A propellant (or propellent) is a

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

that is expelled or expanded in such a way as to create a

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that syst ...

or other motive force in accordance with

Newton's third law of motion Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at rest, or in motio ...

, and "propel" a vehicle,

projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found in ...

, or

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

payload. In vehicles, the engine that expels the propellant is called a

reaction engine A reaction engine is an engine or motor that produces thrust by expelling reaction mass, in accordance with Newton's third law of motion. This law of motion is commonly paraphrased as: "For every action force there is an equal, but opposite, re ...

. Although technically a propellant is the reaction mass used to create thrust, the term "propellant" is often used to describe a substance which is contains both the reaction mass and the fuel that holds the energy used to accelerate the reaction mass. For example, the term "propellant" is often used in chemical rocket design to describe a combined fuel/propellant, although the propellants should not be confused with the

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...

that is used by an engine to produce the energy that expels the propellant. Even though the byproducts of substances used as fuel are also often used as a reaction mass to create the thrust, such as with a chemical rocket engine, propellant and fuel are two distinct concepts. Vehicles can use propellants to move by ejecting a propellant backwards which creates an opposite force that moves the vehicle forward. Projectiles can use propellants that are expanding gases which provide the motive force to set the projectile in motion. Aerosol cans use propellants which are fluids that are compressed so that when the propellant is allowed to escape by releasing a valve, the energy stored by the compression moves the propellant out of the can and that propellant forces the aerosol payload out along with the propellant. Compressed fluid may also be used as a simple vehicle propellant, with the potential energy that is stored in the compressed fluid used to expel the fluid as the propellant. The energy stored in the fluid was added to the system when the fluid was compressed, such as

compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...

. The energy applied to the pump or thermal system that is used to compress the air is stored until it is released by allowing the propellant to escape. Compressed fluid may also be used only as energy storage along with some other substance as the propellant, such as with a

water rocket A water rocket is a type of model rocket using water as its reaction mass. The water is forced out by a pressurized gas, typically compressed air. Like all rocket engines, it operates on the principle of Newton's third law of motion. Water rock ...

, where the energy stored in the compressed air is the fuel and the water is the propellant. In electrically powered spacecraft, electricity is used to accelerate the propellant. An

electrostatic force Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is convention ...

may be used to expel positive ions, or the Lorentz force may be used to expel negative ions and electrons as the propellant. Electothermal engines use the

electromagnetic force In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of ...

to heat low molecular weight gases (e.g. hydrogen, helium, ammonia) into a plasma and expel the plasma as propellant. In the case of a

resistojet rocket A resistojet is a method of spacecraft propulsion ( electric propulsion) that provides thrust by heating a typically non-reactive fluid. Heating is usually achieved by sending electricity through a resistor consisting of a hot incandescent filament ...

engine, the compressed propellant is simply heated using resistive heating as it is expelled to create more thrust. In chemical rockets and aircraft, fuels are used to produce an energetic gas that can be directed through a

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, a ...

, thereby producing thrust. In rockets, the burning of

rocket fuel Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical ...

produces an exhaust, and the exhausted material is usually expelled as a propellant under pressure through a

. The exhaust material may be a

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

, plasma, or a

solid Solid is one of the State of matter#Four fundamental states, four fundamental states of matter (the others being liquid, gas, and Plasma (physics), plasma). The molecules in a solid are closely packed together and contain the least amount o ...

photon rocket A photon rocket is a rocket that uses thrust from the momentum of emitted photons ( radiation pressure by emission) for its propulsion. Photon rockets have been discussed as a propulsion system that could make interstellar flight possible, which r ...

s would use the

relativistic momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass a ...

of photons to create thrust. Even though photons do not have mass, they can still act as a propellant because they move at relativistic speed, i.e., the speed of light. In this case Newton's third Law of Motion is inadequate to model the physics involved and

relativistic physics In physics, relativistic mechanics refers to mechanics compatible with special relativity (SR) and general relativity (GR). It provides a non-quantum mechanics, quantum mechanical description of a system of particles, or of a fluid, in cases where ...

must be used. In chemical rockets, chemical reactions are used to produce energy which creates movement of a fluid which is used to expel the products of that chemical reaction (and sometimes other substances) as propellants. For example, in a simple hydrogen/oxygen engine, hydrogen is burned (oxidized) to create H2O and the energy from the chemical reaction is used to expel the water (steam) to provide thrust. Often in chemical rocket engines, a higher molecular mass substance is included in the fuel to provide more reaction mass. Rocket propellant may be expelled through an expansion nozzle as a cold gas, that is, without energetic mixing and combustion, to provide small changes in velocity to spacecraft by the use of

cold gas thruster A cold gas thruster (or a cold gas propulsion system) is a type of rocket engine which uses the expansion of a (typically inert) pressurized gas to generate thrust. As opposed to traditional rocket engines, a cold gas thruster does not house any ...

s, usually as maneuvering thrusters. To attain a useful density for storage, most propellants are stored as either a solid or a liquid.

Vehicle propellants

A rocket propellant is a

that is expelled from a vehicle, such as a rocket, in such a way as to create a

in accordance with

, and "propel" the vehicle forward. The engine that expels the propellant is called a

. Although the term "propellant" is often used in chemical rocket design to describe a combined fuel/propellant, propellants should not be confused with the

may be used to expel positive ions, or the Lorentz force may be used to expel negative ions and electrons as the propellant. Electothermal engines use the

to heat low molecular weight gases (e.g. hydrogen, helium, ammonia) into a plasma and expel the plasma as propellant. In the case of a

, thereby producing thrust. In rockets, the burning of

produces an exhaust, and the exhausted material is usually expelled as a propellant under pressure through a

. The exhaust material may be a

, plasma, or a

. In powered aircraft without propellers such as jets, the propellant is usually the product of the burning of fuel with atmospheric oxygen so that the resulting propellant product has more mass than the fuel carried on the vehicle. The propellant or fuel may also simply be a compressed fluid, with the potential energy that is stored in the compressed fluid used to expel the fluid as the propellant. The energy stored in the fluid was added to the system when the fluid was compressed, such as

, where the energy stored in the compressed air is the fuel and the water is the propellant. Proposed

s would use the

s, usually as maneuvering thrusters. To attain a useful density for storage, most propellants are stored as either a solid or a liquid. Propellants may be energized by chemical reactions to expel solid, liquid or gas. Electrical energy may be used to expel gases, plasmas, ions, solids or liquids. Photons may be used to provide thrust via relativistic momentum.

Chemically powered

Solid propellant

Composite propellant Ammonium perchlorate composite propellant (APCP) is a solid-propellant rocket fuel. It differs from many traditional solid rocket propellants such as black powder or Solid-fuel rocket#Zinc–sulfur (ZS) propellants, zinc-sulfur, not only in chemi ...

s made from a solid

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

such as

ammonium perchlorate Ammonium perchlorate ("AP") is an inorganic compound with the formula NH4 ClO4. It is a colorless or white solid that is soluble in water. It is a powerful oxidizer. Combined with a fuel, it can be used as a rocket propellant called ammonium pe ...

ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...

, a

synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubbe ...

such as

HTPB Hydroxyl-terminated polybutadiene (HTPB) is an oligomer of butadiene terminated at each end with a hydroxyl functional group. It reacts with isocyanates to form polyurethane polymers. HTPB is a translucent liquid with a color similar to wax paper ...

, PBAN, or

Polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethan ...

(or energetic polymers such as polyglycidyl nitrate or polyvinyl nitrate for extra energy), optional high-explosive fuels (again, for extra energy) such as

RDX RDX (abbreviation of "Research Department eXplosive") or hexogen, among other names, is an organic compound with the formula (O2N2CH2)3. It is a white solid without smell or taste, widely used as an explosive. Chemically, it is classified as a ...

or nitroglycerin, and usually a powdered

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

such as

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

. * Some

amateur An amateur () is generally considered a person who pursues an avocation independent from their source of income. Amateurs and their pursuits are also described as popular, informal, autodidacticism, self-taught, user-generated, do it yourself, DI ...

propellants use

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 nitrat ...

, combined with

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...

, or other fuels and binder compounds. * Potassium perchlorate has been used as an oxidizer, paired with

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...

, and other binders. Propellants that explode in operation are of little practical use currently, although there have been experiments with Pulse Detonation Engines. Also the newly synthesized bishomocubane based compounds are under consideration in the research stage as both solid and liquid propellants of the future.

=Grain

= Solid fuel/propellants are used in forms called

grains A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legumes ...

. A grain is any individual particle of fuel/propellant regardless of the size or shape. The shape and size of a grain determines the burn time, amount of gas, and rate of produced energy from the burning of the fuel and, as a consequence, thrust vs time profile. There are three types of burns that can be achieved with different grains. ; Progressive burn: Usually a grain with multiple perforations or a star cut in the center providing a lot of surface area. ; Degressive burn: Usually a solid grain in the shape of a cylinder or sphere. ; Neutral burn: Usually a single perforation; as outside surface decreases the inside surface increases at the same rate.

=Composition

= There are four different types of solid fuel/propellant compositions: ; Single-based fuel/propellant: A single based fuel/propellant has nitrocellulose as its chief explosives ingredient. Stabilizers and other additives are used to control the chemical stability and enhance its properties. ; Double-based fuel/propellant: Double-based fuel/propellants consist of nitrocellulose with nitroglycerin or other liquid organic nitrate explosives added. Stabilizers and other additives are also used. Nitroglycerin reduces smoke and increases the energy output. Double-based fuel/propellants are used in small arms, cannons, mortars and rockets. ; Triple-based fuel/propellant: Triple-based fuel/propellants consist of nitrocellulose, nitroguanidine, nitroglycerin or other liquid organic nitrate explosives. Triple-based fuel/propellants are used in

cannon A cannon is a large- caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder ("black powder") was the primary propellant before the invention of smokeless powder ...

s. ; Composite: Composites do not utilize nitrocellulose, nitroglycerin, nitroguanidine or any other organic nitrate as the primary constituent. Composites usually consist of a fuel such as metallic aluminum, a combustible binder such as synthetic rubber or

, and an oxidizer such as ammonium perchlorate. Composite fuel/propellants are used in large rocket motors. In some applications, such as the US SLBM Trident II missile, nitroglycerin is added to the aluminum and ammonium perchlorate composite as an energetic plasticizer.

Liquid propellant

In rockets, three main liquid bipropellant combinations are used: cryogenic oxygen and hydrogen, cryogenic oxygen and a hydrocarbon, and storable propellants. ;

Cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

combination system: Used in upper stages and sometimes in booster stages of space launch systems. This is a nontoxic combination. This gives high

specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...

and is ideal for high-velocity missions ; Cryogenic oxygen-hydrocarbon propellant system: Used for many booster stages of space

launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload (spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pad, launch pads, supported by a missile launch contro ...

s as well as a smaller number of

second stage A multistage rocket or step rocket is a launch vehicle that uses two or more rocket ''stages'', each of which contains its own engines and propellant. A ''tandem'' or ''serial'' stage is mounted on top of another stage; a ''parallel'' stage i ...

s. This combination of fuel/oxidizer has high density and hence allows for a more compact booster design. ; Storable propellant combinations: Used in almost all bipropellant low-thrust, auxiliary or reaction control rocket engines, as well as in some in large rocket engines for first and second stages of ballistic missiles. They are instant-starting and suitable for long-term storage. Propellant combinations used for

liquid propellant rocket A liquid-propellant rocket or liquid rocket utilizes a rocket engine that uses liquid propellants. Liquids are desirable because they have a reasonably high density and high specific impulse (''I''sp). This allows the volume of the propellant ta ...

s include: *

Liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an applica ...

and

liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully li ...

and

kerosene Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regi ...

RP-1 RP-1 (alternatively, Rocket Propellant-1 or Refined Petroleum-1) is a highly refined form of kerosene outwardly similar to jet fuel, used as rocket fuel. RP-1 provides a lower specific impulse than liquid hydrogen (LH2), but is cheaper, is st ...

and

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

* Liquid oxygen and

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...

Hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

and mentioned above alcohol or

* Red fuming nitric acid (RFNA) and

* RFNA and

Unsymmetrical dimethylhydrazine Unsymmetrical dimethylhydrazine (UDMH; 1,1-dimethylhydrazine, НДМГ or codenamed Geptil) is a chemical compound with the formula H2NN(CH3)2 that is used as a rocket propellant. It is a colorless liquid, with a sharp, fishy, ammonia-like smell ...

(UDMH) *

Dinitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russia rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...

and UDMH, MMH, and/or

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

Common monopropellant used for

liquid rocket engines A liquid-propellant rocket or liquid rocket utilizes a rocket engine that uses liquid propellants. Liquids are desirable because they have a reasonably high density and high specific impulse (''I''sp). This allows the volume of the propellant ta ...

include: * Hydrogen peroxide *

Hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

* Red fuming nitric acid (RFNA)

Electrically powered

Electrically powered reactive engines use a variety of usually ionized propellants, including atomic ions, plasma, electrons, or small droplets or solid particles as propellant.

Electrostatic

If the acceleration is caused mainly by the Coulomb force (i.e. application of a static

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

in the direction of the acceleration) the device is considered electrostatic. The types of electrostatic drives and their propellants: *

Gridded ion thruster The gridded ion thruster is a common design for ion thrusters, a highly efficient low-thrust spacecraft propulsion method running on electrical power by using high-voltage grid electrodes to accelerate ions with electrostatic forces. History The ...

– using positive ions as the propellant, accelerated by an electrically charged grid **

NASA Solar Technology Application Readiness The NASA Solar Technology Application Readiness (NSTAR) is a type of spacecraft ion thruster called electrostatic ion thruster. It is a highly efficient low-thrust spacecraft propulsion running on electrical power generated by solar arrays. It u ...

(NSTAR) – positive ions accelerated using high-voltage electrodes **

HiPEP High Power Electric Propulsion (HiPEP) is a variation of ion thruster for use in nuclear electric propulsion applications.

as propellant

Electrothermal

These are engines that use electromagnetic fields to generate a plasma which is used as the propellant. They use a nozzle to direct the energized propellant. The nozzle itself may be composed simply of a magnetic field. Low molecular weight gases (e.g. hydrogen, helium, ammonia) are preferred propellants for this kind of system. *

Resistojet A resistojet is a method of spacecraft propulsion (electric propulsion) that provides thrust by heating a typically non-reactive fluid. Heating is usually achieved by sending electricity through a resistor consisting of a hot incandescent filame ...

– using a usually inert compressed propellant that is energized by simple

resistive heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law (also just Joule's law), also known in countries of former U ...

Arcjet An arcjet rocket or arcjet thruster is a form of electrically powered spacecraft propulsion, in which an electrical discharge (arc) is created in a flow of propellant (typically hydrazine or ammonia). This imparts additional energy to the propellan ...

– uses (usually) hydrazine or ammonia as a propellant which is energized with an

electrical arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. ...

Microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

– a type of

Radiofrequency ion thruster Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper ...

Variable specific impulse magnetoplasma rocket The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an electrothermal thruster under development for possible use in spacecraft propulsion. It uses radio waves to ionize and heat an inert propellant, forming a plasma, then a magnetic ...

(VASIMR) – using microwave-generated plasma as the propellant and magnetic field to direct its expulsion

Electromagnetic

Electromagnetic thrusters use ions as the propellant, which are accelerated by the Lorentz force or by magnetic fields, either of which is generated by electricity: * Electrodeless plasma thruster – a complex system that uses

cold plasma A nonthermal plasma, cold plasma or non-equilibrium plasma is a plasma which is not in thermodynamic equilibrium, because the electron temperature is much hotter than the temperature of heavy species (ions and neutrals). As only electrons are ther ...

as a propellant that is accelerated by

ponderomotive force In physics, a ponderomotive force is a nonlinear force that a charged particle experiences in an inhomogeneous oscillating electromagnetic field. It causes the particle to move towards the area of the weaker field strength, rather than oscilla ...

Magnetoplasmadynamic thruster A magnetoplasmadynamic (MPD) thruster (MPDT) is a form of electrically powered spacecraft propulsion which uses the Lorentz force (the force on a charged particle by an electromagnetic field) to generate thrust. It is sometimes referred to as L ...

– propellants include xenon, neon, argon, hydrogen, hydrazine, or lithium; expelled using the Lorentz force *

Pulsed inductive thruster A pulsed inductive thruster (PIT) is a form of ion thruster, used in spacecraft propulsion. It is a plasma propulsion engine using perpendicular electric and magnetic fields to accelerate a propellant with no electrode. Operation A nozzle r ...

– because this reactive engine uses a radial magnetic field, it acts on both positive and negative particles and so it may use a wide range of gases as a propellant including water, hydrazine, ammonia, argon, xenon and many others *

Pulsed plasma thruster A pulsed plasma thruster (PPT), also known as a plasma jet engine, is a form of electric spacecraft propulsion. PPTs are generally considered the simplest form of electric spacecraft propulsion and were the first form of electric propulsion to be ...

– uses a Teflon plasma as a propellant, which is created by an electrical arc and expelled using the Lorentz force *

Helicon Double Layer Thruster The helicon double-layer thruster is a prototype spacecraft propulsion engine. It was created by Australian scientist Dr Christine Charles, based on a technology invented by Professor Rod Boswell, both of the Australian National University. The ...

– a plasma propellant is generated and excited from a gas using a helicon induced by

high frequency High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten ...

band radiowaves which form a magnetic nozzle in a cylinder

Nuclear

Nuclear reactions may be used to produce the energy for the expulsion of the propellants. Many types of nuclear reactors have been used/proposed to produce electricity for electrical propulsion as outlined above.

Nuclear pulse propulsion Nuclear pulse propulsion or external pulsed plasma propulsion is a hypothetical method of spacecraft propulsion that uses nuclear explosions for thrust. It originated as Project ''Orion'' with support from DARPA, after a suggestion by Stanislaw ...

uses a series of nuclear explosions to create large amounts of energy to expel the products of the nuclear reaction as the propellant.

Nuclear thermal rocket A nuclear thermal rocket (NTR) is a type of thermal rocket where the heat from a nuclear reaction, often nuclear fission, replaces the chemical energy of the propellants in a chemical rocket. In an NTR, a working fluid, usually liquid hydrog ...

s use the heat of a nuclear reaction to heat a propellant. Usually the propellant is hydrogen because the force is a function of the energy irrespective of the mass of the propellant, so the lightest propellant (hydrogen) produces the greatest

Photonic

A photonic reactive engine uses

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

s as the propellant and their discrete relativistic energy to produce thrust.

Projectile propellants

Compressed fluid propellants

''Compressed fluid'' or ''compressed gas'' propellants are pressurized physically, by a compressor, rather than by a chemical reaction. The pressures and energy densities that can be achieved, while insufficient for high-performance rocketry and firearms, are adequate for most applications, in which case compressed fluids offer a simpler, safer, and more practical source of propellant pressure. A compressed fluid propellant may simply be a pressurized gas, or a substance which is a gas at atmospheric pressure, but stored under pressure as a liquid.

Compressed gas propellants

In applications in which a large quantity of propellant is used, such as

pressure washing Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure w ...

and

airbrushing An airbrush is a small, Pneumatics, air-operated tool that Atomizer nozzle, atomizes and sprays various media, most often paint but also ink and dye, and Foundation (cosmetics), foundation. Spray painting developed from the airbrush and is c ...

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

may be pressurized by a compressor and used immediately. Additionally, a hand pump to compress air can be used for its simplicity in low-tech applications such as atomizers, plant misters and

s. The simplest examples of such a system are

squeeze bottle A squeeze bottle is a type of container such as a plastic bottle for dispensing a fluid, that is powered by squeezing the container by exerting pressure with the user's hand. Its fundamental characteristic is that manual pressure applied to a r ...

s for such liquids as ketchup and shampoo. However, compressed gases are impractical as stored propellants if they do not liquify inside the storage container, because very high pressures are required in order to store any significant quantity of gas, and high-pressure

gas cylinders A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called ''bottles''. Inside the cylinder the stored contents may be in a state of compressed gas, vapor ...

and pressure regulators are expensive and heavy.

Liquified gas propellants

Principle

Liquified gas propellants are gases at atmospheric pressure, but become liquid at a modest pressure. This pressure is high enough to provide useful propulsion of the payload (e.g. aerosol paint, deodorant, lubricant), but is low enough to be stored in an inexpensive metal can, and to not pose a safety hazard in case the can is ruptured. The mixture of liquid and gaseous propellant inside the can maintains a constant pressure, called the liquid's

vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phas ...

. As the payload is depleted, the propellant vaporizes to fill the internal volume of the can. Liquids are typically 500-1000x denser than their corresponding gases at atmospheric pressure; even at the higher pressure inside the can, only a small fraction of its volume needs to be propellant in order to eject the payload and replace it with vapor. Vaporizing the liquid propellant to gas requires some energy, the

enthalpy of vaporization The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...

, which cools the system. This is usually insignificant, although it can sometimes be an unwanted effect of heavy usage (as the system cools, the vapor pressure of the propellant drops). However, in the case of a

freeze spray Freeze spray (cold spray or vapocoolant) is a type of aerosol spray product containing a liquified gas used for rapidly cooling surfaces, in medical and industrial applications. It is usually sold in hand-held spray cans. It may consist of vario ...

, this cooling contributes to the desired effect (although freeze sprays may also contain other components, such as chloroethane, with a lower vapor pressure but higher enthalpy of vaporization than the propellant).

Propellant compounds

Chlorofluorocarbons (CFCs) were once often used as propellants, 8but since the Montreal Protocol came into force in 1989, they have been replaced in nearly every country due to the negative effects CFCs have on Earth's ozone layer. The most common replacements of CFCs are mixtures of volatile hydrocarbons, typically propane, n-butane and isobutane. 9Dimethyl ether (DME) and methyl ethyl ether are also used. All these have the disadvantage of being flammable. Nitrous oxide and carbon dioxide are also used as propellants to deliver foodstuffs (for example, whipped cream and cooking spray). Medicinal aerosols such as asthma inhalers use hydrofluoroalkanes (HFA): either HFA 134a (1,1,1,2,-tetrafluoroethane) or HFA 227 (1,1,1,2,3,3,3-heptafluoropropane) or combinations of the two. More recently, liquid Hydrofluoroolefin (HFO) propellants have become more widely adopted in aerosol systems due to their relatively low vapor pressure, low global warming potential (GWP), and nonflammability. 0

Payloads

The practicality of liquified gas propellants allows for a broad variety of payloads.

Aerosol sprays Aerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. It comprises a can or bottle that contains a payload, and a propellant under pressure. When the container's valve is opened, the payload is forced out ...

, in which a liquid is ejected as a spray, include paints, lubricants, degreasers, and protective coatings; deodorants and other personal care products; cooking oils. Some liquid payloads are not sprayed due to lower propellant pressure and/or viscous payload, as with

whipped cream Whipped cream is liquid heavy cream that is whipped by a whisk or mixer until it is light and fluffy and holds its shape, or by the expansion of dissolved gas, forming a firm colloid. It is often sweetened, typically with white sugar, an ...

and

shaving cream Shaving cream or shave cream is a category of cream cosmetics used for shaving preparation. The purpose of shaving cream is to soften the hair by providing lubrication. Different types of shaving creams include aerosol shaving cream (also kn ...

or shaving gel. Low-power guns, such as

BB guns A BB gun is a type of air gun designed to shoot metallic spherical projectiles called BBs (not to be confused with similar-looking bearing balls), which are approximately the same size as BB-size lead birdshot used on shotguns ( in diamete ...

paintball Paintball is a competitive team shooting sport in which players eliminate opponents from play by hitting them with spherical dye-filled gelatin capsules called paintballs that break upon impact. Paintballs are usually shot using low-energy a ...

guns, and

airsoft Airsoft is a team game in which participants eliminate opposing players by tag (game), tagging them out of play with airsoft pellets, spherical plastic projectiles shot with mock air gun, air weapons(usually powered by an electronic motor) call ...

guns, have solid projectile payloads. Uniquely, in the case of a

gas duster A gas duster, also known as canned air or compressed air, is a product used for cleaning or dusting electronic equipment and other sensitive devices that cannot be cleaned using water. This type of product is most often packaged as a can that, ...

("canned air"), the only payload is the velocity of the propellant vapor itself.

References

Bibliography

External links

Rocket Propellants
* Rocket propulsion elements, Sutton,George.P, Biblarz,Oscar 7th Ed
Understanding and Predicting Gun Barrel Erosion – Weapons Systems Division Defence Science and Technology Organisation by Ian A. Johnston
{{Authority control Ammunition Ballistics Pyrotechnics Industrial gases

Vehicle propellants

Chemically powered

Solid propellant

=Grain

=Composition

Liquid propellant

Electrically powered

Electrostatic

Electrothermal

Electromagnetic

Nuclear

Photonic

Projectile propellants

Compressed fluid propellants

Compressed gas propellants

Liquified gas propellants

Principle

Propellant compounds

Payloads

See also

References

Bibliography

External links