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Low Earth orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around 800 km (500 mi), while the farthest in LEO, before medium Earth orbit (MEO), have an altitude of 2,000 kilometers, about one-third of the radius of Earth and near the beginning of the inner Van Allen radiation belt.
The term LEO region is used for the area of space below an altitude of 2,000 km (1,200 mi) (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites.
No human spaceflights other than the lunar missions of the Apollo program (1968–1972) have gone beyond LEO. Artemis II is also planned to go beyond LEO in early 2026. All space stations to date have operated geocentric within LEO.
A wide variety of sources define LEO in terms of altitude. The altitude of an object in an elliptic orbit can vary significantly along the orbit. Even for circular orbits, the altitude above ground can vary by as much as 30 km (19 mi) (especially for polar orbits) due to the oblateness of Earth's spheroid figure and local topography. While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to Kepler's third law, this corresponds to a semi-major axis of 8,413 km (5,228 mi). For circular orbits, this in turn corresponds to an altitude of 2,042 km (1,269 mi) above the mean radius of Earth, which is consistent with some of the upper altitude limits in some LEO definitions.
The LEO region is defined by some sources as a region in space that LEO orbits occupy. Some highly elliptical orbits may pass through the LEO region near their lowest altitude (or perigee) but are not in a LEO orbit because their highest altitude (or apogee) exceeds 2,000 km (1,243 mi). Sub-orbital objects can also reach the LEO region but are not in a LEO orbit because they re-enter the atmosphere. The distinction between LEO orbits and the LEO region is especially important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits.
The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s (4.8 mi/s), which translates to 28,000 km/h (17,000 mph). However, this depends on the exact altitude of the orbit. Calculated for a circular orbit of 200 km (120 mi) the orbital velocity is 7.79 km/s (4.84 mi/s), but for a higher 1,500 km (930 mi) orbit the velocity is reduced to 7.12 km/s (4.42 mi/s). The launch vehicle's delta-v needed to achieve low Earth orbit starts around 9.4 km/s (5.8 mi/s).
The pull of gravity in LEO is only slightly less than on the Earth's surface. This is because the distance to LEO from the Earth's surface is much less than the Earth's radius. However, an object in orbit is in a permanent free fall around Earth, because in orbit the gravitational force and the centrifugal force balance each other out. As a result, spacecraft in orbit continue to stay in orbit, and people inside or outside such craft continuously experience weightlessness.
Objects in LEO orbit Earth between the denser part of the atmosphere and below the inner Van Allen radiation belt. They encounter atmospheric drag from gases in the thermosphere (approximately 80–600 km above the surface) or exosphere (approximately 600 km or 400 mi and higher), depending on orbit height. Satellites in orbits that reach altitudes below 300 km (190 mi) decay quickly due to atmospheric drag.
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Low Earth orbit AI simulator
(@Low Earth orbit_simulator)
Low Earth orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around 800 km (500 mi), while the farthest in LEO, before medium Earth orbit (MEO), have an altitude of 2,000 kilometers, about one-third of the radius of Earth and near the beginning of the inner Van Allen radiation belt.
The term LEO region is used for the area of space below an altitude of 2,000 km (1,200 mi) (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites.
No human spaceflights other than the lunar missions of the Apollo program (1968–1972) have gone beyond LEO. Artemis II is also planned to go beyond LEO in early 2026. All space stations to date have operated geocentric within LEO.
A wide variety of sources define LEO in terms of altitude. The altitude of an object in an elliptic orbit can vary significantly along the orbit. Even for circular orbits, the altitude above ground can vary by as much as 30 km (19 mi) (especially for polar orbits) due to the oblateness of Earth's spheroid figure and local topography. While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to Kepler's third law, this corresponds to a semi-major axis of 8,413 km (5,228 mi). For circular orbits, this in turn corresponds to an altitude of 2,042 km (1,269 mi) above the mean radius of Earth, which is consistent with some of the upper altitude limits in some LEO definitions.
The LEO region is defined by some sources as a region in space that LEO orbits occupy. Some highly elliptical orbits may pass through the LEO region near their lowest altitude (or perigee) but are not in a LEO orbit because their highest altitude (or apogee) exceeds 2,000 km (1,243 mi). Sub-orbital objects can also reach the LEO region but are not in a LEO orbit because they re-enter the atmosphere. The distinction between LEO orbits and the LEO region is especially important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits.
The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s (4.8 mi/s), which translates to 28,000 km/h (17,000 mph). However, this depends on the exact altitude of the orbit. Calculated for a circular orbit of 200 km (120 mi) the orbital velocity is 7.79 km/s (4.84 mi/s), but for a higher 1,500 km (930 mi) orbit the velocity is reduced to 7.12 km/s (4.42 mi/s). The launch vehicle's delta-v needed to achieve low Earth orbit starts around 9.4 km/s (5.8 mi/s).
The pull of gravity in LEO is only slightly less than on the Earth's surface. This is because the distance to LEO from the Earth's surface is much less than the Earth's radius. However, an object in orbit is in a permanent free fall around Earth, because in orbit the gravitational force and the centrifugal force balance each other out. As a result, spacecraft in orbit continue to stay in orbit, and people inside or outside such craft continuously experience weightlessness.
Objects in LEO orbit Earth between the denser part of the atmosphere and below the inner Van Allen radiation belt. They encounter atmospheric drag from gases in the thermosphere (approximately 80–600 km above the surface) or exosphere (approximately 600 km or 400 mi and higher), depending on orbit height. Satellites in orbits that reach altitudes below 300 km (190 mi) decay quickly due to atmospheric drag.