Astronomy Cast Ep. 381: Hollowing Asteroids in Science and Fiction

Article written: 15 Jun , 2015
Updated: 28 Dec , 2015
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When we finally make the jump to fully colonizing the Solar System, we’re going to want to use asteroids as stepping stones. We can use them as way stations, research facilities, even as spacecraft to further explore the Solar System. Today we’ll talk about the science and science fiction of hollowing out asteroids.

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3 Responses

  1. Bill says

    You mean like they did in the British comedy, Red Dwarf? Don’t hire anyone named Rimmer.

  2. Bo Zo says

    It sounds cool, but I don’t think hollowing out and spinning up an asteroid is a very good idea. Maybe it’s okay for simulating very low or microgravity, but at 1 gee equivalent, I’m pretty sure the thing would fly apart. Think of the weight of the floor! What holds it “up?” Only the lateral tensile strength of native asteroid rock – fractures and irregularities and all. And the thicker you make the “floor,” the worse the problem gets, because “gravity” gets stronger as you go “down.”

    A much nicer, stronger, neatly cylindrical station could be made from the material you carved out. It could be a refined composite alloy, or some better material (carbon nanotubes etc), instead of raw, irregular, asteroidal rock. You’d only use as much as you needed, instead of having a heavy load of structurally dubious and irregularly shaped “under burden.” It could be nicely symmetrical and thus easier to maintain an even spin.

    I think if you had to put a habitat with centripetal gravity in an asteroid, it would be better to hollow out a cylindrical volume and build a spinning chamber inside of that, rather than trying to spin the whole rock. On a small rock with low gravity, you could build it right on the surface and just pile rubble on top for radiation shielding. Quicker, cheaper, easier, and I think more feasible.

  3. Bo Zo says

    While I’m at it, here’s a slightly crazy idea I had recently:

    Pick a rock, inflate a gigantic (20 km radius?) balloon around it, tether it here and there to the rock so that the rock stays in the center, and fill it with breathable air at standard earth surface temperature and pressure. The air would be a radiation shield. You could keep it warm enough to stay gaseous in various ways (solar heating mirrors, greenhouse gases, plain old electric heaters…)

    You could walk (bounce) around on the surface in shirt sleeves! You could grow farms and jungles right on the surface. And just think of the ornithopters. Every sci fi space colony has ornithopters, right?

    You’d only have microgravity on the surface, but you could build centrifugal habitats inside or right on the surface.

    Problems to be solved:

    The bubble has to co-rotate nicely with the rock, and stay that way. You’d have to regularize the asteroid’s rotation before you started. The tethers might help, but it’s a huge mass of gas. You couldn’t have a lot of sloshing around.

    You need a LOT of air, which is rare in space lol. Exporting it from Earth would be pricey. You’d probably have to make it out of asteroidal ice, so you’d want to pick an appropriate rock.

    It would be a novel and exotic ecosystem, with idk what sorts of weather, etc. Might be problems there.

    You need a pretty big balloon. It would only have to be strong enough to contain one atmosphere of pressure, so the equivalent of ordinary plastic wrap might be good enough. I imagine creating / extruding it like a soap bubble.

    Patching punctures would be an ongoing project. You’d get hit with micro-meteors every day, and occasionally some bigger ones. The bubble would have to be more like a plastic bag than a rubber balloon – it wouldn’t be good if the whole thing went “pop” if you punctured it. Leakage from tiny holes wouldn’t be disastrous, but they’d add up, and you’d have to keep repairing it. I picture little flying robots with spray cans, sealing up the holes. Maybe you could detect the holes from the outside via satellite, or from within via sonic sensors. Really big holes could be patched with space-visqueen lol.

    The material would have to be durable in some very difficult conditions: Hard vacuum on one side, and warm, moist, oxygenated air on the other; solar radiation; extremes of heat and cold… You wouldn’t want it to be flammable, or reactive with water or oxygen. Maybe regular shrink wrap would work, idk, but I picture something like a few layers of graphene.

    What happens on the surface of an asteroid when it suddenly grows an atmosphere? And as it warms up due to the “hot” air? Chemical reactions? Gigantic fires? Explosive cryo-vulcanism? You could preheat / prepare the surface to avoid some of those. Or maybe it’s not even a problem, idk.

    You’d need a “door!” That’s the other problem that I’ve had trouble “solving.” My best ideas are, a flying space port at the height of the bubble, held aloft by a few weak fans; or else shape the bubble into a sort of funnel at one or both poles, so there’d be vacuum right down to the surface, or to polar landing towers.

    Also, you’d have to pay for it, but that’s just a detail.

    When do we start?

    I don’t really think this is feasible, and I don’t even think having an atmosphere on an asteroid would be an advantage. So for the record I think it’s a completely dumb idea! But kinda cool, imho, and maybe possible, and I’ve never seen it anywhere else, so I thought I’d share it here with the UT crowd.

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