[https://www.nasaspaceflight.com/2023/06/themis-prometheus-hot-fire-test/ ''Themis, Prometheus complete first hot-fire tests in France'']</ref>

An abandoned attempt:
* [[Terran 1]] — Attempted orbit on 22 March 2023 using Relativity Space’s methalox [[Aeon 1]] engine; the program was discontinued after the flight.

== Monopropellants ==
{{unreferenced section|date=March 2017}}
; [[High-test peroxide]] : High test peroxide is concentrated [[hydrogen peroxide]], with around 2% to 30% water. It decomposes to steam and oxygen when passed over a catalyst. This was historically used for reaction control systems, due to being easily storable. It is often used to drive [[turbopump]]s, being used on the [[V2-rocket|V2 rocket]], and modern [[Soyuz (rocket family)|Soyuz]].
; [[Hydrazine]] : decomposes energetically to nitrogen, hydrogen, and ammonia (2N<sub>2</sub>H<sub>4</sub> → N<sub>2</sub> + H<sub>2</sub> + 2NH<sub>3</sub>) and is the most widely used in space vehicles. (Non-oxidized ammonia decomposition is endothermic and would decrease performance.)
;[[Nitrous oxide]] : decomposes to nitrogen and oxygen.
; [[Steam]] : when externally heated gives a reasonably modest ''I''<sub>sp</sub> of up to 190 seconds, depending on material corrosion and thermal limits.

== Present use ==
{{As of|December 2025}}, liquid fuel combinations in common use:

; [[Kerosene]] (RP-1) / [[liquid oxygen]] (LOX) : Used for the lower stages of the [[Soyuz-2]], [[Angara A5]], [[Long March 6]], [[Long March 7]], [[Long March 8]], and [[Tianlong-2]]; boosters of [[Long March 5]]; the first stage of [[Atlas V]]; both stages of  [[Electron (rocket)|Electron]], [[Falcon 9]], [[Falcon Heavy]], [[Firefly Alpha]], [[Long March 12]], and [[Angara-1.2]]; and all three stages of [[Nuri (rocket)|Nuri]].
; [[Liquid hydrogen]] (LH) / LOX : Used in the stages of the [[Space Launch System]], [[New Shepard]], [[H3 (rocket)|H3]], [[GSLV]], [[LVM3]], [[Long March 5]], [[Long March 7A]], [[Long March 8]], [[Ariane 6]], [[New Glenn]] and [[Centaur (rocket stage)|Centaur]].
; [[Liquid methane]] (LNG) / LOX : Used in both stages of [[Zhuque-2|Zhuque-2E]], [[Zhuque-3]], [[SpaceX Starship|Starship]] ([[List of Starship launches|doing nearly orbital test flights]]), [[Long March 12A]], and the first stage of the [[Vulcan Centaur]] and New Glenn.
; [[Unsymmetrical dimethylhydrazine]] (UDMH) or [[monomethylhydrazine]] (MMH) / [[dinitrogen tetroxide]] (NTO or {{chem|N|2|O|4}}) : Used in three first stages of the Russian [[Proton (rocket)|Proton booster]], Indian [[Vikas engine]] for [[PSLV]], [[GSLV]], and LVM3 rockets, many Chinese boosters, a number of military, orbital and deep space rockets, as this fuel combination is [[hypergolic]] and storable for long periods at reasonable temperatures and pressures.
; [[Hydrazine]] ({{Chem|N|2|H|4|}}) : Used in deep space missions because it is [[storable propellant|storable]] and hypergolic, and can be used as a monopropellant with a catalyst.
; [[Aerozine-50]] (50/50 hydrazine and UDMH) : Used in deep space missions because it is [[storable propellant|storable]] and hypergolic, and can be used as a monopropellant with a catalyst.

== Table ==
{| class="wikitable" style="float:right; clear:right; margin-left:1em; text-align:center"
|+ To approximate ''I''{{sub|sp}} at other chamber pressures{{clarify|date=January 2016}}<!-- this table is not clear under what conditions this stated multiplier would be used.  From this pressure?  To this pressure?  Over a given range of pressure (delta pressure)? If delta P, then does direction matter? -->
|-
! Absolute pressure {{convert|1|psi|kPa atm|order=flip|disp=unit2|abbr=on|lk=on}} ([[Pound-force per square inch|psi]])
! Multiply by
|-
| {{cvt|1000|psi|kPa atm|order=flip|sigfig=4}}
| 1.00
|-
| {{cvt|900|psi|kPa atm|order=flip|sigfig=4}}
| 0.99
|-
| {{cvt|800|psi|kPa atm|order=flip|sigfig=4}}
| 0.98
|-
| {{cvt|700|psi|kPa atm|order=flip|sigfig=4}}
| 0.97
|-
| {{cvt|600|psi|kPa atm|order=flip|sigfig=4}}
| 0.95
|-
| {{cvt|500|psi|kPa atm|order=flip|sigfig=4}}
| 0.93
|-
| {{cvt|400|psi|kPa atm|order=flip|sigfig=4}}
| 0.91
|-
| {{cvt|300|psi|kPa atm|order=flip|sigfig=4}}
| 0.88
|}

The table uses data from the JANNAF thermochemical tables (Joint Army-Navy-NASA-Air Force (JANNAF) Interagency Propulsion Committee) throughout, with best-possible specific impulse calculated by Rocketdyne under the assumptions of [[adiabatic]] combustion, [[isentropic]] expansion, one-dimensional expansion and shifting equilibrium.<ref>Huzel, D. K.; Huang, D. H. (1971), NASA SP-125, "Modern Engineering for Design of Liquid-Propellant Rocket Engines", (2nd ed.), NASA</ref> Some units have been converted to metric, but pressures have not.

=== Definitions ===
; ''V''<sub>e</sub> : Average exhaust velocity, m/s. The same measure as specific impulse in different units, numerically equal to specific impulse in N·s/kg.
; ''r'' : Mixture ratio: mass oxidizer / mass fuel
; ''T''<sub>c</sub> : Chamber temperature, °C
; ''d'' : [[Bulk density]] of fuel and oxidizer, g/cm<sup>3</sup>
; ''C*'' : Characteristic velocity, m/s. Equal to chamber pressure multiplied by throat area, divided by [[mass flow rate]]. Used to check experimental rocket's [[combustion efficiency]].

=== Bipropellants ===
{| class="wikitable" style="text-align:right;"
! rowspan=3 | Oxidizer
! rowspan=3 | Fuel
! rowspan=3 | Comment
! colspan=10 style="border-right:2px solid grey;" | Optimal expansion from 68.05&nbsp;atm to{{citation needed|reason=Table values need a source|date=April 2016}}
|-
! colspan=5 style="border-right:2px solid grey;"  | 1&nbsp;atm
! colspan=5                                       | 0&nbsp;atm, vacuum <br />(nozzle area ratio 40:1)
|- style="border-bottom:2px solid grey;"
! style="text-align:right;" | ''V''<sub>e</sub>
! style="text-align:right;" | ''r''
! style="text-align:right;" | ''T''<sub>c</sub>
! style="text-align:right;" | ''d''
! style="border-right:2px solid grey; text-align:right;" | ''C*''
! style="text-align:right;" | ''V''<sub>e</sub>
! style="text-align:right;" | ''r''
! style="text-align:right;" | ''T''<sub>c</sub>
! style="text-align:right;" | ''d''
! style="text-align:right;" | ''C*''
|-
| style="text-align:left;" rowspan=10 | [[LOX]]
| style="text-align:left;" | [[liquid hydrogen|{{chem|H|2}}]]
| style="text-align:left;" |''Hydrolox.'' Common.
| 3816
| 4.13
| 2740
| 0.29
| style="border-right:2px solid grey;" | 2416
| 4462
| 4.83
| 2978
| 0.32
| 2386
|-
| style="text-align:left;" | {{chem|H|2|}}:[[beryllium|Be]] 49:51 ||
| 4498
| 0.87
| 2558
| 0.23
| style="border-right:2px solid grey;" | 2833
| 5295
| 0.91
| 2589
| 0.24
| 2850
|-
| style="text-align:left;" | [[methane|{{chem|C|H|4}}]] (methane)
| style="text-align:left;" | ''[[Methalox]]''. Many [[liquid methane|engines]] under development in the 2010s.
| 3034
| 3.21
| 3260
| 0.82
| style="border-right:2px solid grey;" | 1857
| 3615
| 3.45
| 3290
| 0.83
| 1838
|-
| style="text-align:left;" | [[ethane|C<sub>2</sub>H<sub>6</sub>]] ||
| 3006
| 2.89
| 3320
| 0.90
| style="border-right:2px solid grey;" | 1840
| 3584
| 3.10
| 3351
| 0.91
| 1825
|-
| style="text-align:left;" | [[ethylene|C<sub>2</sub>H<sub>4</sub>]] ||
| 3053
| 2.38
| 3486
| 0.88
| style="border-right:2px solid grey;" | 1875
| 3635
| 2.59
| 3521
| 0.89
| 1855
|-
| style="text-align:left;" | [[RP-1]] (kerosene)
| style="text-align:left;" | ''Kerolox''. Common.
| 2941
| 2.58
| 3403
| 1.03
| style="border-right:2px solid grey;" | 1799
| 3510
| 2.77
| 3428
| 1.03
| 1783
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]] ||
| 3065
| 0.92
| 3132
| 1.07
| style="border-right:2px solid grey;" | 1892
| 3460
| 0.98
| 3146
| 1.07
| 1878
|-
| style="text-align:left;" | [[pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]] ||
| 3124
| 2.12
| 3834
| 0.92
| style="border-right:2px solid grey;" | 1895
| 3758
| 2.16
| 3863
| 0.92
| 1894
|-
| style="text-align:left;" | [[diborane|B<sub>2</sub>H<sub>6</sub>]] ||
| 3351
| 1.96
| 3489
| 0.74
| style="border-right:2px solid grey;" | 2041
| 4016
| 2.06
| 3563
| 0.75
| 2039
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | CH<sub>4</sub>:H<sub>2</sub> 92.6:7.4
|
| 3126
| 3.36
| 3245
| 0.71
| style="border-right:2px solid grey;" | 1920
| 3719
| 3.63
| 3287
| 0.72
| 1897
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[oxygen|GOX]]
| style="text-align:left;" | [[hydrogen|GH<sub>2</sub>]]
| style="text-align:left;" | Gaseous form
| 3997
| 3.29
| 2576
| align="left" | —
| style="border-right:2px solid grey;" | 2550
| 4485
| 3.92
| 2862
| align="left" | —
| 2519
|-
| style="text-align:left;" rowspan=9 | [[fluorine|F<sub>2</sub>]]
| style="text-align:left;" | [[liquid hydrogen|H<sub>2</sub>]] ||
| 4036
| 7.94
| 3689
| 0.46
| style="border-right:2px solid grey;" | 2556
| 4697
| 9.74
| 3985
| 0.52
| 2530
|-
| style="text-align:left;" | H<sub>2</sub>:[[lithium|Li]] 65.2:34.0 ||
| 4256
| 0.96
| 1830
| 0.19
| style="border-right:2px solid grey;" | 2680
|
|
|
|
|
|-
| style="text-align:left;" | H<sub>2</sub>:Li 60.7:39.3
|
|
|
|
|
| style="border-right:2px solid grey;" |
| 5050
| 1.08
| 1974
| 0.21
| 2656
|-
| style="text-align:left;" | [[methane|CH<sub>4</sub>]] ||
| 3414
| 4.53
| 3918
| 1.03
| style="border-right:2px solid grey;" | 2068
| 4075
| 4.74
| 3933
| 1.04
| 2064
|-
| style="text-align:left;" | [[ethane|C<sub>2</sub>H<sub>6</sub>]] ||
| 3335
| 3.68
| 3914
| 1.09
| style="border-right:2px solid grey;" | 2019
| 3987
| 3.78
| 3923
| 1.10
| 2014
|-
| style="text-align:left;" | [[monomethylhydrazine|MMH]] ||
| 3413
| 2.39
| 4074
| 1.24
| style="border-right:2px solid grey;" | 2063
| 4071
| 2.47
| 4091
| 1.24
| 1987
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]] ||
| 3580
| 2.32
| 4461
| 1.31
| style="border-right:2px solid grey;" | 2219
| 4215
| 2.37
| 4468
| 1.31
| 2122
|-
| style="text-align:left;" | [[ammonia|NH<sub>3</sub>]] ||
| 3531
| 3.32
| 4337
| 1.12
| style="border-right:2px solid grey;" | 2194
| 4143
| 3.35
| 4341
| 1.12
| 2193
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]]
|
| 3502
| 5.14
| 5050
| 1.23
| style="border-right:2px solid grey;" | 2147
| 4191
| 5.58
| 5083
| 1.25
| 2140
|-
| style="text-align:left;" rowspan=9 | [[oxygen difluoride|OF<sub>2</sub>]]
| style="text-align:left;" | [[liquid hydrogen|H<sub>2</sub>]] ||
| 4014
| 5.92
| 3311
| 0.39
| style="border-right:2px solid grey;" | 2542
| 4679
| 7.37
| 3587
| 0.44
| 2499
|-
| style="text-align:left;" | [[methane|CH<sub>4</sub>]] ||
| 3485
| 4.94
| 4157
| 1.06
| style="border-right:2px solid grey;" | 2160
| 4131
| 5.58
| 4207
| 1.09
| 2139
|-
| style="text-align:left;" | [[ethane|C<sub>2</sub>H<sub>6</sub>]] ||
| 3511
| 3.87
| 4539
| 1.13
| style="border-right:2px solid grey;" | 2176
| 4137
| 3.86
| 4538
| 1.13
| 2176
|-
| style="text-align:left;" | [[RP-1]]
|
| 3424
| 3.87
| 4436
| 1.28
| style="border-right:2px solid grey;" | 2132
| 4021
| 3.85
| 4432
| 1.28
| 2130
|-
| style="text-align:left;" | [[monomethylhydrazine|MMH]] ||
| 3427
| 2.28
| 4075
| 1.24
| style="border-right:2px solid grey;" | 2119
| 4067
| 2.58
| 4133
| 1.26
| 2106
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]] ||
| 3381
| 1.51
| 3769
| 1.26
| style="border-right:2px solid grey;" | 2087
| 4008
| 1.65
| 3814
| 1.27
| 2081
|-
| style="text-align:left;" | MMH:N<sub>2</sub>H<sub>4</sub>:[[water (molecule)|H<sub>2</sub>O]] 50.5:29.8:19.7 ||
| 3286
| 1.75
| 3726
| 1.24
| style="border-right:2px solid grey;" | 2025
| 3908
| 1.92
| 3769
| 1.25
| 2018
|-
| style="text-align:left;" | [[diborane|B<sub>2</sub>H<sub>6</sub>]] ||
| 3653
| 3.95
| 4479
| 1.01
| style="border-right:2px solid grey;" | 2244
| 4367
| 3.98
| 4486
| 1.02
| 2167
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]]
|
| 3539
| 4.16
| 4825
| 1.20
| style="border-right:2px solid grey;" | 2163
| 4239
| 4.30
| 4844
| 1.21
| 2161
|-
| style="text-align:left;" rowspan=2 | [[fluorine|F<sub>2</sub>]]:[[oxygen|O<sub>2</sub>]] 30:70
| style="text-align:left;" | [[liquid hydrogen|H<sub>2</sub>]] ||
| 3871
| 4.80
| 2954
| 0.32
| style="border-right:2px solid grey;" | 2453
| 4520
| 5.70
| 3195
| 0.36
| 2417
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[RP-1]]
|
| 3103
| 3.01
| 3665
| 1.09
| style="border-right:2px solid grey;" | 1908
| 3697
| 3.30
| 3692
| 1.10
| 1889
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | F<sub>2</sub>:O<sub>2</sub> 70:30
| style="text-align:left;" | [[RP-1]]
|
| 3377
| 3.84
| 4361
| 1.20
| style="border-right:2px solid grey;" | 2106
| 3955
| 3.84
| 4361
| 1.20
| 2104
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | F<sub>2</sub>:O<sub>2</sub> 87.8:12.2
| style="text-align:left;" | [[monomethylhydrazine|MMH]]
|
| 3525
| 2.82
| 4454
| 1.24
| style="border-right:2px solid grey;" | 2191
| 4148
| 2.83
| 4453
| 1.23
| 2186
|- style="border-bottom:2px solid grey;"
! Oxidizer
! Fuel
! Comment
! style="text-align:right;" | ''V<sub>e</sub>''
! style="text-align:right;" | ''r''
! style="text-align:right;" | ''T<sub>c</sub>''
! style="text-align:right;" | ''d''
! style="border-right:2px solid grey; text-align:right;" | ''C*''
! style="text-align:right;" | ''V<sub>e</sub>''
! style="text-align:right;" | ''r''
! style="text-align:right;" | ''T<sub>c</sub>''
! style="text-align:right;" | ''d''
! style="text-align:right;" | ''C*''
|-
| rowspan=6 style="text-align:left;" | [[tetrafluorohydrazine|N<sub>2</sub>F<sub>4</sub>]]
| style="text-align:left;" | [[methane|CH<sub>4</sub>]] ||
| 3127
| 6.44
| 3705
| 1.15
| style="border-right:2px solid grey;" | 1917
| 3692
| 6.51
| 3707
| 1.15
| 1915
|-
| style="text-align:left;" | [[ethane|C<sub>2</sub>H<sub>4</sub>]] ||
| 3035
| 3.67
| 3741
| 1.13
| style="border-right:2px solid grey;" | 1844
| 3612
| 3.71
| 3743
| 1.14
| 1843
|-
| style="text-align:left;" | [[monomethylhydrazine|MMH]] ||
| 3163
| 3.35
| 3819
| 1.32
| style="border-right:2px solid grey;" | 1928
| 3730
| 3.39
| 3823
| 1.32
| 1926
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]] ||
| 3283
| 3.22
| 4214
| 1.38
| style="border-right:2px solid grey;" | 2059
| 3827
| 3.25
| 4216
| 1.38
| 2058
|-
| style="text-align:left;" | [[ammonia|NH<sub>3</sub>]] ||
| 3204
| 4.58
| 4062
| 1.22
| style="border-right:2px solid grey;" | 2020
| 3723
| 4.58
| 4062
| 1.22
| 2021
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]]
|
| 3259
| 7.76
| 4791
| 1.34
| style="border-right:2px solid grey;" | 1997
| 3898
| 8.31
| 4803
| 1.35
| 1992
|-
| style="text-align:left;" rowspan=4 | [[chlorine pentafluoride|ClF<sub>5</sub>]]
| style="text-align:left;" | [[monomethylhydrazine|MMH]] ||
| 2962
| 2.82
| 3577
| 1.40
| style="border-right:2px solid grey;" | 1837
| 3488
| 2.83
| 3579
| 1.40
| 1837
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]] ||
| 3069
| 2.66
| 3894
| 1.47
| style="border-right:2px solid grey;" | 1935
| 3580
| 2.71
| 3905
| 1.47
| 1934
|-
| style="text-align:left;" | MMH:N<sub>2</sub>H<sub>4</sub> 86:14 ||
| 2971
| 2.78
| 3575
| 1.41
| style="border-right:2px solid grey;" | 1844
| 3498
| 2.81
| 3579
| 1.41
| 1844
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | MMH:N<sub>2</sub>H<sub>4</sub>:N<sub>2</sub>H<sub>5</sub>NO<sub>3</sub> 55:26:19
|
| 2989
| 2.46
| 3717
| 1.46
| style="border-right:2px solid grey;" | 1864
| 3500
| 2.49
| 3722
| 1.46
| 1863
|-
| style="text-align:left;" rowspan=2 | [[chlorine trifluoride|ClF<sub>3</sub>]]
| style="text-align:left;" | [[monomethylhydrazine|MMH]]:[[hydrazine|N<sub>2</sub>H<sub>4</sub>]]:[[Hydrazine_nitrate|N<sub>2</sub>H<sub>5</sub>NO<sub>3</sub> ]]55:26:19
| style="text-align:left;" | Hypergolic
| 2789
| 2.97
| 3407
| 1.42
| style="border-right:2px solid grey;" | 1739
| 3274
| 3.01
| 3413
| 1.42
| 1739
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]]
| style="text-align:left;" | Hypergolic
| 2885
| 2.81
| 3650
| 1.49
| style="border-right:2px solid grey;" | 1824
| 3356
| 2.89
| 3666
| 1.50
| 1822
|-
| style="text-align:left;" rowspan=9 | [[dinitrogen tetroxide|N<sub>2</sub>O<sub>4</sub>]]
| style="text-align:left;" | [[monomethylhydrazine|MMH]]
| style="text-align:left;" | Hypergolic, common
| 2827
| 2.17
| 3122
| 1.19
| style="border-right:2px solid grey;" | 1745
| 3347
| 2.37
| 3125
| 1.20
| 1724
|-
| style="text-align:left;" | [[monomethylhydrazine|MMH]]:[[beryllium|Be]] 76.6:29.4 ||
| 3106
| 0.99
| 3193
| 1.17
| style="border-right:2px solid grey;" | 1858
| 3720
| 1.10
| 3451
| 1.24
| 1849
|-
| style="text-align:left;" | MMH:[[aluminium|Al]] 63:27 ||
| 2891
| 0.85
| 3294
| 1.27
| style="border-right:2px solid grey;" | 1785
|
|
|
|
|
|-
| style="text-align:left;" | MMH:Al 58:42
|
|
|
|
|
| style="border-right:2px solid grey;" |
| 3460
| 0.87
| 3450
| 1.31
| 1771
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]]
| style="text-align:left;" | Hypergolic, common
| 2862
| 1.36
| 2992
| 1.21
| style="border-right:2px solid grey;" | 1781
| 3369
| 1.42
| 2993
| 1.22
| 1770
|-
| style="text-align:left;" | N<sub>2</sub>H<sub>4</sub>:[[unsymmetrical dimethylhydrazine|UDMH]] 50:50
| style="text-align:left;" | Hypergolic, common
| 2831
| 1.98
| 3095
| 1.12
| style="border-right:2px solid grey;" | 1747
| 3349
| 2.15
| 3096
| 1.20
| 1731
|-
| style="text-align:left;" | N<sub>2</sub>H<sub>4</sub>:Be 80:20 ||
| 3209
| 0.51
| 3038
| 1.20
| style="border-right:2px solid grey;" | 1918
|
|
|
|
|
|-
| style="text-align:left;" | N<sub>2</sub>H<sub>4</sub>:Be 76.6:23.4
|
|
|
|
|
| style="border-right:2px solid grey;" |
| 3849
| 0.60
| 3230
| 1.22
| 1913
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[Pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]]
|
| 2927
| 3.18
| 3678
| 1.11
| style="border-right:2px solid grey;" | 1782
| 3513
| 3.26
| 3706
| 1.11
| 1781
|-
| style="text-align:left;" rowspan=2 | [[nitric oxide|NO]]:[[dinitrogen tetroxide|N<sub>2</sub>O<sub>4</sub>]] 25:75
| style="text-align:left;" | [[monomethylhydrazine|MMH]] ||
| 2839
| 2.28
| 3153
| 1.17
| style="border-right:2px solid grey;" | 1753
| 3360
| 2.50
| 3158
| 1.18
| 1732
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]]:[[beryllium|Be]] 76.6:23.4
|
| 2872
| 1.43
| 3023
| 1.19
| style="border-right:2px solid grey;" | 1787
| 3381
| 1.51
| 3026
| 1.20
| 1775
|-
| style="text-align:left;" rowspan=3 | [[inhibited red fuming nitric acid|IRFNA IIIa]]
| style="text-align:left;" | [[unsymmetrical dimethylhydrazine|UDMH]]:[[diethylenetriamine|DETA]] 60:40
| style="text-align:left;" | Hypergolic
| 2638
| 3.26
| 2848
| 1.30
| style="border-right:2px solid grey;" | 1627
| 3123
| 3.41
| 2839
| 1.31
| 1617
|-
| style="text-align:left;" | [[monomethylhydrazine|MMH]]
| style="text-align:left;" | Hypergolic
| 2690
| 2.59
| 2849
| 1.27
| style="border-right:2px solid grey;" | 1665
| 3178
| 2.71
| 2841
| 1.28
| 1655
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[unsymmetrical dimethylhydrazine|UDMH]]
| style="text-align:left;" | Hypergolic
| 2668
| 3.13
| 2874
| 1.26
| style="border-right:2px solid grey;" | 1648
| 3157
| 3.31
| 2864
| 1.27
| 1634
|-
| style="text-align:left;" rowspan=3 | [[inhibited red fuming nitric acid|IRFNA IV HDA]]
| style="text-align:left;" | [[unsymmetrical dimethylhydrazine|UDMH]]:[[diethylenetriamine|DETA]] 60:40
| style="text-align:left;" | Hypergolic
| 2689
| 3.06
| 2903
| 1.32
| style="border-right:2px solid grey;" | 1656
| 3187
| 3.25
| 2951
| 1.33
| 1641
|-
| style="text-align:left;" | [[monomethylhydrazine|MMH]]
| style="text-align:left;" | Hypergolic
| 2742
| 2.43
| 2953
| 1.29
| style="border-right:2px solid grey;" | 1696
| 3242
| 2.58
| 2947
| 1.31
| 1680
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[unsymmetrical dimethylhydrazine|UDMH]]
| style="text-align:left;" | Hypergolic
| 2719
| 2.95
| 2983
| 1.28
| style="border-right:2px solid grey;" | 1676
| 3220
| 3.12
| 2977
| 1.29
| 1662
|-
| style="text-align:left;" rowspan=4 | [[hydrogen peroxide|H<sub>2</sub>O<sub>2</sub>]]
| style="text-align:left;" | [[monomethylhydrazine|MMH]] ||
| 2790
| 3.46
| 2720
| 1.24
| style="border-right:2px solid grey;" | 1726
| 3301
| 3.69
| 2707
| 1.24
| 1714
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]] ||
| 2810
| 2.05
| 2651
| 1.24
| style="border-right:2px solid grey;" | 1751
| 3308
| 2.12
| 2645
| 1.25
| 1744
|-
| style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]]:[[beryllium|Be]] 74.5:25.5 ||
| 3289
| 0.48
| 2915
| 1.21
| style="border-right:2px solid grey;" | 1943
| 3954
| 0.57
| 3098
| 1.24
| 1940
|- style="border-bottom:2px solid grey;"
| style="text-align:left;" | [[pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]]
|
| 3016
| 2.20
| 2667
| 1.02
| style="border-right:2px solid grey;" | 1828
| 3642
| 2.09
| 2597
| 1.01
| 1817
<!-- Hydrazine doesn't seem to be a useful rocket fuel oxidizer. Please cite your source.
|-
| rowspan=2 style="text-align:left;" | [[hydrazine|N<sub>2</sub>H<sub>4</sub>]]
| style="text-align:left;" | [[diborane|B<sub>2</sub>H<sub>6</sub>]] ||
| 3342
| 1.16
| 2231
| 0.63
| style="border-right:2px solid grey;" | 2080
| 3953
| 1.16
| 2231
| 0.63
| 2080
|-
| style="text-align:left;" | [[pentaborane(9)|B<sub>5</sub>H<sub>9</sub>]] ||
| 3204
| 1.27
| 2441
| 0.80
| style="border-right:2px solid grey;" | 1960
| 3819
| 1.27
| 2441
| 0.80
| 1960
-->
|-
! style="border-top:2px solid grey;" | Oxidizer
! style="border-top:2px solid grey;" | Fuel
! style="border-top:2px solid grey;" | Comment
! style="border-top:2px solid grey; text-align:right;" | ''V<sub>e</sub>''
! style="border-top:2px solid grey; text-align:right;" | ''r''
! style="border-top:2px solid grey; text-align:right;" | ''T<sub>c</sub>''
! style="border-top:2px solid grey; text-align:right;" | ''d''
! style="border-top:2px solid grey; border-right:2px solid grey; text-align:right;" | ''C*''
! style="border-top:2px solid grey; text-align:right;" | ''V<sub>e</sub>''
! style="border-top:2px solid grey; text-align:right;" | ''r''
! style="border-top:2px solid grey; text-align:right;" | ''T<sub>c</sub>''
! style="border-top:2px solid grey; text-align:right;" | ''d''
! style="border-top:2px solid grey; text-align:right;" | ''C*''
|}

Definitions of some of the mixtures:

;[[inhibited red fuming nitric acid|IRFNA IIIa]]: 83.4% [[nitric acid|HNO<sub>3</sub>]], 14% [[nitrogen dioxide|NO<sub>2</sub>]], 2% [[water (molecule)|H<sub>2</sub>O]], 0.6% [[hydrogen fluoride|HF]]
;IRFNA IV HDA: 54.3% HNO<sub>3</sub>, 44% NO<sub>2</sub>, 1% H<sub>2</sub>O, 0.7% HF
;[[RP-1]]: See MIL-P-25576C, basically kerosene (approximately {{chem|C|10|H|18}})
;MMH [[monomethylhydrazine]]: {{chem|C|H|3|N|H|N|H|2}}

Has not all data for CO/O{{sub|2}}, purposed for NASA for Martian-based rockets, only a specific impulse about 250&nbsp;s.

; ''r'' : Mixture ratio: mass oxidizer / mass fuel
; ''V''<sub>e</sub> : Average exhaust velocity, m/s. The same measure as specific impulse in different units, numerically equal to specific impulse in N·s/kg.
; ''C*'' : Characteristic velocity, m/s. Equal to chamber pressure multiplied by throat area, divided by [[mass flow rate]]. Used to check experimental rocket's combustion efficiency.
; ''T''<sub>c</sub> : Chamber temperature, °C
; ''d'' : [[Bulk density]] of fuel and oxidizer, g/cm<sup>3</sup>

=== Monopropellants ===
{| class="wikitable" style="text-align:right;"
! rowspan=2 | Propellant
! rowspan=2 | Comment
! colspan=4 style="border-right:2px solid grey;" | Optimal expansion from{{br}}68.05&nbsp;atm to 1&nbsp;atm{{citation needed|reason=Uncited values need a source|date=April 2016}}
! colspan=4 | Expansion from{{br}}68.05&nbsp;atm to vacuum (0&nbsp;atm){{br}}(Area<sub>nozzle</sub> = 40:1){{citation needed|reason=Uncited values need a source|date=April 2016}}
|- style="border-bottom:2px solid grey;"
! style="text-align:right;" | ''V''<sub>e</sub>
! style="text-align:right;" | ''T''<sub>c</sub>
! style="text-align:right;" | ''d''
! style="border-right:2px solid grey; text-align:right;" | ''C*''
! style="text-align:right;" | ''V''<sub>e</sub>
! style="text-align:right;" | ''T''<sub>c</sub>
! style="text-align:right;" | ''d''
! style="text-align:right;" | ''C*''
|-
| style="text-align:left;" | [[ammonium dinitramide]] (LMP-103S)<ref>{{cite conference |url=http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1270&context=smallsat |title=Expanding the ADN-based Monopropellant Thruster Family |last1=Anflo |first1=K. |last2=Moore |first2=S. |last3=King |first3=P. |conference=23rd Annual AIAA/USU Conference on Small Satellites |id=SSC09-II-4 }}</ref><ref name=15ASMD/>
| style="text-align:left;" | PRISMA mission (2010–2015){{br}}5 S/Cs launched 2016<ref>{{cite conference |title=HPGP® - High Performance Green Propulsion |url=https://polsa.gov.pl/images/news/Swe_Pol_2017_Prezetacje/Swe_Polish-Space-Ind_SpS_ECAPS_Presentation.pdf |last1=Dingertz |first1=Wilhelm |date=10 October 2017 |conference=ECAPS: Polish - Swedish Space Industry Meeting |access-date=14 December 2017 |archive-date=10 December 2021 |archive-url=https://web.archive.org/web/20211210194311/https://polsa.gov.pl/images/news/Swe_Pol_2017_Prezetacje/Swe_Polish-Space-Ind_SpS_ECAPS_Presentation.pdf |url-status=dead }}</ref>
|
| 1608
| 1.24
| style="border-right:2px solid grey;" |
|
| 1608
| 1.24
|
|-
| style="text-align:left;" | [[hydrazine]]<ref name=15ASMD/>
| style="text-align:left;" | common
|
| 883
| 1.01
| style="border-right:2px solid grey;" |
|
| 883
| 1.01
|
|-
| style="text-align:left;" | [[hydrogen peroxide]]
| style="text-align:left;" | common
| 1610
| 1270
| 1.45
| style="border-right:2px solid grey;" | 1040
| 1860
| 1270
| 1.45
| 1040
|-
| style="text-align:left;" | [[hydroxylammonium nitrate]] (AF-M315E)<ref name=15ASMD/>
| style="text-align:left;" |
|
| 1893
| 1.46
| style="border-right:2px solid grey;" |
|
| 1893
| 1.46
|
|-
| style="text-align:left;" | [[nitromethane]]
| style="text-align:left;" |
|
|
|
| style="border-right:2px solid grey;" |
|
|
|
|
|- style="border-top:2px solid grey;"
! Propellant
! Comment
! style="text-align:right;" | ''V''<sub>e</sub>
! style="text-align:right;" | ''T''<sub>c</sub>
! style="text-align:right;" | ''d''
! style="border-right:2px solid grey; text-align:right;" | ''C*''
! style="text-align:right;" | ''V''<sub>e</sub>
! style="text-align:right;" | ''T''<sub>c</sub>
! style="text-align:right;" | ''d''
! style="text-align:right;" | ''C*''
|}

== References ==
<references>
<ref name=15ASMD>{{cite conference |title=Advanced Monopropellants Combustion Chambers and Monolithic Catalyst for Small Satellite Propulsion |conference=15th Annual Space and Missile Defense Conference |date=13 August 2012 |url=https://uppsagd.files.wordpress.com/2012/03/advanced_monopropellants_combustion_chambers_and_monolithic_catalyst_for_small_satellite_propulsion.pdf |last1=Shchetkovskiy |first1=Anatoliy |last2=McKechnie |first2=Tim |last3=Mustaikis |first3=Steven |location=Huntsville, AL |access-date=14 December 2017}}</ref>
</references>

== External links==
* [https://rocketworkbench.sourceforge.net/equil.phtml Cpropep-Web] an online computer program to calculate propellant performance in rocket engines
* [http://www.lpre.de/resources/software/RPA_en.htm Design Tool for Liquid Rocket Engine Thermodynamic Analysis] is a computer program to predict the performance of the liquid-propellant rocket engines.

{{spacecraft propulsion}}

[[Category:Rocket propulsion]]
[[Category:Rocket propellants]]

[[ja:ロケットエンジンの推進剤#液体燃料ロケット]]