Re: Globalstar flares; definition of "LEO"

Jim Varney (
Mon, 16 Feb 1998 09:20:05 -0800

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