egg changed the topic of #kspacademia to: https://git.io/JqLs2 | Dogs are cats. Spiders are cat interferometers. | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer. | We can haz pdf | Logs: https://esper.irclog.whitequark.org/kspacademia
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<UmbralRaptop> (also, getting so into those things means that one stops having a sense of self for a while, right?)
<raptop> !8 Maxwell-Boltzmann House coffee
<galois> raptop: yes
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<SnoopJ> +1
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<raptop> e​gg. — there is no universally good value, *otherwise there would not be a setting*
<raptop> Oh, hey, a reasonable design philosphy
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<Iskierka> given that the atmospheric gradient is known, what is the total mass of air inside an o'neil cylinder
<Iskierka> I tried integrating the (density * circumference) vs height and got obviously-wrong values
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<raptop> I'd assume that the integral of circumference(r)*density(r)*dr would get you the value for any given disk
<raptop> Also, hi!
* egg|anbo|egg pets Iskierka with a cat
<Iskierka> I made the same assumption but the equation that came out the other side gives me values that are too low by a factor of 4 for a 10m radius and are linear with radius. I may not be very good at getting WA to integrate things
* Iskierka pets the cat back
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<raptop> hrm, int_0^R {ρ0 * 2*π*r * exp{+r/h} * dr}?
<raptop> where ρ0 is the density along the axis
<raptop> wait
<Iskierka> I'm confident I got it correct up to getting the pressure-altitude curve P = P0 * e^-((z - (z^2/2r))/H) but I don't know what step I messed up beyond that
<raptop> That's wrong, since I'm assuming constant gravity
<raptop> It meaningfully changes with height
<Iskierka> yes the inconstant gravity is fun, though I managed to work out that much for pressure, which should be able to convert to density
<Iskierka> fun fact: whatever the radius r is, the atmospheric conditions there are equal to those on earth at r/2 altitude, assuming it maintains earthlike surface conditions
<Iskierka> (there being the axis)
<raptop> huh
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<Iskierka> this would mean the largest ones o'neil proposed would go from a 20C living surface to a 1C axis, so is probably the size limit for a comfortable axis. It also puts the axis almost exactly at the limit for altitude sickness
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<Iskierka> ooooh I dum I see why WA gave bad answers
<Iskierka> at some point I forgot to copy the scale height in so it was trying to do powers of thousands
<Iskierka> and now the integral is significantly uglier but might work
<raptop> yay
<Iskierka> it works \o/
<Iskierka> 378 kg/m(length) for a 10m radius
<Iskierka> 37.8 tonnes/m for 100, 3.71 Mt/m for 1000
<Iskierka> and Island 3 at 4 km radius would be 55.79 Mt/m
<Iskierka> or nearly 2 teratonnes of air at 32 km long
<Iskierka> that's gonna take a while to build
<raptop> \o/
<raptop> And yes
<Iskierka> you'd be looking at a pretty similar weight of material just to hold it together though, even with no building weight and making it out of high quality carbon fibre
<Iskierka> unless you do cables EVERYWHERE holding the ground up
<Iskierka> (or use a safety factor well below modern construction standards)
<raptop> rotational gravity keeps on messing with my intuition
<raptop> (regarding the cables holding the ground up)
<Iskierka> 😆
<Iskierka> it would be a very good way to deal with tall buildings by making them "weightless" under tension but it would not be conducive to nice living space to have even small buildings require overhead support
<Iskierka> these ground pressure limits also mean you wouldn't be able to have big hills of artificial wilderness unless they were mostly hollow
<raptop> Just put machinery inside the hills?
* raptop is mostly serious
<Iskierka> Machinery is also heavy you can only put so much per sq m
<raptop> ah
<Iskierka> assuming Island 3 is structurally made of high quality modern CF and about 2m thick, a safety factor of 5 gives you ~ 3 t/m^2
<Iskierka> which ... isn't nothing, but also isn't anything exceptional
<Iskierka> this would make the structure 2.4 teratonnes just for the living surfaces + windows (assuming they're a comparable transparent material)
<Iskierka> you can make it thicker but then you start needing a lot more material. And ideally you'd want to try use a steel to source the structure from asteroids, but that means it has to become much thicker and most if its strength is just supporting itself
* raptop feels like O'neill assumed normal glass and steel, which is making me wonder how detailed his calcs were
<Iskierka> it's viable but ... very heavy
<Iskierka> well, the steel is
<Iskierka> solid glass panels are right out but you can potentially make it work with a supporting lattice taking most of the load
<Iskierka> turns out aside from like, diamond, transparent materials aren't very good in tension
<Iskierka> though since all the stresses are proportional to radius, while Island 3 pushing everything but technically possible, island 1 and 2 and everything in between are quite doable
<Iskierka> and give lots of living space already
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* Iskierka pokes egg with a loose copper wire
<raptop> *zap*