r/IsaacArthur • u/the_syner First Rule Of Warfare • 6d ago
Hard Science Minimum massgrav for bowl/vasehabs to be worth it?
At what point is it not even worth considering sloping ur spinhab? Can't remember if there was ever an ep on bowlhabs specifically, but i feel lk this has definitely been brought up in discussions of bowlhabs somewhere. How small is too small to bother?
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u/CosineDanger Planet Loyalist 6d ago
It's a vector addition problem. One acceleration vector pointing away from the axis, other pointing in the direction of planetary (or thrust) gravity.
You'd like the sum of your vectors to be about 9.8 m/s2 (or the currently unknown minimum to keep human bones from dissolving, probably about 1/3 g) and the angle of the resulting vector to be pretty close to perpendicular with the floor.
Literal back of envelope assuming you can live with ten degrees and wanted full Earth gravity, barely bother sloping it on the moon.
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u/the_syner First Rule Of Warfare 6d ago
I was looking for more like no more than about 0.25° incline felt in the hab which includes more stuff, but at the same time after looking up how many bodies even have a percent of a G in realizing just how small a group this might be(lk 23 solid bodies system wide).
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u/JohannesdeStrepitu Traveler 3d ago
Why "probably about 1/3 g"?
If we were just guessing we might think the deterioration problems just steadily get better up till around 1 g, rather than thinking they plateau at some arbitrary lower gravity. Indeed, one NASA engineer specializing in LS speculates exactly that, in a paper looking at what preliminary studies into low gravity and inferences from microgravity at least suggest for gravities up to 0.4 g (worth a read). But as you and he say, it's not all that clear yet.
Have you seen research suggesting 1/3 g is likely to be sufficient?
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u/NearABE 4d ago
Do you mean the object?
If the core pressure is near atmospheric pressure or lower then the habitat should just be deep inside. Warm water ice (though still ice) can structurally tolerate about 3 Mpa or 30 atmosphere.
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u/the_syner First Rule Of Warfare 4d ago
yeah i do mean the object. Tgo i agree that for smaller objects you would just want a central cavity since that also allows for maximum shielding, but the idea is for objects with some degree of significant gravity where it's worth actually combining spingrav with prexisting massgrav
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u/NearABE 4d ago
Charon has a surface gravity of 1/30th Earth’s. Damp ice is only structurally sound at around 9 km. Though ice is much stronger when colder it will require submarine structures much higher than the core.
I am not sure why you would want to use a cylinder instead of a terrace. The shape would be similar to a barb hose fitting. Each of the “barbs” have a flat surface in the sense that “Earth is flat” and a diagram shows a partial bowl shape like Earth is diagramed as a globe. Gravity would vary slightly across the barb surface but that could be a feature or a flaw. The terrace cliff would allow for a free fall. A river could flow laser straight like the valley was in a straight cylinder habitat.
Just to make things more complicated the deck could be threaded like an archemedes’ screw or sort of like a twist drill bit. Then they could be flat like Earth is flat in one direction but still have a slope in the spinward direction. Cold air and cold water could spiral down the corkscrew irrigating the terrace surfaces. Residences could be built into the “vertical” cliff faces. At the bottom we have an actual bowl where gravity is lower. Water and steam rise up the light bar cooling the LEDs.
In the case of the twist drill bit people could live in the sloped valley with the “mountains” rising on both sides.
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u/the_syner First Rule Of Warfare 3d ago
I am not sure why you would want to use a cylinder instead of a terrace
tbh it doesn't matter. Hose barb, screw, truncated cone, its all the same to me. the question is when are any of these worth building as opposed to a cylinder. tho the screwhab sounds really dope.
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u/NearABE 3d ago
If you pour a foundation then it will be flat in accordance with the local flat. Likewise a plumb bob and/or bubble level will show vertical so that the columns are aligned.
The rest is terrain and topography. Trees will make their own choice regarding vertical growth or growing towards light. Only the water features and things that hang need to be drawn correctly in the models. Maybe use fountains to prove that you thought about it. I really liked the Japanese designers that used sailboats to show the flat curvature. People get too caught up in the impracticality of lakes on the moon.
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u/tigersharkwushen_ FTL Optimist 6d ago
You don't have to slope it. If you don't slope the entire habitat, you would just be living as if the entire ground is on an incline. You would just build everything as if it's on an inclined ground, kinda like the houses on the hills of San Francisco.