Pyrotechnic fastener

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. 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.

Often the term explosive bolt describes pyrotechnic fasteners in general. For example, it is often stated that the Space Shuttle is held to the launch pad with explosive bolts, but it is actually the large "frangible nuts" that each contain two pyrotechnic charges that split the nut into two pieces.

For safety and reliability, exploding bridgewire detonators and slapper detonators are often used in aerospace technology instead of classical blasting caps.

More recent developments have used pulsed laser diodes to detonate initiator through fiber-optic cables, which subsequently fire the main charge.

Gas generators are close cousins of pyrotechnic fasteners. They are used to generate large amounts of gas, as for turbopumps, to inflate balloons, especially airbags; to eject parachutes; and for similar applications.

Compositions used

Various pyrotechnic compositions...
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