History of GPS
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A brief history of the use of GPS navigation tools.While many people use GPS today for everyday communications, few know of its history, or how it got started. Here we will explain the history of GPS, and how it has become the global tool it is today. The concept for GPS first started during the height of the Cold War in 1957. At the time the Soviets had just launched the Sputnik, and a group of scientists in the United States were monitoring the radio transmissions from the satellite. The scientists found that because of the Doppler Effect, the frequencies of Sputnik would be much higher when the satellite moved close to them, and less frequent when it moved away. Because of this, the scientists were able to find the location of the satellite based on their own location do to the level of radio frequency which was transferred from Sputnik based on the Doppler Effect. The first satellite navigation system was called Transit, and it was first used by the United States Navy in 1960. It used a collection of five satellites. By 1978 the first GPS satellite was launched by a company called Rockwell. After Soviet jets shot down the airliner KAL 007 when it accidentally entered Soviet airspace in 1983, the United States government decided that GPS should be extended to the civilian market in order to improve aircraft navigation. By 1994, a total of 24 satellites were launched. Each satellite operates at an altitude of over 12,000 miles. The direction in which the satellites travel is controlled by specific monitoring stations. There are five such stations, and they are located in strategic locations around the world. The atomic clocks on the satellites must be synchronized, and this is one of the objectives of the monitoring stations. Receivers calculate the position of the satellites, and receive the radio transmissions sent by them. The only problem with GPS systems is the changing weather conditions in the atmosphere. Signals may have a difficult time passing through the ionosphere. When the satellite orbits directly overhead, the signal is much clearer, even through the ionosphere. In additional to the atmosphere, there are many structures on the ground which can affect GPS signals. Canyons, buildings, and other structures may be responsible for the reflection of some signals. The clocks on satellites are also affected by general and special relativity. The clocks run at a faster rate than those on the earth, and are corrected by mechanisms on the satellites. |
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