The use of electronics has increased after World War II. Today, military has electronic surveillance devices, jamming devices, GPS (Global positioning System) and precision weapons like guided missiles and smart bombs or GBUs (Guided Bomb Unit) which are more accurate in attacking their target then any other weapon.
Guided missiles are self-propelled air borne projectiles carrying explosive charge and guided in flight towards the target.
Missiles are broadly classified on the basis of:-
· Launch Environment Used
· Guidance Used
1) Air-launched Missiles
2) Surface-launched Missiles
a) Surface-to-Air Missiles
b) Surface-to-Surface Missiles
1 Radar Command Guidance
2 Radio Command Guidance
3 Wire Guidance
4 Inertial Guidance
5 Astro Guidance
6 Terrain Comparison Guidance (TERCOM)
Air-Launched Anti-aircraft Missile:
The air-launched anti-aircraft missile is launched from an airborne aircraft to wipe out its target.
Various parts of this missile are:-
Rocket Motor - Provides thrust to the missile by burning solid propellant material.
Target-Seeker - Searches for the target.
Electronic Guidance Control (EGC) - Guides the missile.
Control Actuation - Adjust the fins on the instruction received from EGC.
Warhead - Explosive device which destroy the target.
Umbilical Cable - Connects the missile onboard electronics with the computer of the aircraft called as ‘avionics’.
Before the launch, the pilot designates a target. The data goes to the missile guidance control. As soon as the missile is launched the target seeker is activated and it searches for the target. The rocket motor burns the solid propellant material which provides thrust to the missile. The wing of the missile provides the necessary lift and the electronic guidance control guides the missile towards the target.
Three types of guidance system are used in general:
Semi-active Radar Homing Guidance
Target has to be illuminated by a radar transmitter from parent radar. The reflected waves are received by the receiver in the nose of the aircraft.
Active Radar Homing Guidance
The missile carries it own target seeking radar. The inbuilt radar hunts for the target. This system is costlier and bulkier and is used in long range missiles also called as ‘beyond visual-range missile’ or BVR missile.
Infrared Homing Guidance
The infrared homing guidance system is mainly designed to destroy the target using infrared homing. It seeks infrared radiations available and are also called as ‘heat seeking’ missiles.
The target image appears as bright and dark shining spots which indicate the hotter and colder regions of the target. This image is called as the ‘infrared signature’ of the target. The infrared sensor array is coupled with a mechanical scanning system which scans a larger section of the sky. It continuously moves reflectors and lens to feed light to the sensors.
The guidance control system figures out position of the target based on the fluctuations in the detected infrared light.
· The Target Seeker.
The infrared sensor that will respond to the wavelength of IR radiation from aircraft are placed in a circular matrix arrangement and grouped into four arrays. An array is one sector of circle.
· Positional Information
If the infrared image falls exactly on the centre of the nose of missile, all the arrays will get IR radiations with equal intensity. When signal from any one array is stronger than other it indicates target has changed the position.
· Speed Information
If target is moving from right to left, right array will receive the image which will generate a pulse. Then the left array will receive the image and will generate a pulse. Measuring the time interval between the two pulses and calculating it with pre-calibrated values speed of target can be known.
· Distance Information
The strength of the signal diminishes as the distance between the missile and target increases. So, measuring the signal strength and comparing it with pre-calibrated values distance of target is obtained.
After calculating speed, position, distance, EGC designates control to fin actuator. Fin actuators are used to actuate the fins to steer the missile.
· Ready to fire missile
· Highly Precise
· Cost Effective
· Could be shoulder launched
· Get deflected by Flares
By - Vishal Bhatnagar