How to produce steel in space?

Question

My steel producing company wants to move into space for reasons. They are commonly known for producing steel from iron ore with all the necessary steps in between. The main question is how they would adapt one of the steel production processes used on Earth, to be used in space.

In this world there are asteroids with:

• High iron content (say >15%).
• Carbon-rich ones.
• And any other 'common asteroid materials' (if needed).

The company is eyeing a large asteroid to settle its first fabrication plant. This is mostly so that they can use the produced microgravity in the production process and as an early access point for materials.

• The company will spend A LOT of time and money to set this up. They will hire whatever scientist they need.
• The tech is slightly futuristic (say 50-ish years?). Anything theoretically plausible.

The company is trying to be the first in the market, with their eventual goal being; To move to further process steel, and eventually get into building spaceships.

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Now the production process:

I imagine a floating, spinning sphere of molten ore. Asteroid pieces get added and molten into the sphere. The pieces are heated and molten through inductive heating of the metallic parts. Through spinning, buoyancy, melting points, and magneticity, materials are extracted from the sphere. The separated hot iron gets further worked into steel. Other materials may be cast into ingots, re-capturing the heat to direct back to the sphere.

Now, most of this is far-fetched. How do I turn this into a believable process of producing steel from raw iron, while using the unique resources/opportunities space offers?

I'd love to make use of microgravity, the lessened loss of heat (no atmosphere), and that I could do all of this 'out in the open'. I am willing to handwave getting everything in place, this question is solely about whether it would work if it got there.

Answer 1

I dont really know how steel is manufactured IRL, so I had to do a little bit of research there to figure some stuff out. Some of my information could be wrong.

Resource hunting and logistics

I know that steel is just iron and carbon, so you need to obtain those 2 things. You have iron rich asteroids, and asteroids with carbon. I dont know if theyre close by where our station needs to be but if the station's asteroid is big enough and the asteroids small enough you could push the resource asteroids to get into orbit around your station's asteroid. If you cant get an asteroid into orbit around your station youll just have to get that resource asteroid in orbit around whatever your stations asteroid is orbiting, as close as you can to the station. That way you can use those resources more easily than if you had to mine at that asteroid and then go ALL the way back to the station. Just bring the mine to you. A little bit of delta V and a lot of time can move stuff around just fine.

You also want icy asteroids. You need water, or at least, oxygen, which you could get from water, from ice. Get Ice.

Utility of oxygen

You want oxygen because simply melting iron ore and adding carbon wont work. Your steel will be impure, and i want pure steel in my space ships. To prevent this, (pure) oxygen is blown through the molten iron which will react with impurities to make the molten iron more pure. This is a massive simplification of steel production, Here is more on the Basic oxygen process that im going off of.

Heat and power management

I originally had 2 paragraphs typed out and then realized a diagram would be easier. So I made one. Ill still provide some additional notes on some things where needed. Power and heat generation are tied together heavily, and thats why the diagram only shows heat, because really, theyre both energy, and in this case, energy that doesnt really leave the system easily, so we should try to redirect it elsewhere.

[Heat goes to water?] At extreme temperatures, water splits into oxygen and hydrogen (thermolysis, you could use electrolysis if energy is no problem). We need oxygen, a lot of it.

[carbon/hydrocarbon filtering for combustion?] Polycyclic aromatic hydrocarbons, which are... maybe existing abundantly or otherwise in space? According to some space nerds at MIT they could make up a good portion of the carbon that exists in space. Those PAHs, specifically pay attention to that hydrocarbon part. A combustion reaction is just a hydrocarbon and oxygen, which turns into CO2, water, and heat. More heat to vent, but also more heat to use for melting ice into h2 and o2, more water to be melted, and co2 which can be split back into carbon and oxygen using little power using these nanomaterials that we cant make much of yet but can make samples of.

Sure, we dont technically need the combustion part of this reaction, but it will help us liberate more carbon and heat from the system than we would without it. We get more carbon, and we get more heat to melt ice with, at the cost of some of our oxygen, which comes from ice. Its worth if you cant get enough carbon to make your desired amount of steel and you have some extra ice laying around. If youre short on ice, maybe want to hold off on it. Combustion isnt necessarily for generating energy, its for liberating more carbon, and trying to recycle as much as possbile.

This is a lot

Even assuming 100% efficiency, this is still going to have a lot of losses in the system, and require a lot of energy. Were definitely going to need to bring in a lot of asteroids, and we should probably invest in some solid power generation. And do something with that hydrogen... but, it is theoretically doable. You dont have to ship steel to space anymore, yippee!

Some questions still remain, like the hydrocarbon filtering, is the extra carbon we can liberate from the process worth the cost in splitting up and filtering carbon from hydrocarbon? Is combustion as a whole even worth it here, or should it just use a completely electricity-based heating system and skip the combustion? What power source (solar is a bad idea if you're far from the sun) do we use and how do we make it work here? These questions will remain unanswered for now, this is mostly an idea for how one could try it.

Answer 2

Frame challenge: Do actual research

If you really want it to be as science-based as possible, you need to find out either yourself or from existing sources, how to produce exactly steel in exactly space. You need to know what is your source material - if asteroids, it could be pure iron instead of FeO as it's on Earth due to atmosphere, whether that asteroid also has required metals to add to a certain type of steel (chrome-vanadium, anyone?), how does melted iron behave in microgravity, does it ever turn itself into something relatively solid, then somehow assemble all the required facilities up there in space, and then start experimenting - because if that company is the first to produce steel in space, it'll stumble upon a lot of obstacles, some of which are outlined in the other answer(s). Heat management could be a minor issue, as it could probably be diverted into heating iron to be put into a furnace, but other, including some weirder processes going on the micro-level (crystallization, cavities, thermal stress) might be the harder obstacle to overcome.

There are no existing processes of creating steel from asteroids in microgravity, and existing processes of making steel employ both gravity and carbon as a material to bind stray oxygen (which would still stay as a component in some types of steel, controlled by weight), which are not directly convertible to space-based. At least your facility would need carbon into their steel, which should be fed from elsewhere, processed as you don't have an easy way to turn asteroid-based carbon into pure form required for steel manufacturing, deployed and used while melting iron, then somehow distributed along the mass of melted metal with enough precision, etc etc.

As an alternative, you might not go deep enough for your story, declaring a steel factory as a something with known parts that should exist in any space-based facility, such as power generators, heat sinks, drills (that dig iron off the asteroid) etc, then put a shade on exact processes going inside it, essentially turning its core into a black box, which is fed iron and something extra, and outputs steel formed into required units (slabs, rolls, raw melted stuff, what you want here actually), although if you want your steel melted, you'll have to enter an entirely new and similarly deep hole regarding how does steel cool into what's usable. There was an article from a steel factory in Russian (this one, for example - there are a lot from the same source that depict various stages in steel production and how IT and ML helps them to do this better) regarding proper cooling of a steel slab, with a ton of nuances unknown to general public, which would be magnified at your space facility. So you can "just" say that it "works", hiding the exact details, as there are too many of them for such an entirely new process.

Answer 3

Rail gun based refinement and delivery process

Arguably the biggest problem you'll face is heat. Heat management in space is tough.

As Chuck points out, O2, carbon etc are all available, as are a bunch of other rarer elements we might to mix into our steel.

And we've got an extremely ready supply of heat - we can focus the sun's light for solar furnaces, considerably more easily than on earth. You could even have a massive array of solar mirrors close to the sun, carefully targeted to an asteroid you're currently working on.

The problem is heat dissipation. In theory, once we've got the steel molten, done all the processing to it, we'd need to then cool it.

But, instead, I'd envisage a massive magnetic array, drawing the steel through into essentially a makeshift railgun, which fires chunks of steel at a "catcher". We don't really need to cool this - radiative heat loss will cool it slowly as it travels. if we need a faster cooling for the crystalline structure of the steel, we'd thin the molten blob into thinner sheets.

Now, this has the excellent outcome that everyone is going to pay your space based steel refinery, who now has a solar array capable of carving "Bill Due" into the face of the moon, and an array of asteroid harvesting rail guns capable of firing chunks of molten steel.