{{Short description|Type of quick release fastener}} {{lead extra info|date=August 2022}} A '''pyrotechnic fastener''' (also called an '''explosive bolt''', or '''pyro''', within context) is a [[fastener]], usually a nut or bolt, that incorporates a [[Explosive material|pyrotechnic charge]] that can be initiated remotely. One or more explosive charges embedded within the bolt are typically activated by an [[Electricity|electric]] current, and the charge breaks the bolt into two or more pieces. The bolt is typically scored around its [[circumference]] at the point(s) where the severance should occur.<ref>{{cite book |date=9 March 1965 |title=U.S. Army Material Command Pamphlet 706-179 - 'Explosive Trains' |url=https://www.bulletpicker.net/pdf/AMCP%20706-179,%20Explosive%20Trains.pdf |archive-url=https://web.archive.org/web/20220819112450/https://www.bulletpicker.net/pdf/AMCP%20706-179,%20Explosive%20Trains.pdf |archive-date=19 August 2022 |url-status=live |publisher=U.S. Army |page=108 }}</ref> Such bolts are often used in space applications to ensure separation between rocket stages, because they are lighter and much more reliable than mechanical [[latch]]es.
[[File:Orion explosive bolt.jpg|thumb|Explosive bolt in an [[Orion (spacecraft)|Orion]] module]]
In applications that require safety, precision and reliability, such as the aerospace industry,<ref>{{Cite web|url=http://neyersoftware.com/Papers/AIAA96/HVD.htm|title = AIAA 96-2874 Development and Qualification Testing of the High Voltage Detonator}}</ref> pyrotechnic fasteners are triggered using [[exploding bridgewire detonator]]s, which were themselves later succeeded by [[slapper detonator]]s. {{cn|date=September 2022}} Classical [[blasting cap]]s are generally avoided for such usage.
More recent developments have used pulsed [[laser diode]]s to detonate [[pyrotechnic initiator|initiator]]s through [[fiber-optic cable]]s,<ref>{{cite web |url=https://psemc.com/products/laser-motor-igniter/ |title=Laser Motor Igniter |date=13 October 2018 |access-date=12 September 2022}}</ref> which subsequently fire the main charge.
[[Gas generator]]s are similar to pyrotechnic fasteners. They are used to generate large amounts of gas, as for turbopumps, to inflate balloons, especially airbags, to eject parachutes and similar applications.
==Compositions used== Various pyrotechnic compositions can be used, depending on the desired burn rate and required amount of energy and volume of gas produced. Some materials, such as [[RDX]], [[Sublimation (chemistry)|sublime]] in vacuum, which limits their usefulness in aerospace applications.<ref>{{cite journal | last1 = Ewing | first1 = Robert G. | last2 = Waltman | first2 = Melanie J. | last3 = Atkinson | first3 = David A. | last4 = Grate | first4 = Jay W. | last5 = Hotchkiss | first5 = Peter J. | date = 1 January 2013 | title = The vapor pressures of explosives | journal = Trends in Analytical Chemistry | volume = 42 | pages = 35–48 | doi = 10.1016/j.trac.2012.09.010 | doi-access= free }}</ref> Composition with the character of [[bipropellant]]s and [[flash powder]]s are often used.{{Citation needed|date=April 2008}}
===Standard pyrotechnic mixtures used by NASA=== * [[Manganese]] / [[barium chromate]] / [[lead chromate]]: Time-delay mix, used for sequencing. Gasless burning.<ref name="ManualDesign">{{cite book |last1 = Bement |first1 = Laurence J. |last2 = Schimmel |first2 = Morry L. |date = 1 June 1995 |title = A Manual for Pyrotechnic Design, Development and Qualification |url = https://dl.acm.org/doi/pdf/10.5555/888141 |publisher = NASA, Langley Research Center |location = Hampton, Virginia |pages = 14–16 |archive-url = https://archive.org/details/nasa_techdoc_19950024937 |archive-date = 22 May 2011 |url-status = live }}</ref> * [[RDX]] / [[nitrocellulose]]: Gas generator, unsuitable for deep space missions, burn rate dependent on pressure.<ref name="ManualDesign"/> * [[Boron]] / [[potassium nitrate]]: Gas generator and rocket-motor igniter, thermally stable, stable in vacuum, burn rate independent of pressure.<ref name="ManualDesign"/> * [[Zirconium]] / [[potassium perchlorate]]: Used in the [[NASA Standard Initiator]] (NSI).<ref>{{cite book |last1 = Hohmann |first1 = Carl |last2 = Tipton |first2 = Bill Jr. |last3 = Dutton |first3 = Maureen |date = 1 October 2000 |title = Propellant for the NASA Standard Initiator |url = https://ntrs.nasa.gov/api/citations/20000120417/downloads/20000120417.pdf |location = Houston |publisher = NASA, Johnson Space Center |page = 1 |archive-url=https://web.archive.org/web/20220411140043/https://ntrs.nasa.gov/api/citations/20000120417/downloads/20000120417.pdf |archive-date=11 April 2022 |url-status=live }}</ref> Rapid pressure rise, little gas but emits hot particles, thermally stable, vacuum stable, long shelf life. Sensitive to static electricity. Known to cause circuit damage during ground testing.<ref name="ManualDesign"/> * [[Lead azide]]: Used as a [[Explosive#Primary|primary explosive]].<ref name="ApolloPyro">{{cite book |last1=Falbo |first1=Mario J. |last2=Robinson |first2=Robert L. |date=1 March 1973 |title=NASA Technical Note D-7141 - Apollo Experience Report: Spacecraft Pyrotechnic Systems |url=https://ntrs.nasa.gov/api/citations/19730011151/downloads/19730011151.pdf |publisher=NASA, Lyndon B. Johnson Space Center, Houston |archive-url=https://web.archive.org/web/20201212011306/https://ntrs.nasa.gov/api/citations/19730011151/downloads/19730011151.pdf |archive-date=12 December 2020 |url-status=live }}</ref>{{rp|38}} Sensitive to impact, friction, and static electricity. Thermally and vacuum stable, if [[dextrin]] is not used for desensitizing. Long shelf life.<ref name="ManualDesign"/> * [[Hexanitrostilbene]]: Used in detonators, linear [[shaped charge]]s, and bulk explosives. Insensitive to stimuli other than explosion. Thermally stable. Vacuum stable.<ref name="ManualDesign"/> Used in deep space applications where [[RDX]] can not be utilized, such as aboard the [[Apollo Lunar Module]]<ref name="ApolloPyro"/>{{rp|23}} Detonates at {{convert|22000|ft/s|m/s}}.<ref name="ManualDesign"/>
==See also== * [[Frangible nut]], the counterpart of the explosive bolt
==References== {{reflist}}
==External links== * [https://yarchive.net/space/spacecraft/explosive_bolts.html Explosive bolts discussion in a mailing list]
[[Category:Fasteners]] [[Category:Pyrotechnics]] [[Category:Spacecraft pyrotechnics]]