Lunar modules still in orbit?

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It doesn't have to lose any energy at all (and in fact
doesn't--orbital motion is conservative). All it has to do is
increase the eccentricity to the point at which perilune goes below
the lunar surface (or just a mountain).

But would this **always** happen if a LM were left in orbit?

It depends on how low an orbit it is. The LM was sufficiently low
that, yes, it would *always* happen over time.

What's the lowest orbitting satellite of the moon right now? Are
there any that are expected to basically orbit the moon forever?


How low can an orbit be around the moon and expect not to crash onto
the moon?


I don't think there are any stable orbits. By the time you get out far
enough that the moons lumps don't bother your orbit, other planets will, so
you'll never find a stable orbit. Maybe something like a polar orbit exists
that has reasonable long-term stability, but nothing will work in the
equatorial plane, in my opinion.

Mike Ross

On Mon, 19 Nov 2007 08:37:25 -0600, "Mike Ross"
wrote:


I don't think there are any stable orbits. By the time you get out far
enough that the moons lumps don't bother your orbit, other planets will, so
you'll never find a stable orbit. Maybe something like a polar orbit exists
that has reasonable long-term stability, but nothing will work in the
equatorial plane, in my opinion.

Good point Mike. Any orbit around the moon seems to be an unstable
orbit, if I understand correctly. So can a satellite ever orbit the
moon for more than a month or two without crashing into the moon?

Anyone with an idea on what holds the record for most lunar orbits?
Back in Apollo days there must have been multiple launches to
photograph possible lunar sites etc. Did any of these last very long?
Stan.

wrote:
Good point Mike. Any orbit around the moon seems to be an unstable
orbit, if I understand correctly. So can a satellite ever orbit the
moon for more than a month or two without crashing into the moon?


No, it's unstable, but not _that_ unstable.
It could take years to perturb it out of lunar orbit either into the
surface or into solar orbit, IIRC.
We purposely crashed the Lunar Orbiters into the moon to get them out of
the way before Apollo arrived, and crashed the jettisoned LM ascent
stages on the Apollo missions to test out the seismometers on the ALSEP
packages.
I haven't been able to find out if any of the Soviet "Luna" orbiters
from the mid 1960s are still in orbit around the Moon.
They used highly elliptical orbits in some later cases; but also used
batteries, not solar panels, for power - so once the batteries died,
there was no way of knowing where they ended up.
BTW, it was Luna 10, not the Lunar Orbiters that first detected the
Mascons: http://en.wikipedia.org/wiki/Luna_10

Pat

Well, the unstablity is on the order of decades, rather than months.
It is POSSIBLE that one of the Russian orbiters or even Apollo LMs may
have beaten the odds just by luck and is still orbiting very low, but
very unlikely. Going by memory, the inventory should be:

USSR/Russia (orbiting missions ONLY considered)
Luna 10
Luna 11
Luna 12
Luna 14
Luna 19
Luna 22
(Luna 15-24 all orbited for a time, missing numbers went on to land)
These were all mapping missions, with low orbits. #s 19 and 22 did
some orbits changes, and may have ended up in high orbits for
radiation or other research.
(Zonds 5-8 were 'swing-around' missions, like Apollo 13 they just
looped around and returned to Earth without orbiting)

USA
Lunar Orbiters 1, 2, 3, 5- directed to lunar impact before Apollo 11
Lunar Orbiter 4- radio had failed, low lunar mapping orbit
Apollo 8- CSM returned to Earth
Apollo 10- LM ascent stage ended up in Solar orbit. I don't remember
if this was intended or perturbed, it did occur soon after the mission
Apollo 11- LM ascent stage left in low lunar orbit
Apollo 12- LM ascent stage directed to lunar impact; this is the one
that "made the Moon ring like a bell for hours" and made the impact of
the LMs and S4B stages a scientific experiment
Apollo 14- LM ascent stage directed to lunar impact
Apollo 15- LM ascent stage directed to lunar impact
Apollo 16- LM ascent stage left in low lunar orbit
Apollo 17- LM ascent stage directed to lunar impact
(missing numbers- A9 did not go to Moon; A13 did not orbit, LM burned
up in Earth's atmosphere
2 Radio Astronomy Explorers (Explorers 35 & 43)- high lunar orbit
Clementine- left lunar obit for asteroid mission, later canceled
Lunar Prospector- directed to lunar impact near South Pole
[I'm going by memory, and I know I've missed one]

Of course, I'm not counting the current missions- Japanese, Chinese,
and European(?)

Mike, what would it be about a polar orbit that may increase
stability. Wouldn't mascons still have an effect whenever the object
approached them? Stan

On Mon, 19 Nov 2007 08:37:25 -0600, "Mike Ross"
wrote:

I don't think there are any stable orbits. By the time you get out far
enough that the moons lumps don't bother your orbit, other planets will, so
you'll never find a stable orbit. Maybe something like a polar orbit exists
that has reasonable long-term stability, but nothing will work in the
equatorial plane, in my opinion.

Mike Ross

wrote:

Mike, what would it be about a polar orbit that may increase
stability. Wouldn't mascons still have an effect whenever the object
approached them? Stan

On Mon, 19 Nov 2007 08:37:25 -0600, "Mike Ross"
wrote:

I don't think there are any stable orbits. By the time you get out far
enough that the moons lumps don't bother your orbit, other planets will,
so
you'll never find a stable orbit. Maybe something like a polar orbit
exists that has reasonable long-term stability, but nothing will work in
the equatorial plane, in my opinion.

Mike Ross


[top-post followed by bottom-post]

Well, if you have a polar orbit (specifically, around the Moon-Earth axis)
you can increase it to the point that the mascons' effects are small,
without getting too close to Earth. I'm just guessing you might find
something stable there, I don't know.

Mike Ross

Mike Ross wrote:
[top-post followed by bottom-post]

Well, if you have a polar orbit (specifically, around the Moon-Earth axis)
you can increase it to the point that the mascons' effects are small,
without getting too close to Earth. I'm just guessing you might find
something stable there, I don't know.


I think the main problem once you get out that far from the Moon is the
effect on the orbit by the varying geometry of the Earth, Sun, and Moon,
whose gravitational interactions will screw it up.

Pat
Mike Ross