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If there's two things i love, it's space-flight, and late 19th century technology, and i hope to implement as much of the latter into as much of the former in my current setting. And one thing that has me particularly interested are Thorsten Nordenfelt's Steam submarines.

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Old, beautiful, cast-iron...and perfect for a sci-fi steam-punk setting.

It made me wonder...how well would they hold up in space?

Or more specifically:

How could it be possible for a spaceship, made from cast-iron and other materials typically used in construction in 19th century Europe, to travel distances similar to those of earth and mars during their transfer-window (38.5 Million Miles), while retaining oxygen inside to keep a crew of humans alive?

Sadly, I'm not sure what propulsion-method could be optimal to allow for the ship to survive as long as possible. Though because i'm working with steam-punk, i'm willing to stretch the scientific advancement in some areas. But either way, there's gonna be some hefty waste-heat to deal with. (also they will be purely traveling from orbit to orbit. Launch and re-entry are out of the question for now.)

And additionally, as the title implied:

How could it be possible for a space station to be made from materials typical of the same period, while supporting a population of humans inside?

The types of stations i'm thinking about specifically are both modular stations such as the ISS and MIR, but also fancier options, such as Bernal Spheres.

The question doesn't concern the life-support systems for now, and is more about structural integrity and retaining pressure.

I'll clarify more things if needed.

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – Monty Wild
    Sep 28, 2023 at 0:33
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    $\begingroup$ Your issues are 1) Brittleness 2) Resistance to (uneven) thermal cycling and 3) Tensile strength. Cast iron is poor at all of these. It has good compressive strength, but while that's very useful in a submarine, a spacecraft has only a few parts that need it. Wrought iron is much better, and can approximate mild steel. It can't be mass-produced that well though, so brass and other copper-based alloys are probably your best option, until you can switch to meteoric nickel-iron. $\endgroup$
    – AI0867
    Sep 28, 2023 at 8:02

8 Answers 8

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Cast iron can be made of the same atoms as steel. Something like blackheart malleable cast iron can have good properties. But it will not be as good as rolled steel. Something that is cast into a mould may freeze quickly at the mould wall, but the inside will cool more slowly, giving you larger crystallites, and separation of the impurities to grain boundaries. Rolling the metal while it is still hot will squash and work-harden the crystallites, and mix in the impurities. This gives much finer and more uniform microstructure.

If you are building the ship in space, you could melt the steel and spray it using a plasma spray. This can work in air, but would be better in space. You could process your metal from an asteroid, and then build up your metal plate from a set of spray coatings. That is more practical than having a steel rolling mill in space. The resulting sheet should have a fine microstructure because each layer has been rapidly cooled.

If you melt the metal and cool it fast enough, you will get a metallic glass. These have almost no regular crystalline structure so they can be very hard. Possibly a bit too hard for a spaceship, that would would like to be tough rather than hard and brittle. However, you cannot easily weld sheets of metallic glass, without the heat of welding giving a softer heat affected zone. You may be forced to overlap and glue them. Or maybe use lovely steampunk rivets, yay!

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  • $\begingroup$ That's some fascinating materials and processes i've never heard of- i like the answer, especially because it implies the use of rivets/bolts, which is what i was after as well, but i'm not sure if the plasma-spray idea could be done with materials/techniques of the time- if it can, this would be really neat. $\endgroup$
    – NimRad
    Sep 27, 2023 at 8:39
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    $\begingroup$ Yes, you've got the important point there: building in space, which satisfies OP's question as asked without having to consider launch mass. So in practice your launch vehicle could be extremely small and made of high-value material, while the long-distance vehicle could be made of mundane material gathered from asteroids etc. $\endgroup$ Sep 27, 2023 at 9:48
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    $\begingroup$ @NimRad Dr. Max Ulrick Schoop of Zurich is credited with the invention and development of the plasma spray process in 1911. Railguns are also that old. This is not 19th C Europe, but there is a lot of other more recent stuff they would need to get into space. $\endgroup$ Sep 27, 2023 at 12:08
  • $\begingroup$ Actually, rivets are not be needed. You could spin a continuous seamless tube on a short former. Boo. $\endgroup$ Sep 27, 2023 at 12:11
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It's Not.

There's your answer. Not with cast iron.

Here's a good visual (and auditory) reason why

The above is a YouTube video from one of my favorite channels - Cutting Edge Engineering - an Australian machinist that specializes in repairing big machinery components. In this video, he is attempting (key word) to repair a series of cracks in a transmission housing, that is made of cast iron - you can watch the whole thing if you like - as he goes on at length as to why cast iron is a terrible material to work with - but in particular to your case - it's very brittle and doesn't handle temperature changes very well.

The timestamp above shows what happens when there is uneven heating across just a small component (relative to the size of a space vessel). Watch for about 1 minute or so - and you'll get what I mean.

'What uneven heating!' I hear you ask? Well, the heat from friction of escaping an atmosphere then going into the cold vacuum of space. Your cast iron space vessel is going to do what that housing did - crack. There goes your air-tight integrity and probably followed in a matter of milliseconds by an explosive decompression.

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    $\begingroup$ "Escaping an atmosphere then going into the cold vacuum of space". That's not what they'll be doing. Inter-orbital specifically means that these ships don't enter or leave a planets surface, so it won't be passing the atmosphere. $\endgroup$
    – NimRad
    Sep 26, 2023 at 20:06
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    $\begingroup$ @NimRad that does not matter. I assume the interior of your ship wont be at 3 Kelvin, like the exterior. These temperature differences, and the constant cycling from turning the engines on and off etc, will cause cracks to form due to uneven thermal expansion. $\endgroup$
    – ErikHall
    Sep 26, 2023 at 20:09
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    $\begingroup$ OP seems interested in an interplanetary ship which could avoid atmospheric heating effects, but even sunlight hitting the ship will cause it to heat unevenly. The ISS, for example, creaks audibly as different parts heat up at different rates, which could be a much bigger problem with a more brittle material. $\endgroup$ Sep 26, 2023 at 20:09
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    $\begingroup$ the real temperatures flux is what is in sun and what is not. $\endgroup$
    – John
    Sep 26, 2023 at 20:19
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    $\begingroup$ @NimRad, Even moving from shadow into full sunlight would cause a cast iron hull to split open. Cast iron is the metal equivalent of glass, and not high quality glass, either. The only way around it is to completely ignore the material properties of cast iron. $\endgroup$ Sep 26, 2023 at 21:45
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As has been pointed out, thermo-mechanical fatigue of cast iron will be a large problem. Merely rotating such a vessel in sunlight will cause differential cooling and heating that will cause stresses that may result in failures.

However, there is a solution. Different materials handle thermo-mechanical fatigue differently. In the Age of Sail, the black powder cannon that were used were often made from cast iron due to its cheapness, but cast iron guns had a tendency to crack or explode after repeated firings. However, brass or bronze guns were found to be more resistant to this fatigue.

So, if your ships are cracking up between the heat of the sun and the cold of space, make them from more flexible materials that can better handle the cyclical strains involved. Just because this is steampunk, doesn't mean that you have to use cast iron. You can use different steel alloys or even brasses and bronzes that have better thermo-mechanical fatigue characteristics, and were still available and widely used in the period in question.

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    $\begingroup$ Copper, brass, and bronze are also more typical materials for low-pressure pressure vessels. Look at, say, antique pressure lamps or fire extinguishers. Cuprous alloys were typical, not cast iron. $\endgroup$ Sep 27, 2023 at 4:58
  • $\begingroup$ How about making the main pressure hull out of cast iron and adding an outer layer of copper or bronze to shield it and help distribute the heat more evenly? $\endgroup$
    – zovits
    Sep 27, 2023 at 7:25
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    $\begingroup$ @zovits You'd still get uneven heating and cooling, which would encourage cracks in the cast iron. It's copper, not a thermal superconductor. $\endgroup$
    – Monty Wild
    Sep 27, 2023 at 7:36
  • $\begingroup$ @zovits even if it worked, what would it accomplish? You're using more copper than an actual copper hull would need, so you can...use a less suitable, harder-to-manufacture iron hull instead? $\endgroup$ Sep 27, 2023 at 13:59
  • $\begingroup$ @ChristopherJamesHuff It'd accomplish OP's stated goal: to have spaceships made of cast iron. $\endgroup$
    – zovits
    Sep 28, 2023 at 7:58
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Metallic (M-Type) asteroids are predominately made up of Nickel / Iron. Which happens to be a quite passable alloy for spaceship hulls.

Tough and versatile, nickel What are the properties of nickel alloy? alloys are resistant to corrosion by a range of media, and stay impressively strong even at temperatures over 1000°C. They are usually well-suited to operating at cryogenic temperatures as well, but it's their resistance to heat that makes them a real favourite for critical applications.

How you get the first ship up there to start mining asteroids... well that's your problem..

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  • $\begingroup$ I think the troy rising series essentially used melted and 'inflated' asteroids as space stations, using a solar mirror array to heat them up $\endgroup$ Sep 28, 2023 at 6:06
  • $\begingroup$ @JourneymanGeek I read some proposals from the 60's / 70's about taking asteroids mining out a center cavity, pumping in some water and a small "clean" nuke. detonate and the steam explosion would leave a large cavity within where we would build the infrastructure for a generation ship. The asteroid providing radiation shielding from cosmic rays and micro meteorites. Sounds like something from Fallout. $\endgroup$
    – Gillgamesh
    Sep 28, 2023 at 13:08
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Large vessels with thick walls made of cast iron will be very heavy. You could make them very small and/or paper thin walls, but that would go against your steampunk aesthetic.

When you look at what size rocket is needed for lifting a payload to orbit, it grows exponentially. However, when you try to scale up existing rocket designs their power does not increase exponentially, in fact you even get diminishing returns. So it makes more sense for such vessels to be constructed in orbit, unless you have engines that work based on principles not known to current science (for example, magical anti-gravity devices).

Space stations don't need to move so it is more plausible. You still have to move the equally massive raw materials to the construction site, but you do that in parts not all at once. You also only do it once, the station doesn't need to zip around.

For ships, the issue continues during space travel. You need a lot of engine power to move such heavy ships quickly, due to $F=ma$. So even if you construct them in orbit, you would need exotic propulsion to justify it.

Perhaps you can devise exotic propulsion methods that work better when larger. For example, nuclear reactors are harder to built in tiny sizes. Perhaps you have something analogous. If bigger ships are more efficient at generating energy and/or propulsion, that would explain why people insist on building such oversized ships instead of smaller and lighter ones. Cast iron is not a great material for space ships, but you can come up with some in-universe reasons why the superior materials cannot be easily used.

The question is, is cast iron by itself necessary, or is it that any similar material will do but cast iron is preferred for whatever reason?

One of the remarkable properties of cast iron is a fair heat capacity and good heat conductivity. Heat management does come up often in space ships. To be fair, there are better ways to do each: Other materials like copper have much heat conductivity, and then there are methods like circulating water. There are also better heat sink materials, but many are not practical for building a vessel (ammonia) or less abundant (lithium). Iron is decent in both aspects. So the obvious thing is to create in-universe need for these.

  • Perhaps weaponry relies heavily on concentrating heat, like lasers. Cast iron dissipates the heat, so the laser is less effective.
  • The reactor could be generating a large amount of heat and using the cast iron hull as a giant heat sink.
  • Maybe there is some kind of warp drive that requires a large amount of cast iron in the ship for some reason (magnetism?).

There are other forms of iron, like steel, that would be similarly useful in these situations, and are also a better material for constructing ships. So you would also have to explain why those other forms are not used instead. In our world, cast iron is sometimes used due to the cheaper and easier manufacturing method. You would need to devise something similar for your setting's industry.

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  • $\begingroup$ I actually did plan for them to have very rudimentary, if under-powered nuclear reactors, though i might need to ask the plausibility of those in a second question. Even though cast-iron would be ideal for the steam-punk aesthetic, the question also includes other materials typical of the time period, so its possible for them to not be purely made of cast iron! just mostly. $\endgroup$
    – NimRad
    Sep 27, 2023 at 4:22
  • $\begingroup$ Concept of a Prestressed Cast Iron Pressure Vessel for a Modular High Temperature Reactor nucleus.iaea.org/sites/htgr-kb/HTR2014/Paper%20list/Track7/… $\endgroup$
    – Mazura
    Sep 29, 2023 at 3:32
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This is a frame challenge.


It's not actually cast iron.

I also love the aesthetic of cast iron, but it is a less-than-ideal material for a lot of steampunk stuff. So, instead, we use something that looks just like it, but it actually isn't.

I give you two new materials:

B.R.A.S.S. and I.R.O.N.

B.R.A.S.S.

The Blast Resistant Alloy for Special Structures is a special material with a golden colour. It's main use is to build structures that have to deal with lots of energy - like engines, reentry shields, guns, and stuff like that. It's not exactly know what it is made of - this is a secret safely kept by the forges that produce the thing - but it is the thing if you need something to withstand damage. It is one of the most impressive materials you can find, secondend only by...

I.R.O.N.

B.R.A.S.S.'s super-powerful cousin, the Ingeniously Riveted Octave-tempered Nanosteel looks like cast iron, but it is actually a specially prepared form of steel made via a proprietary process that somehow uses music to make it settle into a ridiculously strong form.

While those are fantasy metals, I argue that they would help in preserving the suspension of disbelief - it's more difficult to argue that the "special metal" can't do something than it is to do the same for a regular material we use in our day-to-day.

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In use, Space ships and Space stations are vacuum insulated, and will quickly overheat unless a heat pump is used to drive a radiator, or evaporative cooling is used. There is no 'cold of space' as long as you have a conductive skin and an internal heat source (machinery or humans). Since volume increases as the cube of radius, and surface area only as the square of radius, the possibility of becoming "cold" decreases for larger objects.

Radiation from the sun can and will overheat "dark" objects exposed to sunlight, but as it turns out, ordinary reflective surfaces are good enough for all modern space objects. The Apollo command module was just painted white: SkyLab was shielded by the 'micrometeor shield', and when that failed, by a 'space blanket' on an umbrella.

Cast Iron is brittle. Unlike steel, it doesn't have a ductile-to-brittle transition at cold temperatures, because it's already brittle, but as discussed above, in use it won't be exposed to the 'cold of space' anyway.

To maintain heat/cold balance, your cast-iron space object will need to be painted and have active cooling. Apart from that, it won't have heat/cold problems.

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What about using wrought iron instead of cast iron?

Wrought iron is made by repeatedly heating and deforming the raw iron. The iron is heated until it's soft and malleable, then deformed by hammering, bending, rolling, and stretching, a process somewhat similar to kneading bread dough.

This process squeezes out much of the slag, and removes a lot of the carbon, resulting in a more pure iron which lacks the large crystalline structure that makes cast iron brittle.

Wrought iron will eliminate many of the problems with cast iron. It's stronger, more malleable, less brittle, and much less subject to cracking due to temperature changes than cast iron. It's also a product that was familiar and widely used in the 19th century. Processes for mass producing wrought iron by hot rolling existed in the 1800s.

The main disadvantage of wrought iron is that it requires much more time and labor to produce than cast iron. But if you're building a spaceship, presumably you have a budget for that. This doesn't address the weight issue, but it's a big improvement over cast iron for tolerating major tempurature changes.

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