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Jet Propulsion

Lecture - 22

Ujjwal K Saha, Ph. D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Ducted Rocket/Air augmented Rocket

Combine the principles of rocket & ramjet engines.

Gives high performance (Isp) than a chemical rocket within earth’s atmosphere.

Air augmented rockets denote the mixing of air with rocket exhaust.

Two propulsion system with a common combustion chamber operate in sequence.

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Rocket + Ramjet

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Ramrockets for GW• Also known as the ducted rocket or air-augmented rocket or air turbo-rocket.

• Hybrid unit employing both rocket and air-breather features.

• Has virtues of a dense propellant and ability to avoid flame-out.

• Disadvantages include inherent difficulty in varying thrust level.

• Used on USSR SA-6 and is subject of considerable renewed interest.

SA-6 Gainful

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Air Turbo Rocket

An air-breathing propulsion system, combining advantages from both rocket and turbojet technologies.

Rocket + Turbojet

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Air Turbo Rocket

A gas generator produces high pressure, fuel-rich effluent which drives a turbine. The turbine drives a compressor which compresses incoming air. The air and fuel-rich effluent mix and burn in the combustion chamber to produce thrust. In essence, the ATR has a turbojet compressor and a rocket gas generator and turbine.

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The hybrid nature of the system gives the ATR performance characteristics between those offered by rocket and turbojet technologies. The thrust-to-weight ratio of the ATR is higher than a turbojet engine while the propellant consumption rate is lower than a rocket. These characteristics make the engine well suited for long-range and high-speed applications. Applications of this type include first-stage air-breathing boosters for space launch applications.

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NuclearEnergySources

for delivering heat to the propellant usually liquid hydrogen, and then expanded in nozzle to produce high velocity jet (6000-10,000 m/s).

Fission ReactorFusion ReactorRadioactive Isotope Decay

All the types are basically extensions of LPRE

Power Source: Separate from the propellant.

Nuclear Rockets:

Gas heating is done by energy derived from the transformations within the nuclei of atom.

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Heat Fission of UraniumGeneration (in solid reactor material)

transferred to the working fluid

High Thrust Engine, F = 40,000 NSpecific Impulse, ISP = 900 secs.

Developed & tested : 1960

Ground test with hydrogen produced 9, 80, 000 N at a graphite core nuclear reactor level of 4100 MW

Fission Reactor Rocket

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Fission Reactor Rocket

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Radioactive isotope decay engine

gives off radiationconverted to heat

Released energy raises the temperature of working fluid (H2)

Low F engineNot yet developed.

Fusion Rockets:Third method ofcreating nuclear energy that can heat

a working fluid.

Radioactive material

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Electrical Rockets:Nuclear

Elec. Power Source Solar radiation receiversBatteries

Separate from the device

Electrical Propulsion Handicapped by heavy & inefficient power source.

Produces low Thrust (F): 0.005 – 1 N

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2 4

4

2

2

N HNHHN

0.01 0.51000 5000 /e

F NV m s= −= −

Electro thermal

Propellantheated electrically by electric arc or resistors

to produce hot gases, and is accelerated through nozzle

14Hydrogen arc-jet Ammonium arc-jet

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Resisto-jet

Thermal limitation of filament limits ISP = 800 secs Hydrazine resisto-jet

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Works only in vacuumIon Rockets US Air force satellite1979

Charged ions accelerated to 2000-60,000 m/sby electrostatic field.

neutralized to prevent buildup of space charge on vehicles.

ionized by stiffing-off electrons.

Commercial satellite 1997

Xenon

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High amount of electricity is required to produce this electrostatic field.

Nuclear Reactor is used to supply power to engine.Or, solar power to generate electricity.

Chemical Rockets: Produces high F for short duration.Ion Rockets: Operate for weeks/months.

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Magneto plasma Rocket:

Electrical plasma energized hot gas

accelerated byinteraction between

containing ions, electrons and neutral particles

Electric currentMagnetic field

ejected at high velocity (1000-50,000 m/s)

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MPD Thruster

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Solar Thermal Rocket

The heated propellant is fed through a conventional rocket nozzle to produce thrust. The engine thrust is directly related to the surface area of the solar collector and to the local intensity of the solar radiation.

A solar thermal rocket only has to carry the means of capturing solar energy, such as concentrators and mirrors.

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Solar Thermal Rocket

Most proposed designs for solar thermal rockets use hydrogen as their propellant due to its low molecular weight which gives excellent specific impulse (900 seconds), but many other substances could also be used.

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Specific Impulse

• Specific Impulse, Isp, is the ‘gas mileage’• Chemical - Solid Isp 200-300 sec

Liquid Isp 250-450 sec• Electric - Isp 600-3000 sec• Nuclear - Fission Isp 900 sec (solid)

Fusion Isp 5000-10000 sec

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Chemical Rockets have relatively low values of specific impulse, relatively light machinery (low weight), a very high thrust capability, and therefore high acceleration and high specific power (Pjet/mo).

Electrical Rockets carry a heavy, relatively inefficient power source; and hence the specific power is much lower than that of chemical rockets.

SUMMARYSUMMARY

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The very low acceleration potential for the electrical rockets and those using solar radiation energy usually requires a long period of accelerating, and hence these systems are best suited for missions where flight time is long.

The low thrust values of electrical systems imply that they are not useful in fields of strong gravitational gradients, but are best suited for space flight missions.

SUMMARY SUMMARY ––Contd.Contd.

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References1. Hill, P.G., and Peterson, C.R., (1992), Mechanics and

Thermodynamics of Propulsion, Addison Wesley.2. Saravanamuttoo, H.I.H, Rogers, G.F.C, and. Cohen, H, (2001), Gas

Turbine Theory, Pearson Education.3. Oates, G.C., (1988), Aerothermodynamics of Gas Turbine and Rocket

Propulsion, AIAA, New York.4. Mattingly, J.D., (1996), Elements of Gas Turbine Propulsion, McGraw

Hill.5. Cumpsty, N.A., (2000), Jet Propulsion, Cambridge University Press.6. Bathie, W.W., (1996), Fundamentals of Gas Turbines, John Wiley.7. Treager, I.E., (1997), Aircraft Gas Turbine Engine Technology, Tata

McGraw Hill. 8. Anderson, J. D. Jr., (2000), Introduction to Flight, 4th Edition, McGraw

Hill. 9. M.J.L.Turner, (2000), Rocket and Spacecraft Propulsion, Springer.10. Sutton, G.P. and Biblarz, O., (2001), Rocket Propulsion Elements,

John Wiley & Sons.11. Zucrow, M.J., (1958), Aircraft and Missile Propulsion, Vol. II, John

Wiley.12. Barrere, M., Jaumotte, A., Veubeke, B., and Vandenkerckhove, J.,

(1960), Rocket Propulsion, Elsevier.

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