Editing Dinitrogen tetroxide (section)

==Use as a rocket propellant==
Nitrogen tetroxide is used as an oxidizing agent in one of the most important rocket propellant systems because it can be stored as a liquid at room temperature. [[Pedro Paulet]], a [[Peruvian]] [[polymath]], reported in 1927 that he had experimented in the 1890s with a rocket engine that used spring-loaded nozzles that periodically introduced vaporized nitrogen tetroxide and a [[petroleum benzine]] to a [[spark plug]] for ignition, with the engine putting out 300 pulsating explosions per minute.<ref>{{Cite web |last=Gonzales Obando |first=Diana |date=2021-07-22 |title=Pedro Paulet: el genio peruano que se adelantó a su época y fundó la era espacial |url=https://elcomercio.pe/eldominical/ciencia/pedro-paulet-el-genio-peruano-que-fundo-la-era-espacial-noticia/ |access-date=2022-03-13 |website=[[El Comercio (Peru)|El Comercio]] |language=es}}</ref><ref>{{Cite web |last= |first= |date=25 August 1927 |title=Un peruano Pedro Paulet reclama la propiedad de su invento |url=https://elcomercio.pe/bicentenario/1927-l-el-buque-cohete-un-peruano-pedro-paulet-reclama-la-propiedad-de-su-invento-l-bicentenario-noticia/ |access-date=2022-03-13 |website=[[El Comercio (Peru)|El Comercio]] |language=es}}</ref> Paulet would go on to visit the German rocket association [[Verein für Raumschiffahrt|Verein für Raumschiffahrt (VfR)]] and on March 15, 1928, Valier applauded Paulet's liquid-propelled rocket design in the VfR publication ''Die Rakete'', saying the engine had "amazing power".<ref>{{cite book |last1=Mejía |first1=Álvaro |url=https://revistas.ucsp.edu.pe/index.php/persona/article/view/209/230 |title=Pedro Paulet, sabio multidisciplinario |publisher=Universidad Católica San Pablo |year=2017 |isbn= |edition= |location= |pages=95–122 |language=es |access-date=}}</ref> Paulet would soon be approached by [[Nazi Germany]] to help develop rocket technology, though he refused to assist and never shared the formula for his propellant.<ref name=":03">{{Cite news |title=El peruano que se convirtió en el padre de la astronáutica inspirado por Julio Verne y que aparece en los nuevos billetes de 100 soles |language=es |work=[[BBC News]] |url=https://www.bbc.com/mundo/noticias-america-latina-38197437 |access-date=2022-03-11}}</ref>

In early 1944, research on the usability of dinitrogen tetroxide as an oxidizing agent for rocket fuel was conducted by German scientists, although the Germans only used it to a very limited extent as an additive for [[S-Stoff]] (fuming nitric acid). It became the storable oxidizer of choice for many rockets in both the [[United States]] and [[USSR]] by the late 1950s. It is a [[hypergolic propellant]] in combination with a [[hydrazine]]-based [[rocket propellant|rocket fuel]]. One of the earliest uses of this combination was on the [[Titan (rocket family)|Titan family of rockets]] used originally as [[Intercontinental ballistic missile|ICBMs]] and then as [[launch vehicle]]s for many spacecraft. Used on the U.S. [[Project Gemini|Gemini]] and [[Apollo program|Apollo]] spacecraft and also on the [[Space Shuttle]], it continues to be used as station-keeping propellant on most geo-stationary satellites, and many deep-space probes. It is also the primary oxidizer for Russia's [[Proton (rocket)|Proton rocket]].

When used as a propellant, dinitrogen tetroxide is usually referred to simply as ''nitrogen tetroxide'' and the abbreviation ''NTO'' is extensively used. Additionally, NTO is often used with the addition of a small percentage of [[nitric oxide]] that reacts to form [[dinitrogen trioxide]], which inhibits [[stress-corrosion cracking]] of titanium alloys, and in this form, propellant-grade NTO is referred to as ''[[mixed oxides of nitrogen]]'' (''MON'') and can be distinguished by its green-blue color. Larger additions of nitric oxide, up to 25-30%, also lower the freezing point of NTO, improving storability in space conditions.<ref>{{Cite encyclopedia |title=Dinitrogen Tetroxide |chapter=N<sub>2</sub>O<sub>4</sub>/N<sub>2</sub>O<sub>3</sub> Mixtures|encyclopedia=Encyclopedia of Oxidizers |publisher=De Gruyter |last= Schmidt |first=Eckart W. |volume=1|date=2022 |pages=437–453 |doi=10.1515/9783110750294-005 |isbn=978-3-11-075029-4}}</ref> Most spacecraft now use MON instead of NTO; for example, the Space Shuttle reaction control system used MON3 (NTO containing 3% NO by weight).<ref>{{Cite web | url=http://www.friends-partners.org/partners/mwade/props/rocindex.htm | title=Rocket Propellant Index | access-date=2005-03-01 | archive-url=https://web.archive.org/web/20080511232517/http://www.friends-partners.org/partners/mwade/props/rocindex.htm | archive-date=2008-05-11 | url-status=dead }}</ref>

===The Apollo-Soyuz mishap===
On 24 July 1975, NTO poisoning affected three U.S. [[astronaut]]s on the final descent to Earth after the [[Apollo-Soyuz Test Project]] flight. This was due to a switch accidentally left in the wrong position, which allowed the [[Spacecraft attitude control|attitude control]] thrusters to fire after the cabin fresh air intake was opened, allowing NTO fumes to enter the cabin. One crew member lost consciousness during descent. Upon landing, the crew was hospitalized for five days for chemical-induced [[pneumonia]] and [[pulmonary edema]].<ref>[https://news.google.com/newspapers?id=RBgsAAAAIBAJ&sjid=kMgEAAAAIBAJ&dq=apollo%20gas&pg=993%2C1384026 "Brand Takes Blame For Apollo Gas Leak"], ''Florence, AL - Times Daily newspaper'', August 10, 1975</ref><ref>Sotos, John G., MD. [http://www.doctorzebra.com/drz/s_medhx.html#ASTP_incident "Astronaut and Cosmonaut Medical Histories"], May 12, 2008, accessed April 1, 2011.</ref>