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

On Jun 23, 10:05 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 -

Matthew,
Yeah, It really happened. I was just a kid at the time
but
I was at Redstone Arsenal. (not exactly alive)

You can just about put it in the bank that those mascons
are associated with the Titanium rich areas of the Maria, or at least
any area with concentrations of heavier elements.

Ben Therrell
NSA/NASA, 1969 - 1971

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 -

Even the moon's L1 is an orbit of gamma, hard-Xrays and more than
enough secondary/recoil IR/FIR to deal with, and all of that's in
addition to whatever's available as directly from the sun.

BTW, any lander without momentum reaction wheels is nearly a lost
cause, unless their state of the art fly-by-wire as accommodated via
their fast and multiple computer driven fly-by-rocket method has
sufficient loads of spare fuel in order to properly deal with those
pesky downrange mascon issues.

Thwew's also electrostatic dust that's thick and nearly dark as coal
to deal with, plus it's still more than a bit salty as well.

Don't bother doing the physics math on those original fly-by-rocket
missions, as it simply doesn't add up.
-
"whoever controls the past, controls the future" / George Orwell
-
Brad Guth

"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)

On Jun 25, 6:57 am, "Jeff Findley"
wrote:
"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

That's correct, and it's not of any 100 km or less that is going to be
possible without continual reaction thrusting and/or having those
powerful momentum reaction wheels onboard. Either way it's added mass
and taking added energy in order to sustain any given low orbit
mission that's related to our salty old moon.

"(closest approach to the lunar surface) only 450 miles (700 km) above
the north lunar pole"

Such an elliptical orbit of 12 hours for whatever manned missions
would be doable but hardly the Apollo method, that of course never
happened in the first place.

Our gamma and hard-Xray lunar surface of cobalt and titanium mascons
is hardly a substance of Earth, and it's otherwise salty to boot.
-
"whoever controls the past, controls the future" / George Orwell
-
Brad Guth

In article ,
Jeff Findley wrote:
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...
http://science.nasa.gov/headlines/y2..._highorbit.htm

Beware, however, that all such work is based on current maps of the Moon's
gravity... and there are sizable uncertainties in the farside parts of
those maps. They are based on tracking of spacecraft in low orbit, and we
have *no* such tracking data more than 20-30deg into the farside. There
is some indirect information about the farside's gravity field to be had
from looking at spacecraft orbits before and after a farside pass, but the
data analysis is formidably difficult, and getting sane results tends to
require making arbitrary "regularization" assumptions which probably
aren't exactly true.

Worse yet, different analysts make different regularization assumptions:
you can derive more than one plausible-looking map from the same data.
And yes, searches for stable orbits give different results depending on
which map you choose!

Any pronouncements about "very stable" lunar orbits should be viewed with
some skepticism until the farside data gap is filled in.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

On Jun 25, 6:37 pm, (Henry Spencer) wrote:
In article ,

Jeff Findley wrote:
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...
http://science.nasa.gov/headlines/y2..._highorbit.htm

Beware, however, that all such work is based on current maps of the Moon's
gravity... and there are sizable uncertainties in the farside parts of
those maps. They are based on tracking of spacecraft in low orbit, and we
have *no* such tracking data more than 20-30deg into the farside. There
is some indirect information about the farside's gravity field to be had
from looking at spacecraft orbits before and after a farside pass, but the
data analysis is formidably difficult, and getting sane results tends to
require making arbitrary "regularization" assumptions which probably
aren't exactly true.


Would it be possible to map the farside gravity with something like
the GRACE mission? - two satellites in formation tracking each other.
It sounds like this is information that is sorely needed.

John Halpenny

In article om,
John Halpenny wrote:
Beware, however, that all such work is based on current maps of the Moon's
gravity... and there are sizable uncertainties in the farside parts...

Would it be possible to map the farside gravity with something like
the GRACE mission? - two satellites in formation tracking each other.

Yes. In fact, one of the short-list candidates for the next Discovery
mission (the final selection is due soon, I think) is GRAIL, which is more
or less GRACE in lunar orbit.

Mind you, if picked, GRAIL is going to cost nearly half a billion. On a
much smaller scale, both physically and financially :-), there's Lunette:
a 6-kg nanosatellite with an estimated cost under $5M that would ride to
the Moon on a larger orbiter, and then separate and fly formation with it.
Lunette wouldn't be as good as GRAIL -- it would basically just give
reliable global maps with about the same precision as the best current
nearside maps (from Lunar Prospector) -- but it would still eliminate the
farside gap, and for two orders of magnitude less money. Now, if only we
could find two orders of magnitude less money. :-( We're trying...

And Japan's SELENE, which is supposed to fly... well, sometime... (it's
already several years behind schedule) will try to do some farside gravity
mapping, but it's a multi-instrument orbiter and neither the spacecraft
nor the mission plan are ideal for gravity work, and they'll have a really
horrendous data-analysis problem. They do, at least, have money.

It sounds like this is information that is sorely needed.

Yeah, it would be really useful, both for mission planning and for lunar
geoscience. There have been *proposals* to do something about it for a
long time. (Lunette's Principal Investigator, in his younger days, was
part of a proposal to deploy a pair of small satellites from Apollo 18,
for farside gravity mapping...) But nothing has ever actually flown.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

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

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