The Global Positioning System (GPS), is a satellite-based radionavigation system. It is a global navigation satellite system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The GPS does not require the user to transmit any data, and it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The current GPS consists of three major segments. These are the space segment, a control segment, and a user segment. The U.S. Air Force develops, maintains, and operates the space and control segments. GPS satellites broadcast signals from space, and each GPS receiver uses these signals to calculate its three-dimensional location (latitude, longitude, and altitude) and the current time. The space segment (SS) is composed of 24 to 32 satellites in medium Earth orbit. The control segment (CS) is composed of: a master control station (MCS), an alternative master control station, four dedicated ground antennas, and six dedicated monitor stations. The user segment (US) is composed of tens of millions of civil, commercial and scientific users of the Standard Positioning Service. |