|Since the beginning of time, mankind has been trying to figure out a dependable way to know where they were, and to guide them to where they wanted to go and get back again. Seamen followed the coastline to keep them from getting lost. They discovered, when they sailed out into the open sea, that they could use the position of the stars to chart their courses.
Major developments in early navigation were the compass and the sextant. The needle of the compass always points north. So even if they didn't knew where they were, at least they knew in what direction they were traveling. The sextant measures the exact angles of stars, the moon and the sun above the horizon by the use of adjustable mirrors. Early sextants could only measure the latitude and sailors were still not able to work out their longitude.
As this was determined to be a serious enough problem, in the seventeenth century, Great Britain formed a group of well-known scientists called the Board of Longitude. They offered a substantial cash reward to any person who could find a way of working out the longitude of a ship within thirty nautical miles. In 1761, a man named John Harrison developed a timepiece called a chronometer. This invention lost or gained only about one second a day. Sextants and chronometers were used together to provide travelers with their latitude and longitude.
Radio-based navigation systems were developed in the early twentieth century, and were used in World War II. As this technology advanced, both ships and airplanes used ground-based radio-navigation systems. The disadvantage of using a system that uses ground generated radio waves, is that a choice has to made between a high-frequency system that is accurate, but does not cover a wide area, and a low-frequency system that covers a wide area, but is not very accurate.
When Sputnik was launched into space by Russia on October 4th, 1957 it became known that "artificial stars" could be used for navigation. The evening after the launch researchers of the Massachusetts Institute of Technology determined the orbit of the Russian satellite by noting that the Sputnik's radio signal increased as it approached and decreased as it left. So the fact that a satellite's position could be tracked from the ground was the first step in recognizing that a subject's whereabouts on the ground could be determined using radio signals from the satellite.
The U.S. Navy experimented with satellite navigation. In the mid-sixties there was the Transit System that was developed for submarines carrying Polaris nuclear missiles. This system has six satellites that circled the earth in polar orbits. In measuring the Doppler shift of the radio signals the submarines could locate its position within fifteen minutes.
The Global Positioning System, now commonly known GPS was designed and built and is operated and maintained by the U.S. Department of Defense. It used to be known as the Navstar Global Positioning System and was first brainstormed at the Pentagon in 1973 as they were looking for a satellite system that was error-proof. In 1978 the first operational GPS satellite was launched. By the mid-1990s the system was fully operational with 24 satellites.