laser guided missiles by karthik

LASER GUIDED MISSILES

1. INTRODUCTION

Laser guidance is a technique of guiding a missile or other projectile or vehicle to a target

by means of a laser beam. Some laser guided systems utilize beam riding guidance, but most

operate more similarly to semi-active radar homing (SARH). This technique is sometimes called

SALH, for Semi-Active Laser Homing. With this technique, a laser is kept pointed at the target

and the laser radiation bounces off the target and is scattered in all directions (this is known as

“painting the target”, or “laser painting”). The missile, bomb, etc. is launched or dropped

somewhere near the target. When it is close enough that some of the reflected laser energy from

the target reaches it, a laser seeker detects which direction this energy is coming from and adjusts

the projectile trajectory towards the source. As long as the projectile is in the general area and the

laser is kept aimed at the target, the projectile should be guided accurately to the target.

Note that laser guidance is not useful against targets that do not reflect much laser energy,

including those coated in special paint which absorbs laser energy. This is likely to be widely

used by advanced military vehicles in order to make it harder to use laser rangefinders against

them and harder to hit them with laser- guided missiles. An obvious circumvention would be to

aim the laser merely close to the target.

Dept. of Mechanical Engg., B.I.E.T., Davangere.


2. BACKGROUND

Missiles differ from rockets by virtue of a guidance system that steers them towards a

pre-selected target. Unguided, or free-flight, rockets proved to be useful yet frequently

inaccurate weapons when fired from aircraft during the World War II. This inaccuracy, often

resulting in the need to fire many rockets to hit a single target, led to the search for a means to

guide the rocket towards its target. The concurrent explosion of radio-wave technology (such as

radar and radio detection devices) provided the first solution to this problem. Several warring

nations, including the United States, Germany and Great Britain mated existing rocket

technology with new radio- or radar-based guidance systems to create the world's first guided

missiles. Although these missiles were not deployed in large enough numbers to radically divert

the course of the World War II, the successes that were recorded with them pointed out

techniques that would change the course of future wars. Thus dawned the era of high-technology

warfare, an era that would quickly demonstrate its problems as well as its promise.

The problems centered on the unreliability of the new radio-wave technologies. The

missiles were not able to hone in on targets smaller than factories, bridges, or warships. Circuits

often proved fickle and would not function at all under adverse weather conditions. Another flaw

emerged as jamming technologies flourished in response to the success of radar. Enemy jamming

stations found it increasingly easy to intercept the radio or radar transmissions from launching

aircraft, thereby allowing these stations to send conflicting signals on the same frequency,

jamming or "confusing" the missile. Battlefield applications for guided missiles, especially those

that envisioned attacks on smaller targets, required a more reliable guidance method that was less

vulnerable to jamming. Fortunately, this method became available as a result of an independent

research effort into the effects of light amplification.



Dr. Theodore Maiman built the first laser (Light Amplification by Stimulated Emission of

Radiation) at Hughes Research Laboratories in 1960. The military realized the potential

applications for lasers almost as soon as their first beams cut through the air. Laser guided

projectiles underwent their baptism of fire in the extended series of air raids that highlighted the

American effort in the Vietnam War. The accuracy of these weapons earned them the well-

known sobriquet of "smart weapons." But even this new generation of advanced weaponry could

not bring victory to U.S. forces in this bitter and costly war. However, the combination of

experience gained in Vietnam, refinements in laser technology, and similar advances in

electronics and computers, led to more sophisticated and deadly laser guided missiles. They

finally received widespread use in Operation Desert Storm, where their accuracy and reliability

played a crucial role in the decisive defeat of Iraq's military forces. Thus, the laser guided missile

has established itself as a key component in today's high-tech military technology.



3. SEMI ACTIVE RADAR HOMING

Semi-active radar homing, or SARH, is a common type of missile guidance system,

perhaps the most common type for longer range air to air and surface-to-air missile systems. The

name refers to the fact that the missile itself is only a passive detector of a radar signal –

provided by an external (“off board”) source — as it reflects off the target. The basic concept of

SARH is that since almost all detection and tracking systems consist of a radar system,

duplicating this hardware on the missile itself is redundant. In addition, the resolution of a radar

is strongly related to the physical size of the antenna, and in the small nose cone of a missile

there isn't enough room to provide the sort of accuracy needed for guidance. Instead the larger

radar dish on the ground or launch aircraft will provide the needed signal and tracking logic, and

the missile simply has to listen to the signal reflected from the target and point itself in the right

direction. Additionally, the missile will listen rearward to the launch platform's transmitted

signal as a reference, enabling it to avoid some kinds of radar jamming distractions offered by

the target. Contrast this with beam riding systems, in which the radar is pointed at the target and

the missile keeps itself centered in the beam by listening to the signal at the rear of the missile

body. In the SARH system the missile listens for the reflected signal at the nose, and is still

responsible for providing some sort of “lead” guidance. The disadvantages are twofold: One is

that a radar signal is “fan shaped”, growing larger, and therefore less accurate, with distance.

This means that the beam riding system is not accurate at long ranges, while SARH is largely

independent of range and grows more accurate as it approaches the target, or the source of the

reflected signal it listens for. Another requirement is that a beam riding system must accurately

track the target at high speeds, typically requiring one radar for tracking and another “tighter”

beam for guidance. The SARH system needs only one radar set to a wider pattern.


http://www.answers.com/topic/beam-riding

http://www.answers.com/topic/angular-resolution

http://www.answers.com/topic/radar

http://en.wikipedia.org/wiki/Passive_radar

http://en.wikipedia.org/wiki/Surface-to-air_missile


4. MISSILE COMPONENTS

Guided missiles are made up of a series of subassemblies. The various subassemblies

form a major section of the overall missile to operate a missile system, such as guidance, control,

armament (warhead and fuzing), and propulsion. The major sections are carefully joined and

connected to each other. They form the complete missile assembly. The arrangement of major

sections in the missile assembly varies, depending on the missile type.

The guidance section is the brain of the missile. It directs its maneuvers and causes the

maneuvers to be executed by the control section. The armament section carries the explosive

charge of the missile, and the fuzing and firing system by which the charge is exploded. The

propulsion section provides the force that propels the missile.

4.1. Guidance and Control Section

The complete missile guidance system includes the electronic sensing systems that

initiate the guidance orders and the control system that carries them out. The elements for missile

guidance and missile control can be housed in the same section of the missile, or they can be in

separate sections.



Fig 1: Missile components

There are a number of basic guidance systems used in guided missiles. Homing-type, air-

launched, guided missiles are currently used. They use radar or infrared homing systems. A

homing guidance system is one in which the missile seeks out the target, guided by some

physical indication from the target itself. Radar reflections or thermal characteristics of targets

are possible physical influences on which homing systems are based. Homing systems are

classified as active, semiactive, and passive.



4.2. ACTIVE

In the active homing system, target illumination is supplied by a component carried in the

missile, such as a radar transmitter. The radar signals transmitted from the missile are reflected

off the target back to the receiver in the missile. These reflected signals give the missile

information such as the target's distance and speed. This information lets the guidance section

compute the correct angle of attack to intercept the target. The control section that receives

electronic commands from the guidance section controls the missile’s angle of attack.

Mechanically manipulated wings, fins, or canard control surfaces are mounted externally on the

body of the weapon. They are actuated by hydraulic, electric, or gas generator power, or

combinations of these to alter the missile's course.

Fig 2: Active homing system

4.3. SEMIACTIVE

In the semi active homing system, the missile gets its target illumination from an external

source, such as a transmitter carried in the launching aircraft. The receiver in the missile receives

the signals reflected off the target, computes the information, and sends electronic commands to

the control section. The control section functions in the same manner as previously discussed.



Fig 3: Semi active homing system

4.4. PASSIVE

In the passive homing system, the directing intelligence is received from the target.

Examples of passive homing include homing on a source of infrared rays (such as the hot

exhaust of jet aircraft) or radar signals (such as those transmitted by ground radar installations).

Like active homing, passive homing is completely independent of the launching aircraft. The

missile receiver receives signals generated by the target and then the missile control section

functions in the same manner as previously discussed.

Fig 4: Passive homing system



4.5 ARMAMENT SECTION

The armament system contains the payload (explosives), fuzing, safety and arming

(S&A) devices, and target-detecting devices (TDDs).

4.5.1 PAYLOAD

The payload is usually considered the explosive charge, and is carried in the warhead of

the missile. High-explosive warheads used in air-to-air guided missiles contain a rather small

explosive charge, generally 10 to 18 pounds of H-6, HBX, or PBX high explosives. The payload

contained in high-explosive warheads used in air-to-surface guided missiles varies widely, even

within specific missile types, depending on the specific mission. Large payloads, ranging up to

450 pounds, are common. Comp B and H-6 are typical explosives used in a payload. Most

exercise warheads used with guided missiles are pyrotechnic signaling devices. They signal fuze

functioning by a brilliant flash, by smoke, or both. Exercise warheads frequently contain high

explosives, which vary from live fuzes and boosters to self-destruct charges that can contain as

much as 5 pounds of high explosive.

4.5.2 Fusing

The fuzing and firing system is normally located in or next to the missile's warhead

section. It includes those devices and arrangements that cause the missile's payload to function in

proper relation to the target. The system consists of a fuze, a safety and arming (S&A) device, a

target-detecting device (TDD), or a combination of these devices. There are two general types of

fuzes used in guided missiles—proximity fuzes and contact fuzes. Acceleration forces upon

missile launching arm both fuzes. Arming is usually delayed until the fuze is subjected to a given

level of accelerating force for a specified amount of time. In the contact fuze, the force of impact

closes a firing switch within the fuze to complete the firing circuit, detonating the warhead.

Where proximity fuzing is used, the firing action is very similar to the action of proximity fuzes

used with bombs and rockets.



4.5.3 Safety And Arming (S&A) Devices:

S&A devices are electromechanical, explosive control devices. They maintain the

explosive train of a fuzing system in a safe (unaligned) condition until certain requirements of

acceleration are met after the missile is fired.

4.5.4 Target-Detecting Devices (TDD):

TDDs are electronic detecting devices similar to the detecting systems in VT fuzes. They

detect the presence of a target and determine the moment of firing. When subjected to the proper

target influence, both as to magnitude and change rate, the device sends an electrical impulse to

trigger the firing systems. The firing systems then act to fire an associated S&A device to initiate

detonation of the warhead. Air-to-air guided missiles are normally fuzed for a proximity burst by

using a TDDwith an S&A device. In some cases, a contact fuze may be used as a backup. Air-to-

surface guided missile fuzing consists of influence (proximity) and/or contact fuzes. Multifuzing

is common in these missiles.

4.5.5 Propulsion Section

Guided missiles use some form of jet power for propulsion. There are two basic types of

jet propulsion power plants used in missile propulsion systems—the atmospheric (air-breathing)

jet and the thermal jet propulsion systems. The basic difference between the two systems is that

the atmospheric jet engine depends on the atmosphere to supply the oxygen necessary to start

and sustain burning of the fuel. The thermal jet engine operates independently of the atmosphere

by starting and sustaining combustion with its own supply of oxygen contained within the

missile.

Atmospheric jet propulsion system.

There are three types of atmospheric jet propulsion systems—the turbojet, pulsejet, and

ramjet engines. Of these three systems, only the turbojet engine is currently being used in Navy



air-launched missiles. A typical turbojet engine includes an air intake, a mechanical compressor

driven by a turbine, a combustion chamber, and an exhaust nozzle. The engine does not require

boosting and can begin operation at zero acceleration.

Thermal Jet Propulsion System

Thermal jets include solid propellant, liquid propellant, and combined propellant systems.

As an AO, you come in contact with all three systems. The solid propellant and combined

propellant systems are currently being used in some air-launched guided missiles. The majority

of air-launched guided missiles used by the Navy use the solid propellant rocket motor. They

include the double base and multibase smokeless powder propellants as well as the composite

mixtures. Grain configurations vary with the different missiles. Power characteristics and

temperature limitations of the individual rocket motors also vary. In some guided missiles,

different thrust requirements exist during the boost phase as compared to those of the sustaining

phase. The dual thrust rocket motor (DTRM) is a combined system that contains both of these

elements in one motor. The DTRM contains a single propellant grain made of two types of solid

propellant—boost and sustaining. The grain is configured so the propellant meeting the

requirements for the boost phase burns at a faster rate than the propellant for the sustaining

phase. After the boost phase propellant burns itself out, the sustaining propellant sustains the

motor in flight over the designed burning time (range of the missile).



5. MISSILE CONTROL SYSTEM

The heart of a missile is the body, equivalent to the fuselage of an aircraft. The missile body

contains the guidance and control system, warhead, and propulsion system. Some missiles may

consist of only the body alone, but most have additional surfaces to generate lift and provide

maneuverability. Depending on what source you look at, these surfaces can go by many names.

In particular, many use the generic term "fin" to refer to any aerodynamic surface on a missile.

Missile designers, however, are more precise in their naming methodology and generally

consider these surfaces to fall into three major categories: canards, wings, and tail fins.

Fig 5: Components of a missile

The example shown above illustrates a generic missile configuration equipped with all

three surfaces. Often times, the terms canard, wing, and fin are used interchangeably, which can

get rather confusing. These surfaces behave in fundamentally different ways, however, based

upon where they are located with respect to the missile center of gravity. In general, a wing is a



relatively large surface that is located near the center of gravity while a canard is a surface near

the missile nose and a tail fin is a surface near the aft end of the missile.

Most missiles are equipped with at least one set of aerodynamic surfaces, especially tail

fins since these surfaces provide stability in flight. The majority of missiles are also equipped

with a second set of surfaces to provide additional lift or improved control. Very few designs are

equipped with all three sets of surfaces. Most aircraft have fixed horizontal and vertical tails with

smaller movable rudder and elevator surfaces, missiles typically use all-moving surfaces, like

those illustrated below, to accomplish the same purpose.

Fig 6: Deflection of a control surface of missile

In order to turn the missile during flight, at least one set of aerodynamic surfaces is

designed to rotate about a center pivot point. In so doing, the angle of attack of the fin is changed

so that the lift force acting on it changes. The changes in the direction and magnitude of the

forces acting on the missile cause it to move in a different direction and allow the vehicle to

maneuver along its path and guide itself towards its intended target.



6. THE MANUFACTURING PROCESS

6.1. Raw Materials

Fig 7: Construction of missile body

A laser guided missile consists of four important components, each of which contains

different raw materials. These four components are the missile body, the guidance system (also

called the laser and electronics suite), the propellant, and the warhead. The missile body is made

from steel alloys or high-strength aluminum alloys that are often coated with chromium along the

cavity of the body in order to protect against the excessive pressures and heat that accompany a

missile launch. The guidance system contains various types of materials—some basic, others

high-tech—that are designed to give maximum guidance capabilities.

These materials include a photo detecting sensor and optical filters, with which the

missile can interpret laser wavelengths sent from a parent aircraft. The photo detecting sensor's

most important part is its sensing dome, which can be made of glass, quartz, and/or silicon. A



missile's electronics suite can contain gallium-arsenide semiconductors, but some suites still rely

exclusively on copper or silver wiring. Guided missiles use nitrogen-based solid propellants as

their fuel source. Certain additives (such as graphite or nitroglycerine) can be included to alter

the performance of the propellant. The missile's warhead can contain highly explosive nitrogen-

based mixtures, fuel-air explosives (FAE), or phosphorous compounds. The warhead is typically

encased in steel, but aluminum alloys are sometimes used as a substitute.

6.2. Constructing the body and attaching the fins

The steel or aluminum body is die cast in halves. Die casting involves pouring molten

metal into a steel die of the desired shape and letting the metal harden. As it cools, the metal

assumes the same shape as the die. At this time, an optional chromium coating can be applied to

the interior surfaces of the halves that correspond to a completed missile's cavity. The halves are

then welded together, and nozzles are added at the tail end of the body after it has been welded.

Moveable fins are now added at predetermined points along the missile body. The fins

can be attached to mechanical joints that are then welded to the outside of the body, or they can

be inserted into recesses purposely milled into the body.

6.3. Casting the propellant

The propellant must be carefully applied to the missile cavity in order to ensure a

uniform coating, as any irregularities will result in an unreliable burning rate, which in turn

detracts from the performance of the missile. The best means of achieving a uniform coating is to

apply the propellant by using centrifugal force. This application, called casting, is done in an

industrial centrifuge that is well-shielded and situated in an isolated location as a precaution

against fire or explosion.



6.4. Assembling the guidance system

The principal laser components—the photo detecting sensor and optical filters—are

assembled in a series of operations that are separate from the rest of the missile's construction.

Circuits that support the laser system are then soldered onto pre-printed boards; extra attention is

given to optical materials at this time to protect them from excessive heat, as this can alter the

wavelength of light that the missile will be able to detect. The assembled laser subsystem is now

set aside pending final assembly. The circuit boards for the electronics suite are also assembled

independently from the rest of the missile. If called for by the design, microchips are added to

the boards at this time.

The guidance system (laser components plus the electronics suite) can now be integrated

by linking the requisite circuit boards and inserting the entire assembly into the missile body

through an access panel. The missile's control surfaces are then linked with the guidance system

by a series of relay wires, also entered into the missile body via access panels. The photo

detecting sensor and its housing, however, are added at this point only for beam riding missiles,

in which case the housing is carefully bolted to the exterior diameter of the missile near its rear,

facing backward to interpret the laser signals from the parent aircraft.

6.5. Final assembly

Insertion of the warhead constitutes the final assembly phase of guided missile construction.

Great care must be exercised during this process, as mistakes can lead to catastrophic accidents.

Fig 8: Assembly of various components of missile



Simple fastening techniques such as bolting or riveting serve to attach the warhead

without risking safety hazards. For guidance systems that home-in on reflected laser light, the

photo detecting sensor (in its housing) is bolted into place at the tip of the warhead. On

completion of this final phase of assembly, the manufacturer has successfully constructed on of

the most complicated, sophisticated, and potentially dangerous pieces of hardware in use today.

6.6. Byproducts/Waste

Propellants and explosives used in warheads are toxic if introduced into water supplies.

Residual amounts of these materials must be collected and taken to a designated disposal site for

burning. Each state maintains its own policy pertaining to the disposal of explosives, and Federal

regulations require that disposal sites be inspected periodically. Effluents (liquid byproducts)

from the chromium coating process can also be hazardous. This problem is best dealt with by

storing the effluents in leak-proof containers. As an additional safety precaution, all personnel

involved in handling any hazardous wastes should be given protective clothing that includes

breathing devices, gloves, boots and overalls.



7. ADVANTAGES OF LASER GUIDED MISSILES

Laser guided weapons, such as the Lockheed Martin Hellfire, and Lahat and Nimrod,

developed by IAI/MBT offer many advantages for heliborne and airborne use. The SAL seeker

is relatively low cost, offering high precision operational flexibility, despite its adverse weather

limitations.

This concept of operation places high priority on target designation capabilities,

deployed close to the target by unmanned platforms and Special Forces. Not every laser seeker

will be suitable for the task. Only the more sophisticated missiles offer the flexibility and field of

regard ('side looking') capability adequate for effective lock-on after launch targeting. Such

capability seldom requires their seeker to be mounted on a gimbal, to achieve adequate field of

regard, something that simple, low-cost stiff-necked or static seeker assemblies may not support.

Fig 9: LAHAT laser guided missile



The LAHAT laser guided missile is lightweight weapon can be employed by light

helicopters. It can be fired at targets over distances between 8 to 13 kilometers, with devastating

effects against armor as well as softer targets. Besides its potential helicopter application,

LAHAT is considered by several armies for its original role as gun-fired laser-homing munition

for tanks. Nimrod, a much larger missile, has also been evaluated as a helicopter borne weapon.

Utilizing its extended range (over 22 km), this missile is often used in 'lock on after launch'

mode, combining inertial guidance and semiactive laser homing to strike targets at long ranges.

With the availability of such 'net centric' precision attack missiles, the role of attack

helicopters is also re- examined, and several air forces and manufacturers are already considering

using assault helicopters for some attack roles, employed either as a 'sky truck' or in direct

support, when they are fitted with target acquisition systems.



8. THE FUTURE LASER GUIDED MISSILES

Future laser guided missile systems will carry their own miniaturized laser on board,

doing away with the need for target designator lasers on aircraft. These missiles, currently under

development in several countries, are called "fire-and-forget" because a pilot can fire one of

these missiles and forget about it, relying on the missile's internal laser and detecting sensor to

guide it towards its target. A further development of this trend will result in missiles that can

select and attack targets on their own. Once their potential has been realized, the battlefields of

the world will feel the deadly venom of these "brilliant missiles" for years to come. An even

more advanced concept envisions a battle rifle for infantry that also fires small, laser guided

missiles. Operation Desert Storm clearly showed the need for laser guided accuracy, and, as a

result, military establishments dedicated to their missions will undoubtedly invent and deploy

ever more lethal versions of laser guided missiles.



9. CONCLUSION

"In World War II it could take 9,000 bombs to hit a target the size of an aircraft shelter.

In Vietnam, 300. Today we can do it with one laser-guided missile. Laser guided missile can be

fired at targets ranging 8 to 13 kilometers and some like LAHAT laser guided missile up to 22

kilometers. Though many missiles are developed, they don’t find accuracy as in the reaching the

target. Laser guided missile has be one of dangerous missile in war field in past and will be the

future.



10 BIBLIOGRAPHIES

Wikipedia.com

Howstuffworks.com

Missilesthreat.com


laser guided missiles by karthik

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