In the following text, the orbital regimes are defined as follows for near circular orbits:
LEO – altitude below 1500 km;
MEO – altitude from 8000 km to 25000 km;
GEO – altitude from 25000 km to 60000 km (usually 36000 km).
In practice, there are very few spacecraft between LEO and MEO because of the severity of the proton belts. In the GEO regime, the majority of operational spacecraft are in the 36000 km, zero degrees inclination geostationary orbit. The GEO type of environment can be encountered however from about 25000 km to about 60000 km. Highly eccentric orbit (HEO) spacecraft including those in geostationary transfer orbit (GTO) are considered to have both LEO and MEO/GEO requirements. Spacecraft on high inclination orbit with altitude below 8000 km altitude going through the auroral oval are subject to MEO/GEO requirements in addition to the possible LEO requirements. Beyond altitudes where the GEO environment is encountered, there are various regions with different plasma regimes less severe than the GEO environment regarding charging effects.