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PHYSICAL SCIENCE PHYSICAL SCIENCE PHYSICAL SCIENCE PHYSICAL SCIENCE PHYSICAL SCIENCEPHYSICAL SCIENCEPHYSICAL SCIENCEPHYSICAL SCIENCE

THE ADVANTAGES OF DIFFERENT TYPES

OF PROPELLANTS

CONTENTS

1. INTRODUCTION

• ROCKET PROPELLANT

2. TYPES OF PROPELLANTS

• SOLID PROPELLANT

• LIQUID PROPELLANT

• GAS PROPELLANT

• HYBRID PROPELLANT

3. CONCLUSION

4. REFERENCES

INTRODUCTION

Rocket propellant

Rocket propellant is a material used by a rocket as, or to produce in a

chemical reaction, the reaction mass (propulsive mass) that is ejected,

typically with very high speed, from a rocket engine to produce thrust,

and thus provide spacecraft propulsion. In a chemical rocket, propellants

undergo exothermic chemical reactions to produce hot gas. There may

be a single propellant or multiple propellants. In the case of multiple

propellants, one can distinguish fuel and oxidizer. The gases produced

expand and push on a nozzle, which accelerates them until they rush out

of the back of the rocket at extremely high speed. For smaller attitude

control thrusters, a compressed gas escapes the spacecraft through a

propelling nozzle.

Types of propellants

There are four main types of chemical rocket propellants: solid, liquid,

gas and hybrid.

1. Solid propellants

Solid propellants are either "composites" composed mostly of large,

distinct macroscopic particles or single, double, or triple-bases which are

homogeneous mixtures of one or more primary ingredients. Composites

typically consist of a mixture of granules of solid oxidizer

(examples: ammonium nitrate, ammonium per chlorate, potassium

nitrate) in a polymer binder with flakes or powders of: energetic

compounds (examples: RDX, HMX), metallic additives (examples:

Aluminum, Beryllium), plasticizers, stabilizers, and/or burn rate

modifiers (iron oxide, copper oxide).

Advantages of solid propellants

• 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.

• Their simplicity also makes solid rockets a good choice whenever

large amounts of thrust are needed and cost is an issue.

Disadvantages of solid propellants

• Relative to liquid fuel rockets, solid fuel rockets have lower

specific impulse.

• The propellant mass ratios of solid propellant upper stages is

usually in the .91 to .93 range which is as good as 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 are 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.

• 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.

• Solid fuel rockets are intolerant to cracks and voids and often

require post-processing such as x-ray scans to identify faults.

2. Liquid propellants

In a liquid propellant rocket, the fuel and oxidizer are stored in separate

tanks, and are fed through a system of pipes, valves, and turbo pumps to

a combustion chamber where they are combined and burned to produce

thrust. A good liquid propellant is one with a high specific impulse or,

stated another way, one with a high speed of exhaust gas ejection. This

implies a high combustion temperature and exhaust gases with small

molecular weights. However, there is another important factor which

must be taken into consideration: the density of the propellant. Storage

temperature is also important.

Advantages of liquid propellants

• Liquid-fueled rockets have higher specific impulse than solid

rockets.

• They are capable of being throttled, shut down, and restarted.

• On vehicles employing turbo 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, and hydrogen peroxide) are available which

have better specific impulse than the ammonium per chlorate used

in most solid rockets, when paired with comparable fuels.

• While liquid propellants are cheaper than solid propellants. Some

propellants, notably Oxygen and Nitrogen, may be able to

be collected from the upper atmosphere, and transferred up to low-

Earth orbit for use in propellant depots at substantially reduced

cost.

Disadvantages of liquid propellants

• These are generally least moderately difficult to store and handle

due to their low reactivity with common materials.

• Several exotic oxidizers have been proposed 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.

3. Gas propellants

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 for vernier engines,

particularly with inert propellants.

Advantages of gas propellants

• They do not burn (although other liquids in the aerosol

may burn).

• They are readily available and cheap.

• Gaseous fuels lack density.

• Long term storage is possible.

Disadvantage of gas propellants

• The pressure in the can reduces over the lifetime of the

aerosol.

4. Hybrid propellants

A hybrid rocket usually has a solid fuel and a liquid or gas oxidizer. The

fluid oxidizer can make it possible to throttle and restart the motor just

like a liquid-fueled rocket. Hybrid rockets can also be environmentally

safer than solid rockets since some high-performance solid-phase

oxidizers contain chlorine (specifically composites with ammonium per

chlorate), versus the more benign liquid oxygen or nitrous oxide often

used in hybrids. This is only true for specific hybrid systems.

Advantages of hybrid propellants

• These are much cheaper.

• Can be shut down easily.

• Throttle control.

• Much safer to handle.

• Higher theoretical specific impulse.

Disadvantages of hybrid propellants

• Slightly more complex than solids.

• Difficult to make use of hybrid propellants for very large thrusts.

• Less researched.

CONCLUSION

The knowledge that has been obtained through the research of rocket

technology has brought the promise of the eventual commercialization

of space ever closer. If more research and development is invested into

solid-fuel and liquid-fuel technology, the dream of commercializing the

space industry can be can be realized. Perhaps prior to that realization,

whole new technologies for design and construction of spacecraft and

different fuels may be required. However, it is a good bet that further

research and development, cost effectiveness and overall improvement

with the current workhorses of space exploration will be around for

some time.

REFERENCES

• www.wikipedia.com

• www.angelfire.com

• Google images

• www.ph.utexas.edu

• www.braeunig,us

• history.nasa.gov.in

• www.scientificamerican.in