According to NASA, there are three sub-types of Low Earth Orbits; however, all share similar characteristics. The three types are inclined non-polar, polar sun-synchronous and polar non-sun-synchronous. LEO objects include satellites, the Hubble Space Telescope and the International Space Station. These bodies move closely around Earth in a circular orbit. The orbit is influenced by the Earth's atmosphere, which causes drag on the object, and in the long term these bodies will be pulled back to Earth. However, the objects orbit very quickly around the Earth so the drag has minimal effect in the short term. The space shuttle, for example, takes 90 minutes to orbit the Earth, otherwise it would be pulled back down by gravity and drag.
NASA defines Medium Earth Orbits as the second category of orbits. Objects that are MEOs orbit the Earth normally between 12,550 miles and 12,830 miles away, with an orbit time of about 12 hours. NASA defines three further subtypes of MEOs, which are Navigation (used for global positioning systems), Communication (used for telecommunications satellites) and Space Environment (used for space observations). The objects orbiting take a circular pathway around the Earth.
A Geosynchronous Orbit is where the object orbits the Earth remaining in a fixed location above a particular location on the ground. GEOs are situated further away than LEOs and MEOs because they would otherwise fall back to Earth, owing to the slow speeds at which they orbit. GEOs are therefore about 22,000 miles away from Earth. GEOs are used for monitoring weather and for television satellites.
HEOs are egg-shaped. The object's speed varies depending on its positioning in the orbit. Near the Earth, it travels more quickly than at its furthest point away. This type of orbit is used by scientists for making magnetospheric measurements and for placing space observatories.