hi am Prafull more i would like to get details on ppt for seminar topic laser guided vehicle.....

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.

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.

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.
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.

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.

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.

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.