Low Earth Orbit, or LEO, is the region of space between roughly 200 and 2,000 kilometres above Earth's surface. It's the first useful "shelf" beyond the atmosphere and home to the majority of active satellites today, including the International Space Station, almost every Earth-observation satellite, and the Starlink mega-constellation.
Why Engineers Love LEO
- Cheap to reach. A rocket needs less delta-v to get to LEO than any other orbit.
- High resolution. Cameras and radars can see fine detail because they're close to the ground.
- Low latency. A signal round-trip to LEO takes ~5 ms vs ~250 ms for a GEO satellite — critical for broadband internet.
- Strong signals. The free-space path loss is far smaller than from GEO.
The Catch: Drag
The atmosphere doesn't end abruptly. Even at 400 km altitude there's enough thin air to slowly slow a satellite down. Without periodic thruster firings, the ISS would re-enter the atmosphere within a couple of years. CubeSats below 400 km typically last only months before burning up. This is why LEO is "self-cleaning" — but it also means satellites need propellant for station-keeping.
LEO Sub-Bands
- Very low (200–400 km) — short missions, ultra-high-resolution imaging.
- Standard LEO (400–700 km) — ISS, Starlink, most observation satellites.
- Sun-synchronous (~600–800 km) — special orbits that always cross the equator at the same local time, ideal for consistent imaging.
- Upper LEO (1,000–2,000 km) — Iridium, OneWeb, and other comms constellations.
Watching LEO Live
Open the live tracker and notice how the LEO satellites zip across the screen — they complete an orbit in 90 minutes. Compare that with the much slower-moving GPS satellites in MEO and you'll feel Kepler's third law for yourself.