A satellite stays up because it is falling forward fast enough to keep missing the Earth. The lower it orbits, the faster it must travel to balance gravity — so altitude and speed are locked together. That single relationship explains why different missions live at very different heights.
Low Earth Orbit (LEO) runs from roughly 160 to 2,000 km. It is crowded and fast: objects here circle the planet in about 90 minutes to two hours. The ISS, most Earth-observation satellites and the Starlink megaconstellation all live in LEO, close enough that they sweep visibly across the sky and need fresh tracking data often.
Medium Earth Orbit (MEO) sits between LEO and the geostationary belt. Its signature residents are navigation constellations: GPS satellites orbit near 20,200 km and take about 12 hours to lap the Earth, high enough that a handful of them are always in view of any receiver below.
Geostationary Orbit (GEO) is a single special ring at about 35,786 km directly above the equator. At that altitude an orbit takes exactly one day, so the satellite appears to hang motionless over one longitude — ideal for communications and weather satellites that must stare at the same hemisphere. Higher means slower, wider coverage and bigger lag; lower means faster, sharper detail and shorter passes.