If you watch much television, you probably believe that GPS (Satellite Navigation) was invented by General Motors, which is not the truth. They have just capitalized on it and sold a lot of cars because of it.

The Department of Defense created this navigating tool for use by the US military. It provides specially coded satellite signals that can be captured and read by an appropriate receiver. There are many thousands of non-military, non-government GPS users in the world today even though it wasn’t created for that use. A GPS receiver can compute position, velocity, and time. Position may be computed in three dimensions.

The constellation consists of 24 satellites that orbit the earth in 12 hours. Sometimes there are more than 24 when new ones are launched to replace older ones. These satellites are powered by solar energy but have backup batteries so they will continue to operate in the event of a solar eclipse.

The orbits repeat almost the same ground track as the earth turns beneath them once each day. The altitude is planned to that the satellites repeat the same track and configuration of any particular point 24 hours less 4 minutes each day. There are six orbital planes spaced 60 degrees apart and with a fifty-five degree incline with respect to the equatorial plane. The constellation makes possible between five and eight views from any point on earth.

Schriever Air Force Base in Colorado houses the master controls, which measure signals from the satellites and become orbital models for each satellite. The models calculate orbital data and satellite …