Читать книгу Global Navigation Satellite Systems, Inertial Navigation, and Integration - Mohinder S. Grewal - Страница 20

The fully populated GPS constellation includes 31 active satellites with additional operational spares, in six operational planes. The satellites are in circular orbits with four or more satellites in each orbital plane. The orbital planes are each inclined at an angle of 55° relative to the equator and are separated from each other by multiples of 60° right ascension. Each satellite is in a medium Earth orbit (MEO), is nongeostationary, and is approximately circular, with radii of 26 560 km, with orbital period of one‐half sidereal day (≈11.967 hours). Four or more GPS satellites will always be visible from any point on the Earth's surface, where the GPS satellites can be used to determine an observer's position, velocity, and time (PVT) anywhere on the Earth's surface 24 h/d.