Editing Liquid rocket propellant (section)

{{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>