Air to Air Missile

Air-to-Air Missile

DEPARTMENT OF MECHANICAL ENGINEERING, KBN COLLEGE OF ENGINEERING, GULBARGA

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1. INTRODUCTION

At the time of the outbreak of world war, electronics was going momentum.

Its role in World War II ended as radio equipment for communication and radar, sonar

equipment for detection of hostile forces in a particular topography.

The use of electronics in combat technologies increased only after World War

II. Today the military has electronics surveillance equipment like unmanned

reconnaissance aircrafts, anti-surveillance equipment like radar jamming devices,

hand held navigational systems like global positioning systems (GPS), and precision

weapons like guided missiles and smart bombs that are far more accurate than any

other weapon in attacking their targets.

This article elucidates the technology behind air-launched anti-air crafts

guided missiles with infrared guidance systems and their basics design concepts.

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An air-to-air missile (AAM) is a guided missile fired from an aircraft for the

purpose of destroying another aircraft. It is typically powered by one or more rocket

motors, usually solid fuelled but sometimes liquid fueled. Ramjet engines, as used on

the MBDA Meteor (currently in development), are emerging as propulsion that will

enable future medium-range missiles to maintain higher average speed across their

engagement envelope.

Missiles: An Introduction

Guided missiles are self-propelled air-borne projectiles carrying an explosive

charge and guided in flight towards a target. The propulsion system, guidance system

and warhead system are the three separate systems used in guided missiles regardless

of their types.

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Fig. 1. Air-to-air missile block diagram

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2. CLASSIFICATION

Missiles are broadly classified based on the launch environment and the type

of guidance used.

Depending upon the launch environment, missiles are classifued into air

launched missiles and surface launched missiles.

Air-launched missiles are missiles launched from aircrafts. These are further

classified into air-to-air missiles and air-to-ground missiles, which are launched

against air borne targets (like planes and helicopters) and ground targets (like anti-

aircraft guns and infrastructures), respectively.

Surface launched missiles are missiles launched from surface launchers. These

sub-classified into surface-to-air and surface-to-surface missiles (ballistic missiles).

Surface-to-air missiles (like akash missiles) are used to protect territories from hostile

air attack. Ballistic missiles (like agni and prithvi) are targeted against surface targets,

launched well in to the space and then allowed to follow a ballistic trajectory over the

target at the speed of approximately 20 machs.(1 mach=330 meters/second)

Some of the classification based on the type of guidance used are radar command

guidance, radio command guidance, wire guidance, inertial guidance, astro guidance,

terrain comparision (TERCOM) guidance.

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3. AIR-LAUNCHED ANTI-AIRCRAFT MISSILES

The air launched anti-aircraft missiles is launched from an air-borne aircraft to

wipe out an enemy aircraft. Its various parts are shown in fig.1.

The rocket motor provides thrust to propel the missile through air. The wings

provide the necessary lift to keep the missile aloft. The target seeker searches for the

target. The electronic guidance control system is a computer that processes the

information from the seeker, calculates the proper course and guides the missile. The

control actuation section adjusts flight fins near the nose of the missile based on the

instructions from the guidance control system. The flight fins ateer the missile

through the air when required. The warhead system is a explosive device that actually

destroys the enemy aircraft.

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A battery provides power to the on board electronics. An umbilical cable is

used to connect the onboard electronic guidance control system of the missile with the

aircraft’s computer system called ‘avionics’.

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4. WORKING OF THE MISSILE SYSTEM

A typical attack sequence has the following steps. Before launch, the missile is

fixed to launcher mounted in a hanger in one of the aircraft’s wings. When the pilot

has positioned the aircraft ideally behind the enemy, he activates the fire controller to

fire the missile. The avionics of the aircraft sends a command to the missile control

system to activate the rocket motor. The rocket motor burns up a solid propellant

material to generate a high pressure gas that streams out of the back of the missile.

This provides the necessary thrust to the missile to get off the launcher and fly

through the air at supersonic speeds.

Once the propellent has burnt up, the missile glides the rest of the way towards

its target. The wings provide the necessary lift to keep the missile flying. The onboard

electronic guidance control system controls the missile’s course.

Three different types of guidance systems are used in general, namely, semi-

active radar homing guidance system, active radar homing guidance system and

infrared homing guidance system.

In the active radar homing guidance system, the target has to be illuminated by

a radar transmitter from a parent plane for the radar receiver in the nose of the missile

since the radar transmitter will not be present in the missile (see fig-2). The missile

will home on (also called as ‘lock on’) the reflected radar signal with the help of the

inbuilt radar receiver.

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After firing the missile, the pilot has to keep his aircraft at a vulnerable

position for a possible enemy fire and can’t perform any evasive manoeuvre to defend

him from that fire since his manoeuvres will release the missile from the radar lock to

loose the target.

Fig-3 shows the active radar homing guidance system. In this system, the missile

carries its own target-seeking radar (both the transmitter and receiver ). The inbuilt

radar hunts for the target and locks on the target. This missile system is used only for

long-range missiles called as ‘beyond-visual-ranging air-to-air missiles’ and is costlier

and bulkier.

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The infrared homing guidance system is mainly designed to destroy aircraft

using infrared homing. Every hot body emits electromagnetic radiations and

depending upon the temperature of the hot body, the domination of the particular

frequency in the radiation varies. Due to the higher temperature of the engine of the

air-craft, electromagnetic signals are emitted. These radiations fall in the wavelength

regions of red and infrared in the electromagnetic spectrum. Infrared radiations are

also possible from various regions of the aircraft due to factors like friction due to the

air and refraction of sunlight. The various sections of the airframe of an aircraft that

may lead to infrared emission are shown in the fig.4.

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The infrared homing guidance system seeks for infrared radiations available

mainly from the exhaust of the target aircraft due to higher engine heat and

consequently these missiles are called ‘IR missiles’ or ‘heat seeking missiles’. An

infrared missile in pursuit of the target is shown in fig.5.

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5. INFRARED TRACKING

To sense IR emissions from the plane, the infrared seeker is fixed at the nose

of the missile. The target aircraft’s exhausts appear as bright shining spots with a dark

background in the aircraft’s infrared signature, which will be seen by the IR seeker.

The infrared signature of an aircraft along with its visual signature is shown in fig.6.

The infrared signature consists of ‘hot’ and ‘not hot’ regions. The ‘hot’ regions

appear as bright spots in a dark background of ‘not hot’ regions in the infrared

signature contrasting the visual signature, which have black and white spots. The

missiles guidance system uses the data from the infrared sensor to decide the course.

The seeker resembles the charge coupled device (CCD) system used for

acquiring the visual image in a video camera matrix of IR sensors that generates an

electrical signal when exposed to the infrared light given off by hot objects.

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In the current missile systems, the infrared sensor array is coupled with a

mechanical scanning system. The mechanical scanning system scans a larger section

of the sky which continuously moves an optical arrangement of lens and reflectors to

feed light to the sensor.

The guidance control system figures out the position of the target based on the

fluctuations in the detected infrared light. For example, if the target is to the left of the

missile, greater infrared light will be detected by the sensor when the optical

arrangement is aimed to the left than the right.

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6. HOW THE GUIDANCE SYSTEM WORKS

When the missile is fired, the autopilot system is engaged, whose job is to

keep the infrared image of the target aircraft roughly centred on the seeker so that the

missile nose continues to point toward the target. While flying, if the image of the

target becomes off centred on the seeker, the signals from the sensor indicate that the

missile is off-course, and the guidance control system has to decide the new course

and that is done using the proportional navigation technique.

The guidance control system looks at the angle of off-centredness and changes

its angle of flight proportionally. In other words it uses a multiplication factor. If it is

‘2’ and if the missile is 10 degrees off course, it will alter the course by 20 degrees. A

tenth of a second later it will look at the angle and correct.

The course of the missile is corrected with the help of the servo arrangement

that includes a gas generator that feeds high pressure gas to pneumatic pistons. The

pistons can be connected to the fins, that can be tilted.

The command signal from guidance control activates the electric solenoids,

which open and close valves leading to these pistons in order to tilt the fins to steer

the missile towards the direction of the movement of the target. The working of the

control system is intelligent in that anticipating the position of the target and guiding

the missile to the point of interception are similar to a player throwing a ball to a point

where the running catcher will be arriving.

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7. SIMPLIFIED GUIDANCE SYSTEM

Guidance system can be designed for a simple mode of operation and one such

system is shown in fig.7. These systems are not in practice since they include lot of

other parameters apart from the given ones. The rocket motor management and

warhead managements are not included in this discussion.

The target seeker: The infrared sensor that will respond to the wavelength of IR

radiations from the aircraft are to be placed in the noise of the missile in a circular

matrix arrangement as a target seeker and grouped in to four arrays. An array is one

quarter of the circle and this possible arrangement is shown in fig.8. From this

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arrangement, positional information of target, distance of the target from the missile

and the speed of the movement of the target could be derived.

Positional information:

In an instant if the infrared image falls exactly on the center of the nose of the

missile, all the arrays will get IR radiations with equal intensity and produce an equal

amount of signal.

When the signal from any one of the arrays is stronger, the difference in the

signal strength indicates that the infrared image has moved. For example, when array-

1 produces a signal that is stronger than the signals from the other arrays, it indicates

that the target is increasing its altitude. Similarly, if array-3 is getting a stronger

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signal, it indicates that the target is moving to the right of the missile. If the signal

from array-1 and array-3 is stronger, it specifies that the target is moving to the right

of the missile at a higher altitude.

More accurate positional information could be acquired by escalating the number of

arrays in the design of the target seeker. Instead of designating an array as a quarter of

the circle designating it as a sector of a circle will give more arrays.

Speed information: when the missile is in pursuit of a target from the side of

the target, the speed of the movement of target can also be calculated.

For example, when the missile is traveling perpendicular to the target’s left

and the target is moving from right to left of the missile, arrays 3 and 4 will get

stronger signals (see fig.9). As the target travels, the image will be on array-3 for

some time leading to generation pulse from array-3. Then the image moves to array-4

and produces a pulse from array-4. The time interval between these pulse depends on

the speed of the movement of the target. Measuring the time interval between these

pulse and comparing it with precalibrated standard values will give the actual speed of

the target and the direction of the movement the target.

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Distance information: The strength of the signal diminishes as the distance between

the missile and the target increases due to smaller infrared image. So measuring the

signal strength and comparing it with the precalibrated values will give the distance

of the target from the missile.

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8. WORKING OF SIMPLIFIED GUIDANCE SYSTEM

The signals from the individual sensors of the array are added to form a single

signal from the array. Four such blocks for the four arrays are used to feed the signal

from the seeker to the guidance controller, which could be a microprocessor.

After calculating the positional, speed and distance factors for the signal from

the four arrays, the microprocessor designates control signals to the fin actuators. Fin

actuators are used to actuate the fins to steer the missile. Fin positional sensors are

used to indicate fin positions to the guidance controller and a closed loop of control is

established to actuate the fins to the correct positions by the referring to the signals

from fin positional sensors.

A set of the fin actuator and a fin positional sensor is needed for one fin and

hence four sets are required for four fins. In real time, the guidance controller gets the

data from the target seeker and steers the missile until interception is achieved.

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10. APPLICATIONS

• AIM-9 Sidewinder

• Python 4

• Helmet Mounted Sights

• High Off-Boresight Missiles (HOBSM)

• Missile Links

AIM-9 Sidewinder

The Sidewinder Story

The Evolution of the AIM-9 Missile

by Carlo Kopp

Published in Australian Aviation, April, 1994

© 1994, 1997 Carlo Kopp

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Python 4

Fourth Generation AAMs - The Rafael Python 4

by Carlo Kopp

Published in Australian Aviation, April, 1997

© 1997 Carlo Kopp

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Helmet Mounted Sights:

Joint Helmet Mounted Cueing System

(JHMCS)

• Joint Helmet Mounted Cueing System

(JHMCS)

• Joint Helmet Mounted Cueing System

(VSI)

• JHMCS (GlobalSecurity.org)

• JHMCS/AIM-9X images from Elmendorf

• The JHMCS Operational Flight Program

• JHMCS Canadian Update

Elbit DASH Series:

• Elbit Systems Ltd.

General Helmet Mounted Sights Info:

• Helmet-Mounted Displays and Sights

• FLUG REVUE March 1997: Helmet displays for fighter pilots

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Air-to-air Missile Links:

AIM-132 ASRAAM

• AIM-132 ASRAAM (FAS)

• AIM-132 ASRAAM - Wikipedia

• ASRAAM (RAF)

• ASRAAM (UK MoD)

• ASRAAM enters RAAF

• EADS ASRAAM

• MBDA ASRAAM

• MBDA ASRAAM

• MBDA ASRAAM

AIM-7 SPARROW

• AIM-7 Sparrow (USAF)

• AIM-7 Sparrow

• AIM-7 Sparrow - Wikipedia

• The Sparrow Missile (FAS)

AIM-9 SIDEWINDER

• Sidewinder Story (On our site)

• Navy Fact File: AIM-9 Sidewinder

Missile

• AIM-9 Sidewinder (USAF)

• AIM-9X (Raytheon)

• AIM-9X (GlobalSecurity.org)

• AIM-9X ahieves IOC

• AIM-9X makes operational debut

• F-16's first AIM-9X launch

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IRIS-T

• BGT IRIS-T

• BGT/SAAB/Alenia IRIS-T

Matra Magic

• Matra R.550 Magic

(GlobalSecurit.org)

• Matra 550 Magic 2

METEOR

• MBDA Meteor

• Meteor BVRAAM (GlobalSecurity.org)

•

MICA

• EADS MICA

• MBDA MICA

• MICA RF/IR

• Missile MICA

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9. MERITS OF IR MISSILES

Unquestionably, IR missiles are highly decisive and the latest system used

some UV sensing along with IR sensing to ignore flares. Man portable air defence

systems (MANPAD) also used these IR missiles, which are shoulder- launched by the

user from any kind of terrain.examples of the kind are STINGER missiles of

American origin, and IGLA and STERLA missile of Russian origin.

These missiles are used by the terrorist organizations and pose a serious threat to

the commercial airlines, which are more vulnerable due to the absence of any flare

dispensing systems to protect themselves from the attacking missiles.

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10. DEMERITS OF IR MISSILES

IR missiles are highly efficient but can be easily evade by flares. Flares

generate extreme heat away from the aircraft to divert the IR missile. These flares

emit IR radiations of the same wavelength as the aircraft engines and hence a cluster

of flares released from the target aircraft can easily confuse these missiles. Fig.10

shows an airplane releasing flares for evading the IR missile.

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11. CONCLUSION

More modern infra-red guided missiles can detect the heat of an aircraft's skin,

warmed by the friction of airflow, in addition to the fainter heat signature of the

engine when the aircraft is seen from the side or head-on. This, combined with greater

maneuverability, gives them an "all-aspect" capability, and an attacking aircraft no

longer had to be behind its target to fire. Although launching from behind the target

increases the probability of a hit, the launching aircraft usually has to be closer to the

target in a tail-chase engagement.

An aircraft can defend against infra-red missiles by dropping flares that are

hotter than the aircraft, so the missile homes in on the brighter, hotter target. Towed

decoys and infra-red jammers can also be used. Some large aircraft and many combat

helicopters make use of so called "hot brick" infra-red jammers, typically mounted

near the engines. Current research is developing laser devices which can spoof or

destroy the guidance systems of infra-redguided missiles.

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REFERENCES

1. Air to Air Missiles –Author- James vol-6

2. Grinning Rhino and was make availably by Mark @

http://www.militaryid.com/

3. WWW.guided\Air-to-Air Missiles.com

4. WWW.Efymag.com

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CONTENTS

SL. NO. PARTICULARS PAGE

NO. 1. INTRODUCTION 01

2. CLASSIFICATION 04

3. AIR-LAUNCHED ANTI-AIRCRAFT MISSILES 05

4. WORKING OF THE MISSILE SYSTEM 07

5. INFRARED TRACKING 11

6. HOW THE GUIDANCE SYSTEM WORKS 13

7. SIMPLIFIED GUIDANCE SYSTEM 14

8. WORKING OF SIMPLIFIED GUIDANCE SYSTEM 18

9. APPLICATIONS 19

10. MERITS OF IR MISSILES 24

11. DEMERITS OF IR MISSILES 25

12. CONCLUSION 26

REFERENCES 27

Documents

Air to Air Missile