Lunar ice on the rocks Options

[Guest_AlexBlackwell_*]

There's a real interesting paper by Donald B. Campbell et al. entitled "No evidence for thick deposits of ice at the lunar south pole," which is being published in the October 19, 2006, issue of Nature. See the Editor's Summary for a synopsis and links.

See also a related Space.com story and a EurekAlert press release.

[edstrick]

Apart from the generally discounted claim from extremely limited Clementine bistatic radar observations, there has been no radar support for the presence of thick, radar-bright (diffuse internal scattering in a thick non-absorbing layer) ice in lunar polar shadows. Media reports, typical of media controversy-mongering, have presented viewpoints with unequal support in terms of quality and quantity of evidence as opposing sides in the lunar polar ice debate. The "best guess" consensus is that ice is widespread, but at low abundance, and is mixed into the regolith at low percents levels.

But consider.. in 1 cubic meter of regolith, how much is 1% by weight water ice?. A liter?.. several liters?...I'm too lazy to do the math but it's a big resource if it's not wasted in throw-a-way uses.

[helvick]

But consider.. in 1 cubic meter of regolith, how much is 1% by weight water ice?. A liter?.. several liters?...I'm too lazy to do the math but it's a big resource if it's not wasted in throw-a-way uses.

Assuming that it's of similar density to dry sand or gravel on earth regolith would be around 1.5 tons mass per cubic metre. 1% of that by mass of that is 15kg is 15 litres, marginally better than 1% by volume which would have been 10litres.

[Stephen]

Assuming that it's of similar density to dry sand or gravel on earth regolith would be around 1.5 tons mass per cubic metre. 1% of that by mass of that is 15kg is 15 litres, marginally better than 1% by volume which would have been 10litres.

I suspect lunar regolith will be more hardpacked than dry sand or gravel.

There's a discussion of the density of lunar regolith in this article. At one point the authors say that "we consider the density of [lunar] rocks and regolith is 3.0 g/cm3 and 2.0 g/cm3".

Given that there are 100 * 100 * 100 (=1 million) cubic centimetres per cubic metre and a million grams per metric ton (1000 gram per kg and 1000 kg per ton), if we assume a density of 2.0 g/cubic cm then we are talking about 2 million grams (==2 metric tons) per cubic metre.

1% of that == 20kg == 20 litres.

2 tonnes, even at 1/6 of a G, would be an awful lot of dirt to have to shift to obtain enough ice to fill just one watercooler with the wet stuff. (Watercoolers, according to this Wikipedia page, hold 5 gallons or about 18.9 litres.)

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Stephen

[edstrick]

Trick question that's not a trick question

What is an "ore"

An ore is rock material that can be PROFITABLY mined and have an economically valuable resource extracted from it.

When the price of a commodity <copper, for example> goes up, or a more cost effective mining and processing method is developed.. Rock turns into Ore and abandoned mines start working again. When the price goes down, ore turns back into rock and the mine goes bankrupt.

Even at 1% by weight or volume... given the cost of transporting water or hydrogen to the moon, ice-bearing regolith will be a valuable ore.

[Stephen]

Even at 1% by weight or volume... given the cost of transporting water or hydrogen to the moon, ice-bearing regolith will be a valuable ore.

That all depends whether transporting water or hydrogen to the moon is more costly than mining the ice-bearing ore on the moon, extracting the ice from the ore, then shipping it off to the various lunar bases situated in various places around the moon where it will be used.

• For some time to come the moon will have no factories with which to make the earthmoving & ore-extraction equipment which will be required to extract the ice from the ore deposits (which means all that sort of stuff will need to be shipped up from earth, along with any spare parts and repair crews that may from time to time be needed).
• Not all lunar bases--or even any lunar bases--are going to be situated conveniently close to a patch of ice-bearing ore (which means, given the lack of lunar roads and railways and piping systems, shipping the water will probably require tanker rockets or some equivalent to fly it to where it is needed; unless of course somebody were to spend the billions of dollars to build the necessary road(s), rail line(s), or pipe(s)).

You might also bear in mind that the ice-bearing ore is likely to be a strictly limited resource. That not only means that after it is all gone, whether used for rocket fuel, to water lunar gardens, or whatever, lunar residents may well have little other choice but to get their next supply of water from the Earth anyway. It also means there may not be enough of suitable ore there on the moon to justify the expense of setting all the infrastructure etc necessary to extract the ice then ship it to wherever it is needed even if getting it from Earth were more expensive.

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Stephen

[helvick]

Even at 1% by weight or volume... given the cost of transporting water or hydrogen to the moon, ice-bearing regolith will be a valuable ore.

Interestingly (to me at any rate) the fairly high specific heat capacity of water (4186 j/(kg.K)) vs iron (440 j/(kg.K) might make it harder to "smelt" out water from regolith than iron, assuming iron smelting requires raising ore to ~1250C and water "smelting" requires a temperature of slightly over 0C.

Extracting water by raising the temp past 100C would probably be the easiest process to work through but that would definitely require significant amounts of energy (almost 300kwhr/ton just to get the regolith up to working temperature for the start of the process).

[ugordan]

Wikipedia suggests the specific heat capacity of water ice is roughly 2x lower (2.108 kJ/kgK) than its liquid phase. You also have to take into consideration the specific melting heat of water which is 334 kiloJ/kg (see here) for a complete energy cost.

[climber]

That all depends whether transporting water or hydrogen to the moon is more costly than mining the ice-bearing ore on the moon, extracting the ice from the ore, then shipping it off to the various lunar bases situated in various places around the moon where it will be used.

• For some time to come the moon will have no factories with which to make the earthmoving & ore-extraction equipment which will be required to extract the ice from the ore deposits (which means all that sort of stuff will need to be shipped up from earth, along with any spare parts and repair crews that may from time to time be needed).
• Not all lunar bases--or even any lunar bases--are going to be situated conveniently close to a patch of ice-bearing ore (which means, given the lack of lunar roads and railways and piping systems, shipping the water will probably require tanker rockets or some equivalent to fly it to where it is needed; unless of course somebody were to spend the billions of dollars to build the necessary road(s), rail line(s), or pipe(s)).

You might also bear in mind that the ice-bearing ore is likely to be a strictly limited resource. That not only means that after it is all gone, whether used for rocket fuel, to water lunar gardens, or whatever, lunar residents may well have little other choice but to get their next supply of water from the Earth anyway. It also means there may not be enough of suitable ore there on the moon to justify the expense of setting all the infrastructure etc necessary to extract the ice then ship it to wherever it is needed even if getting it from Earth were more expensive.

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Stephen

I some aspects, "Water", could become "Lunar petrol" in the sense that we are ALREADY putting some mean to find it. As you say, then we'll have extraction, transportation, etc...
I guess, water ice, will have FIRST to be studied scientificaly.
I hope we'll have a better use of this ressource compared to what we did/do on Earth for the petrol.
Anyway, even with a 10-20 liters/ton of regolith in some places, the ressource is there for quite a while.

[dvandorn]

A tiny bit of the water at the lunar poles might well already have been transported there from Earth. Hundreds of pounds of water were released by Apollo vehicles and equipment, both on the surface and in lunar orbit. The LM, for example, cooled its systems using ice-encased sublimators. The PLSS backpacks the astronauts wore were also cooled using ice sublimation. Heck, a water seal leak on Apollo 15 resulted in the wholesale dumping of about 30 liters of water onto the surface.

While most of that water was likely lost to space and has been pushed out to the far ends of the solar system by solar winds by now, a little of it must have migrated to the always-cold portions of the lunar poles.

So, just a little tiny bit of the polar water has already been imported...

-the other Doug

[AndyG]

Anyway, even with a 10-20 liters/ton of regolith in some places, the ressource is there for quite a while.

IF that percentage is correct. Surely aeons of regolith-transportation, larger impact-churning and surface solar heating is going to make that highly unlikely for most areas?

Meanwhile, writing in the very small corner left on my envelope, the cost of taking water to the Moon is at the very least 60k$ per kilo, assuming the LEO-Lunar Surface architecture is in place, bought & paid for. Hmmm...$1500 per sip. For long stays that has to make in-situ resource utilisation essential, to my mind - or at least require extremely closed-cycle life support.

As to extracting any local supplies, I'm not sure the energy to release water as vapour is a problem. It can be well over 100C in sunlight-that-lasts-for-weeks, after all. If we could fly Stakhanovites to the Moon, they could be shovelling regolith at 100 tonnes per hour...

Andy

[Stephen]

As to extracting any local supplies, I'm not sure the energy to release water as vapour is a problem. It can be well over 100C in sunlight-that-lasts-for-weeks, after all. If we could fly Stakhanovites to the Moon, they could be shovelling regolith at 100 tonnes per hour...

Ah! but there will not be any sunlight at all down inside those craters of eternal darkness where the ice is supposed to have collected. That's the point! Whatever machinery is used to excavate the ore will therefore either not be solar powered at all or will be reliant on cables (or maybe wireless power) to get the power from solar collectors positioned elsewhere. Eg up on the crater rims.

As for the machinery which releases the ice from the ore, would that be down inside those craters of eternal darkness or somewhere where power was more readily accessible?

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Stephen

[JTN]

The Space Review has recently posted a summary of observations to date, by Paul D. Spudis.

[JonClarke]

The Space Review has recently posted a summary of observations to date, by Paul D. Spudis.

That's a very nice article. It's worth working out some of the first approximation process issues involved assuming 2% water content in the upper regolith.

That is 20kg of water per tonne or, at a density of 2, 40 kg (or L, if you prefer) per cubic metre of regolith.

A commonly used figure is a ration of 30 kg of water per person per day in space. Assuming 90% recycling, as on the ISS, that is 3 kg per person per day, 12kg for a four person crew.

A station with a crew of four would need to process 600 kg of regolith to supply the daily requirements, or 0.3 cubic metres.

Before we could start utilisng the water we would need to know it distribution, grade, and water other ices (CO, CO2, CH4, NH4, SO2 etc.) occur along with it. Plus the mechanical properties of the ice bearing regolith (essential for extractive system design).

With this we could decide whether the ice were best extracted in situ, or excavated and processed somewhere else,

Then we would need a suitable plant to extract the water. I suggest a low pressure, solar heated, and shade cooled fractional distillation process would be best.

So a lot of basic field science, engineering, and mineral processing research is needed before an operational system could be set up.

Jon

[edstrick]

Spudis' article is entirely consistent with everything I know about the lunar polar volatiles observations and theorizing.

I'm rather annoyed that Lunar Recon Orbiter doesn't have a multi-frequency/multi-polarization rader scatterometer/imager. Doesn't have to have gosh-wow-boy-oh-boy resolution. 250 meters or even 1 kilometer (probably getting marginal) wouild be enormously helpful. With multiple wavelengths and polarizations, you can really figure out some real geological physics of the scattering process and the surface materials average properties from location to location and it's sub-resolution mixtures and vertical structure.

I *think* we're including a small experimental radar <military supplied> as a secondary payload, or is it going on the Indian orbiter? ... but I don't think anything planned to fly is multi-wavelength-polarization.