Author Topic: Moon Rocks and the Absence of Regolith  (Read 6716 times)

Offline Dalhousie

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Re: Moon Rocks and the Absence of Regolith
« Reply #180 on: April 08, 2019, 05:58:31 PM »
There will be complex collisions between particles in the ejecta plume as well.

Offline VQ

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Re: Moon Rocks and the Absence of Regolith
« Reply #181 on: April 08, 2019, 09:23:10 PM »
That would be an example of something that escaped lunar gravity.  A closed orbit from any single impulse would likely impact the Moon.  In fact, I think this can be proven mathematically.  You need a second impulse.  For powered ascent, the velocity vector changes either constantly, or at least once subsequently.  So you go up for a while, then you go downrange for a while.  That's equivalent to multiple impulses.  It results in a velocity state that's consistent with a useful closed orbit.  This is why we have to invoke restricted n-body solutions to explain impact ejecta in lunar orbit -- N bodies because anything more than two is an iterative problem, and restricted because we ignore the gravitational effect of dust on the Moon.

An ejectum might rise high enough that Earth's gravity tugs at it just enough to circularize its orbit.  It would be a razor's edge between falling back down to the lunar surface and going into some sort of (open or closed) orbit around the Earth.  Or possibly even the Sun, in even rarer cases.  I would expect this to apply to only a tiny percentage of ejecta, and I think the tenuous clouds are consistent with that.  Particles can also accumulate in the stable Langrange points, depending on their velocity state.

ETA:  Ninja'ed by the newcomer.

The moon is also only approximately a homogeneous sphere. Mass concentrations destabilize circular low lunar orbits; presumably they also could perturb elliptical ones to be non-surface intersecting, at least temporarily?

Offline ka9q

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Re: Moon Rocks and the Absence of Regolith
« Reply #182 on: April 09, 2019, 07:55:04 AM »
An ejectum might rise high enough that Earth's gravity tugs at it just enough to circularize its orbit.
The opposite (an impact) seems more likely. Lunar orbits are notoriously chaotic and unstable; look at the Apollo handbooks for an analysis of various premature shutdowns of the CSM SPS during lunar orbit insertion. IIRC, despite the delta-V being less than a nominal LOI, some scenarios actually ended with eventual lunar impact because of the the earth's gravitational perturbations during the high nearside pass.


Offline JayUtah

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Re: Moon Rocks and the Absence of Regolith
« Reply #183 on: April 09, 2019, 12:00:22 PM »
The opposite (an impact) seems more likely. Lunar orbits are notoriously chaotic and unstable; look at the Apollo handbooks for an analysis of various premature shutdowns of the CSM SPS during lunar orbit insertion. IIRC, despite the delta-V being less than a nominal LOI, some scenarios actually ended with eventual lunar impact because of the the earth's gravitational perturbations during the high nearside pass.

That's a good point.  Overshadowing all this is the notion that there just isn't any sort of passive, long-term stable orbit around the Moon, no matter how carefully it's established to begin with.  Orbits that begin stable will soon become unstable.  I don't mean to suggest that Earth's gravity influence will convert a random trajectory into a circular orbit.  It just has to circularize it enough that the periapsis is safe for some number of revs, so that the ejecta doesn't all just fall back to the surface within a couple hours.  My interpretation of the LADEE findings is that the persistent dust clouds persist because they're being constantly refreshed by new impacts.  My handwaving toward n-body dynamics is meant to suggest a fairly complex orbital system sustaining these clouds, the details of which I haven't thought through or read about completely yet.
"Facts are stubborn things." --John Adams

Online raven

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Re: Moon Rocks and the Absence of Regolith
« Reply #184 on: April 09, 2019, 12:10:39 PM »
I wonder if photon pressure would also have an effect in helping to keep them in orbit.

Offline JayUtah

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Re: Moon Rocks and the Absence of Regolith
« Reply #185 on: April 09, 2019, 12:59:45 PM »
I wonder if photon pressure would also have an effect in helping to keep them in orbit.

If so, a very small effect, I should think.  It's more pronounced for things like artificial satellites whose solar arrays present more of a "sail" surface compared to their mass.  But at the same time, any of the classic perturbation effects should be considered, at least in theory.  The proper interpretation of the dust in the lunar exosphere, I think, is not that this is a persistent cloud of particles that's been there for billions of years, but that it's a persistent set of effects that creates an ongoing, transitory phenomenon.  Dust stays there, not necessarily strictly in orbit, but affected by gravity, electromagnetism, light, collisions, etc. so as to create zones of consistently higher dust concentrations.
"Facts are stubborn things." --John Adams

Offline Zakalwe

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Re: Moon Rocks and the Absence of Regolith
« Reply #186 on: April 09, 2019, 02:58:17 PM »
Hi mako88sb,

I clearly misspoke if you are telling me you have documentation saying it was $10k not $50k per pound of weight reduction. I thought I read it was $50k. My mistake but it still illustrates NASA desire to reduce weight not increase it.

What's your point?
Yes there was a need to reduce weight, but not at any costs. They could easily have taken a load of weight out by removing, say, the ascent engine. Of course, that would be nonsensical. Just as nonsensical as the claim that you are trying to reach for here......they were weight in thermal protection to the legs be wise they thought that they needed it.
Your claim is preposterous. If they were perpetrating a hoax then why on earth would they add thermal protection after stacking for something that never landed? Like the vast majority of hoax claims it is ridiculous when examined.

One other thing.....you have not responded to the many outstanding questions, yet you continue to visit. You were online today, for example. You appear to be getting ready for another stealth flounce now you realise that you cannot answer your interlocutors; hoping to do another crank reset by reappearing later in the hope that your outstanding questions will be forgotten; or you are chortling "hur, hur, hur" at all the attention that you have received.
Which is it?
"The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.' " - Isaac Asimov

Offline JayUtah

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Re: Moon Rocks and the Absence of Regolith
« Reply #187 on: April 09, 2019, 05:56:35 PM »
Your claim is preposterous. If they were perpetrating a hoax then why on earth would they add thermal protection after stacking for something that never landed?

And thereby inviting additional scrutiny and possible suspicion.  Not that what they were doing was at all suspicious as far as the industry is concerned.  But if they were trying to pull off something, why would they do something they would have to explain to people who, like Jr Knowing, wrongly thought post-rollout changes indicated a problem if not an outright no-no.  Why do anything expected or extraordinary?

So many of the hoax claims boil down to random nitpicks with no better narrative than the conventional one.  The claimant notices something and says, "That's not a credible way to fly a space mission."  Okay, granting that arguendo, how is it a plausible way to hoax a space mission?  Enlightenment requires more than just a knee-jerk reflex from "anomaly" to "hoax."

Quote
You were online today, for example.

And at least four separate times yesterday.
"Facts are stubborn things." --John Adams

Offline ka9q

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Re: Moon Rocks and the Absence of Regolith
« Reply #188 on: April 10, 2019, 02:35:11 AM »
If so, a very small effect, I should think.  It's more pronounced for things like artificial satellites whose solar arrays present more of a "sail" surface compared to their mass.
The 2/3 power law is very important here. Dust is much more affected by radiation pressure than larger objects, even when the materials are the same.

Offline ka9q

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Re: Moon Rocks and the Absence of Regolith
« Reply #189 on: April 10, 2019, 02:38:31 AM »
IIRC, the Apollo astronauts made observations that implied a very thin dust cloud around the moon, at least near the terminator. They saw scattered sunlight coming around the limb when they were in darkness. There's also strong evidence that the laser retroreflectors have accumulated significant dust; the Apache Point return signal strength measurements are consistently > 10 dB less than predictions.

I think the hypothesis was some form of electrostatic charging, but I haven't heard anything definite.

Offline Dalhousie

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Re: Moon Rocks and the Absence of Regolith
« Reply #190 on: April 10, 2019, 04:04:50 AM »
IIRC, the Apollo astronauts made observations that implied a very thin dust cloud around the moon, at least near the terminator. They saw scattered sunlight coming around the limb when they were in darkness. There's also strong evidence that the laser retroreflectors have accumulated significant dust; the Apache Point return signal strength measurements are consistently > 10 dB less than predictions.

I think the hypothesis was some form of electrostatic charging, but I haven't heard anything definite.

Dust may move round on the lunar surface through electrostatic processes, however the orbital dust clouds are something quite different.

Offline ka9q

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Re: Moon Rocks and the Absence of Regolith
« Reply #191 on: April 10, 2019, 05:14:43 AM »
Is "orbital" the right word? I can certainly believe that while even small impacts in any particular spot on the moon aren't frequent, they're happening somewhere all the time. This could raise a fairly continuous cloud of suborbital dust particles, ie., microscopic particles of dust that fly off the surface with an impact and return after a possibly long ballistic flight over the surface. That would get around the problem that lunar orbits are chaotic and unstable.

The moon's extremely thin atmosphere is technically known as a surface-bounded exosphere, which means the mean free path is so long that the gas atoms or molecules are more likely to hit the surface than each other. This is kind of the same thing, only with slightly larger individual particles.
« Last Edit: April 10, 2019, 05:18:28 AM by ka9q »

Offline Zakalwe

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Re: Moon Rocks and the Absence of Regolith
« Reply #192 on: April 11, 2019, 01:42:28 AM »
[
Quote
You were online today, for example.

And at least four separate times yesterday.

His "busy travel schedule" seems to be preventing him from posting again. Strangely he's not so busy that finds himself unable to login every day though.....
"The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.' " - Isaac Asimov

Offline Zakalwe

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Re: Moon Rocks and the Absence of Regolith
« Reply #193 on: April 14, 2019, 01:21:20 AM »
Back online yesterday. I wonder if someone has stolen his keyboard??? ::)
"The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.' " - Isaac Asimov

Offline Zakalwe

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Re: Moon Rocks and the Absence of Regolith
« Reply #194 on: April 15, 2019, 03:25:20 AM »
Aaannnd he's back online yesterday, but seemingly unable to have a go at answering his many unanswered questions.
Will he return? Is he a seagull poster? Maybe hoping for a fringe reset? Or should we have a whiparound to buy him a new keyboard?

So many questions..... ::)
"The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.' " - Isaac Asimov