RE: Guided Missiles
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Guided Missile is a self-propelled aerial projectile, containing conventional or nuclear explosives, guided in flight towards a target either by radio signals or by internal mechanisms.
(self-propelled guided weapon system)
AREA OF OPERATION:
GUIDANCE AND CONTROL
It is a method of propelling an object(missile) forward and maintaining its motion.
The motion of missile propulsion depends on the following two laws:
Newton’s third law of motion
Law of conservation of momentum
Types of propulsion:
Atmospheric jet propulsion
Thermal jet propulsion
ATMOSPHERIC JET PROPULSION
The atmospheric (air breathing) jet engine depends on the atmosphere to supply the oxygen necessary to start and sustain burning of the fuel.
There are two types of atmospheric jet propulsion systems
Turbojet engine and
A typical turbojet engine includes
an air intake,
a mechanical compressor driven by a turbine,
a combustion chamber and
an exhaust nozzle.
The ramjet engine is a properly shaped duct.
The pressure rise in the engine is achieved by the ram effect of the incoming air being rammed against the barrier.
THERMAL JET PROPULSION
In thermal jet propulsion , propellants used are basically chemicals, which produces high amount of energy on burning.
They are classified based on the physical state of the propellant used as:
Solid propellants are used to propel the missile.
E.g. (Fuel + Oxidizer)
Asphalt +potassium perchlorate
Al + Ammonium perchlorate
Easy to design, ensures safety.
Thrust cannot be controlled.
Once ignited, the engine cannot be stopped or restarted.
Liquid propellants are used to propel the missiles.
Both fuel and oxidizer are in the liquid state.
e.g.: (fuel + oxidizer)
Liquid hydrogen + liquid oxygen
Gasoline + liquid oxygen
Alcohol + liquid oxygen
Controlling, stopping and starting the
combustion is very easy.
Storage of the propellants is difficult.
Require complicated piping and pumping
equipment to feed the engines
GUIDANCE AND CONTROL SYSTEM
The purpose of a guidance and control system is to direct the missile to target intercept regardless of whether or not the target takes deliberate evasive action.
The guidance function is based on
Information provided by a signal from the target and
Information sent from the launching station.
Every missile guidance system contains two systems:
An altitude control system and
A flight path control system.
The altitude control system maintains the missile in the desired altitude by controlling it in pitch, roll and yaw.
The flight path control system guides the missile to its designated target by determining the flight path errors, generating the necessary corrections and sending them to the missile’s control subsystem.
PHASES OF GUIDANCE
Missile guidance is divided into three phases namely
Missiles are boosted to flight speed by the booster component of the propulsion system.
The boost period lasts from the time the missile leaves the launcher until the booster burns up its fuel.
In missiles with separate boosters, the booster drops away from the missile at burnout.
Midcourse guidance is used to put the missile near the target, where the final phase of guidance can take control.
The terminal phase of missile guidance must have a high degree of accuracy, as well as fast response to guidance signals to ensure an intercept.
Near the end of the flight, the missile may be required to maneuver to its maximum capability in order to make the sharp turns needed to overtake and hit a fast-moving, evasive target.
TYPES OF GUIDANCE SYSTEMS
The guidance systems used in guided missiles are:
An inertial guidance system is one that is designed to fly a predetermined path.
The missile is controlled by self-contained automatic devices called accelerometers (devices that measure accelerations).
In missile control, they measure the vertical, lateral, and longitudinal accelerations of the controlled missile.
Although there may not be contact between the launching site and the missile after launch, the missile can make corrections to its flight path with precision.
It is a type of command guidance in which the missile seeks out the center of a controlled directional radar beam.
The missile's guidance system receives information concerning the position of the missile within the beam and generates its own correction signals, which keep the missile in the center of the beam.
The accuracy of the beam-rider decreases as the range between the missile and the ship increases, therefore, are effective against only short- and medium-range incoming targets.
Homing guidance systems control the path of the missile by
means of a device in the missile that detects and reacts to some
distinguishing feature of (or signal from) the target.
(light, radio, heat, sound waves, or even a magnetic field)
The homing missiles use radar waves to locate the target.
Since the system tracks a characteristic of the target or energy
reflecting off the target, contact between the missile and target is
established and maintained.
Homing guidance methods are normally divided into three types:
semi-active homing and
In the active homing system, target illumination is supplied by a component carried in the missile, such as a radar transmitter.
(target’s distance and speed)
(correct angle of attack to intercept)
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.
In the passive homing system, the directing intelligence is received from the target.
Examples of passive homing include
Infrared rays (such as the hot exhaust of jet aircraft)
Radar signals (such as those transmitted by ground radar installations).
TERCOM GUIDANCE (TERRAIN COUNTER MATCHING)
The system uses radar to scan the ground/terrain that the missile is passing over. The terrain data is compared to the digital maps stored in the computer on the missile.
These stored digital maps are of the area along the intended flight path of the missiles and are gathered by satellites.
If a drift is noticed, the inertial navigation system is corrected and a course correction is made to put the missile back on path.
Missiles fly very low.
Undetectable by enemy radar.
Reduces drift of the missile.
The explosive payload carried by weapons intended for use in combat, delivered by a missile is known as a warhead.
Types of warheads include:
Explosive: An explosive charge is used to disintegrate the target, and damage surrounding areas with a shock wave.
Conventional: Chemicals such as gunpowder store significant energy within their molecular bonds. This energy can be released quickly by a trigger and an electric spark.
Nuclear: A run away nuclear fission or nuclear fusion reaction causes immense energy release.
Chemical : A toxic chemical, such as poisonous gas, is dispersed, which is designed to injure or kill human beings.
Biological: An infectious agent, such as anthrax spores, is dispersed, which is designed to sicken or kill humans.
Kinetic : Collides with the target at high speed. A detonation is not necessarily required.