Choosing moon orbit altitudes

On Jun 23, 9:59 am, "N:dlzc D:aol T:com \(dlzc\)"
wrote:
Dear wrote in message

...

Anybody with some ideas on how NASA selected the
orbital altitudes above the moon for the Apollo
missions?

If you go too high, the orbits rapdily become unstable. That is
a problem when trying to be a satellite of a satellite...

With little/no atmosphere, was it an advantage to
make them as low as possible?

Yes for orbital stability, no for surface communications
purposes.

How low can you go?

A miss is as good as a mile. A satellite was crashed into the
Moon's surface about a year ago, and it was clearing the surface
by less than a mile, I think.http://groups.google.com/group/sci.a...f438b76d22065b
... if you do a little digging into SMART-1, your questions
should be answered.

David A. Smith

Actually for manned Apollo missions, the "standard" orbit for the CSM
was around 60 nautical miles.
For the last three J-mission landings the CSM/LM was placed into an
elliptical orbit with a pericynthion of ten miles in order to drop
off the LM.
By using this low point they increased the fuel efficiency of the LM
so that it could land the heavier payload - the Rover and more
consumables.

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.

If I am not correct I am sure that there are some lunar scientists
from the Apollo era that can elaborate on this.

Matthew Ota
I was alive when men walked on the moon. It really happened. But I was
just a kid at the time