Author Topic: Mining and Processing Lunar Ice  (Read 13467 times)

Offline Patchouli

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Re: Mining and Processing Lunar Ice
« Reply #60 on: 10/05/2011 11:27 PM »
{snip}
Or use that calculator for pipe strength:
Outside diameter: 1200 inches
wall thickness: 1 inch
material strength 40,000  [steel]
burst pressure 100 psi
Doesn't work- it's 67 psi, so safety factor of 2 is 33 psi
So for 15 psi you need something as strong tensional strength of 1/2" of steel. Or if base was 1/2" steel it would work. One could use a high grade steel and have higher safety factor. Or somewhere around 6" of reinforced concrete.
As the dome goes to smaller diameter as it increases in height it's walls don't have to be as thick and strong.
Making the environment pressure lower than 14.7 psi would make a considerable difference in how strong one has to make the walls- so if had larger dome, one probably need less than 10 psi.
The other aspect is you need to seal the foundation of structure so air doesn't leak out- if on bedrock that shouldn't problem, and footing were around 1' deep that would less footing then generally used on earth to support such a structure and would do a lot in direction of preventing any leaks.
{snip}

The main building material on the Moon is likely to be sintered regolith.  This can be made by microwaving local moon dust.

I do not know if the material strength and density of sintered regolith has been published.
Even sintering may not be necessary just pile it on top of an inflatable dome and the internal pressure holds everything up.
Even at 5psi you could support 720lbs of shielding mass per square foot.
« Last Edit: 10/05/2011 11:29 PM by Patchouli »

Offline 93143

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Re: Mining and Processing Lunar Ice
« Reply #61 on: 10/06/2011 12:49 AM »
The problem isn't the structural strength of the dome in the middle; it's the tension at the base.  If the dome is heavy enough, you may get a reasonable value.  If it isn't, you get a ridiculous value.  Lunar domes tend to blow off, and the bigger they are the stronger this tendency is.

This reminds of what Zubrin said in his book "A Case for Mars"- which I considered as wrong.

First the forces at the base would be compressive from the weight of the dome- the bigger the dome the more significant this force would be- and this would always be the case in a vacuum in a gravity well.

Wrong.

Consider a free-body diagram of the dome plus the atmosphere inside it above the edge.

Force upwards is atmospheric pressure times the ground projected area of the dome.  Force downwards is the weight of the dome plus the weight of the air.

If the dome and air weigh nothing, the tension (in force per unit length) at the edge is given by the upwards force divided by the circumference.  This is distinct from the lateral hoop stress induced by the pressure, though for a (hemi)sphere it should have the same value.

Now try some numbers.  Take a 500 m domed crater at 100 kPa (I hope you didn't expect tourists to be strapping on wings in a dome with a 100' diameter; let's not let the discussion drift too far from its roots...).  The upwards force is then 78.54 GN.  For a hemispherical dome, the air will weigh around 0.5 GN, and a half-inch-thick steel dome would weigh around half that.  78 GN yields an edge tension of 25 MN/m, which would put a half-inch of steel under almost 2 GPa.  Tool steel, maybe.  Structural steel?  Nope.  Regolith?  Pfft...

I suspect sintered regolith is similar to concrete, which is great in compression but awful in tension.  How do you propose to anchor this dome?  Or are you going to just continue it underground?

Nulling out 78 GN would require an average projected dome wall areal mass density of 61 Mg/m².  Sound familiar?

...

Notice how this problem only responds linearly to changes in the atmospheric pressure, and how it worsens linearly with crater size...

I'm not saying that reasonably small regolith-shielded domes aren't a good idea.  But the large transparent crater domes being talked about earlier are dubious.
« Last Edit: 10/06/2011 01:53 AM by 93143 »

Offline gbaikie

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Re: Mining and Processing Lunar Ice
« Reply #62 on: 10/06/2011 06:52 AM »
The problem isn't the structural strength of the dome in the middle; it's the tension at the base.  If the dome is heavy enough, you may get a reasonable value.  If it isn't, you get a ridiculous value.  Lunar domes tend to blow off, and the bigger they are the stronger this tendency is.

This reminds of what Zubrin said in his book "A Case for Mars"- which I considered as wrong.

First the forces at the base would be compressive from the weight of the dome- the bigger the dome the more significant this force would be- and this would always be the case in a vacuum in a gravity well.

Wrong.

Consider a free-body diagram of the dome plus the atmosphere inside it above the edge.

Force upwards is atmospheric pressure times the ground projected area of the dome.  Force downwards is the weight of the dome plus the weight of the air.

If the dome and air weigh nothing, the tension (in force per unit length) at the edge is given by the upwards force divided by the circumference.  This is distinct from the lateral hoop stress induced by the pressure, though for a (hemi)sphere it should have the same value.

Now try some numbers.  Take a 500 m domed crater at 100 kPa (I hope you didn't expect tourists to be strapping on wings in a dome with a 100' diameter; let's not let the discussion drift too far from its roots...).  The upwards force is then 78.54 GN.  For a hemispherical dome, the air will weigh around 0.5 GN, and a half-inch-thick steel dome would weigh around half that.  78 GN yields an edge tension of 25 MN/m, which would put a half-inch of steel under almost 2 GPa.  Tool steel, maybe.  Structural steel?  Nope.  Regolith?  Pfft...
Oh, I didn't realize you wanted such a large dome.
If you want to fly, perhaps caves would be better:

"On Earth, lava caves can be quite roomy, with diameters tens of meters across and hundreds of meters long. On the Moon, these dimensions may be much larger – the low gravity of the Moon results in much bigger lunar lava tubes and channels than their terrestrial counterparts, being hundreds of meters across and many kilometers long. Thus, they offer many potential advantages to future lunar inhabitants."

And:
"But the biggest problem with lunar caves is even more fundamental – they aren’t where we want them. Sustained human presence on the Moon is enabled by the presence of the material and energy resources needed to support human life and operations around the Moon. After over a decade of study and exploration, we now know that these locations are near the poles of the Moon. Unfortunately, both poles are in the highlands and finding a lava tube in such non-volcanic terrain is highly unlikely, regardless of the imaginative ramblings of certain science-fiction authors. If a lunar cave were present there, we would certainly consider using it. But it makes no more sense to locate a lunar base near the caves, than it does to build a water-park in the Sahara desert.

The formation of lunar lava tubes and caves is an interesting scientific topic, but their utilitarian value is uncertain, at least until we have established a permanent presence on the Moon. "
http://lunarnetworks.blogspot.com/2009/10/paul-spudis-caves-on-moon.html

So, if tourists go to the Moon to fly, they might go a fair distant from human settlements, but making 500 meter dome would be fairly expensive.
But again it probably require less materials than 500 meter dome on Earth would require.
Perhaps also you could use buffer gases with a higher density than nitrogen.


Offline 93143

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Re: Mining and Processing Lunar Ice
« Reply #63 on: 10/06/2011 08:36 AM »
Just for reference, these are the posts that started the proximate discussion:

My favorite idea is to build a dome over a shadowed polar crater with a glass panel upper part and mirrors around it. When the dome is finished sunlight is reflected in and the first rain storm on the Moon forms a lake on the floor of the crater. After plants are introduced there is the possibility of a self sustaining if small biosphere beyond Earth.
You could build a dome like Marshall Savage suggested in "The Millenial Project" that has water between its geodesic framed glass layers. It is self sealing since escaping water will freeze to seal any micrometeoroid holes.
 You could save a whole bunch of money by building "TerraLuna" using telerobots and then bringing the people. If one atm pressure is used, tourists could strap on wings and fly by their own muscle power as they look down on skateboarders and skiers make jumps six times as high as seen on Earth.

If you build it they will come.

A hundred-foot dome is actually a reasonably small building.  That's not what we're talking about.

But again it probably require less materials than 500 meter dome on Earth would require.

What are you talking about?  Sixty tonnes per square metre is eight metres of solid steel...

Remember, the issue is not the strength of the dome; it's the strength of the ground underneath it.  Dirt, rock, concrete, sintered regolith - anything like that will have miserable strength in tension.  To avoid having to make the dome super heavy, you'd have to extend the dome structure underground, and/or possibly make a complete enclosure...  not too hard with the 100' model (just give it a floor), but a crater dome would be quite the excavation project...

Domes on Earth don't even need to resist the internal atmospheric pressure.  The external atmospheric pressure does that for them.

Quote
Perhaps also you could use buffer gases with a higher density than nitrogen.

First, it wouldn't help much.  You'd need a dome almost two orders of magnitude larger than the one I described for the weight of the air to be a significant fraction of its integrated pressure.  You can't bridge that kind of gap just with heavier gases.  And with a dome big enough for it to help, the force balance would have to be exquisite to avoid a blowoff - solar heating of the enclosed air would probably be enough to make this a non-starter...

(Or you could just make the dome taller without making it wider - more like a tower than a dome...  it still ends up ridiculously big...)

Second, using a heavier gas would cause buoyancy separation.  Earth's atmosphere works fine because (a) it's constantly mixed, and (b) oxygen and nitrogen have roughly the same molecular weight.  You don't want all your breathing oxygen collecting at the top of the dome because you used xenon as a buffer gas...

...

I'm wondering whether a lava tube wouldn't have trouble with blowouts if you tried to fill it with 1 bar of air...  Maybe any large open-air spaces on the moon will simply have to be fully-enclosed structures...
« Last Edit: 10/06/2011 08:47 AM by 93143 »

Offline JohnFornaro

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Re: Mining and Processing Lunar Ice
« Reply #64 on: 10/06/2011 02:04 PM »
Well.  Whatever the dome will be, it will probably not be the main structure.  I'd see it as a scenic opportunity, perhaps with higher priced hotel rooms featuring an Earth view.  It would be a pretty advanced structure, probably not built at first.

The idea of flying around is too far into the future to be thought about more than a sentence or two here in the present time.  The size of the initial habitats would be a better thing to spend time on.

I think there's a possibility of re-purposing semi cylindrical stage sections for a covering by regolith.  The inside would have to be sealed somehow, and enough regolith would have to cover the habitat to make blowout impossible.  The semi-circular end of the habitat would have the airlock.  If they were thrity feet in diameter and sixty feet long, they'd be somewhat larger than a single family residence; four to eight people could be accomodated without crowding.

If a hub and spoke design were considered, a smallish dome could be the central hub.
Sometimes I just flat out don't get it.

Offline Solman

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Re: Mining and Processing Lunar Ice
« Reply #65 on: 10/06/2011 08:24 PM »
 Wouldn't the dome only need to have the same air density as 1 atm. on Earth? Perhaps you need more pressure than that but if this is sufficient, in that case it could have a little over 33ft. of water between the glass and have excess weight which the dome structure could take so that there would be no need to keep pressure precisely balanced. The dome could be quite large and its excess weight handled by a foundation of sintered regolith since the foundation could be wide and deep as need be. The dome need only be partially made of glass-water-glass since regolith can be piled on steel or aluminum or whatever parts of the dome as needed. Alternately, concentrated sunlight from mirrors could reduce the amount of glass-water-glass required for adequate interior illumination.  Balancing dome mass and atmospheric pressure would be necessary during construction but thereafter the dome's mass would exceed internal pressure at its maximum.
 Flight would be less easy but the jumps even a little higher.

Steve Mickler

Offline gbaikie

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Re: Mining and Processing Lunar Ice
« Reply #66 on: 10/06/2011 10:19 PM »
Just for reference, these are the posts that started the proximate discussion:

My favorite idea is to build a dome over a shadowed polar crater with a glass panel upper part and mirrors around it. When the dome is finished sunlight is reflected in and the first rain storm on the Moon forms a lake on the floor of the crater. After plants are introduced there is the possibility of a self sustaining if small biosphere beyond Earth.
You could build a dome like Marshall Savage suggested in "The Millenial Project" that has water between its geodesic framed glass layers. It is self sealing since escaping water will freeze to seal any micrometeoroid holes.
 You could save a whole bunch of money by building "TerraLuna" using telerobots and then bringing the people. If one atm pressure is used, tourists could strap on wings and fly by their own muscle power as they look down on skateboarders and skiers make jumps six times as high as seen on Earth.

If you build it they will come.

A hundred-foot dome is actually a reasonably small building.  That's not what we're talking about.

As for glass dome or ice domes, a relatively small panel, say 10' by 10'
wouldn't require very thick glass [not much than more than 1 inch] or Ice [much more than 1 foot] to withstand 15 psi. A smaller panel should be able to be office window glass. That my guess. But as I said you probably operate with reduced pressure- somewhere around 10 psi or less, and with curved glass [or ice] it would add structural strength.
The Japanese are big with tourist submarines [and Canadians:]
Operating depth (max.)    76 meters (250 feet)
http://www.sirenasubmarine.info/specifications.html
Viewport side - 30 inches x 4.4 inches thick
http://www.sub-find.com/v48.htm
So those windows can withstand more than 7 atm.

But again it probably require less materials than 500 meter dome on Earth would require.
Quote
What are you talking about?  Sixty tonnes per square metre is eight metres of solid steel...

8 cubic meters of steel does weigh about 60 tonnes. but not sure what that has to do with it. 39.37" by 39.37" is 1550 sq inches at 14.7 psi
it's 22,785 lb or about a 1/6th 60 tonnes.
Oh I see you think you have to equal the pressure with weight. If you did that you need little structural strength- sand might give you enough "structural strength". So plastic liner and sand or lunar regolith. That is a hard way to make something- and if any decompression, it could murderous for anything inside. I would guess a foot or two of steel would be overkill.


Quote
Remember, the issue is not the strength of the dome; it's the strength of the ground underneath it.
Nope. The ground underneath isn't a problem in terms of it's strength.

Quote
  Dirt, rock, concrete, sintered regolith - anything like that will have miserable strength in tension. 
Yes generally poor tensile strength, but a tree stump is pretty hard to pull out of the ground. And rock can drilled into and using steel cables it can be anchored to, such that tensile force could break the cable rather than be pulled out of the rock.
But this is assuming one needs a lot tensile strength at the base of the dome- that something weighing million of tons is going leap straight up, as though it was some massive rocket.
Let's look at it as a rocket type thing and look at forces propelling it in a certain directions. All the gas is going in random directions- this random motion [pressure] makes 15 lb force per sq inch in any direction.

We are interested in the upward direction of force which can be "expressed" with 15 psi.
Assertion: The maximum pressure that can go in one direction is the area of it's diameter.
Remember we are concerned about it going up [one direction]- otherwise I see no reason why you are concerned about the tensional strength of dirt.
Let's look at sphere and a cylinder. Both will have a diameter of 2000 feet. Cylinder length/height can be any length 5 feet or 2000 feet.
Let's make it 10 feet.
And let's give the sphere and cylinder walls of 10 feet thick high strength steel.
The radius [1000 times 12] is 12000 inches. Squared is 144,000,000.
Times pi is  452,388,960 square inches.
10 psi is  4,523,889,600 lbs
15 psi is 6,785,834,400 lbs
Lots of force:)
So with 15 psi with cylinder or sphere which is 2000' in diameter
is around 6.78 billion lbs.

An Area of sphere is 4 times pi radius squared. Hemisphere would half of that. Hemisphere would have twice the area as it's diameter.

Well how much cubic feet of steel is in 2000 inside diameter sphere with 10 feet walls. It's 12,566,360 sq feet times 10 [roughly]
So 125,663,600 cubic feet of steel.
A cubic foot of steel is about 489 lbs.
So 125,663,600 cubic feet of steel on earth would weigh
61,449,500,400 lb
On the moon it would 1/6th this 10,241,583,400 lbs.
And a hemisphere would be half of that:
5,120,791,700 lb
5.1 billion lb
Compare to 15 psi: 6.78 billion lbs
And 10 psi: 4.5 billion lbs

Now this is a hideous amount of steel.
On Earth it's 61,449,500,400 lb
Or 30.7 million tons. If steel is worth $1000 per ton,
it's over 30 billion dollars just for the steel.

The golden gate bridge:
"The total combined weight of the Bridge today is 887,000 tons"
http://www.pcimagenetwork.com/golden_gate/golden_gate.html
So it's over 30 times as much mass.
Mass of the World Trade Center:
930,000,000 kg
So more than 30 golden gate bridges or World Trade Centers.
Or 5 hoover dams:
"6.6 million tons"
http://www.buzzle.com/articles/facts-about-hoover-dam.html

Edit: An aircraft carrier displaces 98,000 tonnes:
http://wiki.answers.com/Q/What_is_the_weight_of_an_aircraft_carrier
So over 300 of them :)

Though I haven't made any effort at designing this economically- that
would probably involve anchoring it to bedrock, and using the tensional strength of steel instead of merely it's weigh.
I would guess you could reduce it's steel use by 9/10th.
A such a well designed structure would use less material than a similar size structure on earth.

Oh, didn't really finish with the bit about the cylinder. Sorry.

Another Edit: "I'm wondering whether a lava tube wouldn't have trouble with blowouts if you tried to fill it with 1 bar of air...  Maybe any large open-air spaces on the moon will simply have to be fully-enclosed structures... "
I wouldn't surprised if lava tube experienced more pressure when were created. The pressure to push water up 33' feet on earth is 1 atm, to push lava the same distance up if twice the density of water is 2 atm.
On the moon it's 6 times this height.
Lava tube tend to be fairly level, but if over the miles of lava tube on the Moon if increases height by 100' then the lower portion probably have undergone as much pressure.
Or if it's say 100' under the surface, it shouldn't be a problem- though there could leaks which would need to be found and sealed.

« Last Edit: 10/06/2011 11:16 PM by gbaikie »

Offline Hop_David

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Re: Mining and Processing Lunar Ice
« Reply #67 on: 10/06/2011 11:11 PM »
Wouldn't the dome only need to have the same air density as 1 atm. on Earth?

From the OP: "What would be required to mine Lunar ice, melt it and split it into hydrogen and oxygen?"

Somehow this thread has morphed into a lunar resort with transparent glass domes and enough pressure to accommodate pregnant women.

Even 4/5 of an atmosphere (such as people in Denver must endure) is adequate for pregnant women. (Last I heard people were reproducing okay at the mile high city).

If we're talking about lunar miners doing a 6 month tour of duty, I think you could do with half an atmosphere, especially if it's oxygen enriched.

Offline 93143

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Re: Mining and Processing Lunar Ice
« Reply #68 on: 10/07/2011 03:39 AM »
Oh I see you think you have to equal the pressure with weight. If you did that you need little structural strength- sand might give you enough "structural strength". So plastic liner and sand or lunar regolith. That is a hard way to make something- and if any decompression, it could murderous for anything inside. I would guess a foot or two of steel would be overkill.

You're sort of getting it.  The idea is that either you use a really heavy dome, or you have a big problem with tension at the base.

I never said you had to use steel.  It was just a reference point.  Perhaps I should have said 23 metres of fused quartz, or 66 metres of water ice, so as not to confuse you...

Quote
Quote
Remember, the issue is not the strength of the dome; it's the strength of the ground underneath it.
Nope. The ground underneath isn't a problem in terms of it's strength.

That's a pretty bold assertion.  Let's see if there's adequate support forthcoming...

Quote
Quote
Dirt, rock, concrete, sintered regolith - anything like that will have miserable strength in tension. 
Yes generally poor tensile strength, but a tree stump is pretty hard to pull out of the ground. And rock can drilled into and using steel cables it can be anchored to, such that tensile force could break the cable rather than be pulled out of the rock.

...and that's it.

Surely you realize that without numbers, examples like this (that aren't even remotely on the same scale as the problem at hand) are completely worthless...

A tree stump is "pretty hard" to pull out largely because of its massive root system, which means that a very large chunk of ground, including the part you're trying to use as leverage to pull the stump out, is directly invested in keeping that stump where it is.

Assuming you're right about the anchored cable (you didn't provide so much as an anecdote, never mind an analysis), it still proves nothing, because (a) just as with the tree stump, you get a bonus from the anchoring that's proportional to the square of the difference in diameter between the cable and the anchor structure, whereas with a wall the bonus is merely linear, and (b) the strength of rock is strongly scale-dependent, such that intact chunks of granite can be as much as 1/10 as strong in tension as mild steel, whereas on a large scale it may not perform any better than dirt.

We're dealing with a very large scale here.

I only see two ways to make this work without a truly ridiculous dome mass:

(1) use a complete man-made enclosure, so that you don't have to worry about atmospheric pressure loads on natural rock formations, or

(2) get a comparable mass of regolith weighing down on a man-made structure that has reliable tensile strength.  Either a huge "root system" of sorts, or a partial underground continuation of the dome.

Quote
But this is assuming one needs a lot tensile strength at the base of the dome- that something weighing million of tons is going leap straight up, as though it was some massive rocket.
Let's look at it as a rocket type thing and look at forces propelling it in a certain directions.

I already did that.  I'm not "assuming" anything.

Quote
Well how much cubic feet of steel is in 2000 inside diameter sphere with 10 feet walls. It's 12,566,360 sq feet times 10 [roughly]
So 125,663,600 cubic feet of steel.
A cubic foot of steel is about 489 lbs.
So 125,663,600 cubic feet of steel on earth would weigh
61,449,500,400 lb
On the moon it would 1/6th this 10,241,583,400 lbs.
And a hemisphere would be half of that:
5,120,791,700 lb
5.1 billion lb
Compare to 15 psi: 6.78 billion lbs
And 10 psi: 4.5 billion lbs

The reason your numbers differ from mine is that you've assumed constant wall thickness in the radial direction instead of uniform weight distribution (constant wall thickness in the vertical direction).  This doubles the weight of your dome (or cuts its thickness in half).  For uniform weight distribution, to get the same weight you'd need a peak thickness of 20 feet of steel.  To counter 14.7 psi you'd need 1.3 times that, so 26 feet = 8 metres.

More importantly...  are you really trying to prove that the dome is heavy enough to counter the pressure by simply assuming that it's thick enough to be that heavy?  Where did you get that 10' thickness?  It's not from pressure vessel theory; I know that much...

There are two cases here.  One: a dome thick enough to counter the atmospheric pressure inside it by weight alone.  Two: a dome that exerts a strong tensile load on its base due to internal pressure.  You cannot conflate them and expect to have made a point.

Quote
Now this is a hideous amount of steel.

No argument there.  Even on Mars it would be a mild annoyance to have to acquire that much steel.

Quote
I would guess you could reduce it's steel use by 9/10th.

You would guess?  Based on what?

For a 500-metre radius hemispherical dome, atmospheric pressure could be contained by five inches of steel loaded to 200 MPa, and your 2000'-diameter dome could make do with three inches.  For safety and to allow for lower-strength steel (hot-formed 1020, say), you could double that, and then add a similar mass below ground for anchoring purposes (this last is probably conservative).

...hmm - it does end up about 92% lighter.  Good guess.

Quote
A such a well designed structure would use less material than a similar size structure on earth.

Can you support this assertion?  Remember, on Earth there's no anchoring problem, so you're talking about two feet of solid steel...

Quote
I wouldn't surprised if lava tube experienced more pressure when were created. The pressure to push water up 33' feet on earth is 1 atm, to push lava the same distance up if twice the density of water is 2 atm.
On the moon it's 6 times this height.
Lava tube tend to be fairly level, but if over the miles of lava tube on the Moon if increases height by 100' then the lower portion probably have undergone as much pressure.

This is just handwaving.  First, you're making an unjustified, unsupported assumption about lunar geology, that seems to fly in the face of structural considerations.  If you imagine that something might have happened, and the math says it's impossible, the math wins.  Second, that's not how lava tubes work.  Static pressure calculations are inapplicable.

Quote
Or if it's say 100' under the surface, it shouldn't be a problem- though there could leaks which would need to be found and sealed.

Yes, that's different.

Offline Solman

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Re: Mining and Processing Lunar Ice
« Reply #69 on: 10/07/2011 11:36 AM »
Wouldn't the dome only need to have the same air density as 1 atm. on Earth? Perhaps you need more pressure than that but if this is sufficient, in that case it could have a little over 33ft. of water between the glass and have excess weight which the dome structure could take so that there would be no need to keep pressure precisely balanced. The dome could be quite large and its excess weight handled by a foundation of sintered regolith since the foundation could be wide and deep as need be. The dome need only be partially made of glass-water-glass since regolith can be piled on steel or aluminum or whatever parts of the dome as needed. Alternately, concentrated sunlight from mirrors could reduce the amount of glass-water-glass required for adequate interior illumination.  Balancing dome mass and atmospheric pressure would be necessary during construction but thereafter the dome's mass would exceed internal pressure at its maximum.
 Flight would be less easy but the jumps even a little higher.

Steve Mickler

 Okay this was a total brain lapse on my part. I was confusing the pressure of gas in an enclosure with the pressure that the gas would have if it was part of a Lunar atmosphere. To have one atm. pressure, the atmosphere would have to be six times as dense, but of course we're not talking about Lunar terraforming. Of course lower pressure means less density in the case of a dome.
 I will now skulk away in embarrassment.
Steve
 I will n

Offline JohnFornaro

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Re: Mining and Processing Lunar Ice
« Reply #70 on: 10/07/2011 12:49 PM »
Quote from: Hop David
From the OP: "What would be required to mine Lunar ice, melt it and split it into hydrogen and oxygen?"

There's several ways to read the OP.  The reading could be limited to: What are the specific ways to melt the ice and crack it, without any consideration of the infrastructure used to support the melting and cracking.  My take is that the thread has indeed morphed into a dome of Kublai Khan, with more emphasis on the tourist activities and less on the mining support activities.

Quote
If we're talking about lunar miners doing a 6 month tour of duty, I think you could do with half an atmosphere, especially if it's oxygen enriched.

It occurs to me that probably the home base should be a simulation of Earth's atmo, but the air in the shirtsleeve mining equipment should probably be the low pressure, oxygen rich set up.  So the miners work their eight hour shift, say, in the lo-pressure environment, and recuperate back at the base.  Any de/re-compression takes place as required, and is a part of the work routine.

The idea of the water filled dome "sandwich" seems excessive and impractical for the early stages of the base.  It may be "self-healing" and probably translucent to a degree, but it could not be built early, since it simply requires too much industrial infrastructure itself.  Consider that it would need enormous amounts of pure enough water, structure, sintering, drilling and anchoring, and fairly heavy equipment.
Sometimes I just flat out don't get it.

Offline gbaikie

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Re: Mining and Processing Lunar Ice
« Reply #71 on: 10/07/2011 08:11 PM »
Wouldn't the dome only need to have the same air density as 1 atm. on Earth? Perhaps you need more pressure than that but if this is sufficient, in that case it could have a little over 33ft. of water between the glass and have excess weight which the dome structure could take so that there would be no need to keep pressure precisely balanced. The dome could be quite large and its excess weight handled by a foundation of sintered regolith since the foundation could be wide and deep as need be. The dome need only be partially made of glass-water-glass since regolith can be piled on steel or aluminum or whatever parts of the dome as needed. Alternately, concentrated sunlight from mirrors could reduce the amount of glass-water-glass required for adequate interior illumination.  Balancing dome mass and atmospheric pressure would be necessary during construction but thereafter the dome's mass would exceed internal pressure at its maximum.
 Flight would be less easy but the jumps even a little higher.

Steve Mickler

 Okay this was a total brain lapse on my part. I was confusing the pressure of gas in an enclosure with the pressure that the gas would have if it was part of a Lunar atmosphere. To have one atm. pressure, the atmosphere would have to be six times as dense, but of course we're not talking about Lunar terraforming. Of course lower pressure means less density in the case of a dome.
 I will now skulk away in embarrassment.
Steve
 I will n

If open an empty container at sea level with air pressure at 14.7 psi at 70 F and seal it. The container will have 14.7 psi at 70 F and the same air
density regardless of gravity- zero gee or 10 times earth gravity.

If you want higher density of air at same pressure you could use colder air. Lunar flying could be like skiing- one could have air say -50.
One might also do even colder temperatures and provide heat to the flyers via radiation- they wear suits in which one dials up the heat. And you probably need to pre-heat air they breathed.

Or you use denser buffer gases which are non-toxic.
« Last Edit: 10/07/2011 08:16 PM by gbaikie »

Offline Solman

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Re: Mining and Processing Lunar Ice
« Reply #72 on: 10/07/2011 11:54 PM »
 I thought the air pressure represented the weight of a column of air from sea level to infinity. In order for the Moon to have an atmosphere in which a column of air from ground to infinity weighs 14.7 lb. in^2, that column would have to have six times the mass of a column that would weigh that much on Earth (ignoring gravity weakening with altitude). I was wrong again to say six times denser before - it's six times more massive and extends much higher from the surface.
 
Or do I still have that wrong?
 
Anyway, it seems that there are ways to anchor the dome into the regolith in much the same way a suspension bridge anchors its cables or perhaps by piling thick layers of regolith over subterranean structure around the perimeter of the dome. The glass-water glass skinned large aluminum strut geodome idea would give an almost unobstructed view and the tourist would be able to actually touch the Lunar surface with bare hands.

TerraLuna
"The ultimate playground"

Steve
« Last Edit: 10/07/2011 11:56 PM by Solman »

Offline gbaikie

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Re: Mining and Processing Lunar Ice
« Reply #73 on: 10/08/2011 12:35 AM »
I thought the air pressure represented the weight of a column of air from sea level to infinity. In order for the Moon to have an atmosphere in which a column of air from ground to infinity weighs 14.7 lb. in^2, that column would have to have six times the mass of a column that would weigh that much on Earth (ignoring gravity weakening with altitude). I was wrong again to say six times denser before - it's six times more massive and extends much higher from the surface.

Or do I still have that wrong?


Yeah that is correct but planets aren't in containers.
Containers are "artificial" pressure rather than "natural" pressure.

Getting natural atmosphere on the Moon won't work.
Getting one on Mars is thought to be possible- I have my doubts:)
 
« Last Edit: 10/08/2011 12:37 AM by gbaikie »

Offline Solman

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Re: Mining and Processing Lunar Ice
« Reply #74 on: 10/08/2011 12:45 AM »
 Thanks. Seems like I read that a Lunar atmosphere would have a pretty long half-life though: and new atmosphere could be made constantly by liberating oxygen from regolith but I think a real big dome and then more domes over time at the poles is the way to go first.

Steve

Offline 93143

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Re: Mining and Processing Lunar Ice
« Reply #75 on: 10/08/2011 02:15 AM »
If you want higher density of air at same pressure you could use colder air. Lunar flying could be like skiing- one could have air say -50.
One might also do even colder temperatures and provide heat to the flyers via radiation- they wear suits in which one dials up the heat. And you probably need to pre-heat air they breathed.

Or you use denser buffer gases which are non-toxic.

Why are you trying to increase the air density?  It doesn't help with the blowoff problem, and I already explained why using a dense buffer gas is a bad idea.
« Last Edit: 10/08/2011 05:04 AM by 93143 »

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