Rocket Propulsion.pdf

Propulsion, Types of Rocket Engines, Propellants and their classification, SPRE, LPRE, HPRE, Staging, Space Flights

1. Unit-5: Rocket Propulsion
Prepared by:
Ankur Sachdeva
Assistant Professor, ME

2. Introduction to Propulsion
•Propulsionisamethodbywhichanobjectis
propelledinaparticulardirection.
•Theword“propulsion”stemsfromtheLatinword
propellere,wherepromeansforwardorbackward
andpelleremeansdriveorpush.
•Spacecraftmustproducethrustwhichmustbeequal
tothedragforcecausedduetothefluidmotionover
thebodyofthisspacecraftandthegravitational
force.
•Foracceleratingthespacecraft,oneneedstosupply
higherthrustthanthatofdragforcesand
gravitationalforceactingonit.
Ankur Sachdeva, ME, KIET Group of Institutions

3. Aeropile by Hero
It is really an interesting device for
demonstrating the principle of
reactive thrust, which is the basis of
rocket propulsion.
Ankur Sachdeva, ME, KIET Group of Institutions

4. History of Rocket Engines
•TherealrocketwasinventedbytheChinesearoundthetenthcenturyADwhileexperimenting
withgunpowderandbamboo.
•ThegunpowderwasdiscoveredintheninthcenturyADbyaTaoistalchemist.
•Subsequently,FengJishenmanagedtofirearocketusinggunpowderandbamboo
•AChinesescholar,WanHu,haddevelopedarocketsledthatcomprisedofaseriesofrockets
attachedtotheseat.
Ankur Sachdeva, ME, KIET Group of Institutions

5. Classification of Propulsive Devices
Ankur Sachdeva, ME, KIET Group of Institutions

6. Comparison Between Air-Breathing and
Rocket Engines
Ankur Sachdeva, ME, KIET Group of Institutions

7. Types of Rocket Engines
•On the basis of application:
•Space Rockets
•Military Rockets
•Weather Rockets
•Aircraft propulsion
•On the basis of no. of stages:
•Single stage
•Multi stage
•On the basis of size and range:
•Small-range small rockets
•Large-range large rockets
Ankur Sachdeva, ME, KIET Group of Institutions

8. Chemical Rocket Engines
•Incaseofchemicalrocketengines,chemicalenergyreleasedduringtheburningoffueland
oxidizerisusedtoraisethetemperatureandpressureofthegaswhichisexpandedinaCDnozzle
toproducethrust.
•Generally,thehotgasesathighpressureareacceleratedtohighsupersonicvelocitiesintherange
of1500–4000m/sforproducingthrust.
•bothfuelandoxidizerarebeingcarriedalongwiththeengineunlikeinair-breathingengines.
•Basedonthephysicalstateofthepropellant(fuelandoxidizer),chemicalrocketenginescanbe
broadlydividedintothreecategories:
(1)solidpropellant,
(2)liquidpropellant,
(3)hybridpropellant.
Ankur Sachdeva, ME, KIET Group of Institutions

9. Solid Propellant Rocket Engines
•Solid-propellantrocketengine(SPRE)isoneoftheoldestnon-air-breathing
engines.
•Thesolidpropellantcomposition,whichwasinitiallyblackpowder,underwent
aseriesofchangeswithtime.
•Propellant,whichmainlyconsistsoffuel,oxidizers,andvariousadditives,is
entirelystoredwithinthecombustionchamberintheformofblocksofdefinite
shapecalledgrainandissupportedbythewalls.
•Graincontributestoaround80%–95%ofthetotalmassofanSPRE.
•Theigniterinitiatesthecombustionprocessonthesurfaceofthepropellant
whenactuatedwiththehelpofanelectricalswitch.
•Asaresult,thepropellantgrainswillstartburningandfillingtheempty
combustionchamber,hencebuildingupthechamberpressure.
•Subsequently,thehigh-temperatureandhigh-pressuregasesareexpandedinthe
supersonicnozzletoproducetherequisitethrust.
•Solidrocketengineisconsideredtobeanon-air-breathingvehiclewithoutany
movingparts
Ankur Sachdeva, ME, KIET Group of Institutions

10. Solid Propellant Rocket Engines
Advantages
•Itissimpletodesignanddevelop.
•Itiseasiertohandleandstoreunlikeliquid
propellant.
•DetonationhazardsofmanymodernSPREsare
negligible.
•BetterreliabilitythanLiquidPropellantRocket
Engine(LPRE)(>99%).
•Development and production cost of SPREs is
much smaller than that of LPREs, especially in the
high-thrust bracket
Disadvantages
•It has lower specific impulse compared to
LPREs and hybrid propellant rocket engines
(HPREs).
•It is difficult to turn off its operation unlike in
an LPRE.
•Transport and handling of solid propellants are
quite cumbersome.
•Thecracksonthepropellantcancausean
explosion.
Ankur Sachdeva, ME, KIET Group of Institutions

11. Liquid Propellant Rocket Engines
•Around1927,anAmericanprofessor,RobertGoddard,haddesignedanddevelopedanLPRE.
•Inadditiontohavingaliquidform,thispropellantcanbestoredinaseparatetankandcanbe
controlledeasily,andhencethrustcanbevariedeasilyunlikeinanSPRE.
•AsLPREsarestoredinseparatetanksunlikeSPRE,onecanachieveahigherlevelofthrustandis
thusconsideredtobemorepowerfulthananSPRE.Therefore,itispreferredforlargespacecraft
andballisticmissiles.
•Bothfuelandoxidizerpropellantsarestoredseparatelyinspecialtanksathighpressure.
•Thepressurizedliquidpropellantsareconvertedintosprayconsistingofarraysofdropletswiththe
helpofatomizers.
•Anigniterisusedtoinitiatethecombustionprocessonthesurfaceofthepropellant.
•Asaresult,thepropellantwillstartburningandfilluptheemptythrustchamber,therebybuilding
uppressureinthechamber
•High-temperatureandhigh-pressuregasesareexpandedinaCDnozzletoproducetherequisite
thrust.
Ankur Sachdeva, ME, KIET Group of Institutions

12. Liquid Propellant Rocket Engines
Advantages
•An LPRE can be reused.
•It provides greater control over thrust.
•It can have higher values of specific impulse.
•It can be used for long-duration applications.
•It is easy to control this engine as one can vary the
propellant flow rate easily.
•The heat loss from the combustion gas can be
utilized for heating the incoming propellant.
Disadvantages
•Thisengineisquitecomplexcomparedtothe
SPRE.
•Itislessreliableasthereisapossibilityof
malfunctioningoftheturbopumpinjectorsand
valves.
•Certainliquidpropellantsrequireadditionalsafety
precaution.
•Ittakesmuchlongertodesignanddevelop.
•Itbecomesheavy,particularlyforshort-range
application.
Ankur Sachdeva, ME, KIET Group of Institutions

13. Hybrid Propellant Rocket Engines
•Thisenginecanusebothsolidandliquidtypesofpropellants.
•Mostwidelyusedpropellantcombinationisaliquidoxidizeralongwithasolid
propellant.
•Onlytheoxidizerpropellantinthepresentexampleisstoredinaspecialtankunder
highpressure.
•Thepressurizedpropellantsareconvertedintosprayconsistingofarraysofdroplets
withthehelpofatomizers.
•Itconsistsofmajorcomponents,namely,apropellantfeedsystem,acombustion
chamber,asolidfuelgrain,anignitersystem,andanozzle.
•Someofthepropellantevaporatesduetotherecirculationofhotgasesandcomesinto
contactwiththegaseousfuelthatemanatesfromthesolidfuelgrainsduetopyrolysis
•Thecombustionproductsstartburningandfilltheemptythrustchamber,thereby
buildinguppressureinsidethechamber.
Ankur Sachdeva, ME, KIET Group of Institutions

14. Hybrid Propellant Rocket Engines
Advantages
•An HPRE can be reused.
•It provides greater control over thrust.
•It has relatively lower system cost compared
to the LPRE.
•It can have higher values of average specific
impulse compared to the SPRE.
Disadvantages
•Thisengineisquitecomplexcomparedtothe
LPRE.
•It takes much longer to design and develop.
•It becomes heavy, particularly for short-range
application.
•Certainliquidpropellantsrequireadditional
safetyprecaution
Ankur Sachdeva, ME, KIET Group of Institutions

15. What is a Propellant
•Apropellantconsistsofallthechemicalmaterials,includingfuelandoxidizer,
alongwithcertainadditivesnecessaryforsustainingthecombustionprocessto
producehigh-pressurehotgases,thatwhichareexpandedinanozzletoproduce
thrust.
•Principalingredientsofapropellantarethefuelandtheoxidizer.
•Fuelisachemicalsubstancethatreactswithanoxidizerwhilereleasingthermal
energy
Ankur Sachdeva, ME, KIET Group of Institutions

16. Classification of Propellants
Ankur Sachdeva, ME, KIET Group of Institutions

17. Classification of Propellants
•Homogeneouspropellant:
•fuelandoxidizerarecontainedinthesamemoleculeofthepropellant.
•Heterogenouspropellant:
•solidfuelandoxidizerretaintheirrespectivephysicalidentities.
•Monopropellants:
•A liquid propellant that contains both the fuel and the oxidizer in a single chemical is called a
monopropellant.
•Example:
•HydrogenPeroxide,Hydrazine,Nitroglycerine,andNitromethane
•Bipropellants:
•A liquid propellant in which an oxidizer and a fuel are stored separately in the tanks and mixed in the
combustion chamber.
•Example:
•Liquidoxygenandliquidhydrogen,Liquidoxygenandkerosene.
•Hypergolic propellants:
•Liquid fuel and oxidizer react spontaneously without external ignition energy
•Nonhypergolic propellants:
•Suitableamountofignitionenergyisprovidedtoignitetheliquidfuelandoxidizerforcombustiontotakeplace
Ankur Sachdeva, ME, KIET Group of Institutions

18. GENERAL CHARACTERISTICS OF PROPELLANTS
•Propellantmusthavehighchemicalenergyreleasesothatitcanhavehighercombustiontemperature
leadingtohighcharacteristicvelocityC*.
•ItcanhavelowmolecularweightofcombustionproductleadingtohighexhaustvelocityVeandthuscan
havehighspecificimpulseIsp.
•Itcanhaveahighdensitysuchthatlargeamountofchemicalenergycanbestoredinthesmallestvolume
andthuscanhaveacompactdesign.
•Easytoigniteevenunderlow-pressurecondition.
•Physicallyandchemicallystablewithrespecttotime.
•Smoke-freeandnontoxicinnature.
•Easyandexpensivetomanufactureandhandleduringoperation.
•Easilyavailableandlowprice.
•Lesspronetoexplosionhazard.
•Lowemissionlevel.
Ankur Sachdeva, ME, KIET Group of Institutions

19. Propellant Feed System
•Themainfunctionofthepropellantfeed
systemistosupplytherequisiteamountof
propellantbytransferringitfromthe
propellanttanktothethrustchamberata
higherdesiredpressurebywhichasprayof
liquidpropellantcanbeformed.
•Forthispurpose,thepressureofthe
propellantinthefeedsystemmustberaised,
whichcanbeaccomplishedbysupplying
energy.
Ankur Sachdeva, ME, KIET Group of Institutions

20. Gas Pressure Feed System
•Thisgaspressurefeedsystemisoneofthesimplestmethodsofpressurizingthepropellantinarocketengineinwhich
high-pressuregasisbeingusedtoforcetheliquidpropellantsinaverycontrolledmannerfromtheirrespectivetanks.
•Itconsistsofahigh-pressuregastank,anon-offvalve,apressureregulator,propellanttanks,feedlines
•Propellanttanksarefilledinthebeginningfollowedbyhigh-pressuregastanks.
•Subsequently,ahigh-pressuregasvalveisactuatedtoallowhigh-pressuregastoenterthepropellanttankinaregulated
manneratconstantpressurethroughcheckvalves.
•Oncedesiredpressureisestablishedinthepropellanttanks,thepropellantscanbefedthroughinjectorsintothe
combustionchamberbyactuatingthepropellantvalves.
•Commonly,thepressurizedgasisallowedtopassthrough,evenaftercompleteconsumptionofpropellant,toscavenge
andcleanthefeedlines,particularlyforreusablerocketengines,namely,space-maneuverrockets.
Ankur Sachdeva, ME, KIET Group of Institutions

21. Turbo Feed Pump System
•Turbopumpshelprocketsachieveahighpower-to-weight
ratiobyfeedingpressurizedpropellanttotherocket’s
combustionchamber.
•Thepump-fedsystemusesaturbopumptopressurizeand
feedthepropellantsintothethrustchamberatrelativelyhigh
pressures.
•Theturbopumptypicallyconsistsofoneormorepumping
elementsdrivenbyaturbine.
•Theenergytopowertheturbineitselfisprovidedbythe
expansionofhigh-pressuregases,whichareusually
mixturesofthepropellantsbeingpumped.
Ankur Sachdeva, ME, KIET Group of Institutions

22. Ignition in Solid Rocket Motors
•SolidRocketMotors(SRMs)requireanefficientignition
systemtostartfunctioning.
•Aseparateignitionsystem,calledanigniter,isassembled
intherocketmotortoachievethetask.
•IgnitersforSRMsarebasicallyoftwotypes,viz.,
Pyrogenignitersusedforlargerocketmotorsofballistic
missiles,andPyrotechnicIgnitersusedforsmallrocket
motors.
•Thepropulsiveforceofasolidpropellantmotorisderived
fromthecombustionofsolidpropellantathigh
temperatureandpressure.
•Theigniterinducesthecombustionreactionina
controlledandpredictablemannerbygeneratingheatflux
intheformofhot,densegasesthatrapidlyignitethe
propellantsurface.
•Theigniteralsocontributestowardsthegenerationofa
certainminimumpressureinsidethemotorthatis
adequateforstableandsustainedcombustionofthe
propellant
Ankur Sachdeva, ME, KIET Group of Institutions

23. Staging in Rockets
•Allrocketsusethethrustgeneratedbyapropulsionsystemtoovercome
theweightoftherocket.
•Forfull-scalesatellitelaunchers,theweightofthepayloadisonlyasmall
portionofthelift-offweight.
•Mostoftheweightoftherocketistheweightofthepropellants.
•Asthepropellantsareburnedoffduringpoweredascent,alarger
proportionoftheweightofthevehiclebecomesthenear-emptytankageand
structurethatwasrequiredwhenthevehiclewasfullyloaded.
•Inordertolightentheweightofthevehicletoachieveorbitalvelocity,most
launchersdiscardaportionofthevehicleinaprocesscalledstaging.
Ankur Sachdeva, ME, KIET Group of Institutions

24. Series Staging
•Inserialstaging,thereisasmall,
second-stagerocketthatisplacedon
topofalargerfirst-stagerocket.
•Thefirststageisignitedatlaunchand
burnsthroughthepoweredascentuntil
itspropellantsareexhausted.
•Thefirststageengineisthen
extinguished,thesecondstage
separatesfromthefirststage,andthe
secondstageengineisignited.
•Thepayloadiscarriedatopthesecond
stageintoorbit.
•SerialstagingwasusedontheSaturn
Vmoonrockets.
Ankur Sachdeva, ME, KIET Group of Institutions

25. Parallel Staging
•Inparallelstaging,severalsmallfirststages
arestrappedontotoacentralsustainer
rocket.
•Atlaunch,alloftheenginesareignited.
•Whenthepropellantsinthestrap-onsare
extinguished,thestrap-onrocketsare
discarded.
•Thesustainerenginecontinuesburningand
thepayloadiscarriedatopthesustainer
rocketintoorbit.
•ParallelstagingisusedontheSpaceShuttle.
•Thediscardedsolidrocketboostersare
retrievedfromtheocean,re-filledwith
propellant,andusedagainontheShuttle.
Ankur Sachdeva, ME, KIET Group of Institutions

26. Terminal velocity
•Anobjectwhichisfallingthroughtheatmosphereissubjectedtotwo
externalforces.
•Oneforceisthegravitationalforce,expressedastheweightoftheobject.The
otherforceistheairresistanceordragoftheobject.
•Thenetexternalforce(F)isequaltothedifferencebetweentheweightandthe
dragforces(W-D).
•Whendragisequaltoweight,thereisnonetexternalforceontheobjectandthe
objectwillfallataconstantvelocityasdescribedbyNewton'sfirstlawofmotion.
•Theconstantvelocityiscalledtheterminalvelocity
Ankur Sachdeva, ME, KIET Group of Institutions

27. Terminal velocity
Ankur Sachdeva, ME, KIET Group of Institutions

28. Space Flights
•Rocketenginesareemployedtolaunchaspacecraftfromthesurfaceoftheearth.
•Thespacecraftmovesaroundanorbitoftheearthoranyotherplanetgovernedbythelocal
gravitationalfieldandmomentumofthespacecraft.
•Thisorbitcanbeeithercircularorellipticinshape.
•Forthemotionofthespacecraftinacircularorbit,thegravitationalforceF
gholdingthespacecraft
canbedeterminedbyusingNewton’slawofgravitation:
•Where M is the mass of the planet (earth), m is the mass of the space vehicle
•R is the distance between the two masses, and G is the universal gravity constant (G = 6.67 x 10
−11
m
3
/kg s
2
)
•ω is the angular velocity of the mass m
Ankur Sachdeva, ME, KIET Group of Institutions

29. Space Flights
•The gravitational force F
gis balanced by the pseudo-centrifugal force mω
2
R.
•The angular velocity ω and orbital velocity V
ofrom can be evaluated easily as follows:
•The orbital velocity decreases nonlinearly with the radius of the orbit.
•The time period required to revolvearound this orbit can be determined as follows:
•Thetimeperiodperrevolutionincreaseswiththeradiusoftheorbitatahigherratecomparedto
theorbitalvelocity.
Ankur Sachdeva, ME, KIET Group of Institutions