A satellite is a physical object that orbits, or rotates about, some celestial body. Satellites occur in nature, and our own solar system is a perfect example. The earth and other planets are satellites rotating about the sun. The moon is a satellite to the earth. A balance between the inertia of the rotating satellite at high speed and the gravitational pull of the orbited body keeps the satellite in place.

Satellites are launched and orbited for a variety of purposes. The most common application is communication in which the satellite is used as a repeater. In this chapter, we introduce satellite concepts and discuss how satellites are identified and explained. We summarize the operation of a satellite ground station and review typical satellite applications, with particular emphasis on the Global Positioning System, a worldwide satellite-based navigational system.