SpaceflightMemes

All right, let's talk about that. This is long because I want to convey WHY what you are thinking would be impossible on orbit. This is a process I am an expert in so I can walk you through it, but the same level of complexity exists for virtually any process of manufacture. People not in an industry vastly underestimate that complexity.

First, there is a bit of chicken and egg. We won't need a lot of materials on orbit until we have a lot of people on orbit, but we can't get a lot of people on orbit until we have a lot is material on orbit. But I actually think that is a less important issue that we can imagine might be overcome.

What materials do we use in the vacuum of space? Steel is terrible. It has a low strength to weight ratio and its coefficient of thermal expansion is high and it embrittles when it gets cold.

Aluminum (the industry I started in) is a great material for use in space. And it often comes up in space mining discussions since it is a very abundant element in the universe.

It is also very abundant on Earth. Pick up a rock and it probably has aluminum in it.

So why didn't it come into use until the 20th century?

Aluminum is highly reactive, and it is really hard to separate from most minerals. Today, we use vast amounts of electricity run through carbon electrodes to rip aluminum ions off alumina in molten salt. Now electricity is easy enough to make in space, so we could imagine a supply of that. Same with heat. Carbon is much harder to come by, but we could against imagine ways to do that.

We start to run into trouble when we consider the extremely powerful magnetic field that is created. It is so high that you can't bring a watch close to the cells without messing it up, and you certainly can't use a computer nearby. Of course we have ways around that on Earth, but you can imagine this is exponentially more dangerous at a space station refinery. Molten salts, massive magnets, fried computers, vacuum of space, not a good combo.

But humans are clever, so let's say we figure a way to do all this somehow and have molten aluminum ready to cast. Now we run into the real fundamental problems.

Once you have molten aluminum you have to alloy it. Pure aluminum is about as soft as gold. Depending on the alloy, you will need copper, magnesium, silicon, manganese, and a few others. These will need to be obtained on orbit also, and in highly pure forms. Each of them will have similar but unique issues as I am describing for aluminum. (This by itself is an almost impossible hurdle if you imagine the massive infrastructure needed before you can even cast you first alloyed ingot.) You also need vast amounts of either chlorine gas or some noble gas for pulling hydrogen out of the molten aluminum.

Then you have to cast it. Casting requires removing an enormous amount of heat very quickly. On Earth we use vast amounts of water to do that. We could imagine we grabbed a comet or something and refined the water from it (additional infrastructure) and we will soon need more. If you are thinking that getting rid of heat in a vacuum is easy and we can find a way to do it quickly without water, think again. Heat dissipation is a major problem in spacecraft design.

Ok, solving that we run into the next problem. The thermodynamics of cooling an ingot mean that you have big crystals inside the ingot that you need to dissolve. We preheat the ingot, but now we need to work it to the size we want it. Here, we do that with a gigantic roller. That roller uses a huge amount of organic lubricant, as well as monumental amounts of steel, copper, as well as gold, silicon, etc. We need to have made all that on orbit. And more power.

Hand waving that, now we have wrought aluminum. For some alloys you need to work it more, so you need more rollers, for other types you need to heat it up again to dissolve the alloying elements and spray it with more water to cool it down very quickly. Once you do that you build up residual stresses that warp the plate and makes precision machining impossible. So now you need stretchers to stretch the plates. Those use either huge pneumatic or hydraulic systems to generate immense forces, up to 14 million pounds. You can imagine some catastrophic failures there.

Hand waving that aside, now you have a plate of aluminum. You need to machine it into shapes. Again, we need the infrastructure to get the materials needed to make and then build precision CNC machines and to keep them running with their lubricants, maintenance, etc.

And now we get to the most fundamental problem. The only realistic way to make aluminum is the process I have described, and all that depends on starting with alumina. But we don't mine alumina. Even though aluminum the element is common, we need to find a much rarer ore named bauxite to start the process. The only place to find bauxite is in the tropics in soils that have been highly leached by long exposure to rain. There is not likely to be bauxite in asteroids.

All of this process is even more complicated with titanium. And it's ore is rutile, often found in rare beach sands.

I can imagine ways around some of these issues, and I'm sure you can too. But ALL of them? And getting funding for overcoming all of them? And we need to overcome all of them before the first pound of metal is even produced. Unless technology has an enormous science fiction level breakthrough, no.

And keep in mind this is just one part of the infrastructure. Someone else who is an expert in motor design, power generation, or whatever else would spin just as complicated a story in their area.

And again, I am on your side on this. The risk that we squander easily accessible materials on Earth and lock ourselves out of space is my long term fear. But in my opinion, asteroid mining is absolutely not where we start, and may not ever be viable for metals. We have to get better at using and reusing what is cheap and available now to have a hope of starting the generations long project of getting access to more materials than we have on Earth, probably from other planets or maybe dwarf planets.