Editing Liquid rocket propellant (section)

===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>