These satellites are classified passive or active depending on the way they operate. Passive communication satellites act as a mirror for radio waves. A sending station on Earth beams waves to the satellite, the waves bounce off the satellite, and return to Earth. They reach a receiving station perhaps thousands of miles from the sending station. Active satellites receive signals from sending stations, amplify them, and send them back to Earth.
Navigation satellites help pilots and sailors find their exact positions in all kinds of weather.
Navigators can use it to find their position much as they would use a star. But instead of looking at the satellite, they listen to its radio signals. Resource satellites are used to monitor Earth's natural resources. This series include such satellites as Landsat and Seasat. Scientific satellites carry a variety of instruments around the world.