Low Earth orbit (LEO) starts just 100 kilometers (62 miles) above Earth’s surface and extends up to 2,000 kilometers (1,200 miles). That makes it the closest usable region of space, closer to you than a cross-country drive in many countries. The International Space Station, Starlink satellites, and the vast majority of human spaceflight all happen within this surprisingly thin shell around our planet.
The Altitude Range of LEO
NASA defines low Earth orbit as any Earth-centered orbit at an altitude of 2,000 km (1,200 miles) or less. The lower boundary is loosely set by the Kármán line at about 100 km (62 miles), the altitude widely recognized as the starting point of space. Below that, the atmosphere is too thick for a spacecraft to maintain orbit without burning up or slowing down almost immediately.
Within that 100 to 2,000 km window, there’s enormous variation. A satellite at 200 km skims the upper atmosphere and will fall back to Earth within days or weeks. One at 700 km can stay in orbit for over a century without any propulsion. The sweet spot for most crewed missions and large satellite constellations sits between about 300 and 600 km, where atmospheric drag is manageable but still helps clear out old hardware over time.
Where Things Actually Orbit in LEO
The International Space Station circles Earth at an average altitude of about 387 km (240 miles), in a near-circular orbit that fluctuates between 375 and 400 km. It needs periodic boosts to counteract atmospheric drag, which slowly pulls it lower. At that altitude, an uncontrolled object would naturally fall back to Earth within about five years.
SpaceX’s Starlink internet constellation occupies its primary shell at 550 km. Two additional planned shells sit at 340 km and 1,110 km, giving the constellation layered global coverage. OneWeb and other broadband constellations operate at similar LEO altitudes. The choice of altitude is always a tradeoff: lower means shorter signal delay and easier deorbiting, but requires more satellites to cover the same area and burns more fuel fighting drag.
How LEO Compares to Other Orbits
LEO is dramatically closer than the other major orbital zones. Medium Earth orbit (MEO), used by GPS satellites, begins above the Van Allen radiation belts and stretches up toward geostationary orbit. Geostationary orbit (GEO), where weather and communications satellites hover over a fixed point on Earth, sits at 35,786 km, roughly 18 times farther than LEO’s upper limit and nearly three Earth diameters away.
To put it in everyday terms: if the distance to geostationary orbit were scaled to a 100-meter football field, the entire LEO range would fit within the first 5.5 meters from the goal line. The Moon, at roughly 384,400 km, wouldn’t even be in the same stadium.
Speed and Travel Time
Objects in LEO move fast. Orbital velocity at these altitudes ranges from about 7 to 8 km per second (roughly 17,500 mph). At that speed, the ISS completes a full lap around the planet every 90 minutes, experiencing 16 sunrises and sunsets each day. Getting there from the ground takes only about 8 to 10 minutes of powered rocket flight, though rendezvous with a station or specific orbit can take hours to days of careful maneuvering.
The higher you go within LEO, the slower you need to travel to stay in orbit, and the longer each trip around Earth takes. A satellite at 2,000 km orbits noticeably slower than one at 400 km, though both are still moving at tremendous speed compared to anything on the ground.
Why LEO Has an Upper Limit
The 2,000 km ceiling isn’t arbitrary. Above that altitude, spacecraft begin approaching the inner Van Allen radiation belt, a zone of trapped high-energy protons that starts at roughly 1.6 Earth radii (about 3,800 km from Earth’s center, or around 3,400 km above the surface). The region between LEO and the radiation belts is a transitional zone where radiation exposure climbs and orbital dynamics shift. Satellites above 2,000 km enter medium Earth orbit, where missions require heavier radiation shielding and serve different purposes.
The Crowding Problem
LEO’s proximity and usefulness have made it the most congested region of space. As of February 2024, roughly 31,000 trackable objects orbit Earth, and only about 9,300 of those are active satellites. The rest are defunct spacecraft, spent rocket stages, and debris fragments larger than about 10 cm. Most of this material concentrates in LEO, where collision speeds of 7 to 8 km/s make even small fragments destructive.
At altitudes below about 250 km, atmospheric drag clears debris relatively quickly. Above 500 km, objects can linger for decades. At 700 km, natural deorbit times stretch past 100 years. This is why international guidelines push operators to design satellites that will reenter within 25 years, and why active debris removal missions are now in development targeting clusters of dead satellites in the 700 km range.