Low Earth orbit

A low Earth orbit (LEO) is an orbit around Earth that takes 128 minutes or less to complete, meaning a satellite can circle our planet more than eleven times in a single day. Most human-made objects in outer space, like communication satellites and pieces of space junk, are found in LEO. These objects usually float at an altitude of about 800 kilometers, though some reach up to 2,000 kilometers above Earth.

The area below 2,000 kilometers is called the LEO region. Even if a spacecraft’s highest point is higher or if it doesn’t stay in this area all the time, it still passes through the LEO region. Because so many satellites are here, scientists carefully watch everything in this space to prevent collisions.

Only a few special missions have traveled beyond LEO. The Apollo program from 1968 to 1972 went all the way to the Moon, and in 2026, the Artemis II mission will fly around the Moon. Every space station we’ve built so far, including the International Space Station, orbits within the LEO region.

Defining characteristics

Low Earth orbit (LEO) is a place where objects fly around Earth. Many people measure LEO by how high above Earth the object is. But the height can change a lot, even for objects that fly in a circle. Most definitions say LEO is where objects take about 128 minutes to go around Earth once.

The LEO region is the space where these orbits are. Some objects might fly through this region but not stay there because they go too high. It is important to know the difference when thinking about objects bumping into each other in space.

Orbital characteristics

To stay in a stable low Earth orbit, a spacecraft needs to move at about 7.8 kilometers per second, which is very fast! This speed helps it stay in orbit around Earth. The exact speed can change a little depending on how high the orbit is.

In low Earth orbit, the pull of Earth's gravity is almost the same as it is on the ground. But because the spacecraft is moving so fast, it keeps falling around Earth without ever hitting it. This is why astronauts inside these spacecraft feel like they are floating.

Low Earth orbits are special because they are close to Earth. They are high enough to avoid most of the atmosphere but low enough to not get too much radiation from the Van Allen belts. Some of these orbits can help satellites quickly check on places near the equator, while others can cover more of the Earth.

Use

A low Earth orbit is a special path around our planet that uses the least amount of energy to place satellites. Because of this, satellites in low Earth orbit can send information quickly and clearly. They are also easier for people to reach for repairs or upgrades.

Because satellites in low orbits can only see a small part of Earth at any time, we need many of them working together to keep the whole world connected. These satellites orbit closer to Earth and can move slowly, so they sometimes need a little help to stay in their path.

Some well-known satellites and space stations are in low Earth orbit, like the International Space Station and the Hubble Space Telescope. Others help us connect to the internet from anywhere on Earth, such as Starlink. Many satellites that watch Earth, like those used for weather or maps, also fly in this special orbit.

Space debris

The area around Earth called low Earth orbit is getting crowded with pieces of old satellites and other objects. This is called space debris, and it can be dangerous because these pieces move very fast. If two pieces hit each other, they can break into even more tiny pieces, which can then hit other objects. This can keep happening over and over, creating a big problem for satellites and spacecraft.

NASA keeps track of many of these pieces. They watch over 25,000 objects that are bigger than about the size of a small book. There are also many more smaller pieces that are harder to see, and they all move at very high speeds. Even a tiny piece can cause big damage when it hits something in space.