22 Jan

Space, Control, and User Segments: Understanding GPS

using tracking devicesGlobal Positioning System or GPS is a space-based satellite navigation system that provides users with navigation, positioning, and timing services. It is a network of 30 satellites orbiting the earth at an altitude of 20,000 kilometres. The U.S. government develops, maintains, and controls the system. GPS was originally created for military navigation, but now anyone with a GPS tracking device, be it a mobile phone, Satellite Navigation or Satnav system, or handheld GPS unit, can receive the signals that satellites broadcast.

GPS consists of three segments: the space segment, control segment, and user segment.

Space Segment

The GPS space segment consists of a constellation or group of satellites that transmit radio signals to users. The U.S. Air Force manages at least 24 satellites to ensure their availability all the time. Each GPS satellite orbits the earth twice a day at an altitude of 20,200 km. The satellites are arranged into six orbital planes. This arrangement ensures there are at least four satellites in view from virtually any point on the planet.

Control Segment

The control segment consists of a global network of facilities that monitor the satellites, track their transmission, perform analyses, and send information and commands to the constellation. The current operational control segment is composed of a master and an alternate control station, 12 control and command antennas, and 16 monitoring sites. One of the sites can be found here in New Zealand, while others are located in the United Kingdom, South Korea, Australia, Bahrain, Ecuador, South Africa, Tahiti, Argentina, Alaska, and Washington.

User Segment

The user segment involves GPS receiver equipment and tracking devices that receive signals from the satellites and calculate the user’s current position and time. Like the Internet, GPS is an important part of the global information infrastructure. Its open, free, and dependable nature has led to the development of hundreds of applications that affect every aspect of daily life. The uses of GPS fall into four categories: navigation, mapping, surveying, and timing.


GPS boosts productivity, from farming, to construction, mining, surveying, logistics and supply chain management, and package delivery. Many communications networks, financial markets, banking systems, and power grids depend heavily on GPS for effective time synchronisation. The system also saves lives by reducing accidents, speeding the delivery of disaster relief and emergency services, and aiding search and rescue efforts. It also helps advance scientific aims, such as earthquake monitoring, weather forecasting, and environmental protection.