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1.5 THE BASIC ELEMENTS OF A LIQUID PROPELLANT ROCKET ENGINE SYSTEM

A vehicle system has occasionally been defined as a purposeful conglomeration of subsystems. One of these is the engine system. The definition of the scope of the various vehicle subsystems has not always been uniform and probably, by necessity, never will be. For instance, for vehicle systems in which the propellant tanks simultaneously serve as the vehicle airframe, it may be a matter of opinion whether they are part of the structure or of the engine system. The decision to which subsystem they belong may well depend on the fact whether the tanks will be supplied by the engine manufacturer, or by a separate contractor. Similarly, some, notably the engine system supplier, may consider the guidance system a part of the payload, while the vehicle user will hold that anything without which the vehicle cannot fly reliably and accurately to its destination is not payload. Whatever the definitions may be, it is important that they are used uniformly and consistently in a given project.

For the purpose of this book, we will define a vehicle as being composed of the following major subsystems: (1) Engine system (2) Vehicle structure (3) Guidance system (4) Payload (5) Accessories

In the following, we will concern ourselves with the engine system only, except for brief references to the other systems, as required. We

Table 1-4.-General Data of Some Storable Liquid Rocket Propellants

PropellantFormulaUseMol. wt.Freezing point ∘F{ }^{\circ} \mathrm{F}Boiling point ∘F{ }^{\circ} \mathrm{F}Vapor press., psiaDensity gm/ccStabilityHandling hazardStorabilityMaterials compatibilityCost $/lb
AnilineC6H5NH2\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}Fuel. coolant93.2213640.25 at 160∘F160^{\circ} \mathrm{F}1.022 at 68∘F68^{\circ} \mathrm{F}GoodGoodGoodAl., steel, Teflon, Kel-F........
Bromine pentafluorideBrFs\mathrm{Br} \mathrm{F}_{\mathrm{s}}Oxid., coolant174.9-80.5104.541 at 160∘F160^{\circ} \mathrm{F}2.48 at 68∘F68^{\circ} \mathrm{F}Up to 800∘F800^{\circ} \mathrm{F}Reacts with fuelGoodAl. alloy. 18-8 stainless steel, nickel alloy. copper, Teflon4.75
Chlorine trifluorideClF3\mathrm{Cl} \mathrm{F}_{3}Oxid.92.5-105.453.1580 at 140∘F140^{\circ} \mathrm{F}1.825 at 68∘F68^{\circ} \mathrm{F}Up to 600∘F600^{\circ} \mathrm{F}ToxicGood below 140∘F140^{\circ} \mathrm{F}Al. alloy. 18-8 stainless steel. nickel alloy. copper, Teflon0.50-2.50
92.5% E.A. (ethyl alcohol)C2H5OH\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}Fuel, coolant41.25-18917213 at 160∘F160^{\circ} \mathrm{F}0.81 at 60∘F60^{\circ} \mathrm{F}GoodFlammableGood below 130∘F130^{\circ} \mathrm{F}Al., steel, nickel alloy, Teflon. Kel-F, polyethylene0.15
HydrazineN2H4\mathrm{N}_{2} \mathrm{H}_{4}Fuel. oxid., coolant32.0534.5235.42.8 at 160∘F160^{\circ} \mathrm{F}1.01 at 68∘F68^{\circ} \mathrm{F}Up to 300∘F300^{\circ} \mathrm{F}Toxic, flammableGoodAl., 304.307 stainless steel, Teflon, Kel-F, polyethylene0.50-3.00
95% hydrogen peroxideH2O2\mathrm{H}_{2} \mathrm{O}_{2}Monoprop., oxid.. coolant32.5721.9294.80.05 at 77∘F77^{\circ} \mathrm{F}1.414 at 77∘F77^{\circ} \mathrm{F}Unstable decomp. at 285∘F285^{\circ} \mathrm{F}Hazardous skin contact. flammableDeteriorates at 1%/yr1 \% / \mathrm{yr}.Al., stainless steel. Teflon, Kel-F0.50
98% hydrogen peroxideH2O2\mathrm{H}_{2} \mathrm{O}_{2}Same as above33.4227.5299.20.043 at 77∘F77^{\circ} \mathrm{F}1.432 at 77∘F77^{\circ} \mathrm{F}Same as aboveSame as aboveSame as aboveSame as above1.00
Hydyne (40% "Deta" 60% "UDMH")NH(C2H4NH2)2\mathrm{NH}\left(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{NH}_{2}\right)_{2}, (CH3)2NNH2\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NNH}_{2}Fuel, coolant72.1565140 to 40016.5 at 160∘F160^{\circ} \mathrm{F}0.855 at 60∘F60^{\circ} \mathrm{F}GoodToxicGoodAl., stainless steel, Teflon, Kel-F0.50-2.00
IRFNA (inhibited red fuming nitric acid)82% HNO3\mathrm{HNO}_{3}. 15%NO215 \% \mathrm{NO}_{2}. 2% H2O\mathrm{H}_{2} \mathrm{O}, 1% HFOxid.. coolant55.9-5715017.3 at 160∘F160^{\circ} \mathrm{F}1.57 at 68∘F68^{\circ} \mathrm{F}GoodToxic, hazardous skin contactGoodAl., stainless steel. Teflon, Kel-F, polyethylene0.08-0.10
JP-4 (jet propulsion fuel)C960H10\mathrm{C}_{960} \mathrm{H}_{10}Fuel, coolant128-76270 to 4707.2 at 160∘F160^{\circ} \mathrm{F}0.747 to 0.825 60∘F60^{\circ} \mathrm{F}GoodVapor explosiveGoodAl.. steel, nickel alloy, neoprene, Teflon, Kel-F0.015
MMH (monomethylhydrazine)CH3NH−NH2\mathrm{CH}_{3} \mathrm{NH}-\mathrm{NH}_{2}Fuel, coolant46.08-631878.8 at 160∘F160^{\circ} \mathrm{F}0.878 at 68∘F68^{\circ} \mathrm{F}GoodToxicGoodAl., 304.307 stainless steel, Teflon. Kel-F, polyethylene0.62-6.25

Table 1-4.-General Data of Some Storable Liquid Rocket Propellants (Continued)

PropellantFormulaUseMol. wt.Freezing point ∘F{ }^{\circ} \mathrm{F}Boiling point ∘F{ }^{\circ} \mathrm{F}Vapor press.. psiaDensity gm/cc\mathrm{gm} / \mathrm{cc}StabilityHandling hazardStorabilityMaterials compatibilityCost $/lb
Nitrogen tetroxideN2O4\mathrm{N}_{2} \mathrm{O}_{4}Oxid.92.021170111 at 160∘F160^{\circ} \mathrm{F}1.44 at 68∘F68^{\circ} \mathrm{F}Function of temp.Very toxic, hazardous skin contactGood when dryAl., stainless steel, nickel alloy. Teflon0.075
PentaboraneB5H9\mathrm{B}_{5} \mathrm{H}_{9}Fuel63.17-52.28140.1119 at 160∘F160^{\circ} \mathrm{F}0.61 at 68∘F68^{\circ} \mathrm{F}GoodExplosive on exposure to air, very toxicGoodAl., steel, copper, Teflon, Kel-F. Viton A2.50-5.00
Propyl nitrateC3H7NO3\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{NO}_{3}Fuel, coolant105.09-130.92313.7 at 160∘F160^{\circ} \mathrm{F}1.06 at 68∘F68^{\circ} \mathrm{F}FairSensitive to shockGoodAl., stainless steel, Teflon, Kel-F.......
RP-1 (rocket propellant)Mil-Spec.F25576BFuel, coolant165 to 195-47 to -64342 to 5070.33 at 160∘F160^{\circ} \mathrm{F}0.8 to 0.82 at 68∘F68^{\circ} \mathrm{F}Auto. ignition at 470∘F470^{\circ} \mathrm{F}FlammableGoodAl., steel, nickel alloy, copper. Teflon, Kel-F. Neoprene0.015
TEA (triethylaluminum(C2H5)3Al\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{3} \mathrm{Al}Fuel, start compound114.15-49.93810,40 at 160∘F160^{\circ} \mathrm{F}0.836 at 68∘F68^{\circ} \mathrm{F}Decomp. over 400∘F400^{\circ} \mathrm{F}Ignites on contact with airGoodAl., steel, copper, Teflon.......
TMA (trimethylamine)(CH3)3 N\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}Fuel59.11-17937108 at 160∘F160^{\circ} \mathrm{F}0.603 at 68∘F68^{\circ} \mathrm{F}GoodGoodGoodAl., steel, copper, Teflon........
TMB-1, 3-D ( NNN′\mathrm{NNN}^{\prime} 'N'-tetra-methylbutane-1. 3-diamine)(CH3)2 N−CH2CH2−CH−N(CH3)2C′H3\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~N}- \mathrm{CH}_{2} \mathrm{CH}_{2}- \mathrm{CH}-\mathrm{N}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}^{\prime} \mathrm{H}_{3}Fuel. coolant144.2-1313201.32 at 160∘F160^{\circ} \mathrm{F}0.795 at 68∘F68^{\circ} \mathrm{F}Stable 1 hr. at 500∘F500^{\circ} \mathrm{F}GoodAl., 347 stainless steel, polyethylene.......
TNM (tetranitromethane)C(NO2)4\mathrm{C}\left(\mathrm{NO}_{2}\right)_{4}Oxid.196.0457.32592.38 at 165∘F165^{\circ} \mathrm{F}1.64 at 68∘F68^{\circ} \mathrm{F}Thermal. unstableShock sensitiveGood below 100∘F100^{\circ} \mathrm{F}Al., mild steel, Teflon, Kel-F0.30
UDMH (unsymmetrical dimethylhydrazine)(CH3)2NNH2\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NNH}_{2}Fuel. coolant60.08-7214617.6 at 160∘F160^{\circ} \mathrm{F}0.789 at 68∘F68^{\circ} \mathrm{F}GoodToxicGoodAl., stainless steel, Tefion, Kel-F0.50-2.00
WFNA (white fuming nitric acid)97.5% HNO. 2%H2O2 \% \mathrm{H}_{2} \mathrm{O}, 0.5%NO20.5 \% \mathrm{NO}_{2}Oxid., coolant59.9-451869.09 at 160∘F160^{\circ} \mathrm{F}1.46 to 1.52 at 68∘F68^{\circ} \mathrm{F}Decomp. above 100∘F100^{\circ} \mathrm{F}Toxic, hazardous skin contactFairAl., stainless steel, Teflon, Kel-F, polyethylene0.15

Table 1-5.-General Data of Some Cryogenic Liquid Rocket Propellants

PropellantsFormulaUseMol. wt.Freezing point. ∘F{ }^{\circ} \mathrm{F}Boiling point. ∘F{ }^{\circ} \mathrm{F}Critical press., psiaCritical temp., ∘F{ }^{\circ} \mathrm{F}Density at boiling point gm/cc\mathrm{gm} / \mathrm{cc}StabilityHandle hazardMaterials compatibilityCost $/lb
- A B BietensencisAnmmonia .........NH3\mathrm{NH}_{3}Fuel, coolant17.03108-28Vapor pressure = 500 psia at 160∘F160^{\circ} \mathrm{F}0.683GoodToxic, flammableAl., steel, lead, Tetlon, Kel-F. Vitron A0.04
Liquid fluorineF2\mathrm{F}_{2}Oxid.38.00-364-307808-200.51.509GoodVery toxic. flammableAl., 300 series stainless steel, nickel alloy, brass6.00
Liquid hydrogenH2\mathrm{H}_{2}Fuel, coolant2.016-434.6-422.9187.8-400.30.071GoodFlammableStainless steel, nickel alloy. Al alloy, Kel-F7.00
Liquid oxygen.O2\mathrm{O}_{2}Oxid.32.00-362-297.4735-1821.142GoodGoodAl. . stainless steel. nickel alloy, copper. Teflon, Kel-F0.05
Oxygen difluoride. .OF2\mathrm{OF}_{2}Oxid.54.00.......-299719-72.31.521GoodVery toxic, flammableAl., 300 series stainless steel. nickel alloy, brass....
OzoneO3\mathrm{O}_{3}Oxid.48.00-42016880410.21.46Above 20% explosiveVery toxic, flammableAl. 300 series stainless steel, Teflon, Kel-F⋯\cdots

SENIONG 1ヨYSOd INV77ヨdOdd AINOII ±0\pm 0 NOISEQ

Table 1-6.-Performance of Some Liquid Rocket Monopropellants

PropellantSpecific impulse ISI_{S}, lb−sec/lb2\mathrm{lb}-\mathrm{sec} / \mathrm{lb}^{2}Density impulse ldl_{d}, sec gm/ccApplicationsRemarks
Hydrogen peroxide ( H2O2\mathrm{H}_{2} \mathrm{O}_{2} ) (95%) .140198Gas generators for turbopump and auxiliary drive; small control rocketsDifficult handling
Hydrazine ( N2H2\mathrm{N}_{2} \mathrm{H}_{2} ).............205207Gas generators: small control rocketsDifficult handling (can decompose at high temperature)
Nitromethane ( CH3NO2\mathrm{CH}_{3} \mathrm{NO}_{2} )180204.8Small ordnance rocketsDangerous handling (can detonate unexpectedly)
Methylacetylene. . . . . . . . . . . . .160108.6Gas generators; small rocketsSafe handling; dangerous and very smoky exhaust fumes

a{ }^{\mathrm{a}} Theoretical value at 300psia(Pc)ns300 \mathrm{psia}\left(P_{c}\right)_{\mathrm{ns}}. sea-level optimum expansion, frozen gas composition or frozen equilibrium.

TABLE 1-7.-Theoretical Performance of Some Medium-Energy Storable Liquid Rocket Bipropellant Combinations

OxidizerFuelrwr_{w}rvr_{v}ddTcT_{c}形c∗c^{*}CIC_{I}IsI_{\mathrm{s}}IsdI_{s} dApplications
IRFNA ( 15%NO215 \% \mathrm{NO}_{2} )UDMH2.991.511.26534023.754901.619276348Small air-to-air,
3.241.631.27531524.254351.630275350arr-to-surface
Hydrazine1.47951.28509020.856901.602283362rockets and
1.54991.29510021.156651.608283365upper stages of space vehicles
50% UDMH-50% hydrazine.2.201.261.27525022.455801.610279354
2.421.391.29522023.055101.618277358
Hydyne3.111.701.31529524.154251.620273358
3.331.821.32527024.553751.630272359
RP-1.4.802.481.35535525.852751.636268362
5.142.651.36533026.252251.646267363
TMB-1, 3-D4.092.081.32532525.153351.632270356
4.372.231.33530025.552801.640269358
JP-X (60% JP-4, 40% UDMH)4.132.161.33531024.653201.628269358
92.5% E.A.2.891.471.26493551301.626259326
MMH2.471.381.28529055501.618279357
TMA4.011.611.21528553751.625271328
95% hydrogenUDMH4.542.531.24480021.755301.620278345Manned aircraft,
peroxide4.742.641.25478021.355051.620277346small air-to-air.
Hydrazine2.171.541.26467519.556551.604282355air-to-surface
2.201.571.26467519.556551.604282355rockets, and
50% UDMH-50% Hydrazine3.352.121.25476020.555801.610279349upper stages of
3.472.201.26474020.655601.615279351space vehicles
Hydyne4.682.831.27476521.354851.622276350
4.872.951.28474521.454651.619275352
RP-17.354.181.30478522.154051.627273355
7.584.321.31476522.253901.620271355
TMB-1, 3-D6.203.491.28477021854401622274351
6.453.631.29474521.954151.618272351

Table 1-7.-Theoretical Performance of Some Medium-Energy Storable Liquid Rocket Bipropellant Combinations (Continued)

OxidizerFueltwt_{w}IvI_{v}dTcT_{c}刃c*CfC_{f}IsI_{s}IsdI_{s} dApplications
Nitrogen tetroxideUDMH2.951.611.20568524.555551.632282339Manned aircraft,
Hydyne2.711.611.22565024.155801626282344ICBM, IRBM,
2.951.751.24565524.755251.631280347ALBM, small air-
RP-14.042.261.25574525.754401.636276345to-air rockets.
upper stages of space vehicles
4.502.511.27575526.553851.639274348
TMB-1, 3-D3.551.961.23571525.254951631278342
3.902.151.24571025.954251.645277344
925%E.A.2.591.451.19529052601.635267318
Chlorine trifluorideUDMH3.031.311.38630525.856301.602280386ICBM, IRBM.
3.281.421.40633026.256051.589277388ALBM, and small air-launched rockets, upper stages of space vehicles
Hydvne
RP-1		2981401.43622026.155551.599276395
3201.501.44625026.555351.595274395
3.20142141589029.151401.618258364
12.805.661.68573537045351.636230386
TMB-1, 3-D3.171.391.40603527.653301.608266373
3.601.57143604028.152801.592261374
Bromine pentafluorideHydrazine3.351.371.86557050001.565243453Small air-launched rockets

Table 1-8.-Theoretical Performance of Some High-Energy Storable Liquid Rocket Bipropellant Combinations

OxidizerFuelrwr_{w}rv\mathrm{r}_{\mathrm{v}}dTcT_{\mathrm{c}}π\pic*C1C_{1}lsl_{\mathrm{s}}Is dI_{s} \mathrm{~d}Applications
95%95 \% Hydrogen peroxideHydrazine2.011.411.26477519.557351.601285359ICBM, IRBM,
Pentaborane2.701.1881.037539019.0160671.600302313ALBM
Nitrogen tetroxideUDMH2.611.421.18568523.656501.624285336FBM, ICBM.
Hydrazine1.34931.22539020.958451.610292357IRBM. ALBM.
1.42991.23541521.358151.605290357upper stages
50% UDMH-50% Hydrazine2.001.241.21559022.657251.620288348of space
2.151.331.21557023.056651.636288348vehicles
MMH. .2.161311.20563557201.621288346
Chlorine trifluorideHydrazine2.771.531.51655023259951582294444FBM, ICBM,
2.941.621.52660023.659801.572292444IRBM, ALBM.
50% UDMH-50% Hydrazine2.891.421.45638524.557951596287416upper stages
3.111.531.46642024.957701.598286417of space
MMH3.001.441.44640057631.591285410vehicles
HydrazinePentaborane1.485796443014.764021.644327261ICBM. IRBM

TABLE 1-9.-Theoretical Performance of Some High-Energy Cryogenic Liquid Rocket Bipropellant Combinations

OxidizerFuelrwr_{w}IvdTcT_{c}π\pic*CtC_{t}IsI_{s}I5dI_{5} dApplications
Liquid oxygenRP-1...................2.001.4210.998576021158981.605294293ICBM, IRBM, large space-probe and space craft boosters
2.401.7081.012610022.859531.620300303
2.561.821.02615023.359201.632300306
2.731.941.03620023958651.642299308
Ammonia1.30. 7888505519.359201.608296260
1.408489510019858651.612294261
95% E.A.1.731.2399564024.156051.648287284
1.801.281.00567524.455851.644285285
Hydrazine. 90801.07566019.362351.618313335
50% UDMH-50% Hydrazine1.301.031.02598020.661601.628312318
1.371.081.03590520.961551.629310319
Hydyne1.731.311.02599021.860351.632306312
1.801.361.02603022.260101.639306312
UDMH1.651.1498601021.361151.63131030.4
1.831.2799606522.160401.638307304
TMB-1.3-D2.281.601.01610022.959451.642303306
2.371.661.01612023.259151.650303306

Table 1-10.-Theoretical Performance of Some Very-High-Energy Cryogenic Liquid Rocket Bipropellant Combinations

OxidizerFuelrwr_{w}tvt_{v}dTcT_{c}mc*CIC_{I}IsI_{s}IsdI_{s} dApplications
Liquid oxygenLiquid hydrogen4.020.250.28493510.079801.578391109Space probe and space craft upper stage and booster
19.501.2065496023.453001.610265172
Liquid fluorineHydrazine2.301.541.31795519.472451.615363476Space probe upper stage
2.401.611.32798019.672251.614362478
Liquid hydrogen. .
7.60		3545650511.883651.578410185
Ammonia23.701.1082823018.575151.592372305
3.291.481.18771519.371551.605357421
3.401.531.18774519.571401.612357422

NOTES FOR TABLES 1-7 THROUGH 1-10​

(1) Conditions upon which the performance calculations are based = (a) Combustion chamber pressure =1000psia=1000 \mathrm{psia} (b) Nozzle exit pressure = ambient pressure = 14.7 psia (optimum nozzle expansion ratio at sea-level operation) (c) Chamber contraction ratio (chamber area/nozzle throat area) = infinity (d) Adiabatic combustion (e) Isentropic expansion of ideal gas with shifting composition or shifting equilibrium in the nozzle (2) Symbols: tw=t_{w}= Propellant weight mixture ratio (wt. oxidizer/wt. fuel) Iv=I_{v}= Propellant volume mixture ratio (vol. oxidizer/vol. fuel) d = Bulk density of propellant combination (gm/cc). (The density at boiling point was used for those oxidizers or fuels which boil below 68∘F68^{\circ} \mathrm{F} at one atmosphere pressure) Tc=T_{c}= Theoretical chamber temperature, ∘F{ }^{\circ} \mathrm{F} π=\pi= Average molecular weight of combustion products at TcT_{c} c∗=c^{*}= Theoretical characteristic velocity (ft/sec)

NOTES FOR TABLES 1-7 THROUGH 1-10 (Continued)​

CI=C_{I}= Theoretical thrust coefficient ls=l_{s}= Theoretical maximum specific impulse, lb-sec/lb Isd=I_{\mathrm{s}} d= Theoretical maximum density impulse. sec-gm cc (3) To approximate lsl_{s} and lsdl_{s} d at other chamber pressures.

Pressure (psia): | Multiply by- |

| ---: | | 1000…….1.001000 \ldots \ldots .1 .00 |

further define that the engine system shall comprise all parts without which the propulsive force cannot be generated. Thus, we will include the propellant tanks and their accessories. A system thus defined frequently is called a propulsion system. We know, from the above, that by including the tanks, we may be "infringing" on the vehicle structure by other definitions.

Thus prepared, we may now proceed to subdivide the engine system further into major components or subassemblies as follows: (1) Thrust chamber assembly (2) Propellant feed system: One of the following two is generally used: Pressurized gas propellant feed system and turbopump propellant feed system. The latter includes some type of tank pressurization system (3) Valves and control systems (4) Propellant tankage (5) Interconnect components and mounts

Depending on the engine system selected, one or another subsystem may not be required or may be integrated with another one. Typical liquid propellant rocket engine systems are shown in figures 1-12 and 1-13.

The rocket has occasionally been called the simplest propulsion system known. The simplest form of a solid propellant rocket or of a pressurized gas-fed storable liquid propellant rocket appears to come close to this ideal. Unfortunately, simplicity frequently is synonymous with inflexibility. Due to vehicle requirements, substantial departures from the basic simplicity may become necessary to meet requirements such as: light weight, high performance, thrust control, thrust vector control, restartability, cutoff im-

90099
80098
70097
600. 95
50093
40091
30088

pulse control, propellant utilization control (sometimes called propellant management), storability, ease of handling, etc. Thus, modern rocket engines contain more subsystems than their basic principle of operation may suggest, to meet the often stringent vehicle requirements. This is true for both liquid as well as solid propellant systems. In general however, the liquid propellant engine is the more flexible one, particularly where large systems are considered.

Figure 1-12.-Typical pressurized gas feed liquid propellant rocket engine system.

Figure 1-13. - Typical turbopump feed liquid propellant rocket engine system.