Global Positioning System-GPS
From Isopedia
Technical Information
GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map. A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.
Historical Information
The inspiration for the GPS system came when the Soviets launched the first Sputnik in 1957. While monitoring Sputnik's radio transmissions a team of U.S. scientists discovered something very intriguing. They noted that due to the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower, as it got further away. They discovered that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the distortion. The opposite was also found to be true, if the satellite's position was known, then they had the ability to locate their exact position on Earth
The Global Positioning System (GPS) is a satellite based navigation system made up of at least 24 satellites placed in the Earth's orbit. The first GOS satellite was launched in February of 1978, and the most recent launch was in September of 2005. Since the first launch in 1978 over 50 GPS satellites have been put into orbit. The GPS system was created and to this day is still controlled by the United States Department of Defense. However, in the 1980's, the US government allowed the public to access these satellites free of charge. The cost of maintaining this system is roughly US$400 million per year, and this figure includes the replacement of the older satellites. Each satellite is built to last about 10 years, and after this they are pulled from the orbit and replaced by a fresher model.
The GPS system was made available for civilian use in response to the KAL 007 incident in 1983. After the airline was shot down over the former Soviet Union, President Reagan ordered that the GPS system, once completed, must be accessible by all civilians. Since its completion then, the GPS system is free for everyone to use. The only thing needed is a GPS receiver, which can costs anywhere from $90 all the way to $350. This has led to not only widespread private use, but also more commercial use. Commercial use can be land measurement, navigation and road construction. Private use can extend anywhere from ones home computer to automobiles to finding fish in a pond.
References
Team Members
- Alexandra Hoey
- Thomas McMaster
- Matthew Slowey
- Lauren Wood
