On Jun 26, 6:35 am, BradGuth wrote:
On Jun 23, 8:05 pm, Matthew Ota wrote:





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- Hide quoted text -

- Show quoted text -

Of any 100 km or less altitude of a conventional mission orbit isn't
going to be possible without nearly continual reaction thrusting and/
or having those powerful momentum reaction wheels onboard (especially
for their fly-by-rocket lander that has never once been proof-
tested). Either way it adds considerable mass, taking up valuable
spacecraft volume and therefore taking additional mission energy in
order to get there and sustain any such given low orbit mission that's
related to our salty old naked moon of such pesky mascons.

An elliptical polar orbit seems perfectly doable: "(closest approach
to the lunar surface) only 450 miles (700 km) above the north lunar
pole", although taking some extra time and applied energy in order to
fully establish.

Such an elliptical polar orbit of 12 hours for whatever manned
missions would certainly become doable, but hardly of the nearby
Apollo method, that which of course never actually happened as told to
us in the first place.

Our gamma and hard-Xray lunar surface of such weird cobalt and
titanium mascons is hardly a substance of Earth, and it's otherwise
salty to boot. Not that it should matter to our hybrid rad-hard
astronauts, as those pesky mascons are also going to represent the
most in secondary/recoil photons of gamma and hard-Xrays. Sorry about
that.
-
"whoever controls the past, controls the future" / George Orwell
-
Brad Guth- Hide quoted text -

- Show quoted text -

Besides having to fend off the secondary/recoil worth of the moon's
gamma and hard-Xrays, plus in need of a local solar shade, why is
there any problems with utilizing our moon's L1?

The moon's L1 is not only terrific for accommodating our future moon
related missions, but otherwise for Earth science and astronomy/
astrophysics in general.
-
Brad Guth