What Are the Types of Satellite Orbits?
There are three basic kinds of orbits, depending on the satellite's position relative to Earth's surface:
- Geostationary orbits (also called geosynchronous or synchronous) are orbits in which the satellite is always positioned over the same spot on Earth. Many geostationary satellites are above a band along the equator, with an altitude of about 22,223 miles, or about a tenth of the distance to the Moon. The "satellite parking strip" area over the equator is becoming congested with several hundred television, weather and communication satellites! This congestion means each satellite must be precisely positioned to prevent its signals from interfering with an adjacent satellite's signals. Television, communications and weather satellites all use geostationary orbits. Geostationary orbits are why a DSS satellite TV dish is typically bolted in a fixed position.
- The scheduled space shuttles used a much lower, asynchronous orbit, which means they passed overhead at different times of the day. Other satellites in asynchronous orbits average about 400 miles (644 kilometers) in altitude.
- In a polar orbit, the satellite generally flies at a low altitude and passes over the planet's poles on each revolution. The polar orbit remains fixed in space as Earth rotates inside the orbit. As a result, much of Earth passes under a satellite in a polar orbit. Because polar orbits achieve excellent coverage of the planet, they are often used for satellites that do mapping and photography.
How Are Satellite Orbits Predicted?
Special satellite software, available for personal computers, predicts satellite orbits. The software uses Keplerian data to forecast each orbit and shows when a satellite will be overhead. The latest "Keps" are available on the Internet for amateur radio satellites, too.
Satellites use a variety of light-sensitive sensors to determine their position. The satellite transmits its position to the ground station.