"Matthew Ota" wrote in message
ups.com...
As for the orbital mechanics of lunar obit, yes there is no atmosphere
to consider. You can make your orbit just low enough to clear the
highest mountains.
But they discovered tehat the gravitational field of the moon is not
consistent. There are "mascons", mass concentrations that cause
distortions in orbits, especially low ones.
This is what causes orbital decay of lunar satellites. As I recall
the mascons were located in mare areas.
Low lunar orbits are unstable as a result. Higher orbits are not as
susceptible to the mascon's gravitational effects.

There have been recently discovered lunar orbits that are very stable. I
remember reading a few articles about them within the last year or so...
Google ought to help... Here we go:

http://science.nasa.gov/headlines/y2..._highorbit.htm

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)