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In my world, I have an asteroid station that was spun up to produce artificial gravity.

Characteristics:

  • The asteroid is treated as cylindrical, with a radius of 1.5km and a length of 5km. Assuming a density of 2g/cm3 at the behest of Wikipedia, this produces a mass of 70,680 metric tons, not accounting for any mass lost to the station built into the rock. Materially speaking, the asteroid is solid and rocky.
  • The asteroid is spinning at around 66 meters per second/0.4rpm, to produce 0.3g of artificial gravity.

Methodology

The asteroid was not spun up without preparation - that would obviously cause it to fly apart. My current explanation revolves around coating most of the surface in two meters of steel, with 250m radius openings left at each "pole," one for a docking bay and one for radiators. The station inside the rock has been reinforced to one-g construction standards to prevent cave-ins and the like.

Question

Is this setup structurally realistic, or would this lead to a broken asteroid and lots of dead people? If no, is it possible with stronger materials?

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    $\begingroup$ Working on an answer, but for starters there are six zeros missing in the mass provided. $\endgroup$
    – KerrAvon2055
    Oct 23, 2020 at 3:41
  • $\begingroup$ @KerrAvon2055 checks math Yup, still can't count. Thanks for catching that. $\endgroup$
    – SomewhereOutInSpace
    Oct 23, 2020 at 4:02
  • $\begingroup$ I'll maybe start working on an answer later. But my gut is telling me the massive steel walls weaken the structure and will break themselves apart under the load. If carbon nanotubes are unavailable, I'd be looking more at differening steel meshes for my outer reinforcements. A layer of fine woven material (like a kevlar fabric), a layer of 1mm wire mesh , a layer of 3mm wire mesh, hex grid of 10mm steel wire under tension, and radial 50mm steel wire bands holding it all together. $\endgroup$
    – Ash
    Oct 23, 2020 at 4:12
  • $\begingroup$ is there any particular reason for why you encapsulated an asteroid instead of building an o'neil cylinder with all of that steel? IIRC contemporary material strength should be enough to construct a cylinder of same size. $\endgroup$
    – Darth Biomech
    Oct 23, 2020 at 19:55
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    $\begingroup$ @DarthBiomech The backstory is basically that the asteroid was randomly captured into the Earth-Moon L2 point right around the time space colonization began, and it was colonized in null-g due to a lack of free infrastructure to build a station from scratch. The spin was commissioned thirty years after the fact. This station is actually an exception - all the other big ones are O'neil scale structures. $\endgroup$
    – SomewhereOutInSpace
    Oct 24, 2020 at 0:10

1 Answer 1

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Depending on the asteroid, the steel is not required

There are two ways of looking at this. On the one hand, every square metre of rock on the outside of the asteroid is being thrown away by the 1.5 km of rock above it (albeit in a narrowing slice with diminishing effective gravity as it goes towards the centre). That sounds really scary.

On the other hand, let's look at Mount Thor on Baffin Island. The top 480 m of the cliff is overhanging. Thinking about this, the rock at the bottom of the overhang has 480 m of rock on top of it, getting larger towards the top, all of it pushing down with 1G, and it is only supported on one side by the rock it is joined to. The overhang on the cliff is taking more force with less support than rock on the outer surface of the asteroid would.

There are potential problems with the asteroid, though. Tunnels and chambers need to be carefully constructed and placed to avoid weakening the structural integrity of the asteroid - if a large proportion of the interior volume near the outer edge is intended to be utilised then reinforcement will be required. The actual spinning up of the asteroid needs to be carefully conducted to avoid creating stress fractures.

In short, giant "banding hoops" around the outside of the structure are probably not required if the rock is structurally sound. If steel reinforcement is required, then it can probably double as radiators and make both "ends" of the cylinder usable for other purposes. In order to minimise heat expansion / contraction effects and efficiency of solar cells I would suggest keeping one end of the cylinder pointed at the sun and covered in solar panels while conducting docking operations at the other end.

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