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In a classic O'Neill cylinder space habitat (9km × 30km), how loud are common asteroid strikes from nm to a meter in diameter? (self.askscience)
submitted 2 weeks ago by j4k3 to c/askscience
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[–] [email protected] 35 points 2 weeks ago* (last edited 2 weeks ago) (3 children)

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.

[–] j4k3 8 points 2 weeks ago (2 children)

I figure the double cylinders counter rotating will result in the more at-risk side of a habitable cylinder receiving considerable protection.

In my attempt at hard sci-fi, the interior primarily has the docking structure at one end and mountains at the other, the primary heat radiators are on the mountain side and extend along the length. The primary framing structure of the cylinders are packaged around the generation ship. Upon arrival the generation ship becomes the central hub of the primary habitat. The secondary cylinder is used for biological resources processing and buffering of the habitat's elemental cycles.

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

I also propose that there will be self replicating drones that are more akin to kilometers scale industrial complexes. Self replication is limited by time and limited synthetic intelligence requiring regular support, (so totally unable to make a paperclip universe). 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?

I'm trying to stick to Dr O'Neill's original assumption of only using the engineering materials of the present. I'm making the assumption that the only major advancements are within biology and it basically becomes like computer code as the age of scientific discovery is mostly completed. Biology is the final technology to master and what enables environments with complete elemental cycles balance. The only remaining industrial processes are executed by the rep drones for maintenance and expansion of the habitat.

The drivers of expansion are specifically due to the era being over 400k years into the future when Sol is further into the red giant phase. Cislunar becomes the seat of humanity after we access the first m-type asteroid effectively and long before the story is set. Most of Earth's accessible resources will be exploited completely in less than 100k years. So that drives biology as a technology more than any other force.

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

[–] [email protected] 5 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

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 . 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...

[–] j4k3 1 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

you definitely want to have an outer shell, or this thing is going to go the way of the titanic.

::: spoiler Most definitely, but I'm okay with that, it is part of our real story too–that whole "engineering is only about good enough to get by."

So I'm on a bit of a different plane overall. My main motivation is setting up a plot to point out most of our stories about AI are a machine god mythos with terrible philosophical conclusions. By the same logic in these stories of AI leading to inevitable human extinction, the Earth must be a monoculture of of one organism, and all smarter siblings murder their lesser competing kin.

I'm taking Asimov's ideas of an integrated Daneel and going much further by removing Daneel's godship. Then I'm making a story of alignment and the volatility of humans.

I'm also trying to imagine a real post scarcity society without it being utopian or dystopian. The biology as a technology is not intended to explore a circus show. I think I can get around that using the limitations of staying within the elemental cycles balance.

You're right, my casual and very human memory of 1b versus 1m was foggy and I think that Cool World's video was the primary one I was thinking of, but it could have been from Anton Petrov too. It isn't really important. The pressures could be due to a worst millennia in a million event. This will among nt to nothing anyways. I have no means, qualifications, or connections and the world is geared to exploit those dumb enough to try. There are more billionaires than there are people making a living wage off of writing.

I'm talking in deep time anyways. My notes and graphs have a date stand in on 420,421 After Fusion (AF) as the date because it is easy to remember.

The generation ships are possible because of the largest project of a broken ring structure around the orbit of Mercury. This creates the ships and enough antimatter to accelerate and decelerate on the other side. The story is constrained to a few millennia during the first interstellar migration where Sol is the hub for everything.

I call planets useless gravity prisons of gravitational differentiated scarcity, and completely uninteresting. I also limit colonies to g-type stars.

The rep drones are setting up the resource acquisition and infrastructure required to support the colony. I take the stance that the culture looks at waste very differently. Heat is a major resource commodity. Any waste product is considered unacceptable in almost all circumstances. I'm trying to avoid anything magical and staying very conservative about what and how advancement happens. There must be a reason why things exist as they do. This is a world where people are stewards of the future and take full responsibility for the entire legacy they leave.

Wild mutations have major negative consequences generations later if not more immediately. This is a reason humans are dangerous, for their tendency to do rogue nonsense like this, while more stable and known mechanisms are preferred.

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.

Anyways thanks for the insights on sounds.

[–] [email protected] 2 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

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.

[–] j4k3 1 points 2 weeks ago* (last edited 2 weeks ago)

::: spoiler So the energy required to exit the gravity wells of planets is the main issue. I'm going with the assumption that infinite energy expansion is a fallacy. This is a post fusion era, but the expenditure of unrecoverable resources are a major faux pas. Culturally, they are free to utilize anything available, but expending the collectively held resources of a star system for anything short of an action in the best long term interests of said collective is unthinkable. This is a distant lesson from the stone age of silicon before Wild Earth and the migration to Cislune.

In my writing I've come up with the basic backstory of Sol, but my main focus is on a randomly picked colony around Alsafi.

It is helpful to imagine how the generation ships were equipped with the seeds needed to start a colony, like what kinds of ultra rare resources would be taken with them, and what would be a top priority upon arrival. One of three rep drones would likely slow around the outer stellar halo field to start operations and infrastructure required for resources beyond the elemental snow lines. The main question being resource density and fusion based propulsion.

Fusion is limited by enormous scale and the heat makes it a major challenge. The ultra exotic engineering materials required are considered atrocious because of the enormous amount of waste, heat, and how long even the recoverable byproducts take to incorporate into a sustainable elemental cycle. There is very little time pressure but there is extreme sustainability and conservative long term stability pressure.

I'm constraining the generation ships to 7 parsecs in travel distance due to pragmatic engineering constraints (baseless handwaving magic really, I'm just targeting the number of type G stars available, mostly because I find the lack of present lack of attention on the only type of system known to host life atrocious).

Many gen ships and colonies fail. The first geny ship to Alsafi is lost in transit. The second has a series of unfortunate events that delay the first cylinder construction. After ten generations the entire human population is sterile without gravity.

Indeed, time is not a major factor in most situations. Lifespans are on the order of a half millennium. I want to convey that our size and slice of time is okay to appreciate against a larger canvas and doing so is the only path to a greater future. The present is a primitive stone age and nowhere remotely close to some techno end game. In the present we have far too much hubris and a delusional grandeur that lacks a cultural perspective on our place in the future timeline. We are only a link in a chain.

The one constant in civilizations over time is increasing complexity and the tools needed to wield it. The interesting story is what becomes possible when that complexity is accessible. There is no magic in that story, techno or otherwise. The tools of that age are all around us right now, or at least the building blocks to make them. We simply lack an understanding. Harnessing the complete potential of biology and the way nature creates balance and stability is something we have only scratched the surface of observing, let alone harnessing.

The minutiae become interesting to me, like the logistics, complex social hierarchy after the primitive accruing of the fundamental means of survival, and the lives of average unremarkable persons with their perspective self awareness and nuances brought to light in a critique of the present. These need to be grounded in the conservative reality of an existence where the main differences between then and now are the expansion of accessible complexity and a massive growth in the available wealth.

I think we are likely already able to access and are using many niche materials and processes that the future will abandon as untenable. I see this as both an immense expansion of technology and a techno minimalism. Life is appreciated for exactly what it is. There is no guarantee.

Like, valuing the lives of a few astronauts going to the Moon at billions of dollars in redundancy is ludicrous. You will find many volunteers willing to take far greater risks for far less reward on Earth. These are a resource too and naïveté of this resource is stupidity. We are not a race of demigods like is common in present cultural religious thought. Life is precious, and no one will force another into increased risk, but no one has to force another when the full spectrum of people are considered. A suitable person or group will always volunteer to take on the risk.

So like, when I'm curious about nitrogen, I'm interested in how it might be sourced and moved around in the most stable and efficient way possible. There are likely large networks of transfer orbiting infrastructures and pod like bubble ecosystems made to process and transport resources. Biologically sequestering resources and the solid state of matter are the primary forms of storage. Like the mountains inside the habitat are the primary source of oxygen storage.

[–] [email protected] 2 points 2 weeks ago

This sounds very similar to Arthur C. Clarke's Rama trilogy!

[–] FourPacketsOfPeanuts 7 points 2 weeks ago

They might notice a sinkhole forming pretty soon, and that would be no good.

New fear unlocked

[–] [email protected] 2 points 2 weeks ago* (last edited 2 weeks ago)

The original O'Neill cylinder was just normal mild steel, though. Exotic materials increase the possible size up to planetary. Maybe OP's could be Kevlar? Although, if you really want the dirt and rocks that probably increases the load quite a bit.

[–] teft 10 points 2 weeks ago (1 children)

If you have the technology to build a multi kilometer long space habitat I'm fairly certain someone would think of adding shock and sound absorbing material between the hulls so that you wouldn't hear or feel impacts unless they were catastrophic impacts.

[–] [email protected] 10 points 2 weeks ago (1 children)

Also important to note that the scale of these things can lead to intuitive misunderstandings. For example, if a meteor blows a meter-wide hole through the hull of an O'Neill cylinder, that intuitively sounds like a huge crisis. But in fact it'll take weeks before enough air leaks out through a hole that size to become a problem. As an emergency patch all you need to do is drop a big manhole cover over it on the inside and the air pressure will seal it up against the hole quite tight, making it easier for the repair crew to weld a proper patch onto the actual hull.

[–] FourPacketsOfPeanuts 6 points 2 weeks ago (1 children)

Careful putting that manhole cover in place though! Delta-P is no joke

[–] [email protected] 11 points 2 weeks ago (2 children)

There'd only be a one-atmosphere pressure differential, though. Wouldn't be so bad, depending on which bit of your body gets stuck on the gap (don't sit on it).

This is another thing Hollywood often gets wrong about the vacuum of space. If your spaceship gets a bullet hole in it you could do an emergency patch by sticking your finger in it and you'd be fine.

[–] [email protected] 11 points 2 weeks ago* (last edited 2 weeks ago) (2 children)

It's one of the things I really enjoyed about the early episodes of The Expanse. Lots of attention paid to the hard science of space travel, especially compared to most sci-fi.

Inertia matters. Debris speeding at you from a nearby fight is just as dangerous as someone meaning to attack.

Stuck in a brig when an enemy ship railguns a softball sized hole through the ship you're on? Slap the emergency manual three ring binder up against the hole to make a temporary seal.

It goes off further into less science backed stuff as time goes on, but I really appreciated the "hard science" base it built off of.

[–] FourPacketsOfPeanuts 5 points 2 weeks ago (2 children)

Ah that's true! Quite different to water. Looking it up it seems you hit 2 atmospheres of pressure at only 20 m water depth. No wonder diving accidents are so serious. Sort of reassuring that space will kill you at a more leisurely pace.

[–] [email protected] 1 points 2 weeks ago (2 children)

Yeah but it'll hurt the whole time you're dying. In an implosion like the sub, you'll be dead before you even realize anything is happening.

[–] [email protected] 2 points 2 weeks ago

In actual chamber accidents the people lost consciousness immediately. The one dude didn't even know what had happened or why his ears were sore when they came to rescue him.

[–] [email protected] 1 points 2 weeks ago

it’ll hurt the whole time you’re dying

Not necessarily. If it's a slow leak, you can go from fully functioning, to slightly lightheaded, to dead from hypoxia without any pain or even awareness of your situation.

Destin of SmarterEveryDay demonstrated this under controlled circumstances a few years back. (hypoxia demo starts around 4:30)

[–] [email protected] 2 points 2 weeks ago

The trope of flying through the debris/explosion of the ship you just blew up is kind of ridiculous. That's the last place you want to go.

Finding micrometeorite holes would actually be harder than you would think because it's only 1 atmosphere pressure leaking (or less, you don't have to have 1 atm to exist comfortably). Might be easier to find them from the outside first and then map out where to look.

Those battle scenes where the rail gun shot were visibly going through and just missing...that was frightening. And remember, any shot that misses ruins someone else's day later on.

[–] [email protected] 1 points 2 weeks ago

Which has literally happened on the ISS.

[–] [email protected] 8 points 2 weeks ago (2 children)

Not nearly as loud as the screaming space banshees.

[–] SkybreakerEngineer 3 points 2 weeks ago (1 children)

Banshees, harlequins, and other kinds of xenos can be silenced easily through the proper application of bolters

[–] [email protected] 1 points 2 weeks ago

Sure, if you're just made of marines. The rest of us managed with artillery fire just fine

[–] [email protected] 1 points 2 weeks ago

That's fine. In space, nobody can hear the banshee scream.

[–] solidgrue 8 points 2 weeks ago* (last edited 2 weeks ago) (2 children)

I wonder how regolith might work out as shielding, as proposed in some popular sci-fi series. Its added mass, to be sure, but regolith plus infernal pressure vessels is probably a good trade-off for the mechanical complexity and added mass.

[–] [email protected] 4 points 2 weeks ago (1 children)

infernal pressure vessels

I suspect you meant a different word, but it's honestly better this way.

[–] solidgrue 2 points 2 weeks ago

Lol, yeah I did but now I'm definitely leaving it

[–] GraniteM 2 points 2 weeks ago (1 children)

There was a proposed method of making a space habitat that I found fascinating, though someone smarter than me would have to address its plausibility. This would have been in a book from Heinlein, Asimov, Niven, or Pournelle, possibly a collection of non-fiction essays on colonizing space.

The idea is that you find a sufficiently large asteroid with high iron content. You hollow out a cylinder in the core and pack it with water ice, and then plug the end. Then you spin the thing on its axis while bathing it with lasers or focused solar light. This heats the surface until it is molten. Eventually the heat penetrates to the water ice core, which boils, inflating the molten iron like a balloon. Once the thing has cooled, you have a hollow space where you can start building your habitat, and a nice robust outer layer, and the whole thing is spinning to simulate gravity.

Again, I don't know if this falls into the category of "sounds neat but is totally implausible," or "sounds insane but is actually technically entirely sound," but it stuck with me as a neat way to build a habitat.

[–] [email protected] 1 points 2 weeks ago* (last edited 2 weeks ago)

I'm going to go with “sounds neat but is totally implausible.” Not totally implausible, but it's a lot of work just to roll a bunch of unpredictable dice with the chaotic behavior of the boiling water and the chemical composition of the asteroid.

The water vapor is going to find the path of least resistance and come erupting out of the molten metal, probably quite explosively and you're going to loose a bunch of valuable mass in the process.

EDIT: There may be a way to do this and get more predictable results (if you have a ton of energy to melt the asteroid very fast and very uniformly from all directions at once) but it still sounds unnecessarily complicated. There are simpler, cheaper ways to get better, more controlled outcomes.

[–] MushuChupacabra 6 points 2 weeks ago

Don't skimp and do old-fashioned O'Neill cylinders. Both counter-rotating cylinders should be housed inside an outer hull, to shield the living spaces from cosmic radiation, impacts and such.

[–] [email protected] 5 points 2 weeks ago* (last edited 2 weeks ago)

Best way to know would be to calculate the kinetic energy. Assuming double-digit energy conversion you can just ignore it and use the full amount with reasonable accuracy, since dB is a log scale. Then, use the inverse-square law to wherever you're standing in the cylinder.

A meter-sized asteroid is going to blow a hole big enough the sound won't be the main concern, though. Probably you have two cylinders after that. Thankfully space is empty, and those are rare enough you can steer around them. Grape size impactors are the main thing they worry about on modern space stations.