Although the space beyond Earth’s atmosphere is vast, human-made satellites are typically located in one of three popular orbital regimes: low Earth orbit (LEO), medium Earth orbit (MEO), and geosynchronous orbit (GEO).
Low Earth Orbit (LEO)
The majority of satellites orbiting the Earth do so at altitudes between 160 and 2,000 kilometers. This orbital regime is called low Earth orbit, or LEO, due to the satellites’ relative closeness to the Earth. Satellites in LEO typically take between 90 minutes and 2 hours to complete one full orbit around the Earth. Low altitudes in combination with short orbital periods make LEO satellites ideally situated for remote sensing missions, including Earth observation and reconnaissance.
Fifty-five percent of all operational satellites are in LEO.
Medium Earth Orbit (MEO)
Although over 90 percent of all satellites are situated in LEO (below 2,000 kilometers) and GEO (near 36,000 kilometers), the space between the two most popular orbital regimes can be an ideal environment for a smaller subset of satellite systems. Satellites in this middle-of-the-road region, appropriately named medium Earth orbit, have larger footprints than LEO satellites (meaning they can see more of the Earth’s surface at a time) and lower transmission times time than GEO satellites (meaning they have a shorter signal delay because they aren’t as far away).
Van Allen Radiation Belt
Highly Elliptical Orbits (HEO)
Geosynchronous Earth Orbit (GEO)
The period of a satellite, or how long it takes to orbit the Earth one time, is dependent on its orbital altitude. Satellites in LEO, like the International Space Station, take about 90 minutes to orbit the Earth. Satellites in MEO take about 12 hours to do the same.
Satellites orbiting at 35,786 km have a period precisely equal to one day. Satellites in this orbit, known as geosynchronous Earth orbit, or GEO, observe the Earth as if it were not rotating. Because of this property, satellites in GEO are constantly in the field of view for approximately one-third the planet’s surface.
While about 55 percent of all operational satellites are in LEO, another 35 percent are in GEO, making it the second most popular orbital regime.
Some orbits have special properties that make them ideal for specific satellite missions. Only a small fraction of operational satellites fall into this category.