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Apyrotechnic fastener (also called anexplosive bolt, orpyro, within context) is afastener, usually a nut or bolt, that incorporates apyrotechnic charge that can be initiated remotely. One or more explosive charges embedded within the bolt are typically activated by anelectric current, and the charge breaks the bolt into two or more pieces. The bolt is typically scored around itscircumference 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 mechanicallatches.
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.
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 asRDX,sublime in vacuum, which limits their usefulness in aerospace applications.[4] Composition with the character ofbipropellants andflash powders are often used.[citation needed]
RDX /nitrocellulose: Gas generator, unsuitable for deep space missions, burn rate dependent on pressure.[5]
Boron /potassium nitrate: Gas generator and rocket-motor igniter, thermally stable, stable in vacuum, burn rate independent of pressure.[5]
Zirconium /potassium perchlorate: Used in theNASA Standard Initiator (NSI).[6] 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.[5]
Lead azide: Used as aprimary explosive.[7]: 38 Sensitive to impact, friction, and static electricity. Thermally and vacuum stable, ifdextrin is not used for desensitizing. Long shelf life.[5]
Hexanitrostilbene: Used in detonators, linearshaped charges, and bulk explosives. Insensitive to stimuli other than explosion. Thermally stable. Vacuum stable.[5] Used in deep space applications whereRDX can not be utilized, such as aboard theApollo Lunar Module[7]: 23 Detonates at 22,000 feet per second (6,700 m/s).[5]
^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.
