09-05-2014, 02:07 PM
ADAPTIVE MISSILE GUIDANCE USING GPS
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ABSTRACT :
In the modern day theatre of combat, the need to be able to strike at targets that
are on the opposite side of the globe has strongly presented itself. This had led to the
development of various types of guided missiles. These guided missiles are self -guiding weapons
intended to maximize damage to the target while minimizing collateral damage. The buzzword in
modern day combat is fire and forget. GPS guided missiles, using the exceptional navigational
and surveying abilities of GPS, after being launched, could deliver a warhead to any part of the
globe via the interface pof the onboard computer in the missile with the GPS satellite system.
Under this principle many modern day laser weapons were designed. Laser
guided missiles use a laser of a certain frequency bandwidth to acquire their target. GPS/inertial
weapons are oblivious to the effects of weather, allowing a target to be engaged at the time of the
attacker's choosing. GPS allows accurate targeting of various military weapons including
ICBMs, cruise missiles and precision-guided munitions. Artillery projectiles with embedded
GPS receivers able to withstand accelerations of 12,000 G have been developed for use in 155
mm. GPS signals can also be affected by multipath issues, where the radio signals reflect off
surrounding terrain; buildings, canyon walls, hard ground , etc. These delayed signals can cause
inaccuracy. A variety of techniques, most notably narrow correlator spacing, have been
developed to mitigate multipath errors. Multipath effects are much less severe in moving
vehicles. When the GPS antenna is moving, the false solutions using reflected signals quickly
fail to converge and only the direct signals result in stable solutions. The multiple independently
targeted re-entry vehicles (MIRVs) – ICBMs with many sub-missiles – were developed in the
late 1960s. The cruise missile has wings like an airplane, making it ca pable of flying at low
altitudes. In summary, GPS-INS guided weapons are not affected by harsh weather conditions or
restricted by a wire, nor do they leave the gunner vulnerable for attack. GPS guided weapons,
with their technological advances over previous, are the superior weapon of choice in modern
day warfare.
INTRODUCTION :
Introduction to missile guidance :
Guided missile systems have evolved at a tremendous rate over the past four decades, and recent
breakthroughs in technology ensure that smart warheads will have an increasing role in
maintaining our military superiority. On ethical grounds, one prays that each warhead deployed
during a sortie will strike only its intended target, and that innocent civilians will not be harmed
by a
misfire. From a tactical standpoint, our military desires weaponry that is reliable and effective,
inflicting maximal damage on valid military targets and ensuring our capacity for light ingfast
strikes with pinpoint accuracy. Guided missile systems help fulfill all of these demands.
Concept of missile guidance :
Missile guidance concerns the method by which the missile receives its commands to move
along a certain path to reach a target. On some missiles, these commands are generated internally
by the missile computer autopilot. On others, the commands are transmitted to the missile by
Some external source.
Fig 1.1 Concept of missile guidance
The missile sensor or seeker, on the other hand, is a component within a missile that generates
data fed into the missile computer. This data is processed by the computer and used to generate
guidance commands. Sensor types commonly used today include infrared, radar, and the global
positioning system. Based on the relative position between the missile and the target at any given
point in flight, the computer autopilot sends commands to the control surfaces to adjust the
missile's course.
Mechanical, fiber optic, and ring laser gyroscopes
The purpose of a gyroscope i s to measure angular rotation, and a number of different
Methods to do so have been devised. A classic mechanical gyroscope senses the stability of a
mass rotating on gimbals. More recent ring laser gyros and fiber optic gyros are based on the
interference between laser beams. Current advances in Micro-Electro-Mechanical Systems
(MEMS) offer the potential to develop gyroscopes that are very small and inexpensive While
gyroscopes measure angular motion, accelerometers measure linear motion. The accelerations
from these devices are translated into electrical signals for processing by the missile computer
autopilot. When a gyroscope and an accelerometer are combined into a single device along with
a control mechanism, it is called an inertial measurement unit (IMU) or inertial navigation