35918828 rocket propulsion flight performance

7/30/2019 35918828 Rocket Propulsion Flight Performance

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ROCKETPROPULSIONSYSTEM


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CHAPTER 4

FLIGHT

PERFORMANCE


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INTRODUCTION

It deals with the performance ofrocket-propelled vehicles such as

,missiles, spacecraft, space launch

vehicles, or projectiles.Rocket propulsion systems

provide forces to a flight vehicle andcause it to accelerate (or decelerate),

overcome drag forces, or change

flight direction.


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They are usually applied to

several different flight regimes:

(1)Flight within the atmosphere

(air to surface missiles or

sounding rockets)(2)Near-space environment (earth

satellites)(3)Lunar and planetary flights

(4)Sun escape


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ROCKET

PARTS


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GRAVITY-FREE, DRAG-FREE

SPACE FLIGHT


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IDEAL

ROCKET

EQUATION


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M is the instantaneous mass of therocket, u is the velocity of therocket, v is the velocity of the

exhaust from the rocket, A is thearea of the exhaust nozzle, p is theexhaust pressure and p0 is theatmospheric pressure. During a

small amount of time dt a smallamount of mass dm is exhaustedfrom the rocket. This changes the

mass of the rocket and the velocity

of the rocket and we can evaluatethe change in momentum of the

rocket as


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change in rocket

momentum =M (u + du) - M u = M du


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We can also determine the change

in momentum of the smallmass dm that is exhausted at

velocity v as


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change in exhaustmomentum =

dm (u - v) - dm u = - dm v


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So the total change in momentum

of the system (rocket + exhaust) is


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change in system momentum

=M du - dm v


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FORCES

ON A

ROCKET


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I fli ht k t i bj t d t fo r


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In flight, a rocket is subjected to fourforces; weight, thrust, and the aerodynamicforces,lift and drag.

The magnitude of the WEIGHT depends on themass of all of the parts of the rocket. The weight forceis always directed towards the center of the earth andacts through the center of gravity.

The magnitude of the THRUST depends on themass flow rate through the engine and the velocity andpressure at the exit of the nozzle. The thrust forcenormally acts along the longitudinal axis of the rocket

and therefore acts through the center of gravity. Somefull scale rockets can move, or gimbal, their nozzles toproduce a force which is not aligned with the center ofgravity.


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animation of the motion of the rocketas the nozzle is gimbaled:


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The resulting torque about the center of

gravity can be used to maneuver the rocket. Themagnitude of the AERODYNAMICFORCES depends on the shape, size, andvelocity of the rocket and on properties of the

atmosphere. The aerodynamic forces actthrough the center of pressure.

Alth h th f f t k t


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Although the same four forces act on a rocket as on

an airplane, there are some important differences in the

application of the forces:

1. On an airplane, the lift force (the aerodynamic forceperpendicular to the flight direction) is used to overcome

the weight. On a rocket, thrust is used in opposition toweight. On many rockets, lift is used to stabilize and

control the direction of flight2. On an airplane, most of the aerodynamic forces are

generated by the wings and the tail surfaces. For a

rocket, the aerodynamic forces are generated by the fins,

nose cone, and body tube. For both airplane and rocket,the aerodynamic forces act through the center of

pressure while the weight acts through the center of

gravity.


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3. While most airplanes have a high lift to

drag ratio, the drag of a rocket is usually

much greater than the lift.

4. While the magnitude and direction of the

forces remain fairly constant for an airplane,

the magnitude and direction of the forcesacting on a rocket change dramatically during

a typical flight.


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ROCKET

THRUST


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Thrustis the force which moves the rocketthrough the air, and through space. Thrust is generated

by the propulsion system of the rocket through theapplication of Newton's third law of motion; For everyaction there is an equal and opposite re-action. In thepropulsion system, an engine does work on a gas or

liquid, called a WORKING FLUID and accelerates theworking fluid through the propulsion system. The re-

action to the acceleration of the working fluid produces

the thrust force on the engine. The working fluid isexpelled from the engine in one direction and the thrust

force is applied to the engine in the opposite direction.


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ROCKET

WEIGHT


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W i ht


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Weightis the force generated by thegravitational attraction on the rocket. We are more

familiar with weight than with the other forces acting ona rocket, because each of us have our own weightwhich we can measure every morning on the bathroomscale. We know when one thing is heavy and whenanother thing is light. But weight, the gravitationalforce, is fundamentally different from the other forcesacting on a rocket in flight. The aerodynamic forces,lift and drag, and the thrust force are mechanicalforces. The rocket must be in physical contact with thegases which generates these forces. The gravitationalforce is a field force and the rocket does not have tobe in contact with the source of this force.


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ROCKET

AERODYNAMIC

S


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A d i f


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Aerodynamic forcesaregenerated and act on a rocket as it flies through the

air. Forces are vector quantities having both amagnitude and a direction. The magnitude of the

aerodynamic forces depends on the shape, size

and velocity of the rocket and some properties of the

air through which it flies. By convention, the

single aerodynamic force is broken into two

components: the drag force which is opposed to the

direction of motion, and the lift force which actsperpendicular to the direction of motion. The lift and

drag act through the center of pressure which is the

average location of the aerodynamic forces on an

object.


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FLIGHT

VEHICLES


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LIQUID

PROPELLANT ROCKET


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SOLID

PROPELLANT ROCKET


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A two-stage rocket carries a

propellant and one or more

rocket engines in each stage.The first stage launches the

rocket. After burning its supply

of propellant, the first stage

falls away from the rest of the

rocket. The second stage then

ignites and carries the payload

into earth orbit or even farther

into space. A balloon and a

rocket work in much the sameway. Gas flowing from the

nozzle creates unequal pressure

that lifts the balloon or the

rocket off the ground. Image

credit: World Book diagram


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Launch vehicles used byEuropean nations include the

European Space Agency'sAriane 5 rocket and Russia'sA class and Proton rockets.

These vehicles carry spaceprobes and artificial

satellites into outer space.The A Class rocket has also

carried people into space,and the Proton rocket has

carried International SpaceStation modules. Image

credit: World Bookillustrations by Oxford

Illustrators Limited


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Launch vehicles used byEuropean nations include

the European SpaceAgency's Ariane 5 rocketand Russia's A class and

Proton rockets. Thesevehicles carry space probes

and artificial satellites intoouter space. The A Class

rocket has also carriedpeople into space, and the

Proton rocket has carriedInternational Space Stationmodules. Image credit:

World Book illustrations by

Oxford Illustrators Limited


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The vehicles shown here helped the

United States and the Soviet Unionachieve milestones in theexploration of space. The United

States no longer builds theserockets, but Russia continues to

use the Soviet A Class design in the

Soyuz rocket. A Class (Vostok), Soviet. Carried

Yuri Gagarin, the first person toorbit the earth, in 1961. 126 feet

(38 meters)

Saturn 5, U.S. Launched NeilArmstrong, the first person to set

foot on the moon, in 1969. 363 feet(111 meters) Image credit: WORLD

BOOK illustrations by Oxford

Illustrators Limited


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People use rockets for high-speed, high-power transportation both within Earth's

atmosphere and in space. Rockets are

especially valuable for

(1) military use,

(2) atmospheric research,

(3) launching probes and satellites, and

(4) space travel.

HOW ROCKETS ARE USED?


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MilitaryUse

R k t


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Rockets used by the military vary insize from small rockets used on the battlefield to giant

guided missiles that can fly across oceans. Thebazooka is a small rocket launcher carried by soldiers

for use against armored vehicles. A person using a

bazooka has as much striking power as a small tank.

Armies use larger rockets to fire explosives far behind

enemy lines and to shoot down enemy aircraft. Fighter

airplanes carry rocket-powered guided missiles to

attack other planes and ground targets. Navy ships useguided missiles to attack other ships, land targets, and

planes.


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AtmosphericResearch

S i ti t


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Scientists use rockets to explore Earth'satmosphere. Sounding rockets, also called

meteorological rockets, carry such equipment asbarometers, cameras, and thermometers high into the

atmosphere. These instruments collect information

about the atmosphere and send it by radio to receiving

equipment on the ground.

Rockets also provide the power for experimental

research airplanes. Engineers use these planes in the

development of spacecraft. By studying the flights ofsuch planes as the rocket-powered X-1 and X-15,

engineers learned how to control vehicles flying many

times as fast as the speed of sound.


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Launching

probes

and satellites

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Rockets carry crewless spacecraft calledspace probes on long voyages to explore the solar

system. Probes have explored the sun, the moon, andall the planets in our solar system except Pluto. They

carry scientific instruments that gather information

about the planets and transmit data back to Earth.

Probes have landed on the surface of the moon,

Venus, and Mars.

Rockets that launch satellites and probes are

called launch vehicles. Most of these rockets have fromtwo to four stages. The stages lift the satellite to its

proper altitude and give it enough speed -- about

17,000 miles (27,000 kilometers) per hour -- to stay in

orbit.


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A space probe's speed must reach about 25,000

miles (40,000 kilometers) per hour to escape Earth's

gravity and continue on its voyage.

Engineers created the first launch vehicles by

altering military rockets or sounding rockets to carry

spacecraft. For example, they added stages to some ofthese rockets to increase their speed. Today, engineers

sometimes attach smaller rockets to a launch vehicle.

These rockets, called boosters, provide additional

thrust to launch heavier spacecraft.


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SpaceTravel

R k t


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Rockets launch spacecraft carryingastronauts that orbit Earth and travel into space. These

rockets, like the ones used to launch probes andsatellites, are called launch vehicles.

The Saturn 5 rocket, which carried astronauts to

the moon, was the most powerful launch vehicle everbuilt by the United States. Before launch, it weighed

more than 6 million pounds (2.7 million kilograms). It

could send a spacecraft weighing more than 100,000

pounds (45,000 kilograms) to the moon. The Saturn 5used 11 rocket engines to propel three stages.


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(1)LAUNCH


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Launch: technically, this is thetime that the rocket is travelling up thelaunch rod. It is not yet moving fast enough

for the fins to stabilize the flightaerodynamically. The engine ramps up tofull thrust, briefly exceeding the average

thrust in order to get the rocket up to speed(about 30 mph) before it reaches the end ofthe launch rod.


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(2)

POWERED

FLIGHT


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Powered Flight: flighttime after the rocket has left the launchrod, while the engine is still burning.During this time the rocket is a "free

body", with three forces acting on it: thethrust of the rocket, gravity (the weight ofthe rocket), and wind resistance. Of the

three forces, though, the rocket thrust isby far the dominant one.


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(3)BURN-OUT


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Burn-out: the engine runs outof propellant and the rocket is no longerunder thrust. Since it has just gotten theentire "push" from the engine, though, therocket is now moving at its highest speed- as much as 300 miles per hour. It's

going to keep going up for a while.


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(4)

COASTING

FLIGHT


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Coasting Flight: the flighttime of the rocket after the motor has burnedout. During this time the rocket remains a"free body" with two forces acting on it: gravity

and wind resistance. Because the rocket is,by design, very light, the wind resistance islarge in comparison to the weight (it caneasily be three times the weight of the rocketat peak velocity) and plays a major role in theperformance of the rocket.


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(5)EJECTION


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(6)RECOVERY


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Recovery: with the parachutedeployed, the rocket is returned gently tothe ground so it can be recovered intact

and flown again.


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BASIC

ROCKET

MOTION


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We live in a world that is defined by three

spatial dimensions and one time dimension.

Objects move within this domain in two ways. Anobject translates, or changes location, from onepoint to another. And an object rotates, or

changes its attitude. In general, the motion ofany object involves both translation and rotation.

The translations are in direct response to

external forces. The rotations are in directresponse to external torques or moments

(twisting forces).

The motion of a rocket is particularly complex


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The motion of a rocket is particularly complex

because the rotations and translations are coupled

together; a rotation affects the magnitude and direction

of the forces which affect translations. To understandand describe the motion of a rocket, we usually try to

break down the complex problem into a series of easier

problems. We can, for instance, assume that the rocket

translates from one point to another as if all the mass

of the rocket were collected into a single point called

the center of gravity. We can describe the motion of the

center of gravity by using Newton's laws of motion. Ingeneral, there are fourforces acting on the rocket; the

weight, thrust, drag and lift.

35918828 rocket propulsion flight performance

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