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.[1] 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.

Explosive bolt in an Orion module

In applications that require safety, precision and reliability, such as the aerospace industry,[2] pyrotechnic fasteners are triggered using exploding bridgewire detonators, which were themselves later succeeded by slapper detonators. Classical blasting caps are generally avoided for such usage.

More recent developments have used pulsed laser diodes to detonate initiators through fiber-optic cables,[3] 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.[4] Composition with the character of bipropellants and flash powders are often used.

Standard pyrotechnic mixtures used by NASA

References

  1. ↑ U.S. Army Material Command Pamphlet 706-179 - 'Explosive Trains' (PDF). U.S. Army. 9 March 1965. p. 108. Archived (PDF) from the original on 19 August 2022.
  2. ↑ "AIAA 96-2874 Development and Qualification Testing of the High Voltage Detonator".
  3. ↑ "Laser Motor Igniter". Retrieved 12 September 2022.
  4. ↑ Ewing, Robert G.; Waltman, Melanie J.; Atkinson, David A.; Grate, Jay W.; Hotchkiss, Peter J. (1 January 2013). "The vapor pressures of explosives". Trends in Analytical Chemistry. 42: 35–48. doi:10.1016/j.trac.2012.09.010. Retrieved 19 August 2022.
  5. 1 2 3 4 5 6 7 Bement, Laurence J.; Schimmel, Morry L. (1 June 1995). A Manual for Pyrotechnic Design, Development and Qualification. Hampton, Virginia: NASA, Langley Research Center. pp. 14–16. Archived from the original on 22 May 2011.
  6. ↑ Hohmann, Carl; Tipton, Bill Jr.; Dutton, Maureen (1 October 2000). Propellant for the NASA Standard Initiator (PDF). Houston: NASA, Johnson Space Center. p. 1. Archived (PDF) from the original on 11 April 2022.
  7. 1 2 Falbo, Mario J.; Robinson, Robert L. (1 March 1973). NASA Technical Note D-7141 - Apollo Experience Report: Spacecraft Pyrotechnic Systems (PDF). NASA, Lyndon B. Johnson Space Center, Houston. Archived (PDF) from the original on 12 December 2020.

See also

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