Vacuum pyrolysis of lunar oxygen

[Bill White]

PRODUCTION OF LUNAR OXYGEN THROUGH VACUUM PYROLYSIS

This link is to a 2006 paper by JOHN MATCHETT from THE GEORGE WASHINGTON UNIVERSITY SCHOOL OF ENGINEERING & APPLIED SCIENCE

http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA443950

The advantages of vacuum pyrolysis are said to be:

Solar vacuum pyrolysis takes advantage of the abundant energy available through solar radiation to heat material in a vacuum, where convection losses are eliminated. Once heated above a material’s vaporization temperature, the molecules begin to dissociate into monoxides, metals, and oxygen. While cations and anions are present, the sample is rapidly quenched below the condensation temperature of the monoxides and metals, thus releasing gaseous oxygen. No consumables are needed in the reaction, any type of lunar regolith can be used without beneficiation as a feedstock, and no catalysts are required. Beneficiation is the term used to designate the processing of an ore to concentrate a particularly useful mineral or element. This process is characterized by its total reliance on space resources, namely a high vacuum and solar energy. It allows mission planners to employ the strategy of “living off the land” when higher efficiencies are required. Vacuum reduction and distillation of metals are well-known terrestrial processes.

The entire paper explains the concept in far greater detail.

Also too, this next paper explains how fiber optic technology can be used to delivery concentrated solar energy from the mirrors to the material that will be processed.

http://www.psicorp.com/pdf/library/SR-1395.pdf

[Bill White]

Another quote from the paper linked above, comparing the reduction of ilmenite by hydrogen gas with vacuum pyrolysis:

The reduction of ilmenite by hydrogen gas provides an oxygen yield of 0.104 g O2 produced at 1000oC for every gram of ilmenite collected. The vacuum pyrolysis technique has a theoretical O2 yield is 0.140 g O2 produced for every gram for mare regolith at 10-6 Torr at 1400 oC. The system mass of a pyrolysis plant is estimated to be half the size of a comparable reduction by hydrogen reduction plant using only ten percent of the power. The advantages that vacuum pyrolysis has over the reduction of ilmenite is that any form of regolith can be used, the process is very simple, and the process is well understood. The ilmenite reduction technique must filter regolith for rich ilmenite ore, and provide the resupply of hydrogen gas.

[A_M_Swallow]

In about 4 years time NASA will be able to place ~200 kg payloads on the Moon.  Can we get the pilot plant down to this size?

Sufficient oxygen to power the ascent stage of a lander per year would be nice.  Larger plants can wait until we have a heavy lander.  If necessary the rover to collect the moon dust can be launched on a second launch vehicle, but at a higher cost.

[Warren Platts]

Only one problem with the above scenario: it takes fuel plus an oxidizer to make rocket propellant.

[Bill White]

Only one problem with the above scenario: it takes fuel plus an oxidizer to make rocket propellant.

Yes, indeed! 

However, if lunar ISRU LOX can be brought on-line with far less IMLEO than going straight for the cold trap volatiles (which will require oodles of electric power) vacuum pyrolysis LOX can provide a valuable precursor step towards the economical harvesting of cold trap volatiles.

= = =

Also too, a vacuum pyrolysis LOX plant can also be used to generate electric power.

Two birds, one stone.

[Bill White]

An interesting demo mission might be to produce even a liter of LOX using a GLXP platform. That might be worth a prize.

[JohnFornaro]

Pasted here from the other thread:

If vapor phase pyrolysis of lunar regolith can allow the extraction of LOX, then concentrated passive solar can provide much of the energy input needed without the need for a 20 MW power plant.

Uhhh...  Don't you mean "can allow the extraction of O2"?  All that there pyrolysis, and the O2's gonna be toasty.  Then it must be chilled to the point of liquefaction.  Would that electrical energy for the refrigeration equipment run off of PV panels?

But another thing that occured to me is when melting the water ice, there will be an oxygen surplus, if you're making hydrolox prop.  If you were also pyrolisizing the regolith for O2 elsewhere, that would also be a surplus.  A base would definitely need O2, but what about nitrogen?  Alternatively, where is the aluminum, if solid prop is contemplated?

[Warren Platts]

Only one problem with the above scenario: it takes fuel plus an oxidizer to make rocket propellant.

Yes, indeed! 

However, if lunar ISRU LOX can be brought on-line with far less IMLEO than going straight for the cold trap volatiles (which will require oodles of electric power) vacuum pyrolysis LOX can provide a valuable precursor step towards the economical harvesting of cold trap volatiles.

= = =

Also too, a vacuum pyrolysis LOX plant can also be used to generate electric power.

Two birds, one stone.

Well, the SBSP plan would kill 3 birds with one stone...

Be that as it may, that is indeed the question, which scenario can deliver 4000 mT to L2 to be used for a reusable Mars architecture for the least amount of money, which pretty much equates to IMLEO, I guess.

So Bill, honestly, how many 20-ton cargo shipments would it take to get to the point where you can deliver 4000 mT of propellant to L2 per year.

I don't want to hear about 7 gm/m² mylar.... If you've ever worked with mylar you know its not rigid. They don't use it on Earth for a reason when it comes to solar thermal applications. Solar thermal requires rather precise focusing capability. Look to Earth. See how they do it. Use that for your mass estimate.

[Bill White]

Pasted here from the other thread:

If vapor phase pyrolysis of lunar regolith can allow the extraction of LOX, then concentrated passive solar can provide much of the energy input needed without the need for a 20 MW power plant.

Uhhh...  Don't you mean "can allow the extraction of O2"?  All that there pyrolysis, and the O2's gonna be toasty.  Then it must be chilled to the point of liquefaction.  Would that electrical energy for the refrigeration equipment run off of PV panels?

I stand corrected. It's O2 not LOX and needs to be chilled as does the O2 cracked from water.

But remember, the pyrolysis unit can also be used to produce electricity by transferring waste heat to a working fluid. 

But another thing that occurred to me is when melting the water ice, there will be an oxygen surplus, if you're making hydrolox prop.  If you were also pyrolisizing the regolith for O2 elsewhere, that would also be a surplus.  A base would definitely need O2, but what about nitrogen?  Alternatively, where is the aluminum, if solid prop is contemplated?

The paper I first linked above asserts that metals, oxides and ceramics can theoretically be extracted via thermal distillation.

At a minimum, Al2O3 will be reduced to Al2O2. See page 18

Also, solar wind deposited volatiles such as C, N, H & He will be produced, at least in limited quantities, as a byproduct of the process. See page 12

And remember, shipping fuel to EML from Earth while extracting oxygen from the Moon offers an intermediate step to reduce costs of transporting the infrastructure needed to properly harvest those cold trap volatiles.

Lunar oxygen potentially offers an incremental and scalable approach to ISRU with extraction of cold trap volatiles being the desired end state.

[Bill White]

Be that as it may, that is indeed the question, which scenario can deliver 4000 mT to L2 to be used for a reusable Mars architecture for the least amount of money, which pretty much equates to IMLEO, I guess.

Another question is whether early lunar oxygen extraction - as an incremental step - could reduce the cost of fully developing cold trap volatiles.

[A_M_Swallow]

{snip}

Uhhh...  Don't you mean "can allow the extraction of O2"?  All that there pyrolysis, and the O2's gonna be toasty.  Then it must be chilled to the point of liquefaction.  Would that electrical energy for the refrigeration equipment run off of PV panels?

The melting point of oxygen is 90 K.  At 85°N the Moon's surface temperature drops to 70 K, so it may be possible to liquefy oxygen using only a small amount of refrigeration providing you are willing to wait for a month.

The tanks will need shielding and cooling during the day.

But another thing that occured to me is when melting the water ice, there will be an oxygen surplus, if you're making hydrolox prop.  If you were also pyrolisizing the regolith for O2 elsewhere, that would also be a surplus.  A base would definitely need O2, but what about nitrogen?  Alternatively, where is the aluminum, if solid prop is contemplated?

Nitrogen will probably have to be brought from the Earth and recycled.  The regolith contains plenty of aluminium oxides.

[A_M_Swallow]

{snip}

I don't want to hear about 7 gm/m² mylar.... If you've ever worked with mylar you know its not rigid. They don't use it on Earth for a reason when it comes to solar thermal applications. Solar thermal requires rather precise focusing capability. Look to Earth. See how they do it. Use that for your mass estimate.

On the Earth we have to allow for wind.  The only winds on the Moon are rockets landing and taking off.  A thin layer will drop back to the curved frame it is lying on.

A mirror could be made out of sintered regolith that has been painted with gold or aluminium.  Until we have got 3D printers on the Moon the frames with their parabolic curve will have to come from the Earth.

[Warren Platts]

The melting point of oxygen is 90 K.  At 85°N the Moon's surface temperature drops to 70 K, so it may be possible to liquefy oxygen using only a small amount of refrigeration providing you are willing to wait for a month.

How do you know it's only going to take a month. Also, you'll still have to compress the hell out of the GO2.

{snip}

I don't want to hear about 7 gm/m² mylar.... If you've ever worked with mylar you know its not rigid. They don't use it on Earth for a reason when it comes to solar thermal applications. Solar thermal requires rather precise focusing capability. Look to Earth. See how they do it. Use that for your mass estimate.

On the Earth we have to allow for wind.  The only winds on the Moon are rockets landing and taking off.  A thin layer will drop back to the curved frame it is lying on.

Only if it's cut exactly right; if it's a flat sheet it won't. Also, there's still vibrations on the Moon: witness the flags left by the Apollo astronauts and how the fluttering of these flags became grist for the Apollo Hoax mill. You'll probably want to use regular glass mirrors or else your efficiency starts going downhill.

A mirror could be made out of sintered regolith that has been painted with gold or aluminium.  Until we have got 3D printers on the Moon the frames with their parabolic curve will have to come from the Earth.

Huh? Sintered regolith? So the plan is get out there with some sort of grader that makes perfect parabolas in the dirt, and then sinter them, or is the plan to pre-sinter blocks of regolith, and then carve them into parabolas with grinders? One problem: you lose your suntracking ability with sintered regolith.

Also, what are the total energy requirements? I think Dr. Spudis said somewhere that the energy requirements for beneficiation and ordinary pyrolosis are a factor of 5 more than is required for processing water ice. The vacuum pyrolosis you favor is going to be even more energy intensive. Optimistically, let's tack on another factor of 2. So you're looking at an order of magnitude higher power requirements. Then there's inefficiencies in the collector system itself--especially if you decide to go with crappy mirrors and no suntracking. Not to mention night time--that requires another factor of two for peak power.

So if a basic water plant required 20 MW, then the equivalent system you're proposing would more on the order of 500 MW. This is as large as the largest solar thermal stations on Earth. We're talkin' like 36 hecatares of mirrors--72 football fields. That solar thermal pyrolosys of regolith would beat out PV arrays electrolyzing water is not at all clear IMO. Especially when the necessity of importing hydrogen is taken into account.

[Bill White]

I think Dr. Spudis said somewhere that the energy requirements for beneficiation and ordinary pyrolosis are a factor of 5 more than is required for processing water ice.

Even if we assume a factor of ten - - it will remain true that thermal energy passively harvested from the Sun could very easily be much cheaper to obtain than producing electricity. 

However I am not an "either/or person" and would support testing prototypes of many different systems and let actual results guide final decisions regarding full scale deployment.

[Solman]

 I had always assumed that mirrors would be made out of aluminum. Wouldn't vacuum pyrolysis produce or at least help produce aluminum as a by-product? The mirror mounts and tracking mechanisms seem likewise amenable to production from ISRU derived metals - I assume by teleoperated robots. 3D prototyping would be used from the start wouldn't it? I mean why not? It isn't necessary to build parabolic Al mirrors though.
 Lunar derived LOX as an interim step seems absolutely brilliant to me and vacuum pyrolysis an excellent way to do it. It can start small and add mirrors and furnaces as it goes although subsequent units would be scaled to whatever the most cost effective size is. As Bill White has pointed out - the waste heat can produce electricity which can help with ISRU.
 BTW - it isn't either mirrors or PV - concentrator PV is after all the most efficient and its waste heat can melt ice.

Sol

[Warren Platts]

Even if we assume a factor of ten - - it will remain true that thermal energy passively harvested from the Sun could very easily be much cheaper to obtain than producing electricity.

Like I said above, it's going to be more like a factor of 20, power-wise. And even if the factor is only 10, the fundamental problem is that non-miracle mirrors weigh as much--if not more--as PV solar panels. The reason solar thermal on Earth is compeitive is because on Earth PV panels are relatively a lot more expensive than regular glass mirrors. Moreover, weight is not much of a consideration on Earth. When shipping all that stuff to the Moon, on the other hand, weight is critical.

If you need an order of magnitude more area, then you need to show that the mirrors are going to be an order of magnitude less mass per area compared to PV panels. I don't see that happening, without miracle mirrors.  "Very easily could be much cheaper"? That's a mafor exaggeration because it's not at all obvious how that could be.

However I am not an "either/or person" and would support testing prototypes of many different systems and let actual results guide final decisions regarding full scale deployment.

I respectfully disagree. We can look to Earth technologies and use that as a guide. E.g., does solar thermal on Earth have a major mass/power advantage over PV? Correct me if I'm wrong, but I don't think there is a major mass advantage. Thus, there's no need for endless technology studies. Let's get the ball moving.

[Andrew_W]

{snip}

Only if it's cut exactly right; if it's a flat sheet it won't. Also, there's still vibrations on the Moon: witness the flags left by the Apollo astronauts and how the fluttering of these flags became grist for the Apollo Hoax mill. You'll probably want to use regular glass mirrors or else your efficiency starts going downhill.

So cut it exactly right, use sail makers.

The fluttering of the flags only happened when the astronauts were twisting the pole to work it into the ground.

[A_M_Swallow]

...When shipping all that stuff to the Moon, on the other hand, weight is critical.

Wrong assumption.  I told you how to make mirrors on the Moon using raw materials already on the Moon, so weight is not critical.

This will be the second set of mirrors, the first will still have to come from the Earth.  3D printers can make curves including parabolas.

[A_M_Swallow]

The melting point of oxygen is 90 K.  At 85°N the Moon's surface temperature drops to 70 K, so it may be possible to liquefy oxygen using only a small amount of refrigeration providing you are willing to wait for a month.

How do you know it's only going to take a month. Also, you'll still have to compress the hell out of the GO2.
{snip}

The month is a high level design criteria.  It comes from the lunar Synodic period being 29.530589 days.

[A_M_Swallow]

[snip}

I respectfully disagree. We can look to Earth technologies and use that as a guide. E.g., does solar thermal on Earth have a major mass/power advantage over PV? Correct me if I'm wrong, but I don't think there is a major mass advantage. Thus, there's no need for endless technology studies. Let's get the ball moving.

This is an article about solar thermal generation of electricity on the Earth.
http://www.thegreentechnologyblog.com/2010/sterling-technology-improves-efficiency-in-solar-thermal-electricity-production

This is information on a 25 kW solar electric generator.  On Earth it averages 26% efficiency.
http://www.stirlingenergy.com/how-it-works.htm

A lunar version would need to work over a much wider temperature range, higher incoming solar energy and a day that lasts a month.