The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day.
The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado. These monitor stations measure signals from the SVs which are incorporated into orbital models for each satellites.
Direction of travel or direction between two points. A bearing is measured from the cardinal directions of north or south in reference to true/magnetic north. However, the bearing measurement is never over 90 degrees. Bearing usually refers to the direction to a waypoint in a GPS receiver.
