Illustration of the three ranges of satellite orbits around the Earth. The closest in is the low-Earth orbit (LEO) zone, which extends out to an altitude of 2000 kilometres (km). The Space Telescope and International Space Station orbit within this zone. Second furthest is the medium-Earth orbit (MEO), from 2000 km to 35,768 km above the Earth. The latter is the altitude of geosynchronous orbit, at which a satellite's orbital period is 24 hours. Navigation satellites such as the systems of Galileo and GPS orbit within this region. Beyond this is the realm of high-Earth orbits. NASA's IBEX satellite orbits within this region.