Description
GPS design is based partly on ground-based radio navigation systems developed in the early 1940’s that were used in World War II. These systems were named LORAN and Decca Navigator and were focused on knowing where the enemy was so they could either attack or retreat depending on the size of the forces.
Additional inspiration for modern day GPS systems came when Sputnik was launched by the Soviet Union in 1957. A team of scientists monitored Sputnik’s radio transmissions and discovered that because of the Doppler Effect, the frequency of the signal being transmitted was high as the satellite approached and lower as it moved away. The Doppler Effect is the change in frequency and wave length of a wave as it is perceived by an observer moving relative to the source of the waves.
This team of scientists that was observing Sputnik’s radio transmissions soon realized that since they knew their exact location on the globe, they could pin point where the satellite was along its orbit by measuring the Doppler distortion. This was groundbreaking and very exciting for the military at the time.
The United States Navy used the first satellite navigation system called Transit. It was first successfully test in 1960 and was quite mind-boggling for everyone in the military. When the Navy tested Transit, they did so hoping for some quite specific results. Using a constellation of five satellites, they found that the system could provide a navigational fix approximately once per hour.
In 1967, the Navy developed the Timation satellite which proved the ability to place accurate clocks in space. This is a technology that the GPS system relies on. In the 1970’s, the ground-based Omega Navigation System, based on signal phase comparison, became the first world-wide radio navigation system.
In February of 1978, the first experimental Block-I GPS satellite was launched into space and the development of modern-day GPS systems began. These original satellites were initially made by Rockwell International. Now, the satellites we use for GPS are manufactured by Lockheed Martin.
By 1985, ten more experimental Block-I satellites had been launched into space to validate the concept of GPS and in 1989; the first modern Block-II satellite was launched. By December of 1993, the GPS system achieve initial operational capability and just a month later, a complete constellation of 24 satellites were in orbit with full operational capability declared by NAVSTAR in April of 1995.
A year after that, President Bill Clinton realized the importance of GPS to civilian users as well as military users which prompted him to issue a policy directive that declared GPS to be a dual-use system meaning civilian as well as military. He established an Interagency GPS Executive Board that was responsible for managing GPS as an asset of the United States. the previous examples going off in all directions. So instead of a series of circles, you get a series of spheres.
