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.

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.

Many of the early guidance systems used in missiles where based on gyroscope models. Many of these models used magnets in their gyroscope to increase the sensitivity of the navigational array. In modern day warfare, the inertial measurements of the missile are still controlled by a gyroscope in one form or another, but the method by which the missile approaches the target bears a technological edge. On the battlefield of today, guided missiles are guided to or acquire their targets by using:

· Radar signal
· Wires
· Lasers (or)
· Most recently GPS.

The central idea behind the design of DGPS/GPS/inertial guided weapons is that of using a 3- axis gyro/accelerometer package as an inertial reference for the weapon's autopilot, and correcting the accumulated drift error in the inertial package by using GPS PPS/P-code. Such weapons are designated as "accurate" munitions as they will offer CEPs (Circular Error Probable) of the order of the accuracy of GPS P -code signals, typically about 40ft.

Global Positioning System used in ranging navigation guidance :

The next incremental step is then to update the weapon before launch with a DGPS derived position estimate, which will allow it to correct its GPS error as it flies to the target, such weapons are designated "precise" and will offer accuracies greater than laser or TV guided weapons, potentially CEPs of several feet.For an aircraft to support such munitions, it will require a DGPS receiver, a GPS receiver and interfaces on its multiple ejector racks or pylons to download target and launch point coordinates to the weapons. The development of purely GPS/inertial guided munitions will produce substantial changes in how air warfare is conducted.

Unlike a laser-guided weapon, a GPS/inertial weapon does not require t hat the launch aircraft remain in the vicinity of the target to illuminate it for guidance - GPS/inertial weapons are true fire-and-forget weapons, which once released, are wholly autonomous, and all weather capable with no degradation in accuracy. Existing precision weapons require an unobscured line of sight between the weapon and the target for the optical guidance to work

The proliferation of GPS and INS guidance is a double-edged sword. On the one hand, this technology promise a revolution in air warfare not seen since the laser guided bomb, with single bombers being capable of doing the task of multiple aircraft packages. 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.