Swapnil Kumar Sharma Model Rocketry

8/2/2019 Swapnil Kumar Sharma Model Rocketry

1/22

MODEL ROCKETRYAn Interesting Educational Tool

-by

Swapnil Kumar Sharma Former Child Scientist

Trained and Developed by:

Voluntary Institute for Community Applied Science VICAS, India

HD-86, ADA Colony, Naini, Allahabad, Uttar Pradesh PIN: 211008

e-mail: [email protected]

Visit us at: www.vicasindia.com OR http://vicasindia.blogspot.com

Cellphone No.: +91 94509 61953


2/22

THINGS TO LEARN AND UNDERSTAND BY THE MODEL ROCKETRY ACTIVITY

Through this activity the participants will easily understand the concepts of Physics, Chemistry, and

Mathematics and will know some facts about space which are as follows:

PHYSICS:

How Thrust helps a rocket to fly?

Practical aspect of Center of Gravity and Center of Pressure i.e. how they are related with

each other, their role and importance in a flight of a rocket. How to find the Center of Gravity

and Center of Pressure of an object?

Factor affecting the flight of a Rocket and how? Brief discussion on the wind, gravitational pull,

air friction and thrust and their role.

How stability is attained and its role?

How to determine and check whether an object is balanced/stable by Center of Gravity and

Center of Pressure. Practical application of Newtons Third Law.

Practical application and realization of force, mass and acceleration with their relation

(Newtons Second Law).

Application of equations of motion i.e. v = u + at, S = u + at2 and v2 = u2 + 2aS

CHEMISTRY:

Learn and understand the types of fuels used in propellants.

Role of Oxidizer and fuel and basic difference between them.

MATHEMATICS:

Practical application of Trigonometry and Geometry in real life.

Calculating in determining the approximate height of a flying object in free space with the help

of geometry.

SPACE:

By the videos being displayed the students will get a feel of different situations and conditions

faced by the astronauts in space.

Biological effects on the body of the astronauts in space and detail discussion on their cause. Technical aspect of countdown before any launch.

Comparison between a Model Rocket & Real Rocket and Rocket & Airplane.

TEAM WORK:

Experience of working in a team/group while developing model rocket.

Experience of coordinating with different teams/groups while the launch of model rocket i.e. at

the time of launch there are two recording teams, two tracking teams, one launching team

monitored and instructed by the resource person.


3/22

THRUST:

Thrust (T):

This is the instantaneous force or push produced at a

given time by the operating engine. It is measured in

Newtons.

The Thrust may or may not remain constant throughout

the operation of the engine but follows curve path.

Thrust of the Engine:

This is the reaction Produced due the action of the ho

gases coming out of the nozzle. This force acts in the

direction opposite of the gas coming out.

Maximum Thrust:

It is the highest amount of push produced by the engine

during the whole operation.

Burn out Time or Thrust Duration (tB):

It is the length of the time for which thrust is produced by

the engine i.e. the time from state of ignition to the time

when the ceases to produce thrust.

The instant when the engine ceases to produce thrust is

known as 'Burn Out'

Total Thrust:

It is the total impulse by the engine. If the thrust duration

is broken in small time intervals and thrust is found out for

every small interval, then sum of the products of the smal

time interval and thrust at that time upto all small time

intervals give the total thrust.


4/22

Average Thrust (Tav):

It is the equivalent constant thrust which would act for the same total duration and produces same

amount of total thrust. It is the total thrust divided by the burn out time.

CENTER OF GRAVITY AND CENTER OF PRESSURE:

Center of Gravity/Balancing point:

The center of gravity is a geometric property of any object. The center of gravity is the average

location of the weight of an object. We can completely describe the motion of any object through

space in terms of the translation of the center of gravity of the object from one place to another and

the rotation of the object about its center of gravity if it is free to rotate. If the object is confined to

rotate about some other point, like a hinge, we can still describe its motion. In flight, both

airplanes and rockets rotate about their centers of gravity

The center of mass ormass center is the mean location of all the mass in a system. In the case of

a rigid body, the position of the center of mass is fixed in relation to the body. In the case of a loose

distribution of masses in free space, such as shot from a shotgun or the planets of the solar system,

the position of the center of mass is a point in space among them that may not correspond to the

position of any individual mass. The use of the mass center often allows the use of

simplified equations of motion, and it is a convenient reference point for many other calculationsin physics, such as angular momentum or the moment of inertia. In many applications, such as orbita

mechanics, objects can be replaced by masses located at their mass centers for the purposes of

analysis.

The term center of mass is often used interchangeably with center of gravity, but they are

physically different concepts. They happen to coincide in a uniform gravitational field, but where

gravity is not uniform center of gravity refers to the mean location of the gravitational force acting on

a body. This results in small but measurable gravitational torque that must be accounted for in the

operation of artificial satellites.

The center of mass of a body does not generally coincide with its geometric center, and this property

can be exploited. Engineers try to design a sports cars center of mass as low as possible to make

the car handle better. When high jumpers perform a Fosbury Flop, they bend their body in such a

way that it is possible for the jumper to clear the bar while his or her center of mass does not.

The center of momentum frame is an inertial frame defined as the inertial frame in which the center of

mass of a system is at rest. A specific center of momentum frame in which the center of mass is not


5/22

only at rest, but also at the origin of the coordinate system, is sometimes called the center of mass

frame, or center of mass coordinate system.

Center of Pressure:

As an object moves through a fluid, the velocity of the fluid varies around the surface of the object

The variation of velocity produces a variation of pressure on the surface of the object. Integrating the

pressure times the surface area around the body determines the aerodynamic force on the object

We can consider this single force to act through the average location of the pressure on the surface

of the object. We call the average location of the pressure variation the center of pressure in the

same way that we call the average location of the weight of an object the center of gravity. The

aerodynamic force can then be resolved into two components, lift and drag, which act through the

center of pressure in flight.

Determining the center of pressure is very important for any flying object. To trim an airplane, or to

provide stability for a model rocket or a kite, it is necessary to know the location of the center ofpressure of the entire aircraft.

Calculation of cp:

The figure shows a simplified version of the calculation procedure that you can use to calculate the cp

of a model rocket. We assume that we already know the projected area and location, relative to some

reference location, of each of the major parts of the rocket: the nose, body tube, and fins. The

projected area A of the rocket is the sum of the projected area a of the components.

A = a(nose) + a(tube) + a(fins)

Since the center of pressure is an average location of the projected area, we can say that the area of

the whole rocket times the location of the center of pressure cp is equal to the sum of the projected

area of each component times the distance dof that component from the reference location.

A * cp = [a * d](nose) + [a * d](tube) + [a * d](fins)

The location of each component is the distance of each components center of pressure from the

reference line. So you must calculate or determine the center of pressure of each of the components

For example, the projected area of the body tube is a rectangle. The center of pressure is on the axis,

half way between the end planes.

Mechanically determining of Center of Gravity and Center of Pressure:

For a model rocket, there is a simple mechanical way to determine the center of pressure for each

component or for the entire rocket. Make a two dimensional tracing of the shape of the component, or


6/22

rocket, on a piece of cardboard and cut out the shape. Hang the cut out shape by a string, and

determine the point at which it balances. This is just like balancing a pencil with a string! The point at

which the component, or rocket, is balanced is the center of pressure. You obviously could not use

this procedure for a very large rocket like the Space Shuttle. But it works quite well for a model.

Relation between Center of Gravity and Center of Pressure:

As a model rocket flies through the air, aerodynamic forces act on al

parts of the rocket. In the same way that the weight of all the rocke

components acts through the center of gravity(cg), the aerodynamic

forces act through a single point called the center of pressure (cp).

The relation between center of gravity and center of pressure plays a

major role in the stability of the model rocket. Therefore it is said that

the difference of the distance of center of gravity from the bottom of the model rocket to the distance of the

center of pressure from the bottom of the rocket must be less than the diameter of the tube of the mode

rocket.

FACTORS AFFECTING THE FLIGHT OF A ROCKET:

Thrust:

It is the force which moves a rocket through the air. Thrust is used to overcome the drag of a rocket,

and to overcome the weight of a rocket. Thrust is generated by the engines of the rocket throughsome kind of propulsion system.

Thrust is a mechanical force, so the propulsion system must be in physical contact with a working

fluid to produce thrust. Thrust is generated most often through the reaction of accelerating a mass of

gas. Since thrust is a force, it is a vector quantity having both a magnitude and a direction. The

engine does work on the gas and accelerates the gas to the rear of the engine; the thrust is

generated in the opposite direction from the accelerated gas. The magnitude of the thrust depends

on the amount of gas that is accelerated and on the difference in velocity of the gas through the

engine.

The physics involved in the generation of thrust is introduced in middle school and studied in some

detail in high school and college. To accelerate the gas, we have to expend energy. The energy is

generated as heat by the combustion of some fuel. The thrust equation describes how the

acceleration of the gas produces a force. The type of propulsion system used on an aircraft may vary

from airplane to airplane and each device produces thrust in a slightly different way.


7/22

It is a reaction force described quantitatively by Newtons second and third laws. When a system

expels or accelerates mass in one direction the accelerated mass will cause a proportional but

opposite force on that system.

A rocket is propelled forward by a thrust force equal in magnitude, but opposite in direction, to the

time-rate of momentum change of the exhaust gas accelerated from the combustion chamber through

the rocket engine nozzle. This is the exhaust velocity with respect to the rocket, times the time-rate atwhich the mass is expelled, or in mathematical terms:

T = (dm/dt)v

where:

T is the thrust generated (force)

dm/dt is the rate of change of mass with respect to time (mass flow rate of exhaust);

v is the speed of the exhaust gases measured relative to the rocket.

For vertical launch of a rocket the initial thrust must be more than the weight.

Thrust at zero speed is zero power. Power requires work to be done, so zero velocity indicates zero

work and zero power. Therefore the power of a rocket or aircraft engine is thrust times forward speed.

Power (watts) = thrust (newtons) x speed (metres/second)

Gravitational Pull:

The attraction that one object has for another object due to the invisible force of gravity. The mass ofan object affects its gravitational pull. In context of a rocket it is very important factor as the rocket has

to move above in the space working against the gravitational pull of the earth and to make it to the

space it has to overcome the gravitational pull of it.

Air Friction/Resistance (Drag Force):

Astrodynamic drag force is sometimes called air resistance orair friction refers to forces tha

oppose the relative motion of an object through air. Drag forces act in a direction opposite to the

oncoming moving velocity.

Unlike other resistive forces such as dry friction, which is nearlyindependent of velocity, drag forces depend on velocity.

For a solid object moving through air, the drag is the component of the net aerodynamic force acting

opposite to the direction of the movement. The component perpendicular to this direction is

considered lift. Therefore drag opposes the motion of the object, and in a powered vehicle it is

overcome by thrust.


8/22

In astrodynamics, and depending on the situation, atmospheric drag can be regarded as an

inefficiency requiring expense of additional energy during launch of the space object or as a bonus

simplifying return from orbit.

In order to reduce the drag force we have to make the consideration in designing the shape of the

nose and fins of a rocket.


9/22

Wind:

In order to maintain the stability of a rocket to move in the desired path it is best that not to make a

launch of a rocket where the flow of wind is not favorable to us i.e. if the wind is blowing at very high

speed then the launching of the rocket must not be done. It is also safe not to launch rocket when its

cloudy and raining. The rocket must be launched in an open space i.e. ground for the security

reasons.

STABILITY:

In order to fly a straight and predictable trajectory, A Model Rocket must be stable. Basic Rule of

Stability

A Model Rocket will be Stable if its center of Pressure is behind its center of gravity. Rockets Motion

is a simultaneous combination of Translational and Rotational Motion.


10/22

S.NO. TRANSLATIONAL MOTION ROTATIONAL MOTION

01. Always points same direction Always points different direction

02. Three forces give us this motion

Weight, Drag, Engines thrust

One force gives this force Wind Force

03. Act through center of gravity of Rocket Act perpendicular to the Rockets

center line

04. Gives how high & how Far away lands Gives Stability of the Model Rocket

Stability depends on following factors:

1. Static Margin Difference between Center of Pressure & Center of Gravity.

2. Speed

Determine whether the rocket is balance/stable or not:

To determine this just tie the thread at the center of the gravity point determined by balancing thehanging model rocket through thread. Now try to swing the model rocket above your head and try to

notice the direction of the movement of the model rocket that whether it is moving at which of the

following conditions:

a) with nose at the front

b) fins at the front

c) at some angle with nose pointing upwards

d) at some angle with fins pointing upwards

If the model rocket is moving in the pattern a and c then the model rocket is balance or else there is

some error while the development of the model rocket.

Before coming to the conclusion regarding the stability of the rocket try to repeat the swing test for at

least 5 times and make a note of the pattern of the movement. For a stable rocket at least 4 out of 5

times must satisfy the conditions of stability.

Newtons Second Law of Motion:

The change of momentum of a body is proportional to the impulse impressed on the body, andhappens along the straight line on which that impulse is impressed.

Force = Mass * Acceleration

2nd Law in simple terms:


11/22

The change is the direction of the acceleration is proportional to the force applied to the mass

Basically, i see a ball rolling towards me. I push it really hard; it will roll away really fast. Or i can push

it really lightly and it will roll away really slowly.

Newton's Second Law provides a relationship between the unbalanced force on the object, the mass

of the object and the acceleration that is produced: unbalanced force = mass x acceleration or F =

ma.

The unbalanced force F is measured in newtons (N), the mass m is measured in kilograms (kg) and

acceleration a is measured in metres per second per second (m/s2).

Newton's Second Law of Motion is concerned with the effect that unbalanced forces have on motion

Unbalanced force acting on an object causes it to accelerate. There are two points to note about the

acceleration of an object when an unbalanced force acts on it:

The bigger the unbalanced force acting on the object the bigger the acceleration of the object. The

more mass the object has the more inclined it is to resist any change in its motion. For example, if

you apply the same unbalanced force to a mass of 1000 kg and a mass of 1 kg, the acceleration

(change in motion) of the 1000 kg mass will be much less than that of the 1 kg mass.

Newtons Third Law of Motion:

For every action there is an equal and opposite re-action. What does this mean? This means that forevery force there is a reaction force that is equal in size, but opposite in direction. That is to say that

whenever an object pushes another object it gets pushed back in the opposite direction equally hard.

Let's study how a rocket works on Newton's Third Law.

The rocket's action is to push down on the

ground with the force of its powerfu

engines, and the reaction is that the

ground pushes the rocket upwards with an

equal force.

Three Equations of Motion:

Rockets are propelled by the momentum reaction of the exhaust gases expelled from the tail. Since

these gases arise from the reaction of the fuels carried in the rocket, the mass of the rocket is not


12/22

constant, but decreases as the fuel is expended. The equation of motion for a rocket projected

vertically upward in a uniform gravitational field, neglecting atmospheric friction, is:

Where ,

m is the mass of the rocket and

v is the velocity of the escaping gases relative to the rocket.

The variable quantities in a uniformly accelerated rectilinear motion are time, speed, distance covered

and acceleration. Simple relations exist between these quantities. These relations are expressed in

terms of equations called equations of motion

The equations of motion are:

(1) v = u + at

(3) v2 - u2 = 2aS

Derivation of the First Equation of Motion

Consider a particle moving along a straight line with uniform acceleration 'a'. At t = 0, let the particlebe at A and u be its initial velocity and when t = t, v be its final velocity.

v = u + at I equation of motion

Second Equation of Motion


13/22

From equations (1) and (2)

The first equation of motion is v = u + at.

Substituting the value of v in equation (3), we get

Third Equation of Motion

The first equation of motion is v = u + at.

v - u = at ... (1)

From equation (2) and equation (3) we get,

Multiplying equation (1) and equation (4) we get,

(v - u) (v + u) = 2aS

[We make use of the identity a2 - b2 = (a + b) (a - b)]

v2 - u2 = 2aS III equation of motion


14/22

DERIVATIONS OF EQUATIONS OF MOTION (GRAPHICALLY)

First Equation of Motion

Graphical Derivation of First Equation

Consider an object moving with a uniform velocity u in a

straight line. Let it be given a uniform acceleration a at time t =0 when its initial velocity is u. As a result of the acceleration,

its velocity increases to v (final velocity) in time t and S is the

distance covered by the object in time t.

The figure shows the velocity-time graph of the motion of the

object.

Slope of the v - t graph gives the acceleration of the moving

object.

Thus, acceleration = slope = AB =

v - u = at

v = u + at I equation of motion

Second Equation of Motion

Let u be the initial velocity of an object and 'a' the acceleration produced in the body. The distance

travelled S in time t is given by the area enclosed by the velocity-time graph for the time interval 0 to t

Graphical Derivation of Second Equation

Distance travelled S = area of the trapezium ABDO

= area of rectangle ACDO + area of DABC


15/22

(v = u + at I eqn of motion; v - u = at)

Third Equation of Motion

Let 'u' be the initial velocity of an object and a be the acceleration produced in the body. The distance

travelled 'S' in time 't' is given by the area enclosed by the v - t graph.

Graphical Derivation of Third Equation

S = area of the trapezium OABD.

Substituting the value of t in equation (1) we get,

2aS = (v + u) (v - u)

(v + u)(v - u) = 2aS [using the identity a2 - b2 = (a+b) (a-b)]

v2 - u2 = 2aS III Equation of Motion

FUELS USED AS PROPELLANT

Rocket propellant is mass that is stored in some form of propellant tank, prior to being used as the

propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust. A fuelpropellant is often burned with an oxidizer propellant to produce large volumes of very hot gas. These

gases expand and push on a nozzle, which accelerates them until they rush out of the back of

the rocket at extremely high speed, making thrust. Sometimes the propellant is not burned, but can

be externally heated for more performance. For smaller attitude control thrusters, a compressed gas

escapes the spacecraft through a propelling nozzle.

Chemical rocket propellants are most commonly used, which undergo exothermic chemica

reactions which produce hot gas which is used by a rocket for propulsive purposes.


16/22

Rockets create thrust by expelling mass backwards in a high speed jet (see Newton's Third Law).

Chemical rockets, the subject of this article, create thrust by reacting propellants within a combustion

chamber into a very hot gas at high pressure, which is then expanded and accelerated by passage

through a nozzle at the rear of the rocket. The amount of the resulting forward force, known as thrust,

that is produced is the mass flow rate of the propellants multiplied by their exhaust velocity (relative to

the rocket), as specified by Newton's third law of motion. Thrust is therefore the equal and opposite

reaction that moves the rocket, and not by interaction of the exhaust stream with air around the

rocket. Equivalently, one can think of a rocket being accelerated upwards by the pressure of the

combusting gases against the combustion chamber and nozzle. This operational principle stands in

contrast to the commonly-held assumption that a rocket "pushes" against the air behind or below it.

Rockets in fact perform better in outer space (where there is nothing behind or beneath them to push

against), because there is a reduction in air pressure on the outside of the engine, and because it is

possible to fit a longer nozzle without suffering from flow separation.

The maximum velocity that a rocket can attain in the absence of any external forces is primarily a

function of its mass ratio and its exhaust velocity. The relationship is described by the rocketequation: Vf= Veln(M0 / Mf). The mass ratio is just a way to express what proportion of the rocket is

propellant (fuel/oxidizer combination) prior to engine ignition. Typically, a single-stage rocket might

have a mass fraction of 90% propellant, 10% structure, and hence a mass ratio of 10:1 . The impulse

delivered by the motor to the rocket vehicle per weight of fuel consumed is often reported as the

rocket propellant's specific impulse. A propellant with a higher specific impulse is said to be more

efficient because more thrust is produced while consuming a given amount of propellant.

Lower stages will usually use high-density (low volume) propellants because of their lighter tankage

to propellant weight ratios and because higher performance propellants require higher expansionratios for maximum performance than can be attained in atmosphere. Thus, the Apollo-Saturn V first

stage used kerosene-liquid oxygen rather than the liquid hydrogen-liquid oxygen used on its upper

stages Similarly, the Space Shuttle uses high-thrust, high-density solid rocket boosters for its lift-off

with the liquid hydrogen-liquid oxygen SSMEs used partly for lift-off but primarily for orbital insertion.

CHEMICAL PROPELLANTS

There are three main types of propellants: solid, liquid, and hybrid.

Solid propellants

Solid propellants (and almost all rocket propellants) consist of an oxidizer and a fuel. In the case of

gunpowder, the fuel is charcoal, the oxidizer is potassium nitrate, and sulfur serves as a catalyst.

(Note: sulfur is not a true catalyst in gunpowder as it is consumed to a great extent into a variety of

reaction products such as K2S. The sulfur acts mainly as a sensitizer lowering threshold of ignition.)

During the 1950s and 60s researchers in the United States developed what is now the standard high-

energy solid rocket fuel, Ammonium Perchlorate Composite Propellant (APCP). This mixture is

primarily ammonium perchlorate powder (an oxidizer), combined with fine aluminum powder (a fuel)


17/22

held together in a base of PBAN or HTPB (rubber-like fuels). The mixture is formed as a liquid, and

then cast into the correct shape and cured into a rubbery solid.

Advantages

Solid fueled rockets are much easier to store and handle than liquid fueled rockets, which makes

them ideal for military applications. In the 1970s and 1980s the U.S. switched entirely to solid-fuelled

ICBMs: the LGM-30 Minuteman and LG-118A Peacekeeper (MX). In the 1980s and 1990s, theUSSR/Russia also deployed solid-fuelled ICBMs (RT-23, RT-2PM, and RT-2UTTH), but retains two

liquid-fuelled ICBMs (R-36 and UR-100N). All solid-fuelled ICBMs on both sides have three initial

solid stages and a precision maneuverable liquid-fuelled bus used to fine tune the trajectory of the

reentry vehicle.

Their simplicity also makes solid rockets a good choice whenever large amounts of thrust are needed

and cost is an issue. The Space Shuttle and many other orbital launch vehicles use solid fuelled

rockets in their first stages (solid rocket boosters) for this reason.

Disadvantages

Relative to liquid fuel rockets, solid rockets have a number of disadvantages. Solid rockets have a

lower specific impulse than liquid fueled rockets. It is also difficult to build a large mass ratio solid

rocket because almost the entire rocket is the combustion chamber, and must be built to withstand

the high combustion pressures. If a solid rocket is used to go all the way to orbit, the payload fraction

is very small. (For example, the Orbital Sciences Pegasus rocket is an air-launched three-stage solid

rocket orbital booster. Launch mass is 23,130 kg, low earth orbit payload is 443 kg, for a payload

fraction of 1.9%. Compare to a Delta IV Medium, 249,500 kg, payload 8600 kg, payload fraction 3.4%

without air-launch assistance.)A drawback to solid rockets is that they cannot be throttled in real time, although a predesigned thrus

schedule can be created by altering the interior propellant geometry.

Solid rockets can often be shut down before they run out of fuel. Essentially, the rocket is vented or

an extinguishant injected so as to terminate the combustion process. In some cases termination

destroys the rocket, and then this is typically only done by a Range Safety Officer if the rocket goes

awry. The third stages of the Minuteman and MX rockets have precision shutdown ports which, when

opened, reduce the chamber pressure so abruptly that the interior flame is blown out. This allows a

more precise trajectory which improves targeting accuracy.

Finally, casting very large single-grain rocket motors has proved to be a very tricky business. Defects

in the grain can cause explosions during the burn, and these explosions can increase the burning

propellant surface enough to cause a runaway pressure increase, until the case fails.

Liquid propellants

Current Types

The most common liquid propellants in use today:


18/22

LOX and kerosene (RP-1). Used for the lower stages of most Russian and Chinese boosters, the

first stages of the Saturn V and Atlas V, and all stages of the developmental Falcon 1and Falcon

9. Very similar to Robert Goddard's first rocket. This combination is widely regarded as the most

practical for boosters that lift off at ground level and therefore must operate at full atmospheric

pressure.

LOX and liquid hydrogen, used in the Space Shuttle orbiter, the Centaur upper stage of the Atlas

V, Saturn V upper stages, the newer Delta IV rocket, the H-IIA rocket, and most stages of the

European Ariane rockets.

Nitrogen tetroxide (N2O4) and hydrazine (N2H4), MMH, or UDMH. Used in military, orbital and

deep space rockets, because both liquids are storable for long periods at reasonable

temperatures and pressures. N2O4/UDMH is the main fuel for the Proton rocket. This combination

is hypergolic, making for attractively simple ignition sequences. The major inconvenience is that

these propellants are highly toxic, hence they require careful handling.

Monopropellants such as hydrogen peroxide, hydrazine and nitrous oxide are primarily used

for attitude control and spacecraft station-keeping where their long-term storability, simplicity of

use and ability to provide the tiny impulses needed, outweighs their lower specific impulse as

compared to bipropellants. Hydrogen peroxide is also used to drive the turbopumps on the first

stage of the Soyuz launch vehicle.

Advantages

Liquid fueled rockets have better specific impulse than solid rockets and are capable of being

throttled, shut down, and restarted. Only the combustion chamber of a liquid fueled rocket needs to

withstand combustion pressures and temperatures and they can be regeneratively cooled by the

liquid propellant. On vehicles employing turbopumps, the propellant tanks are at very much less

pressure than the combustion chamber, and thus can be built far more lightly than a solid propellant

rocket case, permitting a higher mass ratio. 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

much better specific impulse than the ammonium perchlorate used in most solid rockets, when paired

with comparable fuels. These facts have led to the use of hybrid propellants: a storable oxidizer used

with a solid fuel, which retain most virtues of both liquids (high ISP) and solids (simplicity).

While liquid propellants are cheaper than solid propellants, for orbital launchers, the cost savings do

not, and historically have not mattered; the cost of propellant is a very small portion of the overall cost

of the rocket.


19/22

Disadvantages

The main difficulties with liquid propellants are also with the oxidizers. These are generally at least

moderately difficult to store and handle due to their high reactivity with common materials, may have

extreme toxicity (nitric acids), moderately cryogenic (liquid oxygen), or both (liquid fluorine, FLOX- a

fluorine/LOX mix). Several exotic oxidizers have been proposed: liquid ozone (O3), ClF3, and ClF5, al

of which are unstable, energetic, and toxic.

Liquid fuelled rockets also require potentially troublesome valves and seals and thermally stressed

combustion chambers, which increase the cost of the rocket. Many employ specially designed

turbopumps which raise the cost enormously due to difficult fluid flow patterns that exist within the

casings.

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.

GOX was used as one of the propellant for the Buran program for the orbital manoeuvring system.

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 fuelled rocket. Hybrid rockets are also

cleaner than solid rockets because practical high-performance solid-phase oxidizers all contain

chlorine, versus the more benign liquid oxygen or nitrous oxide used in hybrids. Because just one

propellant is a fluid, hybrids are simpler than liquid rockets.

Hybrid motors suffer two major drawbacks. The first, shared with solid rocket motors, is that the

casing around the fuel grain must be built to withstand full combustion pressure and often extreme

temperatures as well. However, modern composite structures handle this problem well, and when

used with nitrous oxide and a solid rubber propellent ( HTPB ) , relatively small percentage of fuel is

needed anyway, so the combustion chamber is not especially large.

The primary remaining difficulty with hybrids is with mixing the propellants during the combustion

process. In solid propellants, the oxidizer and fuel are mixed in a factory in carefully controlled

conditions. Liquid propellants are generally mixed by the injector at the top of the combustion

chamber, which directs many small swift-moving streams of fuel and oxidizer into one another. Liquid

fuelled rocket injector design has been studied at great length and still resists reliable performance

prediction. In a hybrid motor, the mixing happens at the melting or evaporating surface of the fuel.

The mixing is not a well-controlled process and generally quite a lot of propellant is left unburned [3]

which limits the efficiency and thus the exhaust velocity of the motor. Additionally, as the burn

continues, the hole down the center of the grain (the 'port') widens and the mixture ratio tends to

become more oxidiser rich.


20/22

There has been much less development of hybrid motors than solid and liquid motors. For military

use, ease of handling and maintenance have driven the use of solid rockets. For orbital work, liquid

fuels are more efficient than hybrids and most development has concentrated there. There has

recently been an increase in hybrid motor development for nonmilitary suborbital work:

The Reaction Research Society, although known primarily for their work with liquid rocket

propulsion, has a long history of research and development with hybrid rocket propulsion.

Several universities have recently experimented with hybrid rockets. Brigham Young University,

the University of Utah and Utah State University launched a student-designed rocket called Unity

IV in 1995 which burned the solid fuel hydroxy-terminated polybutadiene (HTPB) with an oxidizer

of gaseous oxygen, and in 2003 launched a larger version which burned HTPB with nitrous

oxide. Stanford University researches nitrous-oxide/paraffin hybrid motors.

The Rochester Institute of Technology is currently creating a HTPB hybrid rocket to launch smal

payloads into space and to several near Earth objects. Its first launch is scheduled for Summer2007.

Scaled Composites SpaceShipOne, the first private manned spacecraft, is powered by a hybrid

rocket burning HTPB with nitrous oxide. The hybrid rocket engine was manufactured

by SpaceDev. SpaceDev partially based its motors on experimental data collected from the testing

of AMROC's (American Rocket Company) motors at NASA's Stennis Space Center's E1 test

stand. Motors ranging from as small as 1000 lbf (4.4 kN) to as large as 250,000 lbf (1.1 MN) thrust

were successfully tested. SpaceDev purchased AMROCs assets after the company was shut

down for lack of funding.

Inert propellants

Some rocket designs have their propellants obtain their energy from non chemical or even external

sources. For example water rockets use the compressed gas, typically air, to force the water out of

the rocket.

Solar thermal rockets and Nuclear thermal rockets typically propose to use liquid hydrogen for

an Isp(Specific Impulse) of around 600-900 seconds, or in some cases water that is exhausted as

steam for an Isp of about 190 seconds.Additionally for low performance requirements such as attitude jets, inert gases such as nitrogen have

been employed.


21/22

Determining the Height of an object in free space using Trigonometry and Geometry:

The height of an object in the free space can be determined using two methods one is the

Trigonometric and another is the Geometry with the help of the tracking instrument.

Trigonometric method:

Just stand at the distance of 100m apart from the launching point of the model rocket. The tracking

team must be ready with their tracking instrument which has protector attached with it to make the

record of the angle. As soon as the model rocket is launched the tracking team must move their

hands in line of the height attained by the rocket. The angle recorded in the tracking instrument must

be kept in the equation:

tan = Pependicular /Base

where

= the angle recorded in the tracking instrument

Base = 100m

Perpendicular = the height of the object from the groundMake sure that the model rocket launched was whether stable or unstable at the time of flight

because we have to take the record of the model rockets which goes straight in the sky.

Geometric Method:

This method is more accurate then the Trigonometric method but requires 4 teams i.e. 2 tracking

teams and 2 recording teams. In this method the two tracking teams takes their position 100m apart

from the launching point lying diagonal with

each other and the other two corners are

taken by the recording team which make

sure that the model rocket launched was

whether stable or unstable at the time of

flight. This method is based on the theory of

similar triangles. Just scale the 100m+100m

distances apart on the graph paper taking

launching point as the center on the paper

The angle recorded by the tracking teams of

the maximum height attained by the rocket isthen plotted on the graph paper on the either

sides and is extended. The point at which the

two lines intersect is the required point. The

length the perpendicular dropped from the

point to the base is the height attained by the

model rocket as shown in the figure.


22/22

Biological Effects on the body of the Astronauts:

Due to the absent of the gravitational pull in the space it is found that there is increase in the height of

the body of Astronauts present in the space up to 4-6 inches in size. In order to incorporate this

serious threat they are suppose to do the exercises in the space shuttle.

Technological aspect of COUNTDOWN:

The fact is that each and every major and minor components installed in the rocket are assigned

some numbers ranging from 1 to total number of components like 1,2,3,4,5,274 and while

countdown every component is tested and checked and in case if found that any of the component is

not functioning in the desired manner then the launch is stopped at once and is postpone for some

time till the problem is sort out. When the countdown reaches 1 successfully then finally the launch

takes place.

Difference between the Model Rocket and the Real Rocket:

S.NO. MODEL ROCKET REAL ROCKET01. 4 forces throughout flight 4 forces during atmospheric flight

02. All of flight in atmosphere Short time in atmosphere

03. Aerodynamics very important Aerodynamics less important

04. Very short powered flight Long powered flight

05. Solid rocket engine Liquid or solid rocket engine

06. No control Active control

07. Low speed High speed

08. Inexpensive materials Expensive materials

09. Card sheet and paper Aluminum, titanium, nickel alloy

Difference between the Rocket and the Aircraft:

S.NO. AIRCRAFT ROCKET

01. Designed and developed to fly in

atmosphere

Designed and developed to fly in

space.

02. All of flight in atmosphere Short time in atmosphere

03. Aerodynamics very important Aerodynamics less important

04. Liquid fuel engine Liquid or solid rocket engine

Swapnil Kumar Sharma Model Rocketry

Documents

Transcript of Swapnil Kumar Sharma Model Rocketry