[Anthony Briggs]

One of the primary reasons to build on the inside of the asteroid is to counter the radiation. Cosmic rays and solar flares are incredibly harsh, and need at least a couple of metres of heavy stuff like iron or rock to shield the puny meatsacks. Ditto for micro (and not so micro) meteorite impacts. So ‘a thin layer on the outside’ is probably not going to be very desirable.

That said, mining the outside might be a viable option, eg. cutting slabs of rock or iron 10m thick and using solar concentrators to fuse them together. Once that’s done, mining (assuming non-robotic mining) would be easier, since you can have a pressurised shell around the core of the asteroid that’s easier to work in (just respirators/goggles, rather than a bulky space suit). Selling off the iron / platinum / etc. to earth might also be a reasonable way of funding construction of the rest of the habitat.

[Anthony Briggs]

Alan, sorry if the diagram wasn’t too clear – there are three spheres joined together by relatively thick (~200m) sections, so that it won’t tip over.

And they’re thin spheres* – high v geodesic domes with lots of triangles, primarily for their high strength to weight/material ratio, but the side effect is that they’d behave like giant  ping pong balls. Filled with air, it’d be impossible to make them float at a reasonable level, rather than stick ~500m into the air. That’s one of the key purposes of the fresh water inside, it’s actually to weigh the spheres down 🙂

* – well, /relatively/ thin: even a 5m thick wall vs. a 250m radius is only 2%

[Anthony Briggs]

There’s also the Ewok Holocaust 🙂

[Anthony Briggs]

> Harve Bennett and Michael Minor came up with the most compelling concept in the grand history of Star Trek IMHO: the Genesis Device.

Pretty sure Star Trek is fantasy, not science fiction 😉

[Anthony Briggs]

The easiest way that I can think of is to carve out a hollow with some sort of solar concentrating array, or use a concentrator like a 3d printer, to join blobs of molten rock or chunks of rubble.

You might also be able to pick a metal asteroid, which would have a far higher tensile strength (these would also allow you to sell off the rare earth and precious metals inside). Not sure how many of these are close to earth orbit though.

Reinforcing might also be an option – if you catch an asteroid which is partly metal (or capture two asteroids), you can use that to create bands like a barrel, or else construct a mesh/net out of carbon fibre to hold everything together.

[Anthony Briggs]

You don’t need the concrete itself to float — 2m walls with a 500m diameter would be roughly the proportions of a ping-pong ball (~0.5mm x 40mm), so the issue would be getting it *not* to float. That was the rationale behind filling it with fresh water (which is less dense than sea water).

I didn’t realise that seawater eroded concrete quite so well though (https://en.wikipedia.org/wiki/Concrete_degradation#Sea_water ), so something will have to be done about that. Roman concrete would be better, but repairing or replacing 20m panels while 50-100m underwater would be difficult, if not impossible (though some sort of large diving bell / suction cup with a flexible skirt might be able to do it – push it against the hull from outside and pump the water out from both sides, chop out the affected part and replace).

Better though would be not to need maintenance of the shell on 100 year + timeframes.

• Option 1 would be some sort of coating – either paint, or plastic harvested from the ocean gyres and melted down – or else a different substance (solar-sintered, steel-reinforced sand maybe, or just a solar-powered furnace + molds instead of sintering). You might also be able to weld the glass panels together with thermite, for a permanent water-tight seal with no external steel showing.

And yes, the idea would be to become relatively self-sufficent in food/water/energy/housing, capture and cycle carbon/nitrogen/water internally, have a relatively large population and thus be mostly stable and independent, at least compared to most of the current seasteading models.

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