A pyrotechnic fastener (also called an explosive bolt, or pyro, within context) is a

fastener A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...

, 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 Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

current, and the charge breaks the bolt into two or more pieces. The bolt is typically scored around its

circumference In geometry, the circumference (from Latin ''circumferens'', meaning "carrying around") is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out t ...

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

latch A latch or catch (called sneck in Northern England and Scotland) is a type of mechanical fastener that joins two (or more) objects or surfaces while allowing for their regular separation. A latch typically engages another piece of hardware on t ...

es.

In applications that require safety, precision and reliability, such as the aerospace industry, pyrotechnic fasteners are triggered using exploding bridgewire detonators, which were themselves later succeeded by slapper detonators. Classical

blasting cap A detonator, frequently a blasting cap, is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the last two being the most common. The commercial use of explosives uses electri ...

s are generally avoided for such usage. More recent developments have used pulsed

laser diode The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with e ...

s to detonate initiators through

fiber-optic cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...

s, which subsequently fire the main charge.

Gas generator A gas generator is a device for generating gas. A gas generator may create gas by a chemical reaction or from a solid or liquid source, when storing a pressurized gas is undesirable or impractical. The term often refers to a device that uses a ...

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, sublime in vacuum, which limits their usefulness in aerospace applications. Composition with the character of

bipropellant The highest specific impulse chemical rockets use liquid propellants (liquid-propellant rockets). They can consist of a single chemical (a monopropellant) or a mix of two chemicals, called bipropellants. Bipropellants can further be divided into ...

s and

flash powder Flash powder is a pyrotechnic composition, a mixture of oxidizer and metallic fuel, which burns quickly and produces a loud noise regardless of confinement. It is widely used in theatrical pyrotechnics and fireworks (namely salutes, e.g., cherry ...

s are often used.

Standard pyrotechnic mixtures used by NASA

Manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

barium chromate Barium chromate, named barium tetraoxochromate(VI) by the IUPAC, is a yellow sand like powder with the formula BaCrO4. It is a known oxidizing agent and produces a green flame when heated, a result of the barium ions. History The first naturally o ...

lead chromate Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...

: Time-delay mix, used for sequencing. Gasless burning. * RDX /

nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...

: Gas generator, unsuitable for deep space missions, burn rate dependent on pressure. * Boron /

potassium nitrate Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitr ...

: Gas generator and rocket-motor igniter, thermally stable, stable in vacuum, burn rate independent of pressure. *

Zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

/ potassium perchlorate: Used in the

NASA Standard Initiator The NASA Standard Initiator (NSI) is a pyrotechnic device used to set off other pyrotechnic devices. It is the central multi-purpose component of a modular system of detonating cords, pyrotechnics and various other explosive charges with many dif ...

(NSI). 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 An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ...

. Sensitive to impact, friction, and static electricity. Thermally and vacuum stable, if

dextrin Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch and glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α-(1→4) or α-(1→6) glycosidic bonds. Dextrins can be produced from ...

is not used for desensitizing. Long shelf life. *

Hexanitrostilbene Hexanitrostilbene (HNS), also called JD-X, is an organic compound with the formula O2N)3C6H2CHsub>2. It is a yellow-orange solid.Jacques Boileau, Claude Fauquignon, Bernard Hueber and Hans H. Meyer "Explosives" in ''Ullmann's Encyclopedia of In ...

: Used in detonators, linear

shaped charge A shaped charge is an explosive charge shaped to form an explosively formed penetrator (EFP) to focus the effect of the explosive's energy. Different types of shaped charges are used for various purposes such as cutting and forming metal, ini ...

s, 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 Detonates at .

References

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External links

Explosive bolts discussion in a mailing list

Compositions used

Standard pyrotechnic mixtures used by NASA

References

External links

See also