Low Earth orbit (LEO) spans from roughly 160 km (100 miles) above Earth’s surface up to 2,000 km (1,200 miles). This is the region where the International Space Station flies, where most satellite constellations operate, and where nearly all crewed spaceflight takes place. It’s the closest orbital zone to Earth and by far the most crowded.
The Lower and Upper Boundaries
The upper limit of LEO is generally set at 2,000 km (1,200 miles). Above that altitude, you enter the Van Allen radiation belts, zones of charged particles trapped by Earth’s magnetic field that create a harsh environment for satellites and crew. Medium Earth orbit (MEO) picks up above LEO and extends out to roughly 35,786 km, where geostationary orbit (GEO) begins.
The lower boundary is less sharply defined. Satellites generally don’t orbit below about 180 km because atmospheric drag at that altitude is so strong it pulls them back to Earth very quickly. The practical floor for sustained orbits sits around 300 to 400 km, though historically some satellites have dipped as low as 80 to 90 km at their closest point to Earth. For reference, the commonly cited edge of space, the Kármán line, sits at roughly 80 to 100 km, so LEO begins just above where “space” itself starts.
Where Satellites Actually Fly
While LEO technically covers everything up to 2,000 km, the most heavily used zone is between 400 and 1,000 km. Researchers estimate this band could safely hold somewhere between 148,000 and 1.14 million satellites, and it’s filling up fast. Starlink satellites alone now make up an estimated 52% of all mass in LEO, orbiting across multiple altitude shells within this range.
The International Space Station maintains an altitude between 370 and 460 km. It doesn’t stay at a fixed height because atmospheric drag constantly pulls it lower, requiring periodic boosts from onboard thrusters to maintain its orbit. This drag effect is strongest at the lowest altitudes, since atmospheric density drops exponentially as you climb. A satellite at 350 km experiences significantly more drag than one at 600 km, which means it needs more fuel to stay in orbit or it falls back to Earth sooner.
How Fast LEO Satellites Travel
Objects in LEO move fast. A typical orbital speed is around 7.8 km per second (about 17,500 mph). At that velocity, a satellite completes one full trip around the planet in roughly 90 minutes. Compare that to geostationary orbit, where satellites travel at about 3 km per second but take a full 24 hours to circle Earth, matching the planet’s rotation so they appear to hover over one spot.
The relationship between altitude and speed is straightforward: the closer you are to Earth, the faster you need to travel to avoid falling out of orbit. That’s why LEO satellites zip along nearly three times faster than their geostationary counterparts despite being so much closer to the surface.
Why Drag and Debris Matter at LEO Altitudes
Atmospheric drag is the biggest wildcard for satellites in LEO. Even at 400 km, there are enough stray air molecules to gradually slow a spacecraft and lower its orbit over time. The effect is hard to predict precisely because atmospheric density fluctuates with solar activity. When the sun is more active, Earth’s upper atmosphere expands, increasing drag at a given altitude. Satellite operators must plan regular thruster firings to counteract this orbital decay, and the fuel budget for those maneuvers is a major factor in how long a satellite can operate.
The growing number of objects in LEO has also raised concerns about space debris. In 2022, the FCC adopted a new rule requiring satellite operators to deorbit their spacecraft within five years of completing their mission, down from the previous 25-year guideline. At the lowest LEO altitudes, drag handles this naturally, pulling dead satellites back into the atmosphere within months or a few years. But at higher LEO altitudes, closer to 1,000 or 2,000 km, defunct satellites can linger for decades or centuries without intervention.
LEO vs. Other Orbit Types
- Low Earth orbit (LEO): 160 to 2,000 km. Used by the ISS, Starlink, Earth observation satellites, and the Hubble Space Telescope. Orbital period around 90 minutes.
- Medium Earth orbit (MEO): 2,000 to 35,786 km. Home to GPS and other navigation satellite constellations. Orbital periods range from about 2 to 24 hours.
- Geostationary orbit (GEO): 35,786 km above the equator. Used for weather satellites and communications. Satellites here match Earth’s rotation, appearing stationary from the ground.
LEO’s proximity to Earth gives it two main advantages: lower launch costs (less energy needed to reach it) and lower signal latency (data travels a shorter distance). That’s why it’s become the preferred zone for broadband internet constellations and why it remains the only region where humans currently live and work in space.