New technologies
Grind the Asteroid, Print the Part
Why there will never be a steel mill in space, and what replaces it
Ask most people to picture heavy industry off Earth and they picture a steel mill in a bubble. Blast furnace, ladles, a caster, hot orange metal running, and rolls turning out beam and plate the way they do in Gary, Indiana.
It is a natural picture and I think it is wrong in almost every detail.
Why the mill does not go up
A blast furnace is a gravity machine. It is a tall stack, you charge it at the top, and the burden works down through it while gas works up. Take the gravity away and it does not run slower, it does not run — the whole process is a controlled fall.
Then look at what a mill is actually for. A rolling mill exists to make enormous quantities of a few standard shapes, cheaply, on the bet that somebody will want them. That bet works here because a beam mill sits inside a continent full of customers and a rail network to reach them.
Now put that same operation at an asteroid. You have made ten thousand tons of standard shapes, and your customer is one work site that needs a specific bracket. You have built the least appropriate factory imaginable, at the greatest possible distance, to make the thing least likely to be exactly what anybody needs.
What space is actually good at
Here is the thing that gets missed. Space is not simply a worse place to make metal. It is better at some parts of it, and the parts it is good at are the expensive ones.
Vacuum is free. On Earth we spend serious money building vacuum chambers, because the highest-grade metals — turbine blades, medical implants, aerospace alloys — are melted in vacuum arc and electron beam furnaces to keep the atmosphere from ruining them. Up there the chamber is already built and it is infinite.
Sunlight is free and unfiltered, and a mirror is cheap. Point enough concentrated sunlight at rock and you have a furnace with no fuel bill.
And I have written before that lunar regolith is roughly forty percent oxygen by weight, locked up in oxides.2 Drive that off with heat and the oxygen is your air, and what stays behind is metal — iron, aluminum, titanium — right where you are trying to build.
So the raw capability is there. It is the shape of the industry that has to change.
The answer is powder
What a factory ship should produce is not beam and plate. It is metal powder.
Grind the rock, refine it, and put out a feedstock of clean metal powder in drums. That is the product. It is dense, it is stable, it does not care how long the trip takes, it does not need to be any particular shape, and it can become anything.
Then you print.
Additive manufacturing is not a novelty anymore and it is not waiting on a breakthrough. Metal printing is in production right now for rocket engines, for aerospace brackets, for medical parts. There has been a printer aboard the space station for years and metal parts have been printed in orbit.1 The technology is not the hard part. The supply chain is.
What this actually fixes
In my article on lunar robots I said the mechanic robot is the keystone of the fleet, because a fleet without one degrades to scrap the first time a bearing goes. And I said you would ship crates and crates of spares, because a mechanic is only useful if there is something to install.
Those crates are the weakest part of that whole plan, and I knew it when I wrote it.
You cannot predict every part that will fail. So you either ship one of everything and eat the mass, or you ship what you guessed and then wait months for the thing you did not guess. Every remote operation on Earth has this problem. On the Slope it is a warehouse full of parts that never move, sitting there because the one time you need it, flying it in takes three days you do not have. Off Earth it is not three days. It is a launch window.
Ship a printer and a drum of powder instead, and the calculus flips completely. You are no longer shipping parts. You are shipping the capacity to make parts, and the only thing that has to travel from Earth is a file.
That is the sentence I keep coming back to. The only thing that has to cross the distance is the design.
And a design weighs nothing, arrives at the speed of light, and can be revised after you find out what actually broke.
The loop closes
Put the pieces together and you get something that stands on its own.
Robots mine the rock. A factory ship refines it to powder. A printer makes the part. The mechanic robot installs it. And when a printer breaks — and it will — the printer prints the part that fixes the printer.
That is the whole thing. Everything a working site actually consumes, made from what is already there, from a file sent from home.
I want to be careful here, because this is the point where these ideas usually turn into somebody's brochure. There is a great deal of engineering between here and there. Printed metal is not automatically as good as forged metal, and for the parts that carry real load that difference matters and is not solved. Making consistent, clean powder without an atmosphere and without gravity to help you is hard and I have not seen a convincing design for it. That problem gets its own article: Powder or Wire. Printers need heat management, and shedding heat in a vacuum is its own problem.
None of those are physics problems. They are engineering problems, which means they are the kind that get solved by people working on them.
What I would build first
If I had the money I would not start in space at all. I would start with the powder.
Take real meteorite material, or the best lunar and asteroid simulant we have, and work the whole chain here on the ground: grind it, refine it, characterize the powder, print with it, then test the parts to destruction. Publish the numbers, good or bad.
That is unglamorous work and it costs a fraction of anything with a rocket on it. It is also the thing that everything else in this article depends on, and as far as I can tell nobody is doing it at any serious scale.
Same argument I made about worms and about water. We have poured a generation of money into the ride, and pocket change into what happens after the ramp comes down.
The mill is not going to space. A printer and a drum of powder are, and honestly, that was always the better machine.
From one explorer to another, we appreciate you reading this far. We are excited about what this endeavor brings, and we would like you along for the rest of it.
Come join us. Because we are Star Bound.
John LangEditor
Ideas in Star Bound are published open — take them, build them better. Our open proposal.
A note on where this comes from. I am not a metallurgist, a spacecraft engineer, or a degreed engineer of any kind. But I am a practical one, with more than forty years in heavy industrial construction: welding, millwright work, hydraulics, mining, and thirty-three years of electrical construction and commissioning on the North Slope of Alaska, in a place that punishes anything built wrong. Much of that time I have worked as a field engineer, which means I am the one standing in front of the equipment when the drawing turns out to be wrong, and the fix has to be made on the spot, with what is on hand, and has to work the first time. Anyone who has done that long enough learns that a lot of engineering gets corrected in the field by people with more experience than the people who drew it. That is the eye I bring to these subjects: not what should work on paper, but what actually gets built, and what breaks. The facts I take from other people are footnoted so you can check them and read further. The ideas built on top of those facts are my own, and I would rather see them knocked down by somebody who knows better than left standing because nobody looked.
Sources
- AMFG, 3D Printing in Space: A Guide to Lunar and Orbital Additive Manufacturing; Airbus, The world's first metal 3D printer for space is on its way to the ISS. ↩
- The oxygen content of lunar regolith is a standard figure in lunar geology references and in NASA in-situ resource utilization literature. ↩
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