Low, medium, geostationary: the kinds of orbit and what they are for
Why weather satellites, GPS and the ISS fly at such different heights. A guide to low Earth orbit, sun-synchronous orbit, medium orbit, geostationary orbit and highly elliptical orbits.
Low Earth orbit (up to about 2,000 km)
Most satellites live here: the space stations, Earth-observation satellites, and constellations like Starlink. Being close gives sharp images and quick radio contact, and launching there is cheapest. The catch is speed: a low satellite crosses your sky in a few minutes, so you need many of them, or patience, for continuous coverage.
Sun-synchronous orbit
A special low orbit, tilted a little past the poles (about 98°), that slowly turns with the Earth's yearly path around the Sun. The result: the satellite passes over any given place at the same local time every day. That keeps the lighting the same from one image to the next, which is why Earth-imaging satellites such as Korea's Arirang series use it.
Medium Earth orbit (about 2,000 to 35,000 km)
Home of the navigation systems: GPS, Galileo, BeiDou and GLONASS fly around 19,000 to 23,000 km up. From there each satellite sees a large part of Earth, so a few dozen are enough to cover the whole planet.
Geostationary orbit (35,786 km above the equator)
Here one orbit takes exactly as long as Earth takes to spin, so the satellite stays above the same point on the equator. A dish on the ground can be fixed in one direction forever, which is perfect for TV broadcasting (Koreasat) and for weather satellites watching a whole hemisphere (Chollian, Himawari, GOES). From Korea these satellites sit in the southern sky.
Highly elliptical orbits
Stretched orbits that swing close to Earth and then far out. A satellite spends most of its time near the far point, hanging high over one region for hours. Russia has long used them (the Molniya orbit) to cover its northern latitudes, where geostationary satellites sit too low on the horizon.