Pyrotechnic fastener
Encyclopedia
A pyrotechnic fastener 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
.
The term explosive bolt is sometimes used colloquially to describe pyrotechnic fasteners in general, regardless of the actual fastener employed. For example, it has been stated that the Space Shuttle
was held to the launch pad with explosive bolts, when frangible nut
s were actually used.
For safety and reliability, exploding bridgewire detonators and slapper detonator
s are often used in aerospace technology instead of classical blasting cap
s.
More recent developments have used pulsed laser diode
s to detonate initiator
s through fiber-optic cables, which subsequently fire the main charge.
Gas generator
s 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.
, sublimate in vacuum, which limits their usefulness in aerospace applications. Composition with the character of bipropellants and flash powder
s are often used.
Fastener
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
, usually a nut or bolt, that incorporates a pyrotechnic charge
Explosive material
An explosive material, also called an explosive, 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...
that can be initiated remotely. One or more explosive charges embedded within the bolt are typically activated by an electric
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
current, and the charge breaks the bolt into two or more pieces. The bolt is typically scored around its circumference
Circumference
The circumference is the distance around a closed curve. Circumference is a special perimeter.-Circumference of a circle:The circumference of a circle is the length around it....
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
Latch (hardware)
A latch is a type of mechanical fastener that is used to join two objects or surfaces together while allowing for the regular or eventual separation of the objects or surfaces....
.
The term explosive bolt is sometimes used colloquially to describe pyrotechnic fasteners in general, regardless of the actual fastener employed. For example, it has been stated that the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
was held to the launch pad with explosive bolts, when frangible nut
Frangible nut
The frangible nut, commonly confused with an explosive bolt, is a component used in many industries, but most commonly by NASA to sever mechanical connections. It is, by definition, an explosively-splittable nut...
s were actually used.
For safety and reliability, exploding bridgewire detonators and slapper detonator
Slapper detonator
A slapper detonator, also called exploding foil initiator , is a relatively recent kind of a detonator developed in Lawrence Livermore National Laboratory...
s are often used in aerospace technology instead of classical blasting cap
Blasting cap
A blasting cap is a small sensitive primary explosive device generally used to detonate a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite, or plastic explosive....
s.
More recent developments have used pulsed laser diode
Laser diode
The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current...
s to detonate initiator
Pyrotechnic initiator
A pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, e.g. thermites, gas generators, and solid-fuel rockets...
s through fiber-optic cables, which subsequently fire the main charge.
Gas generator
Gas generator
A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many...
s 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 can be used, depending on the desired burn rate and required amount of energy and volume of gas produced. Some materials, such as RDXRDX
RDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It was developed as an explosive which was more powerful than TNT, and it saw wide use in WWII. RDX is also known as cyclonite, hexogen , and T4...
, sublimate in vacuum, which limits their usefulness in aerospace applications. Composition with the character of bipropellants and flash powder
Flash powder
Flash powder is a pyrotechnic composition, a mixture of oxidizer and metallic fuel, which burns quickly and if confined produces a loud report. It is widely used in theatrical pyrotechnics and fireworks and was once used for flashes in photography.Different varieties of flash powder are made from...
s are often used.
Standard pyrotechnic mixtures used by NASA
- ManganeseManganeseManganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
/ barium chromateBarium chromateBarium chromate is a fine light yellow powder with the formula BaCrO4. The chromium occurs in the +6 oxidation state. It is an oxidizing agent, and produces a green flame when heated, the result of barium ions.-Reactions:...
/ lead chromate: Time-delay mix, used for sequencing. Gasless burning. - RDXRDXRDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It was developed as an explosive which was more powerful than TNT, and it saw wide use in WWII. RDX is also known as cyclonite, hexogen , and T4...
/ nitrocelluloseNitrocelluloseNitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...
: Gas generator, unsuitable for deep space missions, burn rate dependent on pressure. - BoronBoronBoron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
/ potassium nitratePotassium nitratePotassium nitrate is a chemical compound with the formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre , from medieval Latin sal petræ: "stone salt" or possibly "Salt...
: Gas generator and rocket-motor igniter, thermally stable, stable in vacuum, burn rate independent of pressure. - ZirconiumZirconiumZirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
/ potassium perchloratePotassium perchloratePotassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...
: NASA standard initiator (NSI). Rapid pressure rise, little gas but emits hot particles, thermally stable, vacuum stable, long shelf life. Sensitive to static electricity. - Lead azide: Used in detonators. Sensitive to impact, friction, and static electricity. Thermally and vacuum stable, if dextrinDextrinDextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α- or α- glycosidic bonds....
is not used for desensitizing. Long shelf life. - HexanitrostilbeneHexanitrostilbeneHexanitrostilbene , also called JD-X, is a heat resistant high explosive developed at the Naval Ordnance Laboratory in the 1960s. Other names include 1,1'-bis[2,4,6-trinitrobenzene]; 1,2-bis--ethylene; hexanitrodiphenylethylene.It is commercially produced by oxidizing trinitrotoluene with a...
: Used in detonators, linear shaped chargeShaped chargeA shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to cut and form metal, to initiate nuclear weapons, to penetrate armor, and in the oil and gas industry...
s, and bulk explosives. Insensitive to stimuli other than explosion. Thermally stable. Vacuum stable. Detonates at 22,000 feet per second.