Building Heavy Machinery on the Moon

kbd512 · 2024-08-22 16:33:50

While we don't have much water or clay to work with on the moon, a rock crusher and electromagnet will still work.

To produce a superior grade Iron or steel product, we require extremely pure Iron and Carbon powder to work with. We first crush and ball mill the Iron oxide powder from the regolith, use an electromagnet to separate out the Iron oxide from the tailings waste, and then perform an electrolytic reduction of the Iron oxide powder using electricity and an electrolyte bath. This produces 99.95%+ purity Iron powder which is a suitable feedstock for a VIM/VAR process that smelts large quantities of nearly-pure Iron with an appropriate charge of Carbon and other alloying elements to produce steel ingots.

It may or may not be worth extracting Titanium and Aluminum at the same time. Aluminum, regardless of alloy content, will be much weaker than a high quality steel. It's very useful for low-stress castings and high voltage conductor wiring in power lines, but that's about it. Titanium cannot go to higher temperatures than Inconel, nor can it be nearly as hard as steel, and any part not subjected to high temperatures is going to be a lot stronger and lighter if it's made from a composite. Nickel, Chromium, Molybdenum, and Vanadium are certainly worth extracting at the same time. Cold hard steel gets the job done more often than not. Nobody with a lick of sense fabricates buildings, bridges, or ships using Titanium and Aluminum. We've certainly tried, over and over again, but they end up becoming maintenance nightmares as they age. A high quality steel doesn't have those problems. The mechanics I knew who worked on Navy jets had some choice words, none repeatable in polite company, about the use of Titanium parts. They had serial numbers and log books for all the Titanium parts on our jets to record operating hours and torquing cycles for Titanium shear bolts. It would be fair to say that they despised Titanium. No such nonsense was required for high strength steel pins and bolts, excluding D6AC or similar steels subject to stress-corrosion cracking, which we no longer use.

A nuclear powered crawler-transporter could potentially reduce the requirement for mining trucks and shovels, as well as their associated support equipment. This machine, which I've proposed before, would combine a bucket wheel excavator and conveyor belt with a rock grinder, so that the machine only keeps and stores bins of extracted Iron oxide powder. The trucks would be far more productive carrying Iron oxide powder to a smelter or integrated steel mill facility. If it could also electrolytically refine the Iron oxide into pure Iron powder, even better. It already requires megawatts of power to move, so why not use a few more to produce pure Iron? Rather than having a small fleet of trucks carrying mountains of overburden and tailings waste all the way to the smelter, most of the "trash" is left wherever the crawler-transporter spits it out at. Trucks can economically travel greater distances to drop off their load of Iron oxide powder at a centralized smelter, or pure Iron powder, because they're not carrying useless rock with them. We don't actually need to have giant dump trucks if we're only transporting metal or metal oxide powders. There's also far less build-up of tailings waste at any one spot, so waste products need not be moved twice.

Carbon and alloying metals could be collected in a similar manner, so that only the desired materials for steel making are transported away from the mining site. Whatever we can realistically achieve in terms of economy of motion and machinery requirements will ultimately pay us back many times, in terms of reduced operating costs. We don't use mobile Iron refining machines here on Earth because we can achieve greater economies of scale since labor, energy, and raw materials are not so limited.

It might be impractical to integrate the electrolytic refining machinery with the regolith processing machine, but if it is feasible, then the giant haul trucks are providing greater value-add by transporting ready-to-melt powders.

Our primary money makers are super grade VIM/VAR steels. If we accidentally locate rich Uranium or Thorium or Lithium deposits, that's also worth extracting. It's certainly possible to mine for Titanium and Aluminum, but those are high energy specialty metals requiring more complex refining processes.

Why can't electrical wiring be pure Iron on the moon or Mars?

It's heavier than Aluminum or Copper for equivalent ampacity, but Iron is very easy to come by and gravity is lower, so there's not as much of an incentive to go after specialty metals for large scale applications.

Calliban · 2024-08-22 16:36:08

On the moon, we could power tools using any compressed gas by taking advantage of the temperature difference between day and night. We would store daytime heat and nighttime cold in pits containing sealed steel containers, i.e a hot tank and a cold tank. Lets say we power our air tools using CO2. The tools will have a high pressure supply line and an exhaust leading to a low pressure plenum. The high pressure line comes from the hot tank and the low pressure plenum leads to the cold tank. The cold tank cools the gas to a low temperature. An extract pipe draws cold gas out of the cold tank and leads to a compressor which pushes the gas it into the hot tank, where it heats up and expands.

This is a kind of heat engine, that raises mechanical power due to the temperature difference between day and night. It works better on the moon because the temperature swings across each day-night cycle are so dramatic. Any gas could be used to generate mechanical power in this way. However, gases like CO2 and SO2 which have high critical points are most efficient, because the amount of compressor work needed to compress the gas from the cold into the hot container is reduced. Given the toxicity of SO2, CO2 would be a better fit for machine tools in habitable volumes.

Last edited by Calliban (2024-08-22 16:38:59)

Calliban · 2024-08-22 16:56:20

Kbd512, I will comment in greater detail tomorrow.

Due to meteorite gardening and solar wind gas trapping, there is already reduced metallic iron in lunar regolith. The question is whether it is abundant enough to supply our needs with less energy than smelting. We don't need to spend energy chemically reducing iron oxides, because nature has done it for us. But the amount digging and magnetic screening of regolith needed, may make it more cost effect to chemically reduce the ilmenite. It really depends on how adundant the natural metallic iron is.

Regarding the titanium dioxide waste produced from ilmenite production. I remember reading a proposal to make reentry heat shields out of it. It is a high melting refractory. If we can make heat shields in space, it frees up a lot of Earth lift off mass for payload.

Last edited by Calliban (2024-08-22 16:58:51)

kbd512 · 2024-08-22 20:32:10

Calliban,

I'm not saying we should discard all Titanium dioxide, especially if we find a significant concentration of it, but it's not really the miracle metal everybody thinks it is. Titanium resists oxidation at high temperatures better than most Iron-based alloys which doesn't contain significant amounts of Nickel and Chromium, but by the time you achieve Inconel's maximum service temperatures, Titanium is silly putty.

For commonly used Titanium alloys, such as Ti-6Al-4V, you require both Aluminum and Vanadium production, along with sky-high temperatures to reduce the Titanium dioxide. If I have a limited supply of Vanadium, then I'd much rather incorporate that into high-strength steel alloys.

Inconel 625 Chemical Composition (982°C max service temp)
Nickel: 58.0 min.
Chromium: 20.0-23.0
Iron: 5.0 max.
Molybdenum: 8.0-10.0
Niobium (plus Tantalum): 3.15-4.15
Carbon: 0.10 max.
Manganese: 0.50 max.
Silicon: 0.50 max.
Phosphorus: 0.015 max.
Sulfur: 0.015 max.
Aluminum: 0.40 max.
Titanium: 0.40 max.
Cobalt: 1.0 max.

Grade 5 Ti-6Al-4V Chemical Composition (350°C to 427°C max service temp)
Titanium: 87.6 - 91
Aluminum: 5.5 - 6.75
Vanadium: 3.5 - 4.5
Iron: ≤ 0.40
Oxygen: ≤ 0.20
Carbon: ≤ 0.080
Nitrogen: ≤ 0.050
Hydrogen: ≤ 0.015

This particular Titanium alloy should be forged at 982°C. You can't use it at anywhere near that temperature and expect it to have any strength left, because it just won't. It melts at a much higher temperatures, but that doesn't mean it's going to be useful as a structural material. If it's not going to be subjected to much force at all, then you can potentially use it at high temperatures. Perhaps some sort of Titanium foam can be used as a heat shield, accepting that it will melt during reentry, just as Inconel will.

Mercury capsules used René-41 tiles (a Nickel-based alloy to protect lower temperature parts of the capsule (600°C to 1,000°C) on the leeward side. The windward side required phenolic ablator tiles. Any vehicle making reentry from the moon will absolutely require ablator-based tiles or fabrics to survive. There are no Iron, Nickel, or Titanium alloys that will survive (merely allow a metal ingot payload to plunge through the atmosphere without burning up or breaking apart).

Apollo reentry temperatures: 2,760°C

Approximate Material Melting Points
Basalt fiber: 1,500°C
Borosilicate glass: 1,650°C
Titanium Melting Point: 1,670°C
SiO2 1,710°C
Al2O3 melts at 2,070°C
SiC: 2,830°C <- The only readily available lunar material capable of surviving a lunar reentry intact

A toughened basalt fiber sprayed with with Silicon Carbide is likely the only viable heat shield material.

It would be great if a lightweight and easy to manufacture (from lunar materials) heat shielding material was available, but the material will require extensive processing in order to be incorporated into a woven flexible heat shield, and it's a single-use structure.

Calliban · 2024-08-26 15:47:55

Titanium dioxide has a melting point of 2133K (1860°C), Cp = 710J/Kg.K and thermal conductivity, k = 8.4W/m.K at room temperature. At 1200K (927°C), Cp is 945J/kg.K and k = 3.28W/m.K. So titanium dioxide has a relatively high melting point and low thermal conductivity at high temperature, which are properties that we want for a heat shield. The shock front during reentry will heat the TiO2 above melting point. But the low thermal conductivity will maintain a high temperature gradient within the material. The TiO2 will sublime during reentry, functioning as an ablative. The heat shield would likely still need fibre reinforcement, as pressure on the shield will be measured in bars. Maybe the whole thing needs to be a woven fibre mat?

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Re: Building Heavy Machinery on the Moon

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