INTRODUCTION
Throughout time people have developed a variety of ways to figure out their position on earth and to navigate from one place to another. Early mariners relied on angular measurements to celestial bodies like sun and stars to calculate their location. The 1920s witnessed the introduction of more advanced technique-radio navigation-based at first on radios that allowed navigators to locate the direction of shore-based transmitters when in range. Later development of artificial satellites made possible the transmission of more precise, line of sight radio navigation signals and sparked a new era in navigation technology. Satellites are first used in position finding in a simple but reliable 2D Navy system called Transit. This laid the groundwork for a system that would later revolutionize navigation for ever-the Global Positioning System.
The Global Positioning System (GPS) is a satellite based navigation system. The concept of GPS was introduced by the United States Department of Defense (DoD). It is in the year 1994 that the GPS was completely developed. The GPS is developed to provide continuous, highly precise positions, velocity and time information to the land, sea, air and space based users. The intent of system is to use a combination of ground stations, orbiting satellites and special receivers to provide
navigation capabilities to virtually everyone, at any time, anywhere in the world, regardless of weather conditions.
THE GPS SEGMENTS
The Space Segment
The space segments, also known as satellite segment, consist of 24 operational satellites revolving around earth in 6 orbital planes approximately 600 GPS satellites are not geosynchronous. First satellite was launched in the year 1978. The satellites take approximately 12 hours to orbit Earth. These satellites revolve the earth in a circular pattern with an inclined orbit. Out of the 24 satellites 21 are working satellites and the