Daryl Bahls wrote: >Although I don't think the definition of orbit regimes is a "science", I'll >give my 2 cents worth. In my experience (~21yrs doing Space Mission >Analysis for two US commercial aerospace companies), I've seen the LEO >definition used primarily for objects below about 2000-2500 km >altitude (or semi-major axis). David Vallado in his new book "Fundamentals of Astrodynamics and Applications" applies this orbital classification scheme: LEO: 800 km or less. Primary perturbation factor: drag MEO: 800 km to 30000 km. Primary perturbation factor: gravitational forces GEO: The geosynchronous belt Deep Space: beyond GEO 800 km may seem low at first, but it does make sense when you consider the orbital behavioral differences for a satellite at 600 km versus 1000 km. Sean Sullivan wrote: >So, if someone comes along and asks "where's LEO?" how does one answer? >The basic idea is that it's the area high enough to permit an orbit and >low enough that it's below the "null zone" where there aren't any >spacecraft. Just where you put the numerical upper bound depends on >how close to zero you want the "spacecraft per 100 km" statistic to be. A population-based definition is too fluid. Once all of the comm constellations are in orbit then the null zone will be pushed too deep into MEO to call it LEO. ____________________________________________________________ Jim Varney 121.398 W, 38.458 N, 8m Sacramento, Calif. Member, Sacramento Valley Astronomical Society