Like the Internet, Global Positioning System(GPS) has military origin, though now it is extensively used in civilian applications. If you are lost in Delhi , and who doesn’t need a bit a help in the nation’s Capital, you just have to seek assistance from your latest mobile phone and you will find out not only where you are but also how to get to your destination.
While many countries have tried to set up GPS systems, the only fully functional and availaible global navigation satellite system belongs to the USA which has put up a constellation of 27 Earth- orbiting satellites in six different orbital planes.
The orbits are planned such that at any time , anywhere in the Earth, there are at least 4 satellites “visible” in the sky. A GPS reciever’ s job is to locate four or more of these satellites, figure out the distance to each , and use this information to deduce its own location. This operation is based on the mathematical principle of trilateration. Basically , your GPS reciever draws a sphere around each of three satellites it can locate. These three spheres intersect in two points- one is in space and other is in ground. The point on the ground at which the three spheres intersect is your location.
We have seen how a system evolves far more than the limited purposes that start its development. What was designed to make smart bombs more accurate is today being used to make sure that children can find their way home.!!