This appendix provides an overview of the programmatic and institutional evolution of the Global Positioning System (GPS), including a history of its growing use in the military and civilian world, a chronology of important events in its development, and a summary of its costs to the government.
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 the sun and stars to calculate their location. The 1920s witnessed the introduction of a more advanced technique -- radionavigation -- based at first on radios that allowed navigators to locate the direction of shore-based transmitters when in range.1 Later, the development of artificial satellites made possible the transmission of more-precise, line-of-sight radionavigation signals and sparked a new era in navigation technology. Satellites were first used in position-finding in a simple but reliable two-dimensional Navy system called Transit. This laid the groundwork for a system that would later revolutionize navigation forever -- the Global Positioning System.
The Global Positioning System is a 24-satellite constellation that can tell you where you are in three dimensions. GPS navigation and position determination is based on measuring the distance from the user position to the precise locations of the GPS satellites as they orbit. By measuring the distance to four GPS satellites, it is possible to establish three coordinates of a user's position____________________