Ammonium Perchlorate Composite Propellant
Encyclopedia
Ammonium perchlorate composite propellant (APCP) is a modern solid rocket
propellant
used in both manned and unmanned rocket vehicles. It differs from many traditional solid rocket propellants such as black powder or Zinc-Sulfur, not only in chemical composition and overall performance, but also by the nature of how it is processed. APCP is cast
into shape, as opposed to powder pressing as with black-powder. This allows for manufacturing regularity and repeatability which are necessary requirements for use in the aerospace industry.
s (depending on the composition and operating pressure
) of 180-260 seconds are adequate. Because of these performance attributes, APCP is regularly implemented in booster applications such as in the Space Shuttle Solid Rocket Booster
s, aircraft ejection seats, and specialty space exploration applications such as NASA's Mars Exploration Rover
descent stage retrorocket
s. In addition, the high power rocketry community regularly uses APCP in the form of commercially available propellant "reloads", as well as single-use motors. Experienced experimental and amateur rocketeers also often work with APCP, processing the APCP themselves.
, all combined into a homogeneous mixture. The propellant is most often composed of ammonium perchlorate
(AP), an elastomer
binder such as hydroxyl-terminated polybutadiene (HTPB) or polybutadiene acrylic acid acrylonitrile prepolymer (PBAN
), small amounts of powdered metal, typically aluminum (Al), and various burn rate
catalysts. In addition, curing
additives induce elastomer
binder cross-link
ing to solidify the propellant before use. The AP serves as the oxidizer, while the binder and aluminum serve as the fuel
. Burn rate catalysts determine how quickly the mixture burns. The resulting cured propellant is slightly viscoelastic (rubbery) which also helps limit fracturing during accumulated damage (such as shipping, installing, cutting) and high acceleration
applications such as hobby or military rocketry.
The composition of APCP can vary significantly depending on the application, intended burn characteristics, and constraints such as nozzle
thermal limitations or specific impulse
(Isp). Rough mass proportions (in high performance configurations) tend to be about 70/15/15 AP/HTPB/Al, though fairly high performance "low-smoke" can have compositions of roughly 80/18/2 AP/HTPB/Al. While metal fuel is not required in APCP, most formulations include at least a few percent as a combustion stabilizer, propellant opacifier
(to limit excessive infrared
propellant preheating), and increase the temperature of the combustion gases (increasing Isp).
High energy fuels:
Low energy fuels acting as binders:
of the gas. Because of these phenomena, there exists an optimal non-stoichiometric composition for maximizing Isp of roughly 16% by mass, assuming the combustion reaction goes to completion inside the combustion chamber
.
The combustion time of the aluminum particles in the hot combustion gas varies depending on aluminum particle size and shape. In small APCP motors with high aluminum content, the residence time of the combustion gases does not allow for full combustion of the aluminum and thus a substantial fraction of the aluminum is burned outside the combustion chamber, leading to decreased performance. This effect is often mitigated by reducing aluminum particle size, inducing turbulence (and therefore a long characteristic path length and residence time), and/or by reducing the aluminum content to ensure a combustion environment with a higher net oxidizing potential, ensuring more complete aluminum combustion. Aluminum combustion inside the motor is the rate-limiting pathway since the liquid-aluminum droplets (even still liquid at temperatures 3000 K) limit the reaction to a heterogeneous globule interface, making the surface area to volume ratio and important factor in determining the combustion residence time and required combustion chamber size/length.
Common APCP formulations call for 30-400 µm AP particles (often spherical), as well as 2-50 µm Al particles (often spherical). Because of the size discrepancy between the AP and Al, Al will often take an interstitial position in a pseudo-lattice of AP particles.
(kg/sec) [and therefore pressure] of combustion gases generated is a function of the instantaneous surface area
, (m2), and linear burn rate
(m/2):
Several geometric configurations are often used depending on the application and desired thrust curve:
is dependent on several subtle factors:
In summary, however, most formulations have a burn rate between 1–3 mm/sec at STP
and 6–12 mm/sec at 68 atm. The burn characteristics (such as linear burn rate) are often determined prior to rocket motor firing using a strand burner test. This test allows the APCP manufacturer to characterize the burn rate as a function of pressure. Empirically, APCP adheres fairly well to the following power-function model:
It is worth noting that typically for APCP, 0.3explosion
, but rather that the explosion would be caused by the pressure surpassing the burst pressure of the container (rocket motor).
Commercial APCP rocket engines usually come in the form of re-loadable motor systems (RMS) and fully-assembled single use rocket motors. For RMS, the APCP "grains" (cylinders of propellant) are loaded into the reusable motor casing along with a sequence of insulator disks and o-ring
s and a (graphite
or glass-filled phenolic resin) nozzle. The motor casing and closures are typically bought separately from the motor manufacturer and are often precision machined aluminum. The assembled RMS contains both reusable (typically metal) and disposable components.
The major APCP suppliers for hobby use are:
To achieve different visual effects and flight characteristics, hobby APCP suppliers offer a variety of different characteristic propellant types. These can range in from fast burning with little smoke and blue flame to classic white smoke and white flame. In addition, colored formulations
are available to display reds, greens, blues, and even flameless black smoke.
In medium and high power rocket applications, APCP has largely replaced black powder as a rocket propellant. Compacted black powder slugs become prone to fracture in larger applications, which can result in catastrophic failure
in rocket vehicles. APCP's elastic material properties makes it less vulnerable to fracture from accidental shock or high acceleration flights. Due to these attributes, widespread adoption of APCP and related propellant types in the hobby has significantly enhanced the safety of rocketry.
, carbon dioxide
, hydrogen chloride
, and a metal oxide (typically aluminium oxide
). The hydrogen chloride can easily dissociate into water and create corrosive hydrochloric acid
, damaging launch equipment and biasing the pH
of local water and rainfall (See acid rain
). Furthermore, for military use, the smoke trail and the infrared radiation from the hot particles make it possible to detect the launch from space. These problems led to the research in smokeless grain which contains nitrogen-containing organic molecules (e.g. ammonium dinitramide
).
(NAR), and the Tripoli Rocketry Association
(TRA). Both agencies set forth rules regarding the impulse classification of rocket motors
and the level of certification
required by rocketeers in order to purchase certain impulse (size) motors. The NAR and TRA require motor manufactures to certify their motors for distribution to vendors and ultimately hobbyists. The vendor is charged with the responsibility (by the NAR and TRA) to check hobbyists for high power rocket certification before a sale can be made. The amount of APCP that can be purchased (in the form of a rocket motor reload) correlates to the impulse classification, and therefore the quantity of APCP purchasable by hobbyist (in any single reload kit) is regulated by the NAR and TRA.
The overarching legality concerning the implementation of APCP in rocket motors is outlined in NFPA 1125. Use of APCP outside hobby use is regulated by state and municipal fire codes. On March 16, 2009, it was ruled that APCP is not an explosive and that manufacture and use of APCP no longer requires a license or permit from the ATF
.
Solid rocket
A solid rocket or a solid-fuel rocket is a rocket engine that uses solid propellants . The earliest rockets were solid-fuel rockets powered by gunpowder; they were used by the Chinese in warfare as early as the 13th century and later by the Mongols, Arabs, and Indians.All rockets used some form of...
propellant
Rocket propellant
Rocket propellant is mass that is stored in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust. A fuel propellant is often burned with an oxidizer propellant to produce large volumes of very hot...
used in both manned and unmanned rocket vehicles. It differs from many traditional solid rocket propellants such as black powder or Zinc-Sulfur, not only in chemical composition and overall performance, but also by the nature of how it is processed. APCP is cast
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
into shape, as opposed to powder pressing as with black-powder. This allows for manufacturing regularity and repeatability which are necessary requirements for use in the aerospace industry.
Uses
Ammonium perchlorate composite propellant is typically used in aerospace propulsion applications, where simplicity and reliability are desired and specific impulseSpecific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
s (depending on the composition and operating pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
) of 180-260 seconds are adequate. Because of these performance attributes, APCP is regularly implemented in booster applications such as in the Space Shuttle Solid Rocket Booster
Space Shuttle Solid Rocket Booster
The Space Shuttle Solid Rocket Boosters were the pair of large solid rockets used by the United States' NASA Space Shuttle during the first two minutes of powered flight. Together they provided about 83% of liftoff thrust for the Space Shuttle. They were located on either side of the rusty or...
s, aircraft ejection seats, and specialty space exploration applications such as NASA's Mars Exploration Rover
Mars Exploration Rover
NASA's Mars Exploration Rover Mission is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars...
descent stage retrorocket
Retrorocket
A retrorocket is a rocket engine providing thrust opposing the motion of a spacecraft, thereby causing it to decelerate.-History:...
s. In addition, the high power rocketry community regularly uses APCP in the form of commercially available propellant "reloads", as well as single-use motors. Experienced experimental and amateur rocketeers also often work with APCP, processing the APCP themselves.
Overview
Ammonium perchlorate composite propellant is a composite propellant, meaning that it has both fuel and oxidizer mixed with a rubbery binderBinder (material)
-See also:*Adhesive or Glue*Cement*Paint...
, all combined into a homogeneous mixture. The propellant is most often composed of ammonium perchlorate
Ammonium perchlorate
Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
(AP), an elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
binder such as hydroxyl-terminated polybutadiene (HTPB) or polybutadiene acrylic acid acrylonitrile prepolymer (PBAN
PBAN
Polybutadiene acrylonitrile copolymer, also noted as polybutadiene — acrylic acid — acrylonitrile terpolymer.This was the binder formulation widely used on the 1960-70's big boosters...
), small amounts of powdered metal, typically aluminum (Al), and various burn rate
Burn rate (chemistry)
In chemistry, the burn rate is a measure of the linear combustion rate of a compound or substance such as a candle or a solid propellant. Burn rate is measured in length over time, such as "mm/second" or "inches/second". Burn rate is a property of combustible substance and it quantifies the...
catalysts. In addition, curing
Curing (chemistry)
Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...
additives induce elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
binder cross-link
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
ing to solidify the propellant before use. The AP serves as the oxidizer, while the binder and aluminum serve as the fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
. Burn rate catalysts determine how quickly the mixture burns. The resulting cured propellant is slightly viscoelastic (rubbery) which also helps limit fracturing during accumulated damage (such as shipping, installing, cutting) and high acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
applications such as hobby or military rocketry.
The composition of APCP can vary significantly depending on the application, intended burn characteristics, and constraints such as nozzle
Nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
thermal limitations or specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
(Isp). Rough mass proportions (in high performance configurations) tend to be about 70/15/15 AP/HTPB/Al, though fairly high performance "low-smoke" can have compositions of roughly 80/18/2 AP/HTPB/Al. While metal fuel is not required in APCP, most formulations include at least a few percent as a combustion stabilizer, propellant opacifier
Opacifier
An opacifier is a substance added to a material in order to make the ensuing system opaque. An example of a chemical opacifier is tin dioxide , which is used to opacify ceramic glazes and milk glass; bone ash is also used....
(to limit excessive infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
propellant preheating), and increase the temperature of the combustion gases (increasing Isp).
Common species
Oxidizers:- Ammonium perchlorateAmmonium perchlorateAmmonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
as the primary oxidizer - Metal-Oxide catalysts as thermiteThermiteThermite is a pyrotechnic composition of a metal powder and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction...
oxidizers
High energy fuels:
- AluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
(high performance, most common) - MagnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(medium performance) - ZincZincZinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
(low performance)
Low energy fuels acting as binders:
- HTPB
- CTPB
- PBANPBANPolybutadiene acrylonitrile copolymer, also noted as polybutadiene — acrylic acid — acrylonitrile terpolymer.This was the binder formulation widely used on the 1960-70's big boosters...
Special considerations
Though increasing the ratio of metal fuel to oxidizer up to the stoichiometric point increases the combustion temperature, the presence of an increasing molar fraction of metal oxides (particularly Al2O3) precipitating from the gaseous solution creates globules of solids or liquids that slow down the flow velocity as the mean molecular mass of the flow increases. In addition, the chemical composition of the gases change, varying the effective heat capacityHeat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
of the gas. Because of these phenomena, there exists an optimal non-stoichiometric composition for maximizing Isp of roughly 16% by mass, assuming the combustion reaction goes to completion inside the combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
.
The combustion time of the aluminum particles in the hot combustion gas varies depending on aluminum particle size and shape. In small APCP motors with high aluminum content, the residence time of the combustion gases does not allow for full combustion of the aluminum and thus a substantial fraction of the aluminum is burned outside the combustion chamber, leading to decreased performance. This effect is often mitigated by reducing aluminum particle size, inducing turbulence (and therefore a long characteristic path length and residence time), and/or by reducing the aluminum content to ensure a combustion environment with a higher net oxidizing potential, ensuring more complete aluminum combustion. Aluminum combustion inside the motor is the rate-limiting pathway since the liquid-aluminum droplets (even still liquid at temperatures 3000 K) limit the reaction to a heterogeneous globule interface, making the surface area to volume ratio and important factor in determining the combustion residence time and required combustion chamber size/length.
Particle size
The propellant particle size distribution has a profound impact on APCP rocket motor performance. Smaller AP and Al particles lead to higher combustion efficiency but also lead to increased linear burn rate. The burn rate is heavily dependent on mean AP particle size as the AP absorbs heat to decompose into a gas before it can oxidize the fuel components. This process may be a rate-limiting step in the overall combustion rate of APCP. The phenomenon can be explained by considering the heat flux to mass ratio: As the particle radius increases the volume (and, therefore, mass and heat capacity) increase as the cube of the radius. However, the surface area increases as the square of the radius, which is roughly proportional to the heat flux into the particle. Therefore, a particle's rate of temperature rise is maximized when the particle size is minimized.Common APCP formulations call for 30-400 µm AP particles (often spherical), as well as 2-50 µm Al particles (often spherical). Because of the size discrepancy between the AP and Al, Al will often take an interstitial position in a pseudo-lattice of AP particles.
Geometric
APCP deflagrates from the surface of exposed propellant in the combustion chamber. In this fashion, the geometry of the propellant inside the rocket motor plays an important role in the overall motor performance. As the surface of the propellant burns the shape evolves (a subject of study in internal ballistics), most often changing the propellant surface area exposed to the combustion gases. The mass fluxMass flux
Mass flux is the rate of mass flow across a unit area .-See also:*Flux*Fick's law*Darcy's law...
(kg/sec) [and therefore pressure] of combustion gases generated is a function of the instantaneous surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
, (m2), and linear burn rateBurn rate (chemistry)
In chemistry, the burn rate is a measure of the linear combustion rate of a compound or substance such as a candle or a solid propellant. Burn rate is measured in length over time, such as "mm/second" or "inches/second". Burn rate is a property of combustible substance and it quantifies the...
(m/2):Several geometric configurations are often used depending on the application and desired thrust curve:
- Circular bore: if in BATESBATESBATES is an acronym for BAllistic Test and Evaluation System, which is a standardized system for measuring solid rocket propellant performance developed by the United States Air Force Research Laboratory in the early 1960s, used for nearly 40 years thereafter, and again beginning in 2010.In modern...
configuration, produces progressive-regressive thrust curve. - End burner: propellant burns from one axial end to other producing steady long burn, though has thermal difficulties, CG shift.
- C-slot: propellant with large wedge cut out of side (along axial direction), producing fairly long regressive thrust, though has thermal difficulties and asymmetric CG characteristics.
- Moon burner: off-center circular bore produces progressive-regressive long burn though has slight asymmetric CG characteristics.
- Finocyl: usually a 5 or 6 legged star-like shape that can produce very level thrust, with a bit quicker burn than circular bore due to increased surface area.
Burn rate
While the surface area can be easily tailored by careful geometric design of the propellant, the burn rateBurn rate (chemistry)
In chemistry, the burn rate is a measure of the linear combustion rate of a compound or substance such as a candle or a solid propellant. Burn rate is measured in length over time, such as "mm/second" or "inches/second". Burn rate is a property of combustible substance and it quantifies the...
is dependent on several subtle factors:
- Propellant chemical composition.
- AP, Al, additive particle sizes.
- Combustion pressure.
- Heat transferHeat transferHeat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
characteristics. - Erosive burning (high velocity flow moving past the propellant).
- Initial temperature of propellant.
In summary, however, most formulations have a burn rate between 1–3 mm/sec at STP
Standard conditions for temperature and pressure
Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...
and 6–12 mm/sec at 68 atm. The burn characteristics (such as linear burn rate) are often determined prior to rocket motor firing using a strand burner test. This test allows the APCP manufacturer to characterize the burn rate as a function of pressure. Empirically, APCP adheres fairly well to the following power-function model:
It is worth noting that typically for APCP, 0.3
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
, but rather that the explosion would be caused by the pressure surpassing the burst pressure of the container (rocket motor).
Model applications
O-ring
An O-ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a disc-shaped cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.The O-ring...
s and a (graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
or glass-filled phenolic resin) nozzle. The motor casing and closures are typically bought separately from the motor manufacturer and are often precision machined aluminum. The assembled RMS contains both reusable (typically metal) and disposable components.
The major APCP suppliers for hobby use are:
- Aerotech Consumer AerospaceAerotech Consumer AerospaceAerotech Consumer Aerospace, established in 1982, is a company that supplies motors, kits and components for mid and high power rocketry.The company's headquarters are located in Cedar City, Utah and its products are sold mainly through US and international dealers...
- Animal Motor Works
- Cesaroni Technology
- Kosdon (by Aerotech)
- Loki Research
To achieve different visual effects and flight characteristics, hobby APCP suppliers offer a variety of different characteristic propellant types. These can range in from fast burning with little smoke and blue flame to classic white smoke and white flame. In addition, colored formulations
Pyrotechnic colorant
A pyrotechnic colorant is a chemical compound which causes a flame to burn with a particular color. These are used to create the colors in pyrotechnic compositions like fireworks and colored fires. The color-producing species are usually created from other chemicals during the reaction. Metal salts...
are available to display reds, greens, blues, and even flameless black smoke.
In medium and high power rocket applications, APCP has largely replaced black powder as a rocket propellant. Compacted black powder slugs become prone to fracture in larger applications, which can result in catastrophic failure
Catastrophic failure
A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....
in rocket vehicles. APCP's elastic material properties makes it less vulnerable to fracture from accidental shock or high acceleration flights. Due to these attributes, widespread adoption of APCP and related propellant types in the hobby has significantly enhanced the safety of rocketry.
Environmental and other concerns
The exhaust from APCP solid rocket motors contain mostly waterWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
, and a metal oxide (typically aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
). The hydrogen chloride can easily dissociate into water and create corrosive hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
, damaging launch equipment and biasing the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of local water and rainfall (See acid rain
Acid rain
Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...
). Furthermore, for military use, the smoke trail and the infrared radiation from the hot particles make it possible to detect the launch from space. These problems led to the research in smokeless grain which contains nitrogen-containing organic molecules (e.g. ammonium dinitramide
Ammonium dinitramide
Ammonium dinitramide ADN is the ammonium salt of dinitraminic acid. ADN decomposes under heat to leave only nitrogen, oxygen, and water. The ions are the ammonium ion NH4+ and the dinitramide N2-. It was originally invented in the Soviet Union, but remained classified until it was discovered...
).
Regulation and legality
In the United States, APCP for hobby use is regulated indirectly by two non-government agencies: the National Association of RocketryNational Association of Rocketry
The National Association of Rocketry is the governing body for the sport/hobby of model rocketry in the United States. It was established in 1957 by Orville Carlisle and G. Harry Stine and is currently headed by Trip Barber. It is the oldest and largest model rocketry governing body in the...
(NAR), and the Tripoli Rocketry Association
Tripoli Rocketry Association
The Tripoli Rocketry Association is one of the two major organizing bodies for high power rocketry in the United States. It was founded in 1964 in the Pittsburgh, PA region as a high school science club, integrating both rocketry and space science...
(TRA). Both agencies set forth rules regarding the impulse classification of rocket motors
Amateur rocket motor classification
Motors for model rockets, high powered rockets, and amateur rockets are classified by total impulse into a set of letter-designated ranges, from A , up to O as the largest...
and the level of certification
Certification
Certification refers to the confirmation of certain characteristics of an object, person, or organization. This confirmation is often, but not always, provided by some form of external review, education, assessment, or audit...
required by rocketeers in order to purchase certain impulse (size) motors. The NAR and TRA require motor manufactures to certify their motors for distribution to vendors and ultimately hobbyists. The vendor is charged with the responsibility (by the NAR and TRA) to check hobbyists for high power rocket certification before a sale can be made. The amount of APCP that can be purchased (in the form of a rocket motor reload) correlates to the impulse classification, and therefore the quantity of APCP purchasable by hobbyist (in any single reload kit) is regulated by the NAR and TRA.
The overarching legality concerning the implementation of APCP in rocket motors is outlined in NFPA 1125. Use of APCP outside hobby use is regulated by state and municipal fire codes. On March 16, 2009, it was ruled that APCP is not an explosive and that manufacture and use of APCP no longer requires a license or permit from the ATF
Bureau of Alcohol, Tobacco, Firearms and Explosives
The Bureau of Alcohol, Tobacco, Firearms and Explosives is a federal law enforcement organization within the United States Department of Justice...
.