Re: definition of "LEO" (was Globalstar)

Philip Chien (
Mon, 16 Feb 1998 12:33:12 -0400

Sean Sullivan <> said:

>I have never seen a "definitive" definition of LEO, and don't know that
>such a thing exists.

There isn't.  The limits are fairly arbitrary, and different sources use
different values.

I use a rather unusual definition myself, but it makes sense.  Most launch
vehicles go in to parking orbits before their upper stages burn/reburn to
send their payloads to their final orbits.  It would be logical to assume
that the parking orbits are LEOs.  So anything achieved by a Delta 2nd
stage, Titan IV core stage, Atlas-Centaur with the Centaur first burn, etc.
etc. would be a LEO.

The trouble is this definition falls apart for the ACE launch where its
Delta 2nd stage set a new record altitude.

My other definition is even lower - the practical radiation limits for
crewed spacecraft.  In other words the maximum altitudes achieved by crewed
spacecraft on earth-orbiting missions.  The only non-lunar crewed
spacecraft to go above 400 km. was Gemini 11 which was raised in to an
elliptical orbit by the Agena stage it docked to in orbit.

Typically the shuttle and Mir are limited to about 400 km, and a new
shuttle altitude record was set on the STS-82 Hubble servicing mission when
Hubble was nudged up a few km.

Of course both of these definitions of LEO are far lower than the ones I've
seen elsewhere, but they work for me.

By my definitions anything beyond the altitude achievable by the shuttle
until the radiation belts is a MEO orbit (including Globalstar, Iridium,
etc.)  The Navstar, Glonass, and other constellations and 12 hour
elliptical orbits count as "High MEOs" and anything with an orbital period
of 22 to 26 hours is GEO.

Philip Chien, KC4YER
Earth News
world (in)famous writer, science fiction fan, ham radio operator,
all-around nice guy, etc.