# How were the boundaries of LEO and MEO (or all geocentric orbits) determined?

From my understanding:

 Low Earth Orbit is from 100 - 1240 miles.
Medium Earth Orbit is from 1240 - 22246 miles.
High Earth Orbit is from 22246 and above.


What is the reason for the exact value chosen? Numbers such as 22246 im guessing are not purely random, so is there some various qualities in space that have to be taken into account once in certain areas?

Low Earth Orbit means orbits less than 2000 km altitude. (2000 km = 1243 mile) This is approximately the out limit of the exosphere. Orbits above this will experience such little drag that they will last forever. Orbits below about 2000km will slowly decay due to atmospheric drag. The value 2000 is a "nice round number" and there is no sharp edge to the atmosphere. The value of 2000km is a convenient choice. But roughly, a spacecraft in Low Earth orbit will need to use rockets from time to time to keep it from spiralling into the atmosphere.

Middle Earth Orbits are orbits that are above the 2000km zone up to the geosynchronous orbit. They are orbits with a period of less than one day.

High Earth Orbit are orbits with a period of more than one day.

• -1 because unsourced answers are not helpful and generally discouraged in science-based SE sties (both Astronomy SE and here) because there's no way for readers to judge if an answer is correct or if someone just makes stuff up. Is it possible to refer to sources where this information was obtained?
– uhoh
Sep 5, 2020 at 2:10

The difference between Medium Earth Orbit and High Earth orbit is found in the period of circular orbits of such heights. For Medium Earth Orbit, the period is less than a day, for High Earth Orbit its more than a day. Between Medium Earth Orbit and High Earth Orbit, at a period of exactly one day, we find geosynchronous orbits (GSO) and their special case, geostationary orbits (GEO). (36,000 km ~= 22,369 mi).

The choice for the border between LEO and MEO is more arbitrary, and depending on the source you'll find different "rules". While sometimes 2000km is used (1243 miles), other times you'll find LEO defined in terms of eccentricity and period (e < 0.25, T <= 128 minutes).

For altitude, definitions vary. See a few different ones:

Merriam-Webster

a usually circular orbit from about 90 to 600 miles (about 140 to 970 kilometers) above the earth

FAA

LEO refers to orbits that are typically less than 2,400 km (1,491 mi) in altitude.

NASA

A geocentric orbit with an altitude much less than the Earth's radius. Satellites in this orbit are between 80 and 2000 kilometers above the Earth's surface

ESA

A low Earth orbit (LEO) is, as the name suggests, an orbit that is relatively close to Earth’s surface. It is normally at an altitude of less than 1000 km but could be as low as 160 km above Earth – which is low compared to other orbits, but still very far above Earth’s surface.

The only thing all definitions of LEO have in common is that the altitudes are usually much smaller than the radius of the Earth. Which, to me, seems like as good as a definition as any other.

Yeah, we could argue about drag and whatnot. But there is no sharp cutoff. And apparently, placing that cutoff as low as 970km is sensible for some, and for others placing it as high as 2,400km.