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CONTENTS

ROCKET DESIGN & ROCKET PROPELLANT

OPERATION

FORCES ON A ROCKET IN FLIGHT

NET THRUST

IMPULSE AND SPECIFIC IMPULSE ROCKET EQUATION

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ROCKET DESIGN & ROCKET

PROPULSION Rocket consists of a propellant, a place to put propellant

& a nozzle. They may also have one or more rocketengines, directional stabilization such as fins, altitude

jets, and a structure called monococqe to hold all thesecomponents together. They use a nose cone which isused to have aerodynamics.

Rocket engines can use propellants, solid propellants,liquid propellants or a hybrid mixture of propellants

(both liquid & solid). After the reaction of the propellant, the hot gases are

liberated as a result of these gases accelerates outthrough the engines, exerting force (thrust) on the

combustion chamber & nozzle, propelling the vehicle.

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ROCKET PROPELLANT:

It is the mass stored in the propellant tank which isejected out from the rocket engine in the form of a fluidjet to produce thrust. Liquid hydrogen burned with anoxidizer such as liquid oxygen or nitric acid to produce

large volumes of very hot gas.

Monopropellants are also used such as NO,H2O2 &hydrazine which are catalytically decomposed to producehot gas.

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OPERATIONRocket thrust is caused by pressures acting on

the combustion chamber & nozzle.In a closed chamber, the pressure is equal in

each direction and no acceleration occurs. If anopening is provided in the bottom of thechamber then the pressure is no longer acting onthe missing section. The remaining pressure

gives a resultant thrust on the side opposite theopening, as well as permitting exhaust to escape.This pressure acts on the exhaust in theopposite direction or accelerate this to a veryhigh speed (Newtons third law)Due conservation of momentum the speed ofthe exhaust of a rocket determines how muchmomentum increase is created for a givenamount of propellant. This is called the rocketspecific impulse. Here the total momentum isalways constant since no external source is usedto its motion.

http://en.wikipedia.org/wiki/File:Rocket_thrust.svg

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FORCES ON A ROCKET IN FLIGHT

Flying rockets are primarily affected by the following:

Thurst from the engine(s)

Gravity from celestial bodies

Drag, if moving in atmosphere (Drag is a forcewhich acts opposite to the direction of the rocket's

motion. This will cause a decrease in theacceleration of the vehicle whilst also producingstructural loads.

Lift

http://en.wikipedia.org/wiki/File:Rktfor.gif

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Net ThrustDue to the supersonic nature of the exhaust jet the exit

pressure can be different to ambient atmosphericpressure. Nozzles are said to be (top to bottom):

Under expanded (above ambient).

Ambient.

Over expanded (below ambient). Grossly over expanded.

The net thrust equation of a rocket is:

Fn= m(dot) ve

m(dot)= propellant flow

ve= the effective exhaust velocity

http://en.wikipedia.org/wiki/File:Rocket_nozzle_expansion.svg

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IMPULSE AND SPECIFIC IMPULSE

The total impulse of a rocket burning its propellant is simply

I= F dt As can be seen from the thrust equation the effective speed of the exhaust

controls the amount of thrust produced from a particular quantity of fuelburnt per second. An equivalent measure, the net thrust-seconds (impulse) per weight unit of

propellant expelled is called specific Impulse "Isp" and this is one of themost important figures that describes a rocket's performance. It is definedsuch that it is related to the effective exhaust velocity by

ve= Isp. g0

Isphas units of secondsg0 is the acceleration at the surface of the

Earth

http://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Impulsehttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Specific_impulsehttp://en.wikipedia.org/wiki/Impulse

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Rocket equation

Here we do not consider the external forces and frictional forces due to earthatmosphere which are negligibly small.

At t=0 m0=initial mass of the rocket including fuel

v0= initial velocity of the rocket

m & v be the mass and the velocity of the rocket at time t.

According to the principle of the conservation of linear momentum we can write

m v = (m- dm) (v + dv) + dm (-vg)

Therefore m dv= dm (v+ vg)

As the gases are moving in opposite directions therefore

v + vg= -u

m dv= -u dm-----------------------------------(1)

dv =-u dm/mAt (t=0 m=m0 & v= v0 ) to (t=t m=m & v= v) and integrating (1)

We get v= v0 + v ln (m / m0)

This is the rocket equation