Navigation satellites were created for the use of ships so that they could know their exact location. The idea for using satellites for navigating first surfaced with the launch of Sputnik 1 on October 4, 1957. When Sputnik transmitted and the radio frequency was plotted on a graph, there was a pattern that is recognizable to scientists. This is known as the Doppler Effect, which is an apparent change in radio frequency from emitted from a moving mass that passes by. Most navigation systems determine location using distance and time. Before, scientists figured that distance could be computed using the velocity and time needed for a radio signal to be sent between two points. An example of navigation satellites is Navistar.
Reconnaissance Satellites
Communication Satellites
Astronomy Satellites
