Editing Liquid rocket propellant (section)

==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. 

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.