Understanding LEO
Why LEO is the busiest region of space
LEO's advantages all stem from proximity. It takes the least energy to reach of any orbit, so launches are cheaper and payloads can be larger. Radio round-trip latency is only a few milliseconds — against roughly a quarter of a second for a geostationary satellite — which is why broadband mega-constellations such as Starlink chose LEO. The short range also sharpens imaging, so most Earth-observation, weather and reconnaissance craft fly here, frequently in Sun-synchronous or polar orbits that pass over every latitude as Earth turns beneath them. Here is how the three main regimes compare:
| Regime | Altitude | Orbital period | Typical occupants |
|---|---|---|---|
| LEO | 200–2,000 km | 90–127 min | ISS, Starlink, Earth observation |
| MEO | 2,000–35,786 km | 2–24 hours | GPS, Galileo navigation |
| GEO | 35,786 km | ~24 hours | Weather, TV, comms relays |
Atmospheric drag and orbital lifetime
Unlike higher orbits, LEO is not empty. The outer wisps of the atmosphere create drag that continuously saps a satellite's speed and lowers its orbit, so craft must periodically fire thrusters to stay aloft or eventually re-enter. This natural clean-out underpins the 25-year rule for post-mission disposal. How long a satellite survives falls steeply with altitude and also depends on its mass-to-area ratio and on solar activity, which heats and swells the upper atmosphere. The values below are order-of-magnitude guides, not guarantees:
| Altitude | Approx. natural orbital lifetime |
|---|---|
| 200 km | Days |
| 300 km | Weeks to months |
| 400 km (ISS) | 1–2 years |
| 600 km | ~25 years |
| 800 km | Over a century |
| 1,000 km+ | Many centuries |
A crowded, closely watched neighbourhood
Most of the tens of thousands of tracked objects in orbit — working satellites, spent rocket bodies and debris — reside in LEO, making it by far the most congested regime. Helpfully, most of its satellites operate below the inner Van Allen radiation belt, which begins near 1,000 km, sparing them the harsh radiation that higher orbits endure. The chief hazard is instead collision: with objects travelling at 7–8 km/s, a single impact can spawn thousands of fragments and, in the worst case, trigger Kessler syndrome, a self-sustaining cascade. Operators counter this by tracking every object and manoeuvring to avoid close approaches; you can explore the current population on our space-debris map.