Solid Rocket

Solid-Fueled Rocket

When the fuel in a solid-fueled rocket is ignited, the gases formed during combustion are forced out the nozzle and the rocket moves forward. The fuel is called the grain and is often formed with a hollow core for longer burning t imes.

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fuel//oxidizer ). ). The Solid rockets are rockets with a motor that uses solid propellants (fuel Chinese invented solid rockets and were using them in warfare by the 13th century. century. All rockets used some form of solid or powdered propellant powdered propellant up until the 20th century. century. Solid rockets are considered to be safe and reliable due to the long engineering history and simple design.

Basic Concepts simple solid rocket motor consists of a casing, nozzle nozzle,, grain (propellant charge), and igniter. The grain behaves like a solid mass, burning in a predictable fashion and producing exhaust gases. The nozzle dimensions are calculated to maintain a design chamber pressure, while producing thrust from the exhaust gases. Once ignited, a solid rocket motor cannot be shut off. Modern designs may also include; steerable nozzle for guidance, avionics, recovery hardware (parachutes), self destruct mechanisms, APU APU''s, and thermal management materials.

Design Design begins with the total impulse required, this determines the fuel/oxidizer mass. Grain geometry and chemistry are then chosen to satisfy the required motor characteristics. The following are chosen or solved simultaneously. simultaneously. The results are exact dimensions for grain, nozzle and case geometries; • •

• •

The grain burns at a predictable p redictable rate, given its surface area and chamber pressure. The chamber pressure is determined by the nozzle n ozzle orifice diameter and grain burn rate. Allowable chamber pressure is a function of casing design. The length of burn time is determined by the grain 'web thickness'.

The grain may be bonded to the casing, or not. Case bonded motors are much more difficult to design, since deformation of both the case and grain, under operating conditions, must be compatible. Common modes of failure in solid rocket motors are; fracture of the grain, failure of case









Another failure mode is casing seal design. Seals are required in casings that have to be opened to load the grain. Once a seal fails, hot gas will erode the escape path and result in failure. This was the cause of the Space Shuttle Challenger disaster .

Grain Solid fuel grains are usually molded from a thermoset elastomer (which dou bles as fuel), additional fuel, oxidizer, and catalyst. ca talyst. HTPB is commonly used for this purpose. Ammonium perchlorate is the most common oxidizer used today. The fuel is cast in different forms for different purposes. Slow, long burning rockets have a cylinder shaped grain, burning from one end to the other. other. Most grains, however, are cast with a hollow cross section, burning from the inside out (and outside in, if not case bonded), as well as from the ends. The thrust profile over time can be controlled by grain geometry. geometry. For example, a star shaped hole down the center of the grain will have greater initial thrust because of the additional surface area. As the star points are burned up, the surface area and thrust are reduced.

Casing The casing may be constructed co nstructed from a range of materials. Cardboard is used for mod el engines. Steel is used for the space shuttle boosters shuttle boosters.. Filament wound graphite epoxy casings are used for high performance motors.

Nozzle A Convergent Divergent design accelerates the exhaust gas out of the nozzle to produce thrust. Sophisticated solid rocket motors use steerable nozzles for rocket control.

Performance Solid fuel rocket motors have a typical t ypical specific impulse of 265 lbf·s/lb (2.6 kN·s/kg). This compares to 285 lbf·s/lb (2.8 kN·s/kg) for kerosene for kerosene//Lox and ~389 lbf·s/lb (3.8 kN·s/kg) 1 for liquid for liquid hydrogen/Lox hydrogen/Lox . For this reason solids are generally used as initial stages in a rocket, with better performing liquid engines reserved for final stages. However, the venerable Star line motors manufactured by Thiokol have a long history as the final boost









Amateur rocketry Solid fuel rockets can be bought for use in model rocketry; rocketry; they are normally small cylinders of fuel with an integral nozzle and a small charge that is set off when the fuel is exhausted. This charge can be used to ignite a second stage stage,, trigger a camera camera,, or deploy a parachute.. parachute Designing solid rocket motors is particularly interesting to amateur rocketry enthusiasts. The design is simple, materials are inexpensive and constructions techniques are safe. Early amateur motors were gunpowder. Later, Later, zinc/sulfur formulations were popular. Typical Typical amateur formulations in use today are; sugar (sucrose, dextrose, and sorbitol are all common)/potassium nitrate, HTPB (a rubber like epoxy)/magnesium/ammonium nitrate, and HTPB or PBAN/aluminum/ammonium perchlorate. Most formulations also include burn rate modifiers and other additives, and also possibly additives designed to create special effects, such as colored flames, thick smoke, or sparks. A hybrid rocket propulsion system typically comprises a solid fuel and a liquid or gas oxidizer . These systems are superior to solid propulsion systems in the respects of safety, throttling, restartability, restartability, and environmental cleanliness. However, hybrid h ybrid systems are slightly more complex than solids, and consequently the y are heavier and more expensive. Common oxidizers include gaseous or liquid oxygen and nitrous oxide. oxide. The Reaction Research Society (RRS), although known primarily for their work with liquid rocket propulsion, has a long history of research and development with hybrid rocket propulsion. Several universities have recently experimented with hybrid rockets. BYU BYU,, the University of Utah and Utah State University launched a student-designed rocket called Unity IV in 1995 which burned the solid fuel Hydroxy-terminated polybutadiene (HTPB) with an oxidizer of gaseous oxygen, and in 2003 launched a larger version which burned HTPB with nitrous oxide. oxide. Portland State University also launched several hybrid rockets in the early 2000's. SpaceShipOne, the first private manned spacecraft, is powered by a hybrid rocket burning SpaceShipOne, HTPB with nitrous oxide. The hybrid rocket engine was manufactured by SpaceDev SpaceDev.. SpaceDev partially based its motors on experimental data collected from the testing of AMROC's (American Rocket Company) motors at NASA's Stennis Space Center 's E1









Rocket fuel From Wikipedia, the free encyclopedia. Jump to: navigation navigation,, search Rocket fuel is the propellant the propellant which is burned with an oxidizer oxidizer to to produce thrust in rockets.. rockets

Contents [hide hide]]

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1 Ov Over ervie view w 2 Solid propellants propellan ts 3 Liquid propellants propella nts 4 Hybrid propellants propellan ts 5 Mixt Mixture ure ratio 6 Propell Propellent ent density 7 See also als o

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8 Ext Extern ernal al link linkss

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Overview Rockets create thrust by expelling mass mass backwards backwards with velocity. Chemical rockets, the subject of this article, create thrust by reacting propellants into very hot gas gas,, which then expands in a nozzle out the back. The thrust produced is the mass flow rate of the propellants multiplied by their exhaust velocity (relative to the rocket), as specified by Newton's Newton 's third law of motion. It is the equal and opposite reaction that moves the rocket, and not any interaction of the exhaust stream with air around the rocket (but see base see base bleed). bleed ). Equivalently, Equivalently, one can think of a rocket being accelerated acce lerated upwards by the pressure of the combusting gases in the combustion chamber and nozzle. Rockets can move faster in outer space, space, because they do not need to overcome air resistance. resistance. The velocity that a rocket can ca n attain is primarily a function of its mass ratio and its exhaust velocity. velocity. The relationship is described by the rocket equation: equation: V f = V eln(M ln(M 0 / M f ). ). The mass ratio is just a way to express ex press how much of the rocket is fuel when it starts









The first stage will usually use high-density (low volume) propellants to reduce the amount of volume exposed to atmospheric drag. drag. Thus, the Apollo-Saturn Apollo-Saturn V first stage used kerosene kerosene--liquid oxygen rather than the liquid hydrogen-liquid hydrogen-liquid oxygen used on the upper stages (hydrogen is highly energetic per kilogram, but n ot per cubic metre). Similarly, the Space Shuttle uses high-thrust, high-density SRBs for its lift-off with the liquid hydrogen-liquid oxygen SSMEs used partly for lift-off but primarily for orbital insertion. There are three main types of propellants: solid, liquid, and hybrid. [edit edit]]

Solid propellants The earliest rockets were created hundreds of years ago by the Chinese Chinese,, and were used primarily for fireworks for fireworks displays and as weapons weapons.. They were fueled with black with black powder , a type of gunpowder of gunpowder consisting consisting of a mixture of charcoal of charcoal,, sulfur sulfur and and potassium potassium nitrate (saltpeter). Rocket propellant technology did not advance until the end of the 19th century, century, by b y which time smokeless powder had powder had been developed, originally for use in firearms and artillery pieces. Solid fuels (and really, all rocket fuels) consist of an oxidizer oxidizer (substance (substance providing oxygen) and a fuel. In the case of gunpowder, the fuel is charcoal, the catalyst is sulfur and the oxidizer is the potassium nitrate. More contemporary recipies employ such compounds as sodium or potassium potassium chlorate and powdered aluminum aluminum.. (This mixture is sometimes known as "white "white powder "; "; not only is it different in appearance than black powder, it has a considerably co nsiderably higher energy density.) density.) However, white powder has insufficient specific impulse for orbital or near-orbital boosters. During the 1950s and 60s researchers in the United States developed what is now the standard high-energy solid rocket fuel. The mixture is primarily ammonium perchlorate powder (an oxidizer), combined with fine aluminum powder (a fuel), held together in a base of PBAN of PBAN or HTPB or HTPB (rubber-like fuels). The mixture is formed as a liquid at elevated temperatures, poured into the rocket casing, and cools to form a single grain bonded to that casing. Solid fueled rockets are much easier to store and handle than liquid fueled rockets, which makes them ideal for military applications. The LGM-30 Minuteman and LG-118A Peacekeeper (MX) Peacekeeper (MX) missiles are four-stage rockets capable of intercontinental suborbital flights.. The first three stages are solid fuelled, and in each case the last stage is a flights precision maneuverable liquid-fuelled bus liquid-fuelled bus used to fine tune the trajectory of the reentry vehicle.











However, solid rockets have lower specific impulse than liquid fueled rockets. It is also difficult to build a large mass ratio solid rocket because almost the entire rocket is the combustion chamber, and must be built to withstand the high combustion pressures. If a solid rocket is used to go all the way to orbit, the payload fraction is very small. (For example, the Orbital Sciences Pegasus rocket is an air-launched three-stage solid rocket orbital booster. Launch mass is 23,130 kg, low earth orbit pa yload is 443 kg, for a payload fraction of 1.9%. Compare to a Delta IV Medium, 249,500 kg, payload 8600 kg, payload fraction 3.4% without air-launch assistance.) Solid rockets are difficult to throttle or shut down before they run out ou t of fuel. Essentially, the burning grain must be vented to lower the chamber pressure. Venting Venting generally involves destroying the rocket, and is usually only done by a range safety officer if officer if the rocket goes awry. The third stages of the Minuteman and MX rockets have precision shutdown ports which, when opened, reduce the chamber pressure so abruptly that the interior flame is blown out. This allows a more precise trajectory which improves targetting accuracy. accuracy. Finally, casting very large single-grain rocket motors has proved to be a very tricky business. Defects in the grain can cause explosions during the burn, and these explosions can increase the burning propellant surface enough to cause a runaway pressure increase, until the case fails. [edit edit]]

Liquid propellants Main article: Liquid article: Liquid rocket propellants Liquid fueled rockets have better specific impulse than solid rockets and are capable of being throttled, shut down, and restarted. Only the combustion chamber of a liquid fueled rocket needs to withstand combustion pressures and temperatures. On vehicles employing turbopumps,, the fuel tanks can be built with less material, permitting a larger mass turbopumps fraction. For these reasons, most orbital launch vehicles and all first- and second-









extreme cold (liquid oxygen), or both (liquid fluorine is a perennial favorite of wild-eyed enthusiasts). Several exotic oxidizers have been p roposed: liquid ozone (O3), ClF3, and ClF5, all of which are unstable, energetic, and toxic. Liquid fuelled rockets also require troublesome and highly stressed pressurization systems, plumbing and combustion chambers, which greatly increase the cost of the rocket. Many employ turbopumps which raise the cost still more. Though all the early rocket theorists proposed liquid hydrogen and liquid oxygen as propellants, the first liquid-fuelled rocket, launched by Robert Goddard on March 16, 1926, used gasoline and liquid oxygen. Liquid hydrogen was first used by the Lockheed CL-400 Suntan reconnaissance aircraft in the mid-1950s. In the mid-1960s, the Centaur and Saturn upper stages were both using liquid hydrogen and liquid oxygen. The highest specific impulse chemistry ever test-fired in a rocket engine was lithium and fluorine,, with hydrogen added to improve the exhaust thermodynamics (making this a fluorine tripropellant). tripropellant ). The combination delivered 542 seconds (542 lbf·s/lb, 5.32 kN·s/kg, 5320 m/s) specific impulse in a vacuum. The impracticality of this chemistry highlights why exotic propellants are not actually used: to make all three components liquids, the hydrogen must be kept below -252 °C (just 21 K) and the lithium must be kept above 180 °C (453 K). Lithium and fluorine are both extremely corrosive, lithium ignites on contact with air, fluorine ignites on contact with most fuels, and hydrogen, while not hypergolic hypergolic,, is an explosive hazard. Fluorine and the hydrogen fluoride (HF) in the exhaust are very toxic, which trashes the environment, makes work around the launch pad difficult, and makes getting a launch license that much more difficult. The rocket exhaust is also ionized, which would interfere with radio c ommunication with the rocket. Finally, Finally, both lithium and fluorine are expensive and rare, enough to actually matter. The common liquid propellant combinations in use today are: •

LOX and kerosene (RP-1). Used for the lower stages of most









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LOX and liquid hydrogen, used in the Space Shuttle, the Centaur upper stage, the newer Delta IV rocket, rocket, and most stages of the European Ariane rockets. Nitrogen tetroxide (N2O4) and hydrazine (N2H4), MMH MMH,, or UDMH.. Used in UDMH military, military, orbital and deep space rockets, because both liquids are storable for long periods at reasonable temperatures and pressures. Hydrazine decomposes energetically to nitrogen and hydrogen, making it a fairly good monopropellant all by itself. This combination is hypergolic,, making hypergolic for attractively simple ignition sequences. The only









nitrous oxide used in hybrids. Because just one propellant is a fluid, hybrids are simpler than liquid rockets. Hybrid motors suffer two major drawbacks. The first, shared with solid rocket motors, is that the casing around the fuel grain must be built to withstand full combustion pressure and often extreme temperatures as well. Modern composite structures handle this problem well. The primary remaining difficulty with hybrids is with mixing the propellants before burning. In solid propellants, the oxidizer and fuel are mixed in a factory in carefully c arefully controlled conditions (and even then it is tricky). Liquid propellants are generally mixed by the injector at the top of the combustion chamber, which directs many small fastmoving streams of fuel and oxidizer into one another. Liquid fuelled rocket injector design has been studied at a t great length and still resists reliable performance prediction. In a hybrid motor, the mixing happens at the surface of the melting or evaporating surface of the fuel. The mixing is not a well controlled process and generally quite a lot of propellant is left unburned, which limits the efficiency and thus the exhaust velocity of the motor. There has been much less development of hybrid motors than solid and liquid motors. For military use, ease of handling and maintenanc e have driven the use of solid rockets. For orbital work, liquid fuels are enough better than hybrids that most development has concentrated there. There has recently been an increase in hybrid motor development for nonmilitary suborbital work: •

The Reaction Research Society (RRS), although known primarily for their work with liquid rocket propulsion, has a long history of









designed rocket called Unity IV in 1995 which burned the solid fuel Hydroxy-terminated polybutadiene (HTPB) with an oxidizer of gaseous oxygen, and in 2003 launched a larger version which burned HTPB with nitrous oxide. •

•

Portland State University also launched several hybrid rockets in the early 2000's. SpaceShipOne, the first private manned spacecraft, is powered by a hybrid rocket burning HTPB with nitrous oxide. The hybrid rocket engine was manufactured by SpaceDev. SpaceDev partially based its motors on experimental data











SpaceDev purchased AMROCs assets after the company was shut down for lack of funding. [edit edit]]

Mixture ratio The theoretical exhaust velocity of a given propellant chemistry is a function of the energy released per unit of propellant mass (specific energy). Unburned fuel or oxidizer drags down the specific energy e nergy.. Surprisingly, Surprisingly, most rockets rocke ts run fuel-rich. The usual explanation for fuel-rich mixtures is that fuel-rich mixtures have lower

M increases the ratio molecular weight exhaust, which by reducing M increases , which is approximately equal to the theoretical exhaust velocity. velocity. This explanation, though found in some textbooks, is wrong. Fuel-rich mixtures actually have lower theoretical exhaust velocities, because

decreases as fast or faster than M .









Another reason for running rich is that off-stoichiometric off-stoichiometric mixtures burn cooler than stoichiometric mixtures, which makes engine eng ine cooling easier. And as most engines are made of metal or carbon, hot oxidizer-rich exhaust is extremely corrosive, where fuelrich exhaust is less so. American engines have all been fuel-rich. Some Soviet engines have been oxidizer-rich. Additionally, Additionally, there is a difference between mixture ratios for optimum Isp and optimum thrust. During launch, shortly after takeoff, high thrust is at a premium. This can be achieved at some temporary reduction of o f Isp by increasing the oxidiser ratio initially, initially, and then transitioning to more fuel-rich mixtures. Since engine size is t ypically scaled for takeoff thrust this permits reduction of the weight of rocket engine, pipes and pumps and the extra propellant use can be more than compensated by increases of acceleration towards the end of the burn by having a reduced dry mass. [edit edit]]

Propellent density Although liquid hydrogen gives a high h igh Isp, its low density is a significant disadvantage: hydrogen occupies about 7x more volume per kilogram than dense fuels such as kerosene. This not only penalises the tankage, but also the pipes and fuel pumps leading from the tank, which need to be 7x bigger and heavier. heavier. (The oxidiser side of the engine e ngine and tankage is of course unaffected.) This makes the vehicle's dry mass very much









ROCKET PROPELLANTS • • • • •

Introduction Liquids Solids Hybrids Tables of Properties

Propellant is Propellant is the chemical mixture burned to produce thrust in rockets and consists









required, thus increasing the mass of the launch vehicle. Storage temperature is also important. A propellant with a low storage temperature, i.e. a cryogenic, will require thermal insulation, thus further increasing the mass of the launcher. launcher. The toxicity of the propellant is likewise important. Safety hazards exist when handling, transporting, and storing highly toxic compounds. Also, some propellants are very corrosive, however, however, materials that are resistant to certain propellants have been identified for use in rocket construction. Liquid propellants used by NASA and in commercial launch vehicles can be classified into three types: petroleum, cryogenics, and hypergolics. Petroleum fuels are those refined from crude oil and are a mixture of complex hydrocarbons, i.e. organic compounds containing only carbon and hydrogen. The petroleum used as rocket fuel is kerosene, or a type of highly refined kerosene called RP-1 (refined petroleum). Petroleum fuels are used in combination with liquid oxygen as the oxidizer. oxidizer. Kerosene delivers a specific impulse considerably less than cryogenic fuels, but it is generally the best performer among the non-cryogenic options. Liquid oxygen and RP-1 are used as the propellant in the first-stage boosters of the Atlas/Centaur and Delta launch vehicles. It also powered the first-stages of the Saturn 1B and Saturn V rockets. Cryogenic propellants are liquefied gases stored at very low temperatures, namely liquid hydrogen (LH2) as the fuel and liquid oxygen (LO2 or LOX) as the oxidizer. LH 2 remains liquid at temperatures of -253 degrees C (-423 degrees F) and LOX remains in a liquid state at temperatures of -183 degrees C (-298 degrees F).









Despite the similarity of the names, hydrazine, MMH and UDMH are different compounds with unique chemical properties. Hydrazine gives the best performance as a rocket fuel, but it has a high freezing point and is too unstable for use as a coolant. MMH is more stable and gives the best performance when freezing point is an issue, such as spacecraft propulsion applications. UDMH has the highest freezing point and is stable enough to be used in large regeneratively cooled engines. Consequently, Consequently, UDMH is often used in launch vehicle applications even though it is the least efficient of the hydrazine fuels. Also commonly used are blended fuels, such as Aerozine 50, which is a mixture of 50% UDMH and 50% hydrazine. Aerozine Aerozine 50 is almost as stable as UDMH and provides better performance. UDMH is used in many Russian, European, and Chinese rockets while MMH is used in the orbital maneuvering system (OMS) and reaction control system (RCS) of the Space Shuttle orbiter. orbiter. The Titan family of launch vehicles and the second stage of the Delta II use Aerozine 50. Hydrazine is also frequently used as a mono-propellant in catalytic decomposition engines . In these engines, a liquid fuel decomposes into hot gas in the presence of a catalyst. The decomposition of hydrazine produces temperatures of about 925 degrees C (1700 degrees F) and a specific impulse of about 230 or 240 seconds.

Solid Propellants Solid propellant motors are the simplest of all rocket designs. They consist of a casing, usually steel, filled with a mixture of solid compounds (fuel and oxidizer) which burn at a rapid rate, expelling hot gases from a nozzle to produce thrust.











easier to manufacture. The final product is rubberlike substance with the consistency of a hard rubber eraser. Composite propellants are often identified by the type of polymeric binder used. The two most common binders are polybutadiene acrylic acid acrylonitrile (PBAN) and hydroxy-terminator hydroxy-terminator polybutadiene (HTPB). PBAN formulations give a slightly higher specific impulse, density, density, and burn rate than equivalent formulations using HTPB. However, However, PBAN propellant is the more difficult to mix and process and requires an elevated curing temperature. HTPB binder is stronger and more flexible than PBAN binder. binder. Both PBAN and HTPB formulations result in propellants that deliver excellent performance, have good mechanical properties, and offer potentially long burn times. Solid propellant motors have a variety of uses. Small solids often power the final stage of a launch vehicle, or attach to payloads to boost them to higher orbits. Medium solids such as the Payload Assist Module (PAM) and the Inertial Upper Stage (IUS) provide the added boost to place satellites into geosynchronous orbit or on









Hydrazine

N2H4

32.05

1.004 g/ml

1.4oC

113.5oC

Methyl Hydrazine

CH3 NHNH NHNH2

46.07

0.866 g/ml

-52.4oC

87.5oC

Dimethyl Hydrazine

(CH3)2 NNH NNH2

60.10

0.791 g/ml

-58oC

63.9oC

NOTES: Chemically, Chemically, kerosene is a mixture of hydrocarbons; the chemical composition depends on its source, but it usually consists of about ten different hydrocarbons, hydrocarbons, each containing from 10 to 16 carbon atoms per molecule; the constituents include n-dodecane, alkyl benzenes, and naphthalene and its derivatives. Nitrogen tetroxide and nitric acid are hypergolic with hydrazine, MMH and UDMH. Oxygen is not hypergolic with any commonly used fuel.

COMPOSITION OF SOLID ROCKET PROPELLANTS Propellant

Type

Composition

Solid Rocket

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