GPS Satellites

The Global Positioning System, known as GPS, is a system of several dozen satellites orbiting around the planet Earth. The satellites transmit a radio signal, which is used for precise positioning and time determination anywhere on Earth's surface or even above it. The signal can be detected by common receivers, such as mobile phones or car navigation etc.



GPS currently comprises a total of 31 active satellites in about 6 circular orbits around the planet Earth at an altitude of 20,200 kilometers. Each orbit has an inclination of 55° in relation with the Earth's equatorial plane, while every orbit is also rotated to each other by 60°. There is 5-6 irregularly spaced active satellites on each orbit (however, several inactive backup satellites are also part of the system).



Each satellite circles around the planet Earth in 11 hours and 58 minutes, which is approximately 2 times a day. To pinpoint the location and time based on the signal transmitted by the satellites, the visibility of least 4 satellites simultaneously is needed. Though for a greater accuracy, the system is designed so that at a time there can be usually 7-10 satellites seen from every point of the Earth's surface. Such configuration allows to determine the position with an accuracy of few meters.