Editing Solid-propellant rocket (section)

===Composite propellants===
A powdered oxidizer and powdered metal fuel are intimately mixed and immobilized with a rubbery binder (that also acts as a fuel). Composite propellants are often either [[ammonium nitrate|ammonium-nitrate]]-based (ANCP) or [[ammonium perchlorate|ammonium-perchlorate]]-based (APCP). Ammonium nitrate composite propellant often uses [[magnesium]] and/or [[aluminium]] as fuel and delivers medium performance (I<sub>sp</sub> of about {{convert|210|isp|abbr=on}}) whereas [[ammonium perchlorate composite propellant]] often uses aluminium fuel and delivers high performance: vacuum I<sub>sp</sub> up to {{convert|296|isp|abbr=on}} with a single-piece nozzle or {{convert|304|isp|abbr=on}} with a high-area-ratio telescoping nozzle.<ref name="spaceandtech.com"/> Aluminium is used as fuel because it has a reasonable specific energy density, a high volumetric energy density, and is difficult to ignite accidentally. Composite propellants are cast, and retain their shape after the rubber binder, such as [[Hydroxyl-terminated polybutadiene]] (HTPB), [[cross-links]] (solidifies) with the aid of a curative additive. Because of its high performance, moderate ease of manufacturing, and moderate cost, APCP finds widespread use in space, military, and amateur rockets, whereas cheaper and less efficient ANCP finds use in amateur rocketry and [[gas generator]]s. [[Ammonium dinitramide]], NH<sub>4</sub>N(NO<sub>2</sub>)<sub>2</sub>, is being considered as a 1-to-1 chlorine-free substitute for ammonium perchlorate in composite propellants. Unlike ammonium nitrate, ADN can be substituted for AP without a loss in motor performance.

Polyurethane-bound aluminium-APCP solid fuel was used in the submarine-launched [[Polaris missile]]s.<ref>{{Cite web|url=https://fas.org/nuke/guide/usa/slbm/a-1.htm|title = Polaris A1 - United States Nuclear Forces}}</ref> APCP used in the [[Space Shuttle Solid Rocket Boosters|space shuttle Solid Rocket Boosters]] consisted of ammonium perchlorate (oxidizer, 69.6% by weight), aluminium (fuel, 16%), iron oxide (a catalyst, 0.4%), polybutadiene [[acrylonitrile]] (PBAN) polymer (a non-urethane rubber binder that held the mixture together and acted as secondary fuel, 12.04%), and an epoxy [[Curing (chemistry)|curing]] agent (1.96%).<ref name="sts-newsref-srb">{{cite web | url = http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html | title = Shuttle Solid Rocket Boosters | publisher = NASA | access-date = 2015-10-02 | archive-date = 2019-04-30 | archive-url = https://web.archive.org/web/20190430095734/https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html | url-status = dead }}</ref><ref name="returntoflight-system-SRB">{{cite web | url = http://www.nasa.gov/returntoflight/system/system_SRB.html | title = Solid Rocket Boosters | publisher = NASA | access-date = 2015-10-02 | archive-date = 2013-04-06 | archive-url = https://web.archive.org/web/20130406193019/http://www.nasa.gov/returntoflight/system/system_SRB.html | url-status = dead }}</ref> It developed a specific impulse of 242 seconds (2.37&nbsp;km/s) at sea level or 268 seconds (2.63&nbsp;km/s) in a vacuum. The 2005-2009 [[Constellation Program]] was to use a similar PBAN-bound APCP.<ref>{{cite news |title=NASA Tests Engine With an Uncertain Future |url=https://www.nytimes.com/2010/08/31/science/space/31rocket.html?hpw |work=[[New York Times]] |date=August 30, 2010 |access-date=2010-08-31 | first=Kenneth | last=Chang}}</ref>

In 2009, a group succeeded in creating a propellant of [[water]] and nanoaluminium ([[ALICE (propellant)|ALICE]]).