General

The global navigation satellite system (GNSS) is a worldwide position and time determination system that includes one or more satellite constellations, aircraft receivers and system integrity monitoring, augmented as necessary to support the required navigation performance for the intended operation. The Global Positioning System (GPS) is the name given to the American GNSS satellite constellation. The design GPS constellation contains 24 GPS satellites, orbiting the earth twice a day at an altitude of 10,900 NM (20,200 km). They are arranged in six separate orbital planes, with four satellites in each. There are approximately 32 operational satellites, however, at any given time, one or more may be decommissioned or be out of service temporarily for maintenance.