Antennas for satellites: Around the world with antennas made for three-axis stabilized spacecraft

Every satellite in orbit carries one or more antennas whose characteristics are determined by the coverage requirements of its communications system. There are dozens of surveillance and remote sensing satellites in low earth orbit (LEO), at altitudes less than approximately 2500 km. These satellites see an ever-changing land or seascape. There are also dozens of satellites designed specifically for communications and TV broadcast service. Most of the latter are in a 24-hour geosynchronous orbit (GEO) at 35,800 km altitude so that the satellite sees an apparently stationary earth beneath it. In between LEO and GEO, an important constellation of satellites in 12-hour orbits (20,200 km altitude) is emerging. These are the Navstar satellites of the Global Positioning System (GPS), designed to broadcast precise navigational information to both military and commercial users anywhere on earth.