Mining lunar ice

[Warren Platts]

Interesting link, but they seem rather indiosyncratic and old fashioned, e.g.:

1. An obvious mission that has exploration and potential feed forward implications to other locations is production of oxygen from lunar regolith;

1.1 Science implication: We don’t really know solar wind & Helium-3 content of lunar soil because we don’t know how much was lost from the Apollo samples because of agitation during the return.

Getting oxygen from regolith is soooo passé. When we go after regolith, it will be for the silicon and metals. Cracking water ice generates a large surplus of oxygen anyway.

If you want a science implication of ice mining, a core sample from the ice deposits would be very interesting to look at.

[douglas100]

From Warren Platts

 Cracking water ice generates a large surplus of oxygen anyway.[/quote]

Not if you're using the products of the cracked ice as propellants. To create excess oxygen for other purposes you would have to first reduce the regolith with the hydrogen (getting the extra products you mention),
then electolyse the water produced to regenerate the hydrogen. You would end up with the same quantity of hydrogen you started with (minus process losses, of course)  but excess oxygen for other uses.

[Warren Platts]

 Cracking water ice generates a large surplus of oxygen anyway.

Not if you're using the products of the cracked ice as propellants. To create excess oxygen for other purposes you would have to first reduce the regolith with the hydrogen (getting the extra products you mention),
then electolyse the water produced to regenerate the hydrogen. You would end up with the same quantity of hydrogen you started with (minus process losses, of course)  but excess oxygen for other uses.

Well, actually they like to run their LO2/LH2 rockets on the rich side. A "mixture ratio" (by mass) of 5 is typical, meaning they combust 5 tons of LO2 per each ton of LH2. However, the natural ratio is 8 (16 protons & neutrons per 2 protons). Thus: 5+1=6, whereas 8+1=9, and 9/6=1.5; so to make 1 ton of propellant, you have to crack 1.5 tons of water, meaning you have 1/2 ton of extra O2 per ton of propellant that will probably wind up being vented off, because there is no use for that much O2.

[JohnFornaro]

then it stands to reason that such steel would be able to be used at such temperatures to dig up ice, does it not?

Not necessarily a fer shure a priori conclusion. I don't know my way around the subject.  What I do know is that the Cryo treatment is like hyper quenching.  The steel is used at "normal" temperatures, and that's where its improved wear characteristics are used.  About the use in guns, the articles I've read have been pretty squishy on statistics and pretty impressive on marketing.  People are claiming greater accuracy.

As to the electric Bobcat: it seems to me that the center of gravity of the vehicle is exactly the same on the Moon as on the Earth.  If there was such a thing as a closed cycle diesel engine, I don't see why not, in principle, it couldn't be used in vacuum.

That issue of cryo steel requires a good understanding of its brittleness as compared to ice. Incalloy looks promising from the fact sheet.

But the other problem with a jackhammer approach to chipping the ice is the vibration.  I was thinking that little lander I sketched out was maybe six feet in diameter.  I don't think it would have sufficient mass to survive hours of jack hammering.  So I waved away that method with a laser.

It occurred to me that perhaps steam jets would also work as a fractionating tool.  The ice has to be cracked so that not too much of it melts back.

Anyhow, I made one more pass at that lander.  Two hours of my life well spent!

The platform (AA) would stand on the legs (N) with all that moving equipment below, and the O2 and H2 tanks above, as well as all the other stuff (AC), not to scale.

The DTA lander (AG) would set the whole shebang on the surface; the ISRU plant (AD), and the power reactor (AE).  Those are supposed to be nozzles (AF).  The plant and reactor would be connected by a flexible power cord, to accomodate terrain differences, and to allow for additional plants to be attached to the reactor.

Does the DTAL just hover and let down the plant and the reactor?  I think so, to minimize heating the ice surface, and to allow the possibility of dropping the reactor on one flight, then hooking up several plants on subsequent flights.

If the evap chamber (L) is fixed, then the water vapor line (M) should go on the bottom half.  I sketched some more about how that would work, but I gotta new idea.

[douglas100]

From Warren Platts:

because there is no use for that much O2.

You could export the excess oxygen to propellant depots to reduce the mass of propellant brought from Earth to support lunar operations. Whether this would be cost effective, I have no idea.

[JohnFornaro]

The girlz in the fab shop said that the first design was too complicated, and suggested a different approach to harvesting the ice.

A vapor trap (AH) is pressed into the ice by piston mechanism (AI).  The rim ofthe trap has either covective coils or heating elements (AL) which melt the trap into the ice, collecting vapor thru vapor pipe (M).  The rim is designed to be self sealing, so that little vapor is lost to space.  The vapor pipe must be flexible enough to accomodate the extension and rotation movement.

This vapor trap assembly is mounted to shaft (P), like the other version.  It rotates 360 degrees, and melts off the regolith (AK) to it's working depth.  The regolith is going to have ice and chunks of rock, and maybe layers of ejecta.  The ice harvester (AA) will not have a lot of mass to press thru anything other than ice and minimal rocky imperfections.  This means that prospecting satellite (AM) will have to accurately characterize the crater in question, so that the composition of the ice is well known.

Spudis has said that the ice is "pure", but he cannot possibly know as of today, just how pure it is, and to what extent it contains granular impurities.

The first harvester/reactor demonstration project probably ought to be contained in one unit, including the DTAL (AG).  It does not solve all problems, but demonstrates the techniques.  To get useful amounts of fuel, the idea will have to be scaled up, hence the idea of reactor/harvester clusters (AN).  After these units harvest the ice within their radii, the assembly will have to be relocated, perhaps with Bobcat (AO).

[JohnFornaro]

Hopefully it's not Ice-9

[Warren Platts]

From Warren Platts:

because there is no use for that much O2.

You could export the excess oxygen to propellant depots to reduce the mass of propellant brought from Earth to support lunar operations. Whether this would be cost effective, I have no idea.

These ice deposits should be so pure, it will only take relatively small excavations to make the lunar base self-sufficient for its local propellant needs.

According to the ULA alternative lunar architecture, a lunar base once it gets going will require at least ~300 tons per year  to be lofted to L2--whether it comes from the Earth, Moon or elsewhere makes no difference.

This in turn will require that the lunar base produce approximately ~800 tons of LH2/LO2 propellant, which will in turn require cracking ~1,200 tons of water ice, which will in turn require excavating a pit about half the size of a standard Olympic-sized swimming pool.

At today's prices, importing 300 tons of propellant from Earth is going to run you at least $12,000 USD/kg (~$3.5 billion USD) per year. So yes, I would think that local propellant production (ISRU) would be supremely cost effective.

If you want something to do with the extra oxygen, you could make ALLOX rockets. Aluminum is the densest rocket fuel known to man. The Isp is low, but the engine thrust/weight ratio is stupendous. A DTAL-sized lander could in theory lift on the order of 100 tons to lunar orbit.

[neilh]

The girlz in the fab shop said that the first design was too complicated, and suggested a different approach to harvesting the ice.

A vapor trap (AH) is pressed into the ice by piston mechanism (AI).  The rim ofthe trap has either covective coils or heating elements (AL) which melt the trap into the ice, collecting vapor thru vapor pipe (M).  The rim is designed to be self sealing, so that little vapor is lost to space.  The vapor pipe must be flexible enough to accomodate the extension and rotation movement.

This vapor trap assembly is mounted to shaft (P), like the other version.  It rotates 360 degrees, and melts off the regolith (AK) to it's working depth.  The regolith is going to have ice and chunks of rock, and maybe layers of ejecta.  The ice harvester (AA) will not have a lot of mass to press thru anything other than ice and minimal rocky imperfections.  This means that prospecting satellite (AM) will have to accurately characterize the crater in question, so that the composition of the ice is well known.

Spudis has said that the ice is "pure", but he cannot possibly know as of today, just how pure it is, and to what extent it contains granular impurities.

The first harvester/reactor demonstration project probably ought to be contained in one unit, including the DTAL (AG).  It does not solve all problems, but demonstrates the techniques.  To get useful amounts of fuel, the idea will have to be scaled up, hence the idea of reactor/harvester clusters (AN).  After these units harvest the ice within their radii, the assembly will have to be relocated, perhaps with Bobcat (AO).

This is a really neat concept -- I like the idea of using heat to vaporize the ice for extraction. I wonder though how quickly heat would need to be applied to the ice, as it would be rapidly dissipated throughout the ice itself.

[sdsds]

As a large-scale extraction technique consider this:

Construct a lid enclosing a crater that contains ice.  Direct energy into the ice by any available means, conceivably simply a mirror which reflects sunlight onto the ice through a window in the lid.  The ice sublimates to become gaseous water vapor.  Blow any available inert gas through the enclosure, ducting the exhaust to a temperature and pressure controlled extraction facility where the water vapor condenses out of the inert gas, which can be recycled back into the enclosure for further vapor extraction.

Note the presence of dust or rocks mixed into the ice is a non-issue.  Note neither the lid nor the extraction facility are exposed to particularly extreme temperatures.  Note that the extraction facility (at least) could be reused at another crater when the first one goes dry.  Note that by sealing the crater floor the lid forms a pressure vessel which could be temperature controlled by adding more (or less) reflected sunlight, into which a breathable atmosphere could be introduced.

[Bill White]

As a large-scale extraction technique consider this:

Construct a lid enclosing a crater that contains ice.  Direct energy into the ice by any available means, conceivably simply a mirror which reflects sunlight onto the ice through a window in the lid.  The ice sublimates to become gaseous water vapor.  Blow any available inert gas through the enclosure, ducting the exhaust to a temperature and pressure controlled extraction facility where the water vapor condenses out of the inert gas, which can be recycled back into the enclosure for further vapor extraction.

Note the presence of dust or rocks mixed into the ice is a non-issue.  Note neither the lid nor the extraction facility are exposed to particularly extreme temperatures.  Note that the extraction facility (at least) could be reused at another crater when the first one goes dry.  Note that by sealing the crater floor the lid forms a pressure vessel which could be temperature controlled by adding more (or less) reflected sunlight, into which a breathable atmosphere could be introduced.

A "light tube" fashioned from one way glass might work. Aim passive solar collectors at a light tube that would channel the sunlight into the domed crater.

http://en.wikipedia.org/wiki/Light_tube#Optical_fiber

Alternatively, install Fresnel lens into the lid and aim reflected passive solar at the lens.

http://en.wikipedia.org/wiki/Fresnel_lens

Also, once you collect some water you can heat that water with solar power and spray hot water onto the regolith surface. Enclosing a water bearing cold trap crater with an airtight dome will create myriad possibilities.
 

[JohnFornaro]

Thank you Neil.

The Fab girlz still said it was too complex.  "Get rid of the shaft (P)", was one of the comments raised, albeit in a less than polite fashion.

So the entire assembly (AA) and (AH) combined became the ice harvester. Reactor (AP) provides electricity, thru conductors (AS), leading to heat thingamabob (AR), which methodically melts the ice down wo the regolith, an estimated distance of 2M.  There's (ME) for scale.  In the demonstration module, the melting cone can actually expand as it goes down.  Telemetry (AQ) is provided, natch.  Vapor pipe (M) leads to the cracking chamber, unlabled for some reason. 

Not sure what the pressure of the water vapor should be, but the harvester will have to set down on the surface to start working.  The lip (AT) will be key to avoiding pressure failure (PTOO).  At landing, the harvester is on the surface, and the lip is retracted, but features heating elements.  At first, ice is melted at a low enough pressure to ensure sealing, and the harvester sinks a certain distance into the ice-olith.  It is hoped (scientific hope, so it's alright) that water leakage and freezing at the lip will maintain a good seal, but it does not have to be perfect.  At the proper depth, the lip moves outward, melting its way into a secure embedment into the ice-olith.  At that point vapor pressure can be increased and production can speed up.

Electric Bobcat (AO) will come in handy removing the O2 and H2 tanks from the harvester, and replacing them with empties.

Note that rock and other solid detritus will end up sinking to the bottom of the negative ice cylinder.

[JohnFornaro]

But does it scale? the girlz asked.  Heck yeah!

The ice harvester (AA) is hexagonal, it turns out.  An array of them melt their way into the ice-olith.  As they hit bottom, the Bobcat moves them forward in an orderly fashion, probably emptying out the tanks and performing maintenance on individual harvesters as needed.

The power arrangement is different.  The perimeter of the harvester is wired and provided with connectors, which lead to the reactor (AP), by a flexible, movable connection which goes from the reactor to the moving array of harvesters.  Alternatively, there is a adjustable bus along the edge of the array nearest the reactor, which maintains a fixed connection to the reactor, but can be segmentally adjuested to follow the array.

Now the complexity of the Bobcat can be removed.  Depending on the size of these things, a grid (AO) can be erected over a portion the ice field.  The harvesters (AA) hang from the grid, and are raised and lowered in an orderly fashion.  They can also be moved to new positions.

In fact, the grid itself can move as shown in the side view.  The last harvester remains in position to provide a vapor seal for the next to last harvester.  Then it is moved to the left, along with its grid section, and the ice is methodically removed to the floor of the crater.

At this point, one wonders about tanks at all.  Maybe the vapor is piped into the grid, and collected at a large central cracking station, which can double as a filling station, and removes all those pesky individual tanklets from the picture.  Each harvester would then be a vapor harvester only.  Rather than resting on the surface, the entire harvester sinks into the ice-olith.

The added complexity of the reconfigurable grid allows the scale of the harvesting factory to match the fuel requirements of the LV fleet.  A swath of the crater can be excavated in each pass, and the whole thing can just move itself to perform the next pass in the opposite direction.

Many small, simple harvesters begin to take advantage of mass production techniques.  Now the grid is going to be kind of tricky to figure out, but it too will be made of many similar parts.

[Warren Platts]

I can see why Neil might think that using heat to remove snow and ice would be a good idea since he's from Pasadena where it never snows. Bill, you're from Chicago. You should know better. There's a reason they don't use light tubes and Fresnel lenses for removing snow from the streets of Chicago. Any mayor that listened to you guys would be out the door faster than you can say "Jane Byrne".

Look guys, I know an Olympic sized swimming pool doesn't hold a whole lot of water, but it's more than you all seem to realize. You need to get that much in one year.

Yes, building domes over entire craters would create myriads of possibilities--just think, you could tranform the entire crater into a big lake with artificial islands. Heck it could even have a golf course with real grass! Imagine playing real golf in 1/6 g! It would be AWESOME!

If we're going to make this a science fiction thread, can we at least make it a hard-core SF thread? Something inbetween the space operas and picture books for toddlers. Something big enough to be useful for a 1st generation Moon base yet something small enough to be doable.

[JohnFornaro]

Pulease, said the girls at the fab shop.  Reconfigurable grid?  That's simpler?  Plus, when they said "scale" they didn't mean planet wide, they meant, what size is this stuff supposed to be, so we can make it?

Oh.  Assuming an olympic sized pool of ice every year, it works out that we need about 200 cubic meters of ice every month.  So step No.1 is to sink a square ice harvester, the demonstration project, into the field of ice.  Then step No.2 is the chamfered ice harvester (AA), and it's tower (AZ), which melt out the next ten meters of ice in one axis.  Then it turns 90 degrees and starts melting along the other axis.  Additional towers and harvesters are added as the treasury prints money.

Alternatively, it just goes in one direction, and the original square harvester melts a new 1m square hole in time for the arrival of the second chamfered harvester and its tower.

Not sure how the seal works on the telescoping vapor pipe (M).  The fixed location reactor, cracking station, and storage tanks will be fed by this telescoping vapor pipe.  Fixed sections might be installed every five to ten meters, but that would require interrupting the vapor flow, so this problem is still out there.  As are, truth be told, most of the other problems in this scheme, but hey.  Problems like, what happens if we encounter a boulder?

The debris scraper cleans the floor of the crater to a sufficient degree for the electrically powered tower to crawl along.  The Bobcat, which we still need, provides ballast for the tower when the harvester needs to be raised to advance the tower 1m.  It may be that ice below the 2m mark will be left in the crater.

I'm thinking that every thing in this factory is launched from Earth, because the first thing we have to manufacture is fuel and water.  If Treasury can print out dollar bills at the rate of....