Low Earth orbit

Orbitalaltitudes

File:Sunrise To Sunset Aboard The ISS.OGG Low Earth Orbit (LEO) is a region of Earth's orbit that is close to the planet's surface and extends up to an altitude of 2,000 kilometers (1,200 mi) above the Earth's surface. This orbit is below the Van Allen radiation belts and is the most commonly used orbit for satellites, especially those that require close observation of the Earth, such as weather satellites and spy satellites, as well as for human spaceflight missions like those conducted by the International Space Station (ISS).

Characteristics

LEO has several characteristics that distinguish it from higher orbits. Satellites and spacecraft in LEO are subject to atmospheric drag, which causes orbital decay and requires periodic boosts to maintain their orbit. The presence of the atmosphere up to around 600 kilometers (370 mi) means that satellites in lower LEO orbits do not have long operational lifetimes unless their orbits are regularly maintained.

The speed required to maintain a stable LEO is about 7.8 kilometers per second (28,080 kilometers per hour; 17,450 miles per hour), making it the orbit with the highest velocity requirement. This high speed means that objects in LEO orbit the Earth approximately every 90 minutes, allowing for frequent observation of specific Earth locations by satellites in sun-synchronous orbits.

Uses

LEO is utilized for a variety of applications, including but not limited to:

• Earth observation for weather forecasting, environmental monitoring, and military reconnaissance.
• Satellite communications, although geostationary orbits are more commonly used for this purpose due to their fixed position relative to the Earth's surface.
• Space exploration, serving as the staging point for missions to other orbits or celestial bodies.
• Human spaceflight, with the International Space Station being the most prominent example of a manned spacecraft in LEO.

Challenges

Operating in LEO comes with several challenges. The risk of collision with space debris is significantly higher in LEO due to the dense population of objects, including defunct satellites and fragments from previous collisions. This risk necessitates active space situational awareness and debris mitigation strategies.

Atmospheric drag, as mentioned, is another challenge, requiring satellites to carry additional fuel for orbital adjustments or rely on external means of propulsion support, such as spacecraft equipped with ion thrusters.

Future of LEO

The future of LEO is seen as increasingly commercialized, with numerous private companies, such as SpaceX and OneWeb, planning to deploy large constellations of small satellites to provide global internet coverage. This has raised concerns about the sustainability of LEO due to the potential increase in space debris and the need for enhanced traffic management and debris mitigation strategies.