The Bard in Green

I’ve been using Linux primarily for 24 years and exclusively for like… 10-12. When I HAVE to use another OS (for work or something) I miss all my tools and feel powerless. It drives me nuts.

One of my biggest curiosities ATM is how to source nitrogen to breathe. What are the rarest resources in terns of the solar wind and stellar evolution of a system? Nitrogen seems to get blown away with a very distant ice line that should largely determine its availability right? It doesn’t seem to form compounds with staying power on any smaller objects.

Another benefit of mining the atmosphere of Venus. While Venus has a much higher C02 to N2 ratio than Earth, it has SO MUCH atmosphere that it has 4 times as much nitrogen as Earth does.

There’s frozen nitrogen on Titan, and smaller amounts of it on the other moons of the giant planets. If you have the fuel and time to get out to the Kuiper belt, there’s probably 50 times more drifting around frozen out there, even before you start mining dwarf planets (sounds like your setting has plenty of time).

There’s also N2 available in the the planetary atmospheres of Jupiter, Saturn, Uranus and Neptune. A tiny amount, as a percentage of those atmospheres, but again, considerably more than is present on Earth in terms of mass available, if you can get at. Mining Jupiter’s atmosphere is an orders of magnitude more challenging problem than mining Venus’s. But if you CAN mine Jupiter’s atmosphere, you’ll have all the light elements you’ll ever need. We could build thousands of Earth surfaces worth of space habitats and have plenty of water and atmosphere to fill them up with.

Again, I think the best solution is Venus. You get carbon for megastructure hulls, water, oxygen, hydrogen, nitrogen, sulfur. It’s all roiling around in a toxic vapor mix, yes, but it’s all very useful if you can distill it out, which is all known science and there’s just SO MUCH OF IT.

In other star systems, I’d look for similar solutions.

I’m very interested in any plot holes I should look into in this basic layout.

I’m trying to stick to Dr O’Neill’s original assumption of only using the engineering materials of the present.

In that case, you definitely want to have an outer shell, or this thing is going to go the way of the titanic. That being the case, your impactors aren’t going to make a lot of noise, unless there’s crew in / on the outer shell (which there totally could / would be) and there’s a lot of impactors or they’re pretty big. There’s definitely some interesting stories to be told there.

I also propose that there will be self replicating drones that are more akin to kilometers scale industrial complexes.

Are these floating around in space, harvesting asteroids and comets and building more habitats? Or are they trundling around on the inner surface of your cylinder building structures and repairing damage? If the latter, they probably make more sense as a swarm organism then as a essentially a titanic bulldozer. Especially because you’re exploring biotech.

If they’re floating around in space, an overlooked source of mass for constructing megastructures is the carbon in the atmosphere of Venus. Carbon is a great material for building / reinforcing your shells, especially if you can get it into some of it’s more interesting forms like nanotubes (which might be MUCH easier to do with biological processes than with current industrial processes). Some back of the envelope math suggests to me that there’s enough carbon in the atmosphere of Venus to build thousands of square kilometers of 10 meter thick megastructure shell without taking more than a few percent of what’s available. If you take more, this has the added effect of lowering Venus’s atmospheric pressure to the point you might be able to mine or even terraform it. A win / win IMHO. That’s part of why I suggested a meta alloy of carbon and iron (basically super steel).

Any civilization capable of tackling O’Neill Cylinder / generation ship scale projects would have no problem mining the atmosphere of Venus using space elevators.

400k years into the future when Sol is further into the red giant phase.

I highly recommend watching this video. It’s going to give you some hard numbers on the timeline of the sun’s evolution.
https://www.youtube.com/watch?v=gZ3HACbDMuE

tl:dw; The sun’s going to get hotter and brighter before it becomes a red giant, but we have literally 100s of millions of years before that will start being very noticeable. Enough time for the dinosaurs to die out and mammals to evolve all the way to humans probably 8 times over before we start having problems. 400k years isn’t enough for this to be even noticeable.

Also note that if you’re exploring the future era of increasing solar radiation, it’s been proposed that we just move the earth into a wider orbit. If a civilization is capable of thinking truly long term, this is doable even with modern technology and could buy the earth potentially billions of years more life (I’ve heard it said that when the sun becomes a red giant, it will heat up the moons of Jupiter for long enough that they could have liquid water on the surface and evolve life… there’s no reason the Earth couldn’t keep going that whole time too if we just moved it).

https://room.eu.com/article/saving-earth-from-an-expanding-sun <- I don’t find the 100 million year timeline in this article to be that credible… see the Cool Worlds video I posted above. It’s a very, very low estimate that takes some alarmist, worst case scenario thinking.

https://www.thespacereview.com/article/2547/1

I still wonder of the sounds unique of such a place.

There are different ways you could end up with interesting sounds in a place like that without resorting to sloppy enough engineering for the habitat to be vulnerable to major impactors.

• With the biotech angle, consider having a somewhat different mix of atmospheric gasses (or even large bodies of water for aquatic adapted people to live in). That will change the nature of sound.
• All the biotech critters are going to make for quite an alien soundscape anyway, I imagine.
• The ambient machinery maintain the place is probably going to make strange sounds all the time.
• If your inhabitants are post human (your time scale is big enough that evolution, in addition to deliberate genetic manipulation could play a role), they could have hyper acute hearing, or even hearing adapted to specific frequencies for <reasons>. They might pick up on all sorts of sounds a normal human ear couldn’t hear. If you want to really play with sound, lean into that aspect.

Beyond that though, sounds native to the structure itself I don’t think would be very different from those of earth, unless it’s very poorly built in which case, it’s doomed and I don’t find it’s long or even mid term habitability prospects very credible.

Upon arrival the generation ship becomes the central hub of the primary habitat.

Where are your generation ships going? If they go to red dwarf stars (which they should), keep in mind their tendency to flair up.

https://www.space.com/red-dwarfs-activity-bad-news-alien-life

That will pose an interesting challenge for your engineers.

I imagine at that scale the gravitational interaction between the two bodies becomes a significant factor and would result in some sound. When does the Roche limit begin to become significant in very layperson terms?

At the scale you’re talking about, I think about 22 KM apart is where you start to gravitational interactions starting to produce a resonance. Move them closer and yeah, you’ll get effects. Depends on the tolerance of your building materials… hums aren’t great for things like bridges and sky scrapers in the long term… they’re probably not great for O’Neill cylinders either, especially one’s built of mostly modern steel. Again, I think if it gets to the point where your population can pick up on it, they have problems.

Except if they have hyper hearing as I speculated above. Their hearing could even be tuned to the faint resonance of the orbiting cylinders, so that if they pick up on even a minor change they know that something is very wrong and can take action.

I could see a scenario where a quiet hum is a warning sign of disasters to come…

Impactors are actually a significant hazard to O’Neill cylinders. Unless your megastructure has some well designed mitigation strategies, it’s doomed.

That’s not an answer to your question, but we have to take it into account in order to answer it.

One of the most practical suggestions for such mitigation is an outer shell that can absorb most impacts, combined with some kind of active countermeasures that can shoot down impactors big enough or with a high enough relative velocity to pose a threat that could potentially penetrate the outer shell.

Most likely, the outer shell wouldn’t rotate like the inner shell. There are a number of reasons for this, one of them being it’s easier to dock with the thing, another being it’s easier to repair the outer shell without having to deal with it having spin gravity that is flinging your repair equipment off into the vacuum of space. There are a number of proposed solutions for traversing from a rotating inner shell to a non-rotating outer shell and back again.

In this case, there’s going to be a layer of vacuum in between the outer shell and the inner shell. That means the answer to your question is “totally silent”. A meter wide asteroid can crash into your outer shell at 10,000 mph and the inhabitants of your inner shell won’t hear a peep. Anyone in or on the outer shell would feel or hear something, depending on a whole set of factors from the material the shell is made of to how far away the impact is to whether or not they’re in a space suit.

But let’s say you have an O’Neill cylinder without an outer shell (IMHO, if you’re going to go through the immense effort to build one of these things, this is a bad idea unless you have some amazing hypothetical deflector shield technology we have no idea how to build) and let’s say an impactor gets through your deflector shield. Let’s additionally assume that your shell is made out of some kind of meta alloy composed mostly of nickel iron and carbon nanotubes. Something that has the tensile strength to support a 30 km long structure (for the curious, the physics that governs this is exactly the same as the physics that governs suspension bridges). Let’s also assume there’s around 200 feet of dirt and rock in between the shell and the people walking around on the inside of your space habitat.

The average velocity of a random meteor that might hit the International Space Station is 50 to 100 KM per second. Most micrometeorites that hit the ISS are basically grains of dust and are too small to produce an audible sound. A number of years ago, something slightly bigger hit a window and left some visible damage. IIRC, no one heard it, they just noticed the damage after the fact.

For an asteroid impact to be audible in the environment we’ve described, it would have to be a significant impactor, big and fast enough to cause significant damage. It’s quite possible that the impact could put a hole in the outer shell where dirt starts getting sucked out into the vacuum of space, and the inhabitants still wouldn’t hear a damn thing. They might notice a sinkhole forming pretty soon, and that would be no good. (Especially because it means spin gravity is literally helping the vacuum of space to suck material out of the habitat).

If something hits the O’Neill cylinder loud enough for the inhabitants to hear it, in all probability, they have a really big problem.