Assuming we are talking about an era when Sol has a thriving space industry and the Solar system is broadly colonized. Current materials science supports structures up to 8 kilometers in diameter, and if large scale graphene production is possible, up to 100km in diameter, at least according to Isaac Arthor.
I am wondering what resources would be difficult for a colony ship to reproduce in-situ on an one way trip to the first interstellar expansions of humanity. I picture a true generation ship might be primarily designed around the transport of some of the largest prefabricated sections of a future centrifugal spin gravity habitat.
- Using hard science to speculate, what types of materials and components would only be available with the massive industry present in humanity’s original home?
I picture the main outer ring frame structure of an O’Neil cylinder, like some kind of curved beam, would be prefabricated and sent in a few pieces for later assembly. If the O’Neil cylinder was to be 8km in diameter, 3 pieces would make the generation ship at least 5.7km long.
-
What is practical to transport assuming fusion is in the cards, as are self replicating drones for resource extraction in a region like the astroid belt, and assuming planets are resource poor gravity prisons we avoid in favor of mobility?
-
How might carbon get utilized for large structure fabrication in space as far as processes?
-
What about metals and space based fabrication. How can you picture the production happening in ways that would only be possible in a highly advanced space based economy?
I know this is highly speculative and I hope the mods will let it fly to ask this. I know most nerds are curious about this kind of thing. I’m only interested in the most conservatively realistic of hard science fiction/futurism.
The cheapest materials would be what can be acquired in space without having to launch from Earth. As a result, you’re going to want to build your O’Neill cylinder out of some combination of iron, aluminum, titanium, and silicon dioxide.
The last of which might be particularly useful, as it is the main ingredient of fiberglass while also being the most common substance on Moon and asteroids. As a result, you probably want to build your cylinder primarily out of fiberglass. You can get pretty decently sized cylinders, as fiberglass has a higher strength-to-weight ratio than steel. Apparently, 24km diameter is a viable figure. Scale up length the same way, and you’ll get 96km. So a 24km x 96km O’Neill cylinder made out of fiberglass.
That would be about 7238 km^2 of usable surface area. Half that to 3619 km^2 to make room for windows (as originally envisioned by O’Neill), and assuming a density comparable to New York City (about 11,300 people/km^2), you’ll get around 40 million people. Or about the population of Tokyo.
That’s seems plenty for any sensible space colonization strategy we might adopt in the future. And what’s best is that you don’t really need any fancy technology. Just use solar power to power mass drivers and deliver raw materials from the moon or asteroid via electricity. And it won’t be any special materials either. Raw regolith can be made into fiberglass, so cost can be kept surprisingly low. The only question is scaling it all up, which may unfortunately be too expensive or will take a very long time to happen. Ultimately, this is still sci-fi, albeit on the hard side of it, since no fancy new technology is require.
I’d like to see a pressure vessel made of fibreglass that size… Not happening. Wall thickness in pressure vessels scales
Simple calculator, assuming steel… a 24 km diameter pressure vessel at 15psi is over 13 metres thick steel wall to contain the pressure. https://checalc.com/calc/vesselThick.html
Just the volume of steel required would be astronomical. You might be able to do this out of a similar mass of fibreglass… But forget launching it from Earth (would have to be made in situ).
And, largely, forget the fantasy renderings of what O’Neill cylinders look like – they are anything but lightweight.
This is sci-fi stuff. No one is seriously saying we could build this anytime soon. It will require a radical advancement in space travel capability. But the interesting part of this is that it doesn’t any new technology. It needs only the technology that we currently have, just scaled up massively.
As it is an O’Neill cylinder, the raw material needs will be truly huge. We’re literally building a city on the scale of Tokyo but in space. So we are just assuming that someday, we can move around that amount of stuff in space.
It’s far more than building a city the size of tokyo. It’s the mass required. If you weighed Tokyo, and then engineered a hypothetical Tokyo in space, you’d find that the mass of the equivalent materials would be orders of magnitude higher than even your worst estimates.
Back of the envelope, you put Tokyo in a cylinder with a similar surface area to actual tokyo, the volume of steel in the walls of the containing cylinder (just the pressure vessel) would be about … 60 billion cubic metres, or something like 450 billion metric tonnes of steel. As a point of comparison, tokyo tower is… 4000 tonnes.
As another point of comparison: our global annual steel production is currently around 2 billion metric tonnes per year. It would take 200+ years worth of global production to build just the pressure vessel for a tokyo in space. Unless you’re building this at your source of raw materials, it just doesn’t happen.
Yes, that’s the point. It’s far beyond the actual city of Tokyo in terms of construction difficulty and scale. But it doesn’t need any new technologies to be invented to be doable. Just the ability to build on that scale.
But the point is if you get your materials from the Moon, for example, it’s vastly more economical to just build a Moon colony (or another Moon colony) than a space colony of the same size.
Then you’ll have to deal with Lunar gravity, which may be unacceptable for long durations. Humans may have to live in giant space stations if we want to live in space. And since they can be truly massive, it may be more desirable than what some might think.
The ideal solution is probably not to build a colony in the middle of space, but rather find a celestial body with the necessary materials with gravity low enough to be acceptable.
Moon gravity too strong? Try smaller moons. Phobos? Europa? Charon?
First, you’ve got to realize that you’re making several very bold assumptions given current physics: (1) that we can build O’Neill cylinders with current or future materials that resemble anything like sci fi expects (probably not – pressure vessels are hard, mkay). (2) that we have a means to accelerate something larger than a probe to a significant fraction of light speed (this is actually the least difficult problem, but I suggest you look at the energy and travel time requirements). (3) that there’s any conceivable way for this thing to stop upon arrival (much harder problem without magic engines).
If all of the above are reasonable, then, well, you bootstrap manufacturing in situ in the asteroid belt or in a planetary ring or whatever. Not a huge problem. You obviously need to target a second or third generation solar system in order to find metals and heavier elements on arrival, but that’s trivial if you’ve solved the “stopping upon arrival using the energy and mass you brought with you” problem.
If you could send very small self replicating factories that could take their time to arrive, and upon arrival built a huge laser array used to slow down your larger shipments as they were inbound, you might be able to pull it off… With a few thousand years of preplanning. ;)
I agree with nearly all of your points. The stopping problem is the same as the accelerating problem. Assuming near infinite energy reserves, but limited power generation, then the ship would accelerate for half the trip, turn around, and then decelerate for the 2nd half. Depending on the amount of power that can be generated, earth gravity may be possible during the trip (except for the turn around in the middle).
The accelation problem is easier because you can build massive infrastructure in your home system that doesn’t need to make the journey, so it doesn’t incur the tyranny of the rocket equation. Still need massive infrastructure and huge amounts of energy, but it’s much easier to imagine a dyson swarm of lasers firing at the mirror at the back of the spaceship. :)
That’s what Hail Mary Project did.
There’s no reason that we would expand out at the speed of light in one direction. It’s well within the realm of possibility that we can intercept rogue planets or large asteroids to use as long time habitats. Also we can expand in millions of directions at once at sub-light speed. The journey make take a million years, but we’ll reach a million places at once.
I didn’t say speed of light – just a significant fraction of it. Even 1% is extremely ambitious from an energy budget perspective. 10% or higher is probably achievable for small outbound probes using laser based acceleration – but they’ll just cruise by systems without any means to stop. For large “settlement” ships or similar, even getting 1% would be colossal amounts of energy (like percentages of the sun’s total output). So, yes, you’ll need to take the slow road.
Rogue planets come within a few light years of Earth. We could probably have a low speed, multi-generational ship to intercept one in a few hundred years. Once we’re on we’re hopefully good forever. Likely we’ll come close enough to some other interstellar bodies we could populate as we travelled. Exponential growth is bound to take off.
Yeah, if we aren’t in a hurry, and we can set up some fusion reactors and such on them and build whole civilizations on these rogue planets in the dark, it would work. Depends on how early and often we set up shop on passing planets, but in theory we could colonize much of the galaxy in a few revolutions around the milky way. So, under a billion years. ;)
I’m guessing if we’ve reached a level of tech to build a functional generational ship we would be patient.
The materials have been shown and proven in theory. It is simply a matter of building the space based manufacturing and infrastructure required. This is like Romans talking about what it will take to build nuclear power plants if they could somehow imagine them. I laid out the economy scale that I am talking about at the outset. This is an order of magnitude, or more, larger total human economic output. An era when this construction scale is not very novel.
Assuming we are talking about an era when Sol has a thriving space industry and the Solar system is broadly colonized.
If we are colonizing the rest of the Solar system, we figured out large scale and pressure vessels already. Once we are building in space with materials sourced from space, most of the problems go away.
Worst case, a ship can use nuclear detonations to both accelerate and decelerate easily within the limits of known materials. This has been thoroughly researched in a US program that was only canned as part of anti nuclear proliferation act. This system can easily handle both ends and traveling faster than any current method. It is a worst case. If we can master fusion, there are other ways as well.
I said generation ships too. I don’t care if it is slow and I think humans could cope just fine on a large enough ship, assuming we don’t find ways to put humans on ice.
I highly recommend checking out Isaac Arthur’s content on YT as he goes though all of this kind of stuff in detail but even further into possibility and future tech. I’m getting much more specific into a time and constraints than what IA does in general.
we figured out large scale and pressure vessels already
No. This is an assumption not borne of physics or engineering. There is no magic material that will make large scale pressure vessels suddenly viable. It (and space elevators) are mathematical constructs, not real things.
Use this calculator. https://checalc.com/calc/vesselThick.html – punch in 15 psi for pressure, and 100F for temperature. Play with your pressure vessel. Wall thickness of large scale habitats will need to be many metres of solid steel (or equivalent material). Even if you magically mass produce carbon nanotubes or something, you still need hundreds of millions of tonnes of carbon to pull off any large scale vessel. Your talking about ingesting entire asteroids just for building materials. You don’t launch that shit on an interstellar journey.
Why ship pieces instead of shipping manufacturing capability (nano 3D printing etc) and use resources at the end point? By then presumably we’ve got asteroid mining down, no?
I think it would likely be similar to engineering materials today. The highest performing materials are very difficult to manufacture and we are talking about pushing them near their limits. I think a lot of the substructure will be made in-situ, but I think the most stressed parts of the main structure will require the largest scales of manufacturing. Like Sam Zeloof made a chip fab in a garage, so why doesn’t he start producing the next Nvidia GPU. It is that kind of difference here. A lot can be done there, but nothing like what can be done on the cutting edge of what humans are capable of making at out largest and most advanced facilities.
Fair cop.
