pyrotechnic fastener
{{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 pyrotechnic charge that can be initiated remotely. One or more explosive charges embedded within the bolt are typically activated by an 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.{{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
}} Such bolts are often used in space applications to ensure separation between rocket stages, because they are lighter and much more reliable than mechanical latches.
File:Orion explosive bolt.jpg module]]
In applications that require safety, precision and reliability, such as the aerospace industry,{{Cite web|url=http://neyersoftware.com/Papers/AIAA96/HVD.htm|title = AIAA 96-2874 Development and Qualification Testing of the High Voltage Detonator}} pyrotechnic fasteners are triggered using exploding bridgewire detonators, which were themselves later succeeded by slapper detonators.
{{cn|date=September 2022}} Classical blasting caps are generally avoided for such usage.
More recent developments have used pulsed laser diodes to detonate initiators through fiber-optic cables,{{cite web |url=https://psemc.com/products/laser-motor-igniter/ |title=Laser Motor Igniter |date=13 October 2018 |access-date=12 September 2022}} which subsequently fire the main charge.
Gas generators 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, sublime in vacuum, which limits their usefulness in aerospace applications.{{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
}} Composition with the character of bipropellants and flash powders 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.{{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
}}
- RDX / nitrocellulose: Gas generator, unsuitable for deep space missions, burn rate dependent on pressure.
- Boron / potassium nitrate: Gas generator and rocket-motor igniter, thermally stable, stable in vacuum, burn rate independent of pressure.
- Zirconium / potassium perchlorate: Used in the NASA Standard Initiator (NSI).{{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
}} 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.
- Lead azide: Used as a primary explosive.{{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
}}{{rp|38}} Sensitive to impact, friction, and static electricity. Thermally and vacuum stable, if dextrin is not used for desensitizing. Long shelf life.
- Hexanitrostilbene: Used in detonators, linear shaped charges, and bulk explosives. Insensitive to stimuli other than explosion. Thermally stable. Vacuum stable. Used in deep space applications where RDX can not be utilized, such as aboard the Apollo Lunar Module{{rp|23}} Detonates at {{convert|22000|ft/s|m/s}}.
See also
- Frangible nut, the counterpart of the explosive bolt
References
{{reflist}}
External links
- [http://yarchive.net/space/spacecraft/explosive_bolts.html Explosive bolts discussion in a mailing list]