| Acronym | Type of the orbit |
|---|---|
| LEO | Low Earth Orbit |
| Although definitions of LEO vary from source to source, we define LEO as orbits having apogees and perigees below 3000 km. The large majority of all satellites are in Low Earth Orbit. | |
| MEO | Medium Earth Orbit |
| Although definitions of MEO vary from source to source, we define MEO as orbits having apogees greater than 3000 km but less that 30000 km. These are sometimes used by navigation (e.g., GPS) and communications (e.g., Odyssey) missions. | |
| GEO | Geosynchronous Earth Orbit |
| A satellite in circular orbit around the Earth's equator at 23000 miles altitude (36000 km) will remain stationary over the same location on Earth (i.e., the spacecraft goes around once in its orbit for every revolution of the Earth). This feature is very useful for communications satellites (allowing one satellite to provide continual coverage to a given area of the Earth's surface). As a result, the majority of satellites in geosynchronous orbit are commsats. Some satellites have orbits slightly higher or lower than GEO, but for simplicity sake, all satellites with apogees and perigees between 30000 and 40000 km are termed GEO. (A geostationary orbit is a geosynchronous orbit in which the spacecraft is constrained to a constant latitude.) | |
| HEO | Highly Elliptical Orbit |
| This class covers orbits which have large eccentricities (are highly elliptical). Although definitions of HEO vary from source to source, we define HEO as orbits having perigees below 3000 km with apogees above 30000 km. | |
| VHO | Very High Orbit |
| This type of orbit includes all orbits which have perigees at or above GEO and apogees above GEO, yet remain in orbit around the Earth (or Earth-Moon system). Orbits in this class are often highly elliptical, with apogees several hundred thousand kilometers in altitude. |
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