ROCKET PROPELLANT

1.1 Introduction: Apropellantis a material that produces pressurized gas that: a) can be directed through a nozzle, thereby producing thrust (rocket propellant used in arocket motor); b) fills the interior of an ammunition cartridge or the chamber of a gun or cannon, leading to the expulsion of a bullet or shell (gunpowder,smokeless powder, and large gun propellants); c) can fill an expansible bag or membrane, such as an automotive airbag (gas generator propellants). d) can be placed in a sealed tube and act as a deflagrant low explosive charge in mining and demolition, producing a low velocity heave effect (gas pressure blasting). Rocket propellantis mass that is stored in some form ofpropellanttank, prior to being used as the propulsive mass that is ejected from arocket enginein the form of afluidjetto producethrust. A fuel propellant is often burned with an oxidizer propellant to produce large volumes of very hot gas. These gases expand and push on a nozzle, which accelerates them until they rush out of the back of therocketat extremely high speed, creating thrust. Sometimes the propellant is not burned, but can be externally heated for more performance. For smallerattitude controlthrusters, a compressed gas escapes the spacecraft through a propelling nozzle.

1.2 Principle: Rockets create thrust by expellingmassbackwards in a high speed jet (Newton's Third Law). Chemical rockets create thrust by reacting propellants within a combustion chamber into a very hotgasat high pressure, which is then expanded and accelerated by passage through a nozzle at the rear of the rocket. The amount of the resulting forward force, known as thrust, that is produced is themass flow rateof the propellants multiplied by their exhaust velocity (relative to the rocket), as specified byNewton's third law of motion. Thrust is therefore the equal and opposite reaction that moves the rocket, and not by interaction of the exhaust stream with air around the rocket. Equivalently, one can think of a rocket being accelerated upwards by the pressure of the combusting gases against the combustion chamber and nozzle. This operational principle stands in contrast to the commonly-held assumption that a rocket "pushes" against the air behind or below it. Rockets in fact perform better inouter space(where there is nothing behind or beneath them to push against), because there is a reduction in air pressure on the outside of the engine, and because it is possible to fit a longer nozzle without suffering from flow separation, in addition to the lack of air drag The maximum velocity that a rocket can attain in the absence of any external forces is primarily a function of itsmass ratioand itsexhaust velocity. The relationship is described by therocket equation : The mass ratio is just a way to express what proportion of the rocket is propellant (fuel/oxidizer combination) prior to engine ignition. Typically, asingle-stage rocketmight have amass fractionof 90% propellant, 10% structure, and hence a mass ratio of 10:1. The impulse delivered by the motor to the rocket vehicle per weight of fuel consumed is often reported as the rocket propellant'sspecific impulse. A propellant with a higher specific impulse is said to be more efficient because more thrust is produced while consuming a given amount of propellant. [1] Lower stages will usually use high-density (low volume) propellants because of their lighter tankage to propellant weight ratios and because higher performance propellants require higher expansion ratios for maximum performance than can be attained in atmosphere. Thus, the Apollo-Saturn Vfirst stage usedkerosene-liquid oxygenrather than the liquid hydrogen-liquid oxygen used on its upper stages Similarly, theSpace Shuttleuses high-thrust, high-densitysolid rocket boostersfor its lift-off with the liquid hydrogen-liquid oxygenSpace Shuttle Main Enginesused partly for lift-off but primarily for orbital insertion.1.3 Heating Value: Theheating valueorenergy valueof asubstance, usually afuelorfood(seefood energy), is the amount ofheatreleased during the combustion of a specified amount of it. The energy value is a characteristic for each substance. It is measured in units ofenergyper unit of the substance, usuallymass, such as: kJ/kg,kJ/mol,kcal/kg,Btu/lb. Heating value is commonly determined by use of abomb calorimeter. The heat of combustion forfuelsis expressed as the HHV, LHV, or GHV1.3.1 Higher Heating Value: The quantity known as higher heating value (HHV) (orgross energyorupper heating valueorgross calorific value(GCV) orhigher calorific value(HCV)) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. Such measurements often use a temperature of 25C. This is the same as the thermodynamic heat of combustion since theenthalpychange for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is liquid. The higher heating value takes into account thelatent heat of vaporizationofwaterin the combustion products, and is useful in calculating heating values for fuels wherecondensationof the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion).1.3.2 Lower Heating Value: The quantity known as lower heating value (LHV) (net calorific value(NCV) orlower calorific value(LCV)) is determined by subtracting theheat of vaporizationof the water vapor from the higher heating value. This treats any H2O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat. LHV calculations assume that the water component of a combustion process is in vapor state at the end of combustion, as opposed to thehigher heating value(HHV) (a.k.a.gross calorific valueorgross CV) which assumes that all of the water in a combustion process is in a liquid state after a combustion process. The LHV assumes that thelatent heat of vaporizationofwaterin the fuel and the reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below 150C cannot be put to use. The above is but one definition of lower heating value adopted by theAmerican Petroleum Institute(API) and uses a reference temperature of 60F (15.56C). Another definition, used by Gas Processors Suppliers Association (GPSA) and originally used by API (data collected for API research project 44), is theenthalpyof all combustion products minus the enthalpy of the fuel at the reference temperature (API research project 44 used 25C. GPSA currently uses 60F), minus the enthalpy of thestoichiometricoxygen(O2) at the reference temperature, minus theheat of vaporizationof the vapor content of the combustion products. The distinction between the two is that this second definition assumes that the combustion products are all returned to the reference temperature and the heat content from the condensing vapor is considered not to be useful. This is more easily calculated from the higher heating value than when using the preceding definition and will in fact give a slightly different answer.1.3.3 Gross Heating Value: Gross heating value(seeAR) accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels likewoodorcoal, which will usually contain some amount of water prior to burning.

2. TYPES OF ROCKET PROPELLANT: There are various kinds of fuel which are widely used in Rocket. They are broadly classified as 1) Chemical Propellant2) Ion Propellant

1.3.1 Chemical Propellant: Chemical rocket propellants are most commonly used, which undergoexothermicchemical reactionsto produce hot gas used by arocketforpropulsive purposes. There are four main types of chemical rocket propellants: solid, storable liquid, cryogenic liquid and liquid monopropellant. Hybrid solid/liquid bi-propellant rocket engines are starting to see limited use as well. Chemical Propellant also can be classified as given below: a) Solid Propellantb) Liquid Propellantc) Gas Propellantd) Hybrid Propellant1.3.2 Ion Propallant : Anion thrusteris a form ofelectric propulsionused forspacecraft propulsionthat createsthrustby acceleratingions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use theCoulomb forceand accelerate the ions in the direction of the electric field. Electromagnetic ion thrusters use theLorentz forceto accelerate the ions. The term "ion thruster" by itself usually denotes the electrostatic or gridded ion thrusters. Ion thrusters create very small levels ofthrustcompared to conventionalchemical rocketsbut achieve very highspecific impulse, or propellant mass efficiencies, by accelerating their exhausts to very high speed. However, ion thrusters carry a fundamental price: thepowerimparted to the exhaust increases with the square of its velocity while the thrust increases only linearly. Normal chemical rockets, on the other hand, can provide very high thrust but are limited in totalimpulseby the small amount ofenergythat can be stored chemically in the propellants.[1]Given the practical weight of suitable power sources, the accelerations given by these types of thrusters is frequently less than one thousandth ofstandard gravity.An additional advantage of ion thrusters is that because they operate essentially as electric (or electrostatic) motors, a greater fraction of the input power is converted into kinetic exhaust power than in a chemical rocket, because chemical rockets operate as heat engines subject to theCarnot limitthat applies to every heat engine.Due to their relatively high power needs, given the specific power of power supplies, and the requirement of an environment void of other ionized particles, ion thrust propulsion is currently only practical in space. Some rocket designs have their propellants obtain their energy from non chemical or even external sources. For examplewater rocketsuse the compressed gas, typically air, to force the water out of the rocket.Solar thermal rocketsandNuclear thermal rocketstypically propose to use liquid hydrogen for anIsp(Specific Impulse)of around 600900 seconds, or in some cases water that is exhausted as steam for anIspof about 190 seconds.Additionally for low performance requirements such as attitude jets, inert gases such as nitrogen have been employed. Inert propellant is the example of ion propellant

3. Solid Propellant:

3.1 Introduction:

Asolid rocketor asolid-fuel rocketis arocket enginethat usessolid propellants(fuel/oxidizer). The earliest rockets were solid-fuel rockets powered bygunpowder; they were used by theChinesein warfare as early as the 13th century and later by theMongols,Arabs, andIndians.[1]All rockets used some form of solid or powderedpropellantup until the 20th century, whenliquid rocketsandhybrid rocketsoffered more efficient and controllable alternatives. Solid rockets are still used today inmodel rocketsand on larger applications for their simplicity and reliability.Since solid-fuel rockets can remain in storage for long periods, and then reliably launch on short notice, they have been frequently used in military applications such asmissiles. The lower performance of solid propellants (as compared to liquids) does not favor their use as primary propulsion in modern medium-to-large launch vehicles customarily used to orbit commercial satellites and launch major space probes. Solids are, however, frequently used as strap-on boosters to increase payload capacity or as spin-stabilized add-on upper stages when higher-than-normal velocities are required. Solid rocketsareused as light launch vehicles for low Earth orbit (LEO) payloads under 2 tons or escape payloads up to 1000 pounds.

3.2 Historical Development: Solid rockets were invented by the Chinese, the earliest versions were recorded in the 13th century.Hyder Ali, king ofMysore, developed war rockets with an important change: the use of metal cylinders to contain the combustion powder. Castable solid rockets engines were invented byJohn Whiteside Parsonswhen he replacedblack powderwithasphaltandpotassium perchlorateto give a much higher Isp The availability of black powder (gunpowder) to propel projectiles was a precursor to the development of the first solid rocket. Ninth centuryChineseTaoistalchemistsdiscovered black powder while searching for theelixir of life; this accidental discovery led to experiments as weapons such asbombs,cannon, incendiaryfire arrowsand rocket-propelled fire arrows. The discovery of gunpowder was probably the product of centuries of alchemical experimentation.[5] Exactly when the firstflightsof rockets occurred is contested. A common claim is that the first recorded use of a rocket in battle was by the Chinese in 1232 against theMongolhordes atKai Feng Fu. This is based on an old Mandarin civil service examination question which reads "Is the defense of Kai Feng Fu against the Mongols (1232) the first recorded use of cannon?". Another question from the examinations read "Fire-arms began with the use of rockets in the dynasty of Chou (B. C. 1122-255)--in what book do we first meet with the word p'ao, now used for cannon?.The first reliable scholarly reference to rockets in China occurs in the Ko Chieh Ching Yuan (The Mirror of Research) which states that in 998 A.D. a man named Tang Fu invented a rocket of a new kind having an iron head. There were reports of fire arrows and 'iron pots' that could be heard for 5leagues(25km, or 15 miles) when they exploded upon impact, causing devastation for a radius of 600 meters (2,000 feet), apparently due to shrapnel.The lowering of the iron pots may have been a way for a besieged army to blow up invaders. The fire arrows were either arrows with explosives attached, or arrows propelled by gunpowder, such as the KoreanHwacha. Solid propellants are either "composites" with separate fuel and oxidizer or "double bases" which contain both fuelandoxidizer in thesamemolecule. In the case of gunpowder (a composite) the fuel is charcoal, the oxidizer is potassium nitrate, and sulphur serves as a catalyst. (Note: sulphur is not a true catalyst in gunpowder as it is consumed to a great extent into a variety of reaction products such asK2S. The sulphur acts mainly as a sensitizer lowering threshold of ignition.) During the 1950s and 60s researchers in the United States developedAmmonium Perchlorate Composite Propellant(APCP). This mixture is typically 69-70% finely groundammonium perchlorate(an oxidizer), combined with 16-20% finealuminiumpowder (a fuel), held together in a base of 11-14%PBANorHTPB(polybutadiene rubber fuel). The mixture is formed as a thickened liquid and then cast into the correct shape and cured into a firm but flexible load-bearing solid. APCP solid propellants are the most widely used in spaceflight launch vehicles and are also used in many military missiles. The military, however, uses a wide variety of different types of solid propellants some of which exceed the performance of APCP. A comparison of the highest specific impulses achieved with the various solid and liquid propellant combinations used in current launch vehicles 3.3 Basic Concept: A simple solidrocket motorconsists of a casing,nozzle,grain(propellant charge), andigniter.

Fig. 3.1 SOLID ROCKET MOTOR

The grain behaves like a solid mass,burningin a predictable fashion and producing exhaust gases. Thenozzledimensions are calculated to maintain a designchamberpressure, while producingthrustfrom the exhaust gases. Once ignited, a simple solid rocket motor cannot be shut off, because it contains all the ingredients necessary for combustion within the chamber in which they are burned. More advanced solid rocket motors can not only bethrottledbut also be extinguished and then re-ignited by controlling the nozzle geometry or through the use of vent ports. Also,pulsed rocket motorsthat burn in segments and that can be ignited upon command are available.Modern designs may also include a steerable nozzle for guidance,avionics, recovery hardware (parachutes),self-destructmechanisms,APUs, controllable tactical motors, controllable divert and attitude control motors, and thermal management materials.3.4 Design: Design begins with the totalimpulserequired, which 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. The results are exact dimensions for grain, nozzle, and case geometries: The grain burns at a predictable rate, given its surface area and chamber pressure. The chamber pressure is determined by the nozzle 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 or may not be bonded to the casing. Case-bonded motors are more difficult to design since the deformation of the case and the grain under flight must be compatible.Common modes of failure in solid rocket motors include fracture of the grain, failure of case bonding, and air pockets in the grain. All of these produce an instantaneous increase in burn surface area and a corresponding increase in exhaust gas and pressure, which may rupture the casing.Another failure mode is casingsealdesign. 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 theSpace ShuttleChallengerdisaster.3.5 Grain Geometry: Solid rocket fueldeflagratesfrom 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. Themass flux(kg/s) [and, therefore, pressure] of combustion gases generated is a function of theinstantaneoussurface areaAs, (m2), and linearburn ratebr(m/s):

Regardless of the composition, however, all propellants are processed into A similar basic geometric form, referred to as a propellant grain. As a rule , propellant grains are cylindrical in shape to fit neatly into a rocket motor in order to maximize volumetric efficiency. The grain may consist of a single cylindrical segment (Fig 3.2), or may contain many segments. Usually , a central core that extends the full length of the grain is introduced, in order to increase the propellant surface area initially exposed to combustionFig. 3.2 HALLOW CYLINDER GRAIN The core may have a wide variety of cross-sections such as circular, star, cross, dog-bone, wagon-wheel, etc . , however, for amateur motors, the most common shape is circular. The core shape has a profound influence on the shape of the thrust-time profile, as shown in Fig 3.3Fig. 3.3 CORE SHAPE AND INFLUENCE ON HRUST CURVE Circular Bore: if inBATESconfiguration, 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.

3.6 Casing: The casing may be constructed from a range of materials. Cardboard is used for smallblack powdermodel motors, whereas aluminum is used for larger composite-fuel hobby motors. Steel is used for thespace shuttle boosters. Filament woundgraphite epoxy casingsare used for high-performance motors. The casing must be designed to withstand the pressure and resulting stresses of the rocket motor, possibly at elevated temperature. For design, the casing is considered apressure vessel. To protect the casing from corrosive hot gases, a sacrificial thermal liner on the inside of the casing is often implemented, whichablatesto prolong the life of the motor casing.3.7 Nozzle: Aconvergent-divergentdesign accelerates the exhaust gas out of the nozzle to produce thrust. The nozzle must be constructed from a material that can withstand the heat of the combustion gas flow. Often, heat-resistant carbon-based materials are used, such as amorphousgraphiteorcarbon-carbon.Some designs include directional control of the exhaust. This can be accomplished by gimballing the nozzle, as in the Space Shuttle SRBs, by the use of jet vanes in the exhaust similar to those used in theV-2 rocket, or by liquid injection thrust vectoring (LITV). An earlyMinutemanfirst stage used a single motor with fourgimballednozzles to provide pitch, yaw, and roll control. LITV consists of injecting a liquid into the exhaust stream after the nozzle throat. The liquid then vaporizes, and in most cases chemically reacts, adding mass flow to one side of the exhaust stream and thus providing a control moment. For example, theTitan IIIC solid boosters injectednitrogen tetroxidefor LITV; the tanks can be seen on the sides of the rocket between the main center stage and the boosters. 3.8 Performance: A typical well designed ammonium perchlorate composite propellant (APCP) first stage motor may have a vacuum specific impulse (Isp) as high as 285.6s (Titan IVB SRMU).This compares to 339.3s for kerosene/liquid oxygen (RD-180) and 452.3s for hydrogen/oxygen (Block II SSME) bipropellant engines. Upper stage specific impulses are somewhat greater: as much as 303.8s for APCP (Orbus 6E), 359s for kerosene/oxygen (RD-0124) and 465.5s for hydrogen/oxygen (RL10B-2). Propellant fractions are usually somewhat higher for (non-segmented) solid propellant first stages than for upper stages. The 117,000 pound Castor 120 first stage has a propellant mass fraction of 92.23% while the 31,000 pound Castor 30 upper stage recently developed for Orbital Science's Taurus II COTS (International Space Station resupply) launch vehicle has a 91.3% propellant fraction with 2.9% graphite epoxy motor casing, 2.4% nozzle, igniter and thrust vector actuator, and 3.4% non-motor hardware including such things as payload mount, interstage adapter, cable raceway, instrumentation, etc. Castor 120 and Castor 30 are 93 and 92inches in diameter, respectively, and serve as stages on the Athena IC and IIC commercial launch vehicles. A four stage Athena II using Castor 120s as both first and second stages became the firstcommercially developedlaunch vehicle to launch a lunar probe (Lunar Prospector) in 1998. Solid rockets can provide high thrust for relatively short periods of time. For this reason, solids have been used as initial stages in rockets (the classic example being theSpace Shuttle), while reserving high specific impulse engines, especially less massive hydrogen fueled engines for higher stages. In addition, solid rockets have a long history as the final boost stage for satellites due to their simplicity, reliability, compactness and reasonably highmass fraction. A spin-stabilized solid rocket motor is sometimes added when extra velocity is required, such as for a mission to a comet or the outer solar system, because a spinner does not require a guidance system (on the newly added stage). Thiokol's extensive family of mostly titanium-casedStarspace motors has been widely used, especially on Delta launch vehicles and as spin-stabilized upper stages to launch satellites from the cargo bay of the Space Shuttle.Starmotors have propellant fractions as high as 94.6% but add-on structures and equipment reduce the operating mass fraction by 2% or more. Higher performing solid rocket propellants are used in large strategic missiles (as opposed to commercial launch vehicles). HMX, C4H8N4(NO2)4, a nitramine with greater energy than ammonium perchlorate, is the main ingredient in NEPE-75 propellant used in the Trident II D-5 Fleet Ballistic Missile. It is because of explosive hazard that the higher energy military solid propellants are not used in commercial launch vehicles except when the LV is an adapted ballistic missile already containing HMX propellant (example: Minotaur IV and V based on retired Peacekeeper ICBMs). The Naval Air Weapons Station at China Lake, CA developed a new compound, C6H6N6(NO2)6, called simplyCL-20(China Lake compound#20). Compared to HMX, CL-20 has 14% more energy per mass, 20% more energy per volume, and a higher oxygen-to-fuel ratio. One of the motivations for development of these very high energy density military solid propellants is to achieve mid-course exo-atmospheric ABM capability from missiles small enough to fit in existing ship-based below-deck vertical launch tubes and air-mobile truck-mounted launch tubes. CL-20 propellant compliant with Congress' 2004 insensitive munitions (IM) law has been demonstrated and may, as its cost comes down, be suitable for use in commercial launch vehicles, with a very significant increase in performance compared with the currently favored APCP solid propellants. An attractive attribute for military use is the ability for solid rocket propellant to remain loaded in the rocket for long durations and then reliably launched at a moment's notice.

3.9 Propellant Familys:Black Powder (BP) Propellants Composed ofcharcoal(fuel),potassium nitrate(oxidizer), andsulfur(additive),black powderis one of the oldestpyrotechniccompositions with application to rocketry. In modern times, black powder finds use in low-power model rockets (such asEstesand Quest rockets), as it is cheap and fairly easy to produce. The fuel grain is typically a mixture of pressed fine powder (into a solid, hard slug), with a burn rate that is highly dependent upon exact composition and operating conditions. Due to its sensitivity to fracture (and, therefore, catastrophic failure upon ignition) and poor performance (specific impulsearound 80s), BP does not typically find use in motors above 40Ns.Zinc-Sulfur (ZS) Propellants Composed of powderedzincmetal and powdered sulfur (oxidizer), ZS or "micrograin" is another pressed propellant that does not find any practical application outside of specialized amateur rocketry circles due to its poor performance (as most ZS burns outside the combustion chamber) and incredibly fast linear burn rates on the order of 2m/s. ZS is most often employed as a novelty propellant as the rocket accelerates extremely quickly, leaving a spectacular large orange fireball behind it. "Candy" propellants In general,candypropellants are an oxidizer (typically potassium nitrate) and a sugar fuel (typicallydextrose,sorbitol, orsucrose) that are cast into shape by gently melting the propellant constituents together and pouring or packing theamorphouscolloidinto a mold. Candy propellants generate a low-medium specific impulse of roughly 130s and, thus, are used primarily only by amateur and experimental rocketeers.Double-Base (DB) Propellants DB propellants are composed of twomonopropellantfuel components where one typically acts as a high-energy (yet unstable) monopropellant and the other acts as a lower-energy stabilizing (and gelling) monopropellant. In typical circumstances,nitroglycerinis dissolved in anitrocellulosegel and solidified with additives. DB propellants are implemented in applications where minimal smoke is required yet medium-high performance (Ispof roughly 235s) is required. The addition of metal fuels (such as aluminum) can increase the performance (around 250s), thoughmetal oxidenucleationin the exhaust can turn the smoke opaque.Composite propellants A powdered oxidizer and powdered metal fuel are intimately mixed and immobilized with a rubbery binder (that also acts as a fuel). Composite propellants are often eitherammonium nitrate-based (ANCP) orammonium perchlorate-based (APCP). Ammonium nitrate composite propellant often uses magnesium and/or aluminum as fuel and delivers medium performance (Ispof about 210s) whereasAmmonium Perchlorate Composite Propellantoften uses aluminum fuel and delivers high performance (vacuum Ispup to 296s with a single piece nozzle or 304s with a high area ratio telescoping nozzle).Composite propellants are cast, and retain their shape after the rubber binder, such asHydroxyl-terminated polybutadiene(HTPB),cross-links(solidifies) with the aid of a curative additive. Because of its high performance, moderate ease of manufacturing, and moderate cost, APCP finds widespread use in space rockets, military rockets, hobby and amateur rockets, whereas cheaper and less efficient ANCP finds use in amateur rocketry andgas generators. Ammonium dinitramide, NH4N(NO2)2, is being considered as a 1-to-1 chlorine-free substitute for ammonium perchlorate in composite propellants. Unlike ammonium nitrate, ADN can be substituted for AP without a loss in motor performance.In 2009, a group succeeded in creating a propellant ofwaterand nanoaluminum (ALICE). TheConstellation programused a mix ofaluminum,ammonium perchlorate, a polymer ofpolybutadieneandacrylonitrile,epoxyandiron oxide. High-Energy Composite (HEC) propellants Typical HEC propellants start with a standard composite propellant mixture (such as APCP) and add a high-energy explosive to the mix. This extra component usually is in the form of small crystals ofRDXorHMX, both of which have higher energy than ammonium perchlorate. Despite a modest increase in specific impulse, implementation is limited due to the increased hazards of the high-explosive additives.Composite Modified Double Base propellants Composite modified double base propellants start with a nitrocellulose/nitroglycerin double base propellant as a binder and add solids (typically ammonium perchlorate and powdered aluminum) normally used in composite propellants. The ammonium perchlorate makes up the oxygen deficit introduced by using nitrocellulose, improving the overall specific impulse. The aluminum also improves specific impulse as well as combustion stability. High performing propellants such as NEPE-75 used in Trident II D-5, replace most of the AP with HMX, further increasing specific impulse. The mixing of composite and double base propellant ingredients has become so common as to blur the functional definition of double base propellants.Minimum-signature (smokeless) propellants One of the most active areas of solid propellant research is the development of high-energy, minimum-signature propellant usingCL-20(China Lakecompound #20), C6H6N6(NO2)6, which has 14% higher energy per mass and 20% higher energy density than HMX. The new propellant has been successfully developed and tested in tactical rocket motors. The propellant is non-polluting: acid free, solid particulates free, and lead free. It is also smoke free and has only a faint shock diamond pattern that is visible in the otherwise transparent exhaust. Without the bright flame and dense smoke trail produced by the burning of aluminized propellants, these smokeless propellants all but eliminate the risk of giving away the positions from which the missiles are fired. The new CL-20 propellant is shock-insensitive (hazard class 1.3) as opposed to current HMX smokeless propellants which are highly detonable (hazard class 1.1). CL-20 is considered a major breakthrough in solid rocket propellant technology but has yet to see widespread use because costs remain high. 3.10 Advantages: Solid propellant rockets are much easier to store and handle than liquid propellant rockets. High propellant density makes for compact size as well. These features plus simplicity and low cost make solid propellant rockets ideal for military applications. In the 1970s and 1980s the U.S. switched entirely to solid-fueled ICBMs: theLGM-30 MinutemanandLG-118A Peacekeeper(MX). In the 1980s and 1990s, the USSR/Russia also deployed solid-fueled ICBMs (RT-23,RT-2PM, andRT-2UTTH), but retains two liquid-fueled ICBMs (R-36andUR-100N). All solid-fueled ICBMs on both sides had three initial solid stages, and those with multiple independently targeted warheads had a precision maneuverable bus used to fine tune the trajectory of the re-entry vehicles. U.S. Minuteman III ICBMs were reduced to a single warhead by 2011 in accordance with the START treaty leaving only the Navy's Trident sub-launched ICBMs with multiple warheads.Their simplicity also makes solid rockets a good choice whenever large amounts of thrust are needed and cost is an issue. TheSpace Shuttleand many other orbitallaunch vehiclesuse solid-fueled rockets in their first stages (solid rocket boosters) for this reason. 3.11 Disadvantages: Relative to liquid fuel rockets, solid rockets have lowerspecific impulse. The propellant mass ratios of solid propellant upper stages is usually in the .91 to .93 range which is as good or better than that of most liquid propellant upper stages but overall performance is less than for liquid stages because of the solids' lower exhaust velocities. The high mass ratios possible with (unsegmented) solids is a result of high propellant density and very high strength-to-weight ratio filament-wound motor casings. A drawback to solid rockets is that they cannot be throttled in real time, although a programmed thrust schedule can be created by adjusting the interior propellant geometry. Solid rockets can be vented to extinguish combustion or reverse thrust as a means of controlling range or accommodating warhead separation. Casting large amounts of propellant requires consistency and repeatability which is assured by computer control. Casting voids in propellant can adversely affect burn rate so the blending and casting takes place under vacuum and the propellant blend is spread thin and scanned to assure no large gas bubbles are introduced into the motor. 3.12 Advance Research: Leveraging from its deep expertise in the field ofhybrid rocket propulsionand thefast burning solid fuels, SPG has started a research and development program in the area of (Solid Fuel Ramjets) SFRJ. Due to their inherent simplicity SFRJ's present a cost effective option for a wide range of applications that demand a sustained thrust force during a substantial portion of their mission profile. UAV's and target drones are believed to be the primary candidates for SFRJ propulsion. Testing program with a 2,000 lb thrust class paraffin-based SFRJ is ongoing.Fig.3.4 SFRJ The SFRJ cycleis the same as the ramjet cycle except that the fuel exists in solid form within the chamber and the stoichometry of combustion is controlled by the regression rate of the fuel. The fuel is not a propellant in the solid rocket motor sense but a pure fuel, inert without external oxidizer much like in ahybrid rocket motor. A wide range of fuels can be used from polymers such as PMMA or PE to long-chain alkanes such as paraffin or cross-linked rubbers such as HTPB. Because the fuel exists in the solid form, inclusion of solid metals is significantly easier than in a liquid fueled ramjet. SFRJ's offer some very significant advantages over liquid fuel ramjets such as: Extremely simple compared with liquid fueled rockets or ramjets? In its simplest form, a SFRJ is basically a tube with a fuel grain cast in it. Higher fuel density in the solid phase for pure hydrocarbons and even higher if metal additives are used Easy inclusion of metal fuels such as boron, magnesium or beryllium which raise the heat of combustion and/or the density and therefore the density impulse capability compared with liquid ramjets Solid fuel acts as an ablative insulator, allowing higher sustained combustion chamber exit temperature levels (and hence specific thrust) with less complexity Fuel is stored within the combustion chamber allowing for more efficient packaging and higher mass fractions than liquid ramjets No need for pumps, external tankage, injectors or plumbing for fuel delivery

4. LIQUID PROPELLANT:4.1 Historical Development: On March 16, 1926,Robert H. Goddardusedliquid oxygen(LOX) andgasolineaspropellantsfor his first successful liquid rocket launch. Both are readily available, cheap, highly energetic, and dense. Oxygen is a moderatecryogen air will not liquefy against a liquid oxygen tank, so it is possible to store LOX briefly in a rocket without excessive insulation. Gasoline has since been replaced by differenthydrocarbonfuels, for exampleRP-1- a highly refined grade ofkerosene. This combination is quite practical for rockets that need not be stored, and to this day, it is used in thefirst stagesof most orbitallaunchers, as well as the long-range offensivemissilesofChinaandNorth Korea.

Fig.4.1 FIRST LIQUID FUEL ROCKET During the 1950s there was a great burst of activity by propellant chemists to find high-energy liquid propellants better suited to the military. Military rockets need to sit in silos for many years, able to launch at a moment's notice. Propellants requiring continuous refrigeration, and which cause their rockets to grow ever-thicker blankets of ice, are not practical. As the military is willing to handle and use hazardous materials, a great number of dangerous chemicals were brewed up in large batches, virtually all of which were dead ends. For instance, in the case ofnitric acid, the acid itself (HNO3) is unstable, and corrodes most metals, making it difficult to store. The addition of large amounts ofdinitrogen tetroxide(N2O4) makes the mixture red, but keeps it from changing composition, leaving the problem that nitric acid will eat any container it is placed in, releasing gases that can build up pressure in the process. The breakthrough was the addition of a littlehydrofluoric acid(HF), which forms a self-healing metal fluoride on the interior of tank walls and makesInhibitedRed Fuming Nitric Acid storable. Although the development of military propellants was treated with the greatest secrecy, the trick to inhibiting nitric acid was published shortly after its discovery in 1954 and Russian rockets with the same fuel appeared shortly afterwards, the first being the SS-1B ("Scud"). Eventually the chemists gave up stabilizing HNO3with N2O4, and just used straight N2O4, which is a slightly better oxidizer anyway. (In the propellant table below, note that N2O4is always in equilibrium with NO2, and so mixtures are sometimes quoted with the latter.)

4.2 Principle: As with conventionalsolid fuelsrockets, liquid fueled rockets burn a fuel and an oxidizer, however, both in a liquid state. Two metal tanks hold the fuel and oxidizer respectively. Due to properties of these two liquids, they are typically loaded into their tanks just prior to launch. The separate tanks are necessary, for many liquid fuels burn upon contact. Upon a set launching sequence two valves open, allowing the liquid to flow down the pipe-work. If these valves simply opened allowing the liquid propellants to flow into the combustion chamber, a weak and unstable thrust rate would occur, so either a pressurized gas feed or a turbopump feed is used. The simpler of the two, the pressurized gas feed, adds a tank of high pressure gas to the propulsion system. The gas, an unreactive, inert, and light gas (such as helium), is held and regulated, under intense pressure, by a valve/regulator. The second, and often preferred, solution to the fuel transfer problem is a turbopump. A turbopump is the same as regular pump in function and bypasses a gas-pressurized system by sucking out the propellants and accelerating them into the combustion chamber. The oxidizer and fuel are mixed and ignited inside the combustion chamber and thrust is created.

4.3 Performance: The National Aeronautics and Space Administration (NASA) is focusing on the development of advanced chemical rocket engines. These engines shall be required to operate at higher chamber pressures than the present Space Shuttle Main Engine. Higher chamber pressures will provide greater rocket engineperformance. In general, the performance of propellants has been documented for sea-level expansion from 1000 psia chamber pressure. The objective of this is to establish a propellant performance database of liquid hydrocarbon and aluminum hydrocarbon fuels using advanced engine parametric. Interest in liquid hydrocarbon fuels has been maintained throughout the years simply because of the inherent ease of handling, long storage life, low toxicity, low cost and high density. Liquid hydrocarbons have been found beneficial in a number of liquid propellant rocket engines. For example, the largest liquid propellant rocket engine to date, the F-I engine, employed a hydrocarbon, RP-I (Rocket Propellant- I, kerosene), as the fuel and regenerative coolant. Recent propellant performance and mission studies have accentuated the benefits of employing this advanced chemical propulsion concept. Propellant performance increases have been documented with respect to mixture ratio and metal loading for beryllium, lithium and aluminum metallized propellants. Aluminum and beryllium metallic additions to liquid bipropellant systems were found to improve the performance of orbital transfer vehicle missions. Additionally, metallized propellants offer benefits over conventional liquid bipropellant systems in planetary missions. For instance, metalizedpropellants facilitate a 20 to 33 percent increase in delivered payload tothe Mars surface .

4.3 Propellant Types: The most common liquid propellants in use today: LOXandkerosene(RP-1). Used for the first stages of theSaturn VandAtlas V, and all stages of the developmentalFalcon 1andFalcon 9. Very similar toRobert Goddard'sfirst rocket. This combination is widely regarded as the most practical for boosters that lift off at ground level and therefore must operate at full atmospheric pressure. LOXandliquid hydrogen, used in theSpace Shuttleorbiter, the Centaur upper stage of the Atlas V,Saturn Vupper stages, the newerDelta IV rocket, theH-IIArocket, and most stages of the EuropeanArianerockets. Nitrogen tetroxide(N2O4) andhydrazine(N2H4),MMH, orUDMH. Used in military, orbital, and deep space rockets because both liquids are storable for long periods at reasonable temperatures and pressures. N2O4/UDMH is the main fuel for theProton rocket. This combination ishypergolic, making for attractively simple ignition sequences. The major inconvenience is that these propellants are highly toxic, hence they require careful handling. Monopropellantssuch ashydrogen peroxide,hydrazine, andnitrous oxideare primarily used forattitude controland spacecraftstation-keepingwhere their long-term storability, simplicity of use, and ability to provide the tiny impulses needed, outweighs their lower specific impulse as compared to bipropellants. Hydrogen peroxide is also used to drive the turbopumps on the first stage of the Soyuz launch vehicle.

HydrogenMany early rocket theorists believed thathydrogenwould be a marvellous propellant, since it gives the highestspecific impulse. As hydrogen in any state is very bulky, for lightweight vehicles it is typically stored as a deeply cryogenic liquid. This storage technique was mastered in the 1960s as part of theSaturnandCentaurupper-stage programs. Even as a liquid, hydrogen has low density, requiring large, heavy tanks and pumps, and the extreme cold requires heavy and/orpotentially dangeroustank insulation. This extra weight reduces the mass fraction of the vehicle and offsets the specific impulse advantage. Most rockets that use hydrogen fuel use it in upper stages only, where a low thrust-to-empty-mass ratio can be tolerated and where a hydrogen stage's low total mass reduces the size of the lower stages. Those rockets that use hydrogen fuel in their lower stages, like theSpace Shuttle,Delta IV, andAriane 5, often use powerful and dense solid rocket motors at liftoff to improve their acceleration off the pad and thus reduce gravity losses early in flight.Lithium/fluorineThe highest specific impulse chemistry ever test-fired in a rocket engine waslithiumandfluorine, with hydrogen added to improve the exhaust thermodynamics (all propellants had to be kept in their own tanks, making this atripropellant). The combination delivered 542 s specific impulse in a vacuum, equivalent to an exhaust velocity of 5320 m/s. 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 -252C (just 21 K) and the lithium must be kept above 180C (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, is an explosive hazard. Fluorine and the hydrogen fluoride (HF) in the exhaust are very toxic, which makes working around the launch pad difficult, damages the environment, and makes getting a launch license that much more difficult. The rocket exhaust is also ionized, which would interfere with radio communication with the rocket. Finally, both lithium and fluorine are expensive and rare, enough to actually matter. This combination has therefore never flown.

4.5 Advantages: Liquid fueled rockets have higherspecific impulsethan solid rockets and are capable of being throttled, shut down, and restarted. Only the combustion chamber of a liquid fueled rocket needs to withstand high combustion pressures and temperatures and they can be regeneratively cooled by the liquid propellant. On vehicles employingturbo pumps, the propellant tanks are at very much less pressure than the combustion chamber. For these reasons, most orbital launch vehicles use liquid propellants.The primary performance advantage of liquid propellants is due to the oxidizer. Several practical liquid oxidizers (liquid oxygen,nitrogen tetroxide, andhydrogen peroxide) are available which have better specific impulse than theammonium perchlorateused in most solid rockets, when paired with comparable fuels. These facts have led to the use of hybrid propellants: a storable oxidizer used with a solid fuel, which retain most virtues of both liquids (high ISP) and solids (simplicity). (The newest nitramine solid propellants based on CL-20 (HNIW) can match the performance of NTO/UDMH storable liquid propellants, but cannot be controlled as can the storable liquids.)While liquid propellants are cheaper than solid propellants, for orbital launchers, the cost savings do not, and historically have not mattered; the cost of the propellant is a very small portion of the overall cost of the rocket.[citation needed]Some propellants, notably Oxygen and Nitrogen, may be able to becollectedfrom theupper atmosphere, and transferred up tolow-Earth orbitfor use inpropellant depotsat substantially reduced cost. 4.6 Disadvantages: The main difficulties with liquid propellants are also with the oxidizers. These are generally at least moderately difficult to store and handle due to their high reactivity with common materials, may have extreme toxicity (nitric acids), moderately cryogenic (liquidoxygen), or both (liquidfluorine, FLOX- a fluorine/LOX mix). Several exotic oxidizers have been proposed: liquidozone(O3),ClF3, andClF5, all of which are unstable, energetic, and toxic.Liquid fueled rockets also require potentially troublesome valves and seals and thermally stressed combustion chambers, which increase the cost of the rocket. Many employ specially designed turbo pumps which raise the cost enormously due to difficult fluid flow patterns that exist within the casings.

5. GAS PROPELLANT:5.1 Introduction: A gas propellant usually involves some sort of compressed gas. However, due to the low density and high weight of the pressure vessel, gases see little current use, but are sometimes used forvernier engines, particularly with inert propellants. Gas core reactor rocketsare a conceptual type of rocket that is propelled by the exhausted coolant of agaseous fission reactor. The nuclear fission reactor core may be either agasorplasma. They may be capable of creatingspecific impulsesof 3,0005,000s (30 to 50kNs/kg, effective exhaust velocities 30 to 50km/s) andthrustwhich is enough for relatively fastinterplanetarytravel.Heat transferto theworking fluid(propellant) is bythermal radiation, mostly in theultraviolet, given off by thefissiongas at a working temperature of around 25,000 C.

5.2 Propellant Type: GOX (gaseous oxygen)was used as one of the propellants for theBuran programfor the orbital maneuvering system.

6. HYBRID PROPELLANT:6.1 Introduction: Ahybrid rocketis arocketwith arocket motorwhich usespropellantsin two different states of matter - one solid and the other either gas or liquid. The Hybrid rocket concept can be traced back at least 75 years.[1] Hybrid rockets exhibit advantages over bothliquid rocketsandsolid rocketsespecially in terms of simplicity, safety, and cost.[2]Because it is nearly impossible for the fuel and oxidizer to be mixed intimately (being different states of matter), hybrid rockets tend to fail more benignly than liquids or solids. Likeliquid rocketsand unlikesolid rocketsthey can be shut down easily and are simply throttle-able. The theoreticalspecific impulse()performance of hybrids is generally higher than solids and roughly equivalent tohydrocarbon-basedliquids.as high as 400s has been measured in a hybrid rocket using metalized fuels.[3]Hybrid systems are slightly more complex than solids, but thesignificant hazardsof manufacturing, shipping and handling solids offset the system simplicity advantages.6.2 Historical Development: In 1998SpaceDevacquired all of the intellectual property, designs, and test results generated by over 200 hybrid rocket motor firings by theAmerican Rocket Companyover its eight year life.SpaceShipOne, the first private manned spacecraft, was powered by SpaceDev's hybrid rocket motor burningHTPBwithnitrous oxide. However nitrous oxide was the prime substance responsible for the explosion that killed three in the development of the successor of SpaceShipOne atscaled compositesin 2007.SpaceDev was developing theSpaceDev Streaker, an expendable small launch vehicle, andSpaceDev Dream Chaser, capable of both suborbital and orbital human space flight. Both Streaker and Dream Chaser use hybrid rocket motors that burnnitrous oxideand the synthetic rubberHTPB. SpaceDev was acquired bySierra Nevada Corporationin 2009, becoming its Space Systems division, which continues to develop Dream Chaser for NASA'sCommercial Crew Developmentcontract. Space Propulsion Groupwas founded in 1999 by Dr. Arif Karabeyoglu, Prof. Brian Cantwell and others from Stanford University to develop high regression-rate liquefying hybrid rocket fuels. They have successfully fired motors as large as 12.5 in. diameter which produce 13,000lbf. using the technology and are currently developing a 24 in. diameter, 25,000lbf. motor to be initially fired in 2010.Orbital Technologies Corporation(Orbitec) has been involved in some US government funded research on hybrid rockets including the "Vortex Hybrid" concept.Environmental Aerospace Corporation (eAc) was incorporated in 1994 to develop hybrid rocket propulsion systems. It was included in the design competition for theSpaceShipOnemotor but lost the contract toSpaceDev.TheReaction 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.Copenhagen Suborbitals, a Danish rocket group, has designed and test-fired several hybrids using N2O at first and currently LOX. Their fuel is epoxy, paraffin, or polyurethane. Several universities have recently experimented with hybrid rockets.BYU, theUniversity of Utah, andUtah State Universitylaunched a student-designed rocket called Unity IV in 1995 which burned the solid fuelhydroxyl-terminated polybutadiene(HTPB) with an oxidizer of gaseous oxygen, and in 2003 launched a larger version which burned HTPB withnitrous oxide.Stanford Universityis the institution where liquid-layer combustion theory for hybrid rockets was developed. The SPASE group at Stanford is currently working with NASA Ames Research Center developing the Peregrine Sounding rocket which will be capable of 100km altitude. TheWARRstudent-team at theTechnical University of Munichis developing hybrid engines and rockets since the beginning of the 1970s. Usingacids,oxygenornitrous oxidein combination withpolyethyleneorHTPB. The development includes test stand engines as well as airborne versions, like the first German hybrid rocketBarbarella.University of Brasilia's Hybrid Team has extensive research in paraffin/nitrous oxide hybrids having already made more than 50 tests fires. Hybrid Team is currently working liquefied propellant, numeric optimization and rocket designMany other universities, such asPurdue University, theUniversity of Michiganat Ann Arbor, theUniversity of Arkansas at Little Rock,Hendrix College, theUniversity of Illinois,Portland State University, andTexas A&M Universityhave hybrid motor test stands that allow for student research with hybrid rockets.Boston University's student-run"Rocket Team", which in the past has launched only solid motor rockets, has completed several static tests of motors using paraffin and HTPB solid fuels and nitrous oxide as the oxidizer; the latest design is a 500psig, 75lbf thrust HTPB/N2O design dubbed "Mk.II."[9]Florida Institute of Technologyhas successfully tested and evaluated hybrid technologies with their Panthr Project.A United Kingdom-based team (laffin-gas) is using four N2O hybrid rockets in a drag-racing style car. Each rocket has an outer diameter of 150mm and is 1.4m long. They use a fuel grain of high-density wound paper soaked in cooking oil. The N2O supply is provided by Nitrogen-pressurised piston accumulators which provide a higher rate of delivery than N2O gas alone and also provide damping of any reverse shock.Also in the United Kingdom theBloodhound SSCteam haveThe Falcon Projectled byDaniel Jubbdeveloping a hybrid rocket using HTP and and HTPB.There are a number of hybrid rocket motor systems available for amateur/hobbyist use in high-powered model rocketry. These include the popularHyperTeksystems and a number of 'Urbanski-Colburn Valved' (U/C) systems such asRATTWorks,Skyripper Systems,West Coast Hybrids,Contrail Rockets, andPropulsion Polymers. All of these systems usenitrous oxideas the oxidizer and a plastic fuel (such as PVC or PolyPropylene) or a polymer-based fuel such as HTPB. This reduces the cost per flight compared to solid rocket motors, although there is generally more 'GSE' (ground support equipment) required with hybrids.InItalyone of the leading centers for research in hybrid propellants rockets is CISAS (Center of Studies and Activities for Space) "G. Colombo",University of Padua. The activities cover all stages of the development: from theoretical analysis of the combustion process to numerical simulation using CFD codes, and then by conducting ground tests of small scale and large-scale rockets (up to 20kN, N2O-Paraffin based motors). One of these engines flew successfully in 2009.

6.3 Principle: In its simplest form a hybrid rocket consists of apressure vessel(tank) containing the liquidpropellant, thecombustion chambercontaining the solid propellant, and a valve isolating the two. When thrust is desired, a suitable ignition source is introduced in the combustion chamber and the valve is opened. The liquid propellant (or gas) flows into the combustion chamber where it is vaporized and then reacted with the solid propellant.Combustionoccurs in a boundarydiffusion flameadjacent to the surface of the solid propellant. 6.4 Propellant type: Generally the liquid propellant is theoxidizerand the solid propellant is thefuelbecause solid oxidizers areproblematicandlower performingthan liquid oxidizers. Furthermore, using a solid fuel such asHTPBorparaffinallows for the incorporation of high-energy fuel additives such asaluminum,lithium, ormetal.Common oxidizers include gaseous or liquidoxygenornitrous oxide. Common fuels includepolymerssuch aspolyethylene,cross-linkedrubbersuch asHTPBor liquefying fuels such asparaffin.6.5 Hybrid Safety: Generally, well designed and carefully constructed hybrids are very safe. The primary hazards associated with hybrids are: Pressure vessel failures- Chamber insulation failure may allow hot combustion gases near the chamber walls leading to a "burn-through" in which the vessel ruptures. Blow back- For oxidizers that decompose exothermically such asnitrous oxideorhydrogen peroxide, flame or hot gasses from the combustion chamber can propagate back through the injector, igniting the oxidizer and leading to a tank explosion. Blow-back requires gases to flow back through the injector due to insufficient pressure drop which can occur during periods of unstable combustion. Blow back is inherent to specific oxidizers and is not possible with oxidizers such asoxygenornitrogen tetroxideunless fuel is present in the oxidizer tank. Hard starts- An excess of oxidizer in the combustion chamber prior to ignition, particularly for monopropellants such asnitrous oxide, can result in a temporary over-pressure or "spike" at ignition.Because the fuel in a hybrid does not contain an oxidizer, it will not combust explosively on its own. For this reason, hybrids are classified as having noTNT equivalentexplosive power. In contrast,solid rocketsoften have TNT equivalencies similar in magnitude to the mass of the propellant grain.Liquidstypically have TNT equivalencies calculated based on the amount of fuel and oxidizer which could realistically intimately combine before igniting explosively; this is often taken to be 10-20% of the total propellant mass. For hybrids, even filling the combustion chamber with oxidiser prior to ignition will not generally create an explosive with the solid fuel, the explosive equivalence is often quoted as 0%.6.6 Advantages: Advantages compared with bipropellant liquid rockets Mechanically simpler - requires only a single liquid propellant resulting in less plumbing, fewer valves, and simpler operations. Denser fuels - fuels in the solidphasegenerally have higher density than those in the liquid phase Metal additives - reactive metals such as aluminum,magnesium,lithiumorberylliumcan be easily included in the fuel grain increasingspecific impulse()Advantages compared with solid rockets Higher theoreticalobtainable Less explosion hazard - Propellant grain more tolerant of processing errors such as cracks More controllable - Start/stop/restart and throttling are all achievable with appropriate oxidizer control Safe and non-toxic oxidizers such asliquid oxygenandnitrous oxidecan be used Can be transported to site in a benign form and loaded with oxidizer remotely immediately before launch, improving safety.

6.7 Disadvantages: Hybrid rockets also exhibit some disadvantages when compared with liquid and solid rockets. These include: Oxidizer-to-fuel ratio shift ("O/F shift") - with a constant oxidizer flow-rate, the ratio of fuel production rate to oxidizer flow rate will change as a grain regresses. This leads to off-peak operation from a chemical performance point of view. Low regression-rate (rate at which the solid phase recedes) fuels often drive multi-port fuel grains. Multi-port fuel grains have poor volumetric efficiency and, often, structural deficiencies. High regression-rate liquefying fuels developed in the late 1990s offer a potential solution to this problem.[4]For a well-designed hybrid, O/F shift has a very small impact on performance becauseis insensitive to O/F shift near the peak.In general, much less development work has been performed with hybrids than liquids or solids and it is likely that some of these disadvantages could be rectified through further investment inresearch and development.

7. GEL PROPELLANT:7.1 Introduction: Agel(from thelat.gelufreezing, cold, ice orgelatusfrozen, immobile) is a solid,jelly-likematerialthat can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilutecross-linkedsystem, which exhibits no flow when in the steady-state.[1]By weight, gels are mostly liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid. It is the crosslinks within the fluid that give a gel its structure (hardness) and contribute to stickiness (tack). In this way gels are a dispersion of molecules of a liquid within a solid in which the solid is the continuous phase and the liquid is the discontinuous phase.7.2 Composition: Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects. This internal network structure may result from physical bonds (physical gels) or chemical bonds (chemical gels), as well as crystallites or other junctions that remainintactwithin the extending fluid. Virtually any fluid can be used as an extender including water (hydrogels), oil, and air (aerogel). Both by weight and volume, gels are mostly fluid in composition and thus exhibit densities similar to those of their constituent liquids. Edible jelly is a common example of a hydrogel and has approximately the density of water.

7.3 Types: HydrogelsHydrogel(also called aquagel) is a network of polymer chains that are hydrophilic, sometimes found as acolloidalgel in whichwateris the dispersion medium. Hydrogels are highlyabsorbent(they can contain over 99.9%water) natural or syntheticpolymers. Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content. Common uses for hydrogels include currently used as scaffolds intissue engineering. When used as scaffolds, hydrogels may contain human cells to repair tissue. hydrogel-coated wells have been used for cell culture[2] environmentally sensitive hydrogels which are also known as 'Smart Gels' or 'Intelligent Gels'. These hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change. as sustained-release drug delivery systems. provide absorption, desloughing and debriding of necrotic and fibrotic tissue. hydrogels that are responsive to specific molecules, such as glucose or antigens, can be used asbiosensors, as well as in DDS. used in disposablenappieswhere they absorburine, or insanitary napkins contact lenses(siliconehydrogels,polyacrylamides) EEGandECGmedical electrodes using hydrogels composed ofcross-linkedpolymers (polyethylene oxide,polyAMPSandpolyvinylpyrrolidone) water gel explosives rectal drug delivery and diagnosisOther, less common uses include breast implants now used in glue. granules for holdingsoilmoisture in arid areas dressings for healing ofburnor other hard-to-healwounds. Wound gels are excellent for helping to create or maintain a moist environment. reservoirs intopical drug delivery; particularly ionic drugs, delivered byiontophoresis(seeion exchange resin)Common ingredients are e.g.polyvinyl alcohol,sodium polyacrylate,acrylatepolymers andcopolymerswith an abundance ofhydrophilicgroups.Natural hydrogel materials are being investigated for tissue engineering; these materials include agarose, methylcellulose,hyaluronan, and other naturally derived polymers. OrganogelsAnorganogelis anon-crystalline,non-glassythermoreversible (thermoplastic) solidmaterialcomposed of aliquidorganicphase entrapped in a three-dimensionally cross-linked network. The liquid can be, for example, anorganic solvent,mineral oil, orvegetable oil. Thesolubilityandparticledimensions of the structurant are important characteristics for theelasticproperties and firmness of the organogel. Often, these systems are based onself-assemblyof the structurant molecules.[3][4]Organogels have potential for use in a number of applications, such as inpharmaceuticals,[5]cosmetics, art conservation,[6]and food.[7]An example of formation of an undesired thermoreversible network is the occurrence of wax crystallization inpetroleum.[8]XerogelsAxerogelis a solid formed from a gel by drying with unhindered shrinkage. Xerogels usually retain high porosity (15-50%) and enormous surface area (150900 m2/g), along with very smallporesize (1-10nm). Whensolventremoval occurs under hypercritical (supercritical) conditions, the network does not shrink and a highly porous, low-density material known as anaerogelis produced. Heat treatment of a xerogel at elevated temperature produces viscoussintering(shrinkage of the xerogel due to a small amount of viscous flow) and effectively transforms the porous gel into a denseglass. 7.4 Application: Many substances can form gels when a suitablethickener or gelling agentis added to their formula. This approach is common in manufacture of wide range of products, from foods to paints and adhesives.In fiber optics communications, a soft gel resembling "hair gel" in viscosity is used to fill the plastic tubes containing the fibers. The main purpose of the gel is to prevent water intrusion if the buffer tube is breached, but the gel also buffers the fibers against mechanical damage when the tube is bent around corners during installation, or flexed. Additionally, the gel acts as a processing aid when the cable is being constructed, keeping the fibers central whilst the tube material is extruded around it.Hydrogels existing naturally in the body include mucus, the vitreous humor of the eye, cartilage, tendons and blood clots. Their viscoelastic nature results in the soft tissue component of the body, disparate from the mineral-based hard tissue of the skeletal system. Researchers are actively developing synthetically derived tissue replacement technologies derived from hydrogels, for both temporary implants (degradable) and permanent implants (non-degradable). A review article on the subject discusses the use of hydrogels for nucleus pulposus replacement, cartilage replacement, and synthetic tissue models.8. INERT PROPELLANT:8.1 Introduction: Some rocket designs have their propellants obtain their energy from non chemical or even external sources. For examplewater rocketsuse the compressed gas, typically air, to force the water out of the rocket.Solar thermal rocketsandNuclear thermal rocketstypically propose to use liquid hydrogen for anIsp(Specific Impulse)of around 600900 seconds, or in some cases water that is exhausted as steam for anIspof about 190 seconds.Additionally for low performance requirements such as attitude jets, inert gases such as nitrogen have been employed.

8.2 Ion Thrusters: Gridded electrostatic ion thrusters A diagram of how a gridded electrostatic ion engine (Kaufman type) works Gridded electrostatic ion thrusterscommonly utilizexenongas. This gas has no charge and isionizedby bombarding it with energetic electrons. These electrons can be provided from a hotcathodefilamentand when accelerated in the electrical field of the cathode, fall to the anode (Kaufman type ion thruster). Alternatively, the electrons can be accelerated by the oscillating electric field induced by an alternating magnetic field of a coil, which results in a self-sustaining discharge and omits any cathode (radiofrequency ion thruster).The positively charged ions are extracted by an extraction system consisting of 2 or 3 multi-aperture grids. After entering the grid system via the plasma sheath the ions are accelerated due to the potential difference between the first and second grid (named screen and accelerator grid) to the final ion energy of typically 1-2 keV, thereby generating the thrust.Ion thrusters emit a beam of positive charged xenon ions only. To avoid charging-up the spacecraft, anothercathodeis placed near the engine, which emits electrons (basically the electron current is the same as the ion current) into the ion beam. This also prevents the beam of ions from returning to the spacecraft and thereby cancelling the thrust.

9. RECENT WORKS:9.1 Introduction: Researchers are developing a new type of rocket propellant made of a frozen mixture of water and "nanoscale aluminum" powder that is more environmentally friendly than conventional propellants and could be manufactured on the moon, Mars and other water-bearing bodies. The aluminum-ice, or ALICE, propellant might be used to launch rockets into orbit and for long-distance space missions and also to generate hydrogen for fuel cells, said Steven Son, an associate professor of mechanical engineering at Purdue University.Purdue is working with NASA, the Air Force Office of Scientific Research and Pennsylvania State University to develop ALICE, which was used earlier this year to launch a 9-foot-tall rocket. The vehicle reached an altitude of 1,300 feet over Purdue's Scholer farms, about 10 miles from campus."It's a proof of concept," Son said. "It could be improved and turned into a practical propellant. Theoretically, it also could be manufactured in distant places like the moon or Mars instead of being transported at high cost."Findings from spacecraft indicate the presence of water on Mars and the moon, and water also may exist on asteroids, other moons and bodies in space, said Son, who also has a courtesy appointment as an associate professor of aeronautics and astronautics.The tiny size of the aluminum particles, which have a diameter of about 80 nanometers, or billionths of a meter, is key to the propellant's performance. The nanoparticles combust more rapidly than larger particles and enable better control over the reaction and the rocket's thrust, said Timothe Pourpoint, a research assistant professor in the School of Aeronautics and Astronautics."It is considered a green propellant, producing essentially hydrogen gas and aluminum oxide," Pourpoint said. "In contrast, each space shuttle flight consumes about 773 tons of the oxidizer ammonium perchlorate in the solid booster rockets. About 230 tons of hydrochloric acid immediately appears in the exhaust from such flights."ALICE provides thrust through a chemical reaction between water and aluminum. As the aluminum ignites, water molecules provide oxygen and hydrogen to fuel the combustion until all of the powder is burned."ALICE might one day replace some liquid or solid propellants, and, when perfected, might have a higher performance than conventional propellants," Pourpoint said. "It's also extremely safe while frozen because it is difficult to accidentally ignite."The research is helping to train a new generation of engineers to work in academia, industry, for NASA and the military, Son said. More than a dozen undergraduate and graduate students have worked on the project."It's unusual for students to get this kind of advanced and thorough training - to go from a basic-science concept all the way to a flying vehicle that is ground tested and launched," he said. "This is the whole spectrum."Research findings were detailed in technical papers presented this summer during a conference of the American Institute of Aeronautics and Astronautics. The papers will be published next year in the conference proceedings.Leading work at Penn State are mechanical engineering professor Richard Yetter and assistant professor Grant Risha.The Purdue portion of the research is based at the university's Maurice J. Zucrow Laboratories, where researchers created a special test cell and control room to test the rocket. The rocket's launching site was located on a facility maintained by Purdue's School of Veterinary Medicine."Having a launching site near campus greatly facilitated this project," Pourpoint said.Other researchers previously have used aluminum particles in propellants, but those propellants usually also contained larger, micron-size particles, whereas the new fuel contained pure nanoparticles.Manufacturers over the past decade have learned how to make higher-quality nano-aluminum particles than was possible in the past. The fuel needs to be frozen for two reasons: It must be solid to remain intact while subjected to the forces of the launch and also to ensure that it does not slowly react before it is used.Initially a paste, the fuel is packed into a cylindrical mold with a metal rod running through the center. After it's frozen, the rod is removed, leaving a cavity running the length of the solid fuel cylinder. A small rocket engine above the fuel is ignited, sending hot gasses into the center hole, causing the ALICE fuel to ignite uniformly."This is essentially the same basic procedure used in the space shuttle's two solid-fuel rocket boosters," Son said. "An electric match ignites a small motor, which then ignites a bigger motor."Future work will focus on perfecting the fuel and also may explore the possibility of creating a gelled fuel using the nanoparticles. Such a gel would behave like a liquid fuel, making it possible to vary the rate at which the fuel is pumped into the combustion chamber to throttle the motor up and down and increase the vehicle's distance.A gelled fuel also could be mixed with materials containing larger amounts of hydrogen and then used to run hydrogen fuel cells in addition to rocket motors.

10. REFERENCE:http://en.wikipedia.org/wiki/Rocket_propellanthttp://en.wikipedia.org/wiki/Hybrid_rockethttp://en.wikipedia.org/wiki/Ion_drivehttp://en.wikipedia.org/wiki/Propellanthttp://www.spg-corp.com/solid-fuel-ramjets.htmlhttp://www.spg-corp.com/advanced-hybrid-rocket-fuels.htm http://www.spg-corp.com/nytrox-propellants.htmlhttp://www.nasa.gov/topics/earth/features/tsunami20111205.htmlhttp://rocketfuel.com/http://en.wikipedia.org/wiki/Heat_of_combustionhttp://en.wikipedia.org/wiki/Gel http://www.nasa.gov/mission_pages/LADEE/mainhttp://www.nakka-rocketry.net/th_grain.htmlhttp://en.wikipedia.org/wiki/Solid-fuel_rocket#Grain_geometryhttp://www.science.uva.nl/onderwijs/thesis/centraal/files/f523116749.pdfhttp://www.diversifiedcpc.com/PDF/intro.pdf

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