Pidgeon process for the Moon base ISRU?

In summary: The Sabatier reaction you linked do require expendable water input, which is problematic on Moon.Although water can be recycled, it is not without costs. The Sabatier reaction you linked do require expendable water input, which is problematic on Moon. Methane can be converted to heavy hydrocarbons, recycling up to half of hydrogen atoms which are otherwise lost in water electrolysis. This would reduce the need for water, and therefore reduce the amount of water needed to produce oxygen.
  • #1
trurle
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I am evaluating the possibility what magnesium may be the most-easily obtainable structural material on Moon.
The following ISRU sequence is proposed:
1) Regolith melt electrolysis produce ingots made of ferro-silicon, as by-product of breathable oxygen production
2) Ferro-silicon ingots are crushed and mixed with magnesium-rich crushed rocks
3) The mix is heated to ~1150C in ceramic or steel vessel to release magnesium vapour, similar to Pidgeon process

I invite the comments and proposal on following topics:
1) Suitability of Moon rocks for the Pidgeon process (seems major constituents are all compatible with process, although i have doubts regarding minor components like sodium, titanium or chromium which may result in unwanted by-products)
2) On Earth, Pidgeon process is evolving to high-pressure, high-temperature variants. Is it different for the conditions on the Moon?
3) Plausible magnesium alloying with Moon feed-stocks to improve alloy properties?
4) General comments and suggestions on the image of the ISRU scheme attached to this post?
 

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One thing to consider is whether any process is dependent on gravity to separate quantities and of course on the moon the gravity is much less.

Also power on the moon would be limited to solar cell production after awhile so any process using electricity may suffer from lack thereof.
 
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trurle said:
4) General comments and suggestions on the image of the ISRU scheme attached to this post?
The seemingly abandoned 'FeNi sand' line of products might be able to challenge the 'most-easily obtainable' claim based on energy requirement.
While the amount of soil to be moved might be more, the energy requirement might be still lower since there is just one heating and no electrolysis in the process.
But to spice up things you can try throwing some metal powder based 3D printing into the pot too.
 
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  • #4
Rive said:
The seemingly abandoned 'FeNi sand' line of products might be able to challenge the 'most-easily obtainable' claim based on energy requirement.
While the amount of soil to be moved might be more, the energy requirement might be still lower since there is just one heating and no electrolysis in the process.
But to spice up things you can try throwing some metal powder based 3D printing into the pot too.
I have a doubts about FeNi sand availability and energy intensity of smelting. The typical concentration of FeNi of meteorite origin in lunar soil is about 0.04%-0.2%, and most of it may be heavily agglutinated with the rock material. Separation (by hammering/forging and magnetic separation) may be energy intensive, and smelting itself is at 1500C, while 1150C required for magnesium production and 700C for magnesium smelting.
I must point out what rock melt electrolysis step in magnesium production chain is likely should be done anyway for breathable oxygen production, resulting in energy spent for electrolysis irrelevant to structural material production expenditure. Of course, rock melt electrolysis machine may be useless for unmanned base, in this case argument for the FeNi is true.
 
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trurle said:
I must point out what rock melt electrolysis step in magnesium production chain is likely should be done anyway for breathable oxygen production,
The necessity of this part is often overestimated: technology to recycle CO2 (without plants) is already available. New oxygen will be needed only if new living area needs to be filled.

trurle said:
The typical concentration of FeNi of meteorite origin in lunar soil is about 0.04%-0.2%, and most of it may be heavily agglutinated with the rock material. Separation (by hammering/forging and magnetic separation) may be energy intensive
Too many 'maybe', on both side, no way to be sure without further input. I've just wanted to point out that this product line seems to be unjustly neglected there, especially with some potential in 3D printing :smile:
Harvesting sand on the moon for FeNi feels like a perfect task for mass produced 'cheap' autonomous vehicles, running on solar power alone.
But most of it is Sci-Fi right now, anyway.
 
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  • #6
Rive said:
The necessity of this part is often overestimated: technology to recycle CO2 (without plants) is already available. New oxygen will be needed only if new living area needs to be filled.
Sabatier reaction you linked do require expendable water input, which is problematic on Moon. Metabolic water can supply only half of demand for breathable oxygen even if 100% recycled, with the rest (about 0.8kg per man per day) need to be imported or transported from Moon poles, at least doubling the life-support mass budget for realistic oxygen recycling efficiency of 50%.
With food (carbohydrates) metabolizing and water electrolysis, the total Sabatier process equation is:
CH2O+O2+H2O=>CH4+2O2
Alternative to water is expendable hydrogen input, which lighter but have unsolved storage problems, and require an 67% instead of 50% recycling efficiency to close oxygen-supply budget. 67% oxygen recycling efficiency is extremely problematic, because it either limit moonwalk (off-base) time or require to capture CO2 produced during moonwalks.
Sabatier process can be more efficient if methane is converted to heavy hydrocarbons, recycling up to half of hydrogen atoms which are otherwise lost from cycle, of if fat-rich diet is considered, but all these options require even higher recycling efficiencies, in the 70-80% range.

On the other hand, oxygen production by rock melt electrolysis do not require to recycle carbon dioxide at all, have no expendable inputs not available at any Moon site, and place no constraint on diet. My basic assumption for Moon base is 0% recycling of CO2 and 75% recycling of H2O with ISRU O2 input. This is a partially-open cycle which allows to run life support on metabolic water and require only dry food and regolith as inputs.
 
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  • #7
trurle said:
Sabatier reaction you linked do require expendable water input,
If you check that link again, in the middle somewhere there are some lines about recovering H2. Accepting the H loss was an engineering decision for the ISS due the problems with handling pyrolytic graphite in zero g environment. At full swing this system is expected to just cleanly split CO2 to C and O2.
 
  • #8
Rive said:
If you check that link again, in the middle somewhere there are some lines about recovering H2. Accepting the H loss was an engineering decision for the ISS due the problems with handling pyrolytic graphite in zero g environment. At full swing this system is expected to just cleanly split CO2 to C and O2.
Methane splitting does help to reduce hydrogen leakage from the life support system, correct. And just bring you to the point when oxygen leakage by wasted CO2 become dominant. How much realistically you expect to capture CO2, especially with vacuum-suit constraints? Even 50% CO2 capture required for Sabatier process with no methane decomposition is tough. Also, molecular O2 leakage may be an issue.

This topic actually related to "CO2 scrubber challenge" review during which i have found no Moon-base suitable scrubber hardware last year. May be somebody can propose one?
 
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1. What is the Pidgeon process for ISRU on the Moon base?

The Pidgeon process is a method for extracting oxygen from lunar regolith (soil) through reduction with hydrogen gas at high temperatures. This process was first developed by Dr. William Pidgeon in the 1960s and has been adapted for use on the Moon to support in-situ resource utilization (ISRU) for future lunar bases.

2. How does the Pidgeon process work?

In the Pidgeon process, lunar regolith is heated to temperatures of around 1000°C and mixed with hydrogen gas. The hydrogen reacts with the oxygen in the regolith, producing water vapor and leaving behind metallic iron and other minerals. The water vapor is then cooled and condensed, resulting in liquid water that can be used for various purposes on the Moon.

3. What are the benefits of using the Pidgeon process for ISRU on the Moon?

The Pidgeon process has several benefits for ISRU on the Moon. It is a relatively simple and efficient method for extracting oxygen from regolith, which can be used for breathing, fuel, and other purposes. It also produces water as a byproduct, which is a valuable resource for sustaining human life on the Moon.

4. Are there any challenges or limitations to using the Pidgeon process on the Moon?

One of the main challenges of using the Pidgeon process on the Moon is the high energy requirements. Heating the regolith to 1000°C requires a significant amount of energy, which may be difficult to obtain on the Moon. Additionally, the process may produce toxic byproducts, such as hydrogen sulfide, which would need to be properly managed.

5. Is the Pidgeon process the only method for ISRU on the Moon?

No, there are other methods being explored for ISRU on the Moon, such as the Sabatier process and the Bosch reaction. Each method has its own advantages and limitations, and it is likely that a combination of processes will be used for ISRU on the Moon to optimize efficiency and resource utilization.

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