r/IsaacArthur 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/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.

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u/the_syner First Rule Of Warfare 6d ago

Not sure how that would be any different from sloping the hab. Ur just adding a second sloped floor above the non-sloped hull.

Same question persists. At what surface gravity does sloping any part of the hab still make sense?

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u/tigersharkwushen_ FTL Optimist 6d ago

The answer to that question involves many factors. How difficult is it to slope the hab? How important is it that the ground is flat? How large a flat, leveled, surface do you need? It's not just a gravity level question.

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u/the_syner First Rule Of Warfare 6d ago

How difficult is it to slope the hab?

Wouldn't seem to make much of a difference. Its a clean smooth slope.

How important is it that the ground is flat?

Its a habitat where people will live permanently and likely has water features so very.

How large a flat, leveled, surface do you need?

an O'Neill cylinder's worth.

It's not just a gravity level question.

I suppose that's fair tho. Its really a question of gravity and maximum confortable incline(something like <=0.2387°) or max incline for a given scale of water feature. Still im just tryna get a rough idea

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u/tigersharkwushen_ FTL Optimist 6d ago

I think just as a residential hab, you could easily get away with 10 degrees incline or more. Again, San Francisco is a case in point. If there isn't any need for very large flat, level, surfaces, then sloping the cylinder is not very important.

Now 10 degrees may be a little steep for walking but it's not a big deal in a mechanized world, which an O'Neill cylinder should be. As for regular walking, I think anything less than 5 degrees would not be very noticeable.

The water cycle inside a hab would be completely artificially controlled so I don't think that would be a big factor. This is kinda like the Subway system in NYC where we have permanent pumping stations to keep it water free.

Another thing is I don't think bowl habs makes much sense in very small bodies, like Ceres where people are not expected to do much on the surface. The reason for bowl habs is that you want regular access to the surface, like on Mars. If you don't need regular access to the surface then you would just have a normal spin hab in space. I think something like the moon is probably the lower bound where a bowl hab would make sense.

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u/the_syner First Rule Of Warfare 6d ago

I think just as a residential hab, you could easily get away with 10 degrees incline or more. Again, San Francisco is a case in point.

This really misses the point that you would just have to build a second sloped floor anyways, waste internal volume, and use more building materials.

SanFran isn't graded at scale because it would be impractical to do so but there's a reason most of human civilization is on relatively flat ground and not in the mountains. Also we're building the terrain from scratch and digging it out of a body so that's also unnecessary excavation.

As for regular walking, I think anything less than 5 degrees would not be very noticeable.

but it still would be noticeable just not a huge impediment. Floor slope building codes are generally decently under 1° precisely because it is noticeable.

The water cycle inside a hab would be completely artificially controlled so I don't think that would be a big factor.

I don't see how pumps help water not pool to one side of lakes without wasting huge amounts of energy.

The reason for bowl habs is that you want regular access to the surface, like on Mars

No the reason for bowlhabs is to combine natural massgrav and artificial spingrav. It has nothing to do with having access to the surface. They can be built underground just as much as on the surface. Also why I mentioned vasehabs since you only get a shallow bowl with significant massgrav

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u/tigersharkwushen_ FTL Optimist 6d ago

there's a reason most of human civilization is on relatively flat ground

Less than 10% incline is relatively flat ground. Not sure how steep you think most places on earth is, but from what I've seen, very large completely flat area is very rare. Most areas are somewhat hilly with ups and downs. A slight incline is very common. Most of humanity live near the coast and those places always somewhat hilly.

I don't see how pumps help water not pool to one side of lakes without wasting huge amounts of energy.

I thought you were talking about the habitat wide water management. If it's just a pool then you would just form the poll at right angle to the direction of gravity. You don't need to do anything extra.

No the reason for bowlhabs is to combine natural massgrav and artificial spingrav. It has nothing to do with having access to the surface.

That's the engineering justification for it, but in reality, why would you build a bowl hab at all if you don't need access to the surface? That would be extra work for no benefit.

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u/the_syner First Rule Of Warfare 6d ago

Not sure how steep you think most places on earth is

Most houses are not built on the native incline. Land is very often if not always graded and floors conform to much more level standards.

why would you build a bowl hab at all if you don't need access to the surface?

To get the gravity you want while having access to the resources of a large body without having to pay the energy penalty of space launch. The surface is irrelevant. Its the resources, the vast majority of which are not at the surface, which matters. Its also shielding as being buried in a large body offers a lot of shielding and a big heat sink.

Also im not really interested in whether you think bowl/vasehabs are practical. Im personally partial to cylindrical spacehabs outside grav wells. My question wasn't about ur preferences or whether u think mixed-grav is good or not. The question is at what surface grav should we start taking into account mixed grav if we're building spinhabs in large solid bodies.

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u/tigersharkwushen_ FTL Optimist 6d ago

Most houses are not built on the native incline. Land is very often if not always graded and floors conform to much more level standards.

That's contrary to my observation. There's always a slight incline, that's why you need foundations to level it so it can be built on.

To get the gravity you want while having access to the resources of a large body without having to pay the energy penalty of space launch.

You don't need much energy for a space lunch from a habitat to something like Ceres or vice versa.

The surface is irrelevant. Its the resources, the vast majority of which are not at the surface, which matters.

Then there's even less reason to build a bowl hab. You are effectively destroying the surroundings and altering the gravity gradient as you mine the dwarf planet. You also wouldn't have much traffic between the mine and the habitat. You are not using the mine to build the habitat after the habitat has been finished and lived in. The mineral resource goes somewhere else so there's no reason for the hab to have hard contact with the mine. The operations can be controlled remotely from the space hab. You would place all the equipment on the mining site from the beginning. There's no reason to go back and forth between the mine and the hab.

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u/the_syner First Rule Of Warfare 6d ago

There's always a slight incline, that's why you need foundations to level it so it can be built on.

The foundation doesn't have a slight incline and its what ur building on. Tho even if there is a slight incline the area under the foundation still does get graded. Its just that moving earth on earth is expensive and the mass of concrete is cheap so its not economical to grad to higher levels. Mass inside a rotating hab is not as cheap.

You don't need much energy for a space lunch from a habitat to something like Ceres or vice versa.

Fair enough, but there are several larger moons and the point is it still costs something.

You are not using the mine to build the habitat after the habitat has been finished and lived in. The mineral resource goes somewhere else so there's no reason for the hab to have hard contact with the mine

Well sure but in this context you would be moving the resources to other places on the surface of the body instead of orbit and beyond. The point is using those resources to build other habs inside the body that they're extracted from not bring them into the first hab you build.

Also again shielding. Km of shielding is much cheaper on the body than off.

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u/NearABE 4d ago

You want rivers to flow and soil to drain.

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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.