Satellites from Sputnik to SATCOM

GPS receivers will vary drastically depending on application. A typical handheld unit can display position in terms of latitude and longitude as well as provide both speed and direction computations. In most aircraft applications, position information is interfaced with a navigation database. This is frequently accomplished by accommodating GPS as part of the Flight Management System (FMS).

Rate X Time = Distance
The principle of GPS operation is based on time. Each satellite is scheduled to transmit two "L" band radio signals complete with a digital code that includes exact time of transmission. If the clock in the receiver is exactly synchronized with the satellite transmitter, an exact computation can be made to determine the distance between the two. This computation is based on the radio signal travelling at 186,000 miles per second and the ability of the receiver to know exactly when the signal was transmitted by the satellite and exactly when the signal was received.

Each satellite that is in range of the receiver will supply a radio transmission on a scheduled basis. The receiver then performs multiple computations and determines an exact distance to each satellite. Using the equation Rate X Time = Distance, and knowing the relative position of each satellite, the receiver can then process the data and come up with a very exact position based on the World Geodetic System map datum absolute earth's coordinates in degrees of latitude and longitude.

Only a few centuries have passed since communication was accomplished using smoke signals produced from fire and green wood. What will the future hold?