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GPSGlobal Positioning System, pronounced as three letters. A system of 24 satellites orbiting the earth; also refers to the devices which receive signals from the satellites and determines a position from that data.
The satellites orbit the earth at approximately 12,000 miles above the surface and make two complete orbits every 24 hours. Each satellite transmits radio signals containing data on that satellite's location along with the exact time. The satellites have atomic clocks that are precise to within a billionth of a second.
As each signal travels at the speed of light, the longer it takes the receiver to get the signal, the farther away the satellite is. By knowing how far away a satellite is, the receiver knows that it is located somewhere on the surface of an imaginary sphere centered at the satellite. By using three satellites, GPS can calculate the longitude and latitude of the receiver based on where the three spheres intersect. Accuracy increases with the number of satellites the receiver can "see." The Datastorm has a GPS receiver in the UCB that tells the positioner where it is located. Along with compass and tilt sensor information, the positioner uses the data to determine where to point the dish.
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