How fast do satellites orbit Earth?

A satellite doesn't stay up through propulsion, but through speed: it constantly falls toward Earth, but moves sideways so fast that it falls past it. The speed needed for this depends on the altitude of the orbit. The closer to Earth, the stronger the pull, and the higher the required speed: high orbits are slow, low orbits dizzyingly fast. That's why there's no single figure for the question of speed, but a scale in which every orbital altitude has its own value.

Satellites in low Earth orbit fly at about 7.8 kilometers per second and circle Earth in about 90 minutes; the International Space Station thus orbits the planet about 16 times a day. Earth observation and weather satellites, as well as the large internet-access constellations, orbit at similar altitudes. For ground stations, this speed means that a single satellite stays visible in the sky for only a few minutes before the next one replaces it. Since residual atmosphere still causes drag in that zone, these satellites slowly lose altitude and burn up on reentry if their orbit isn't corrected.

The situation is very different at 35,786 kilometers above the equator. There, a satellite takes 23 hours, 56 minutes and 4 seconds to complete one orbit, the same time it takes Earth to rotate once on its axis, and it appears motionless when seen from the ground: the basis for TV and weather satellites with fixed antennas. Its orbital speed is about 3 kilometers per second, much lower than in low orbit. Between the two lie the medium orbits, where navigation satellites like Galileo or GPS operate; these need several hours to complete one orbit.