What are Low Earth Orbits (LEO)?

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Sep 7, 2022

Low Earth orbits (LEO) are Earth-centered orbits with an altitude of 200-2000 km above the surface of the Earth. The majority of Earth’s satellites are found in LEO including the International Space Station (ISS). LEO satellites are commonly used for Communication, Military reconnaissance, and imaging applications such as Google Earth which helps in determining Earth’s geographical aspects such as glacial levels, desert coverage, and lake shrinkage.

A satellite in an LEO completes around 16 orbits per day (128 minutes per orbit) which indicate that they move at an incredibly fast rate around the earth. A low earth orbit satellite requires the lowest amount of energy and cost for launch and placement in the LEO due to its proximity to the earth’s surface. It provides high bandwidth and communication latency as it is the closest orbit to the earth and its corresponding base stations on the surface.

LEO Satellites have a much smaller field of view when compared with satellites that traverse at higher altitudes which makes the LEO satellite only cover and communicate with a small region of the earth at any given time. To overcome this limitation, a network (or “constellation”) of satellites is required in the LEO orbit to provide continuous global coverage. In general, about 30 satellites are required to provide coverage of the earth at all times.

For a satellite to remain in an LEO orbit, it needs to travel at a speed of 17,500 miles per hour (7.8 kilometers per second). This speed which is required for a satellite to maintain its orbit around the earth is known as Orbital velocity. 

If the satellite’s Orbital Velocity is higher than the optimal value, it faces the risk of flying out of orbit, into space. If the orbital velocity is kept too low, the satellite will be pulled back to earth due to gravity causing it to crash and burn. Hence, the correct orbital velocity must be maintained to ensure the gravity of the earth balances the inertia of the satellite, pulling it down to the earth’s surface just enough to enable the satellite to traverse in its intended orbit. The speed of the satellite in an orbit is inversely proportional to the altitude from the earth’s surface. So the higher the satellite is from the surface of the earth, the lower the required orbital velocity.

Key parameters of Low Earth Orbits (LEO)

Parameters

LEO Attributes

The altitude of LEO From Earth

200 - 2000 Kms

Orbital Velocity for a satellite in LEO

17,500 mph (7.8 km/s)

Orbits Completed in a Day for a Satellite

16 Orbits per day

Satellites Needed

30 for Global Coverage

Satellite Life

3-7 Years

Propagation Loss

Low

Network Complexity

Complex

Transmission Delay

<20 ms 

Broadband Capability

Poor