Liquid rocket propellant: Difference between revisions

[[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>[[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]]

[[File:Opel RAK liquid-fuel rocket plane Friedrich Sander.jpg|thumb|left|Friedrich Sander, Opel RAK technician August Becker and Opel employee Karl Treber (from right to left) in front ofwith liquid-fuel rocket-plane prototype while test operation at Opel Rennbahn in Rüsselsheim]]

In Germany, engineers and scientists became enthralled with liquid propulsion, building and testing rockets in the late 1920s within [[Opel RAK]] in Rüsselsheim. According to [[Max Valier]]'s account, Opel RAK rocket designer [[Friedrich Wilhelm Sander]] launched two liquid-fuel rockets at Opel Rennbahn in [[Rüsselsheim]] on April 10 and April 12, 1929. These Opel RAK rockets were the first European, and after Goddard the second liquid-fuel rockets, in history. {{clarify|date=July 2023}}

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=":0">{{cite book |last1=Clark |first1=John D. |title=Ignition! An Informal History of Liquid Rocket Propellants |date=1972 |publisher=Rutgers University Press |isbn=978-0-8135-9583-2 |page=9}}</ref> 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. 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>

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. 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.

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=":0"Clark2018 /> for example [[RP-1]]{{snd}} a highly refined grade of [[kerosene]]. This combination is quite practical for rockets that need not be stored.

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 siltsoot and combustion by-products that could clog engine plumbing. In addition, they lacked the cooling properties of ethyl alcohol.

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 m³³}} 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 in any state is very bulky compared to other fuels; it is typically stored as a deeply cryogenic liquid, a technique mastered in the early 1950s as part of the [[Thermonuclear weapon#American developments|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>

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

The liquid-rocket engine propellant combination ofbipropellant [[liquid oxygen]] and hydrogen offers the highest specific impulse of currently usedfor conventional rockets. This extra performance largely offsets the disadvantage of low density., Lowwhich density of a propellant leads torequires larger fuel tanks. However, a small increase in specific impulse in an upper stage application can havegive a significant increase in payload-to-orbit capabilitymass.<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>

Launch pad fires due to spilled kerosene are more damaging than hydrogen fires, primarily for two main reasons: First, kerosene
*Kerosene burns about 20% hotter in absolute temperature than hydrogen. The second reason is 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 18&nbsp;[[Atomic mass unit|{{sc|amu}}]] compared to 29.9&nbsp;[[Atomic mass unit|{{sc|amu}}]] 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.

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 a vacuum, 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,. lithiumLithium ignites on contact with air, and fluorine ignites most fuels on contact with most fuels, 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>

During the 1950s, the Department of Defense initially proposed lithium/fluorine as ballistic missile propellants. A 1954 accident at a chemical works wherethat released a cloud of fluorine was released into the atmosphere convinced them to instead use LOX/RP-1 instead.

Liquid [[methane]] has a lower specific impulse than liquid hydrogen, but is easier to store due to its higher boiling point and density, as well as its lack of [[hydrogen embrittlement]]. It also leaves less residue in the engines compared to kerosene, which is beneficial for reusability.<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> In addition, it canis beexpected producedthat its production on Mars will be possible via the [[Sabatier reaction]]. In NASA's [[Mars Design Reference Mission|Mars Design Reference Mission 5.0]] documents (between 2009 and 2012), [[Methane#fuel|liquid methane]]/[[liquid oxygen|LOX]] (methalox) was the chosen propellant mixture for the lander module.

* [[Vulcan Centaur]] successfully reached orbit on its first try, called 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 |language=en}}</ref> The rocket, developed by [[United Launch Alliance]], uses the [[Blue Origin|Blue Origin's]] [[BE-4]] engine, though the second stage uses the hydrolox [[RL10]].

* [[SpaceX Starship|Starship]] hadachievedafailed[[transatmospheric launch,orbit]] intendedon to be aits [[transatmosphericIFT-3|third orbitflight]],on2014 AprilMarch 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> after two failed 2023attempts. The rocket, developed by [[SpaceX]], uses the [[SpaceX Raptor|Raptor]] engine.

[[SpaceX]] developed the [[Raptor (rocket engine family)|Raptor]] engine for its Starship super-heavy-lift launch vehicle.<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 |quote="We are going to do methane." Musk announced as he described his future plans for reusable launch vehicles including those designed to take astronauts to Mars within 15 years. |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> It has been used in [[SpaceX Starship developmentflight tests|test flights]] fromsince 2019 to 2023. SpaceX had previously used only [[RP-1]]/LOX in their engines.

Blue Origin developed the BE-4 LOX/LNG engine for their [[New Glenn]] and the United Launch Alliance Vulcan Centaur. The BE-4 will provide 2,400 kN (550,000 lbf) of thrust. Two flight engines had been delivered to ULA by mid 2023.

;[[Kerosene]] (RP-1) / [[liquid oxygen]] (LOX): Used for the lower stages of the [[Soyuz (rocket)|Soyuz-2]] boosters, the first stagesstage of [[SaturnAtlasV]] and the [[Atlas (rocket family)|Atlas family]], and both stages of [[Electron (rocket)|Electron]], and[[Falcon 9]], [[Falcon 9Heavy]], and [[Firefly Alpha]]. Very similar to Robert Goddard's first rocket.

;[[Liquid hydrogen]] (LH) / LOX: Used in the stages of the [[Space Shuttle]], [[Space Launch System]], [[Ariane 5]], [[Delta IV]], [[New Shepard]], [[H-IIB]], [[GSLV]] and [[Centaur (rocket stage)|Centaur]].