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Oceans on rotating habitats with lower gravity

Anonymous Sun 06 Sep 18:12:16 2020 No.12092163 View Reply Original Report

Quoted By: >>12093577 >>12093809

Hey /sci/, i heard that even with advanced materials like mass-produced perfect carbon nanotubes, you could only have an ocean about 500 meters deep on a rotating space habitat running at 1g.
They didnt provide how they made the calculation, so i cant see how they got that, but i want to know how deep you could go with lower gravity, and how exactly you calculate that number?
I just want to imagine the deepest possible comfiest oceans floating in space

Anonymous

Anonymous Mon 07 Sep 2020 02:23:43 No.12093468 Report

Quoted By:

anyone?

Anonymous

Anonymous Mon 07 Sep 2020 02:46:34 No.12093511 Report

Quoted By:

You're not going to get any serious answers without some numbers

Anonymous

Anonymous Mon 07 Sep 2020 03:16:38 No.12093577 Report

Quoted By:

>>12092163
Most of the rotating habitat figures you see are going to be taking launch costs of materials into account over the material physics involved.

Essentially, the physics of a rotating habitat put the materials under the same forces they'd experience in a suspension bridge. Yes, materials have an upper limit in terms of tensile strength, but when you need to place a heavier load on them, you avoid suspension and build on the ground. Adding structural reinforcement to a rotating habitat is as simple as melting ice and applying it to the outer surface in layers. While the external ice adds mass to the structure, it also becomes a part of structural integrity. It's pretty much the same idea as building a rotating habitat inside an icy body, but in reverse.

Anonymous

Anonymous Mon 07 Sep 2020 05:10:05 No.12093809 Report

Quoted By: >>12093847

>>12092163
Assuming carbon nanotubes have a tensile strength of 63GPa, and a density of 1400kg/m3, the equation for the maximum radius of a ring spinning to produce 1g of gravity is (Tensile Strength)/(gravity*density of material) which for nanotubes (and with a 50% safety margin) would be 2300 km in radius.
To tack on an ocean, simply multiply the density of water, 1000kg/m3, times the depth of the ocean in m, and add that number to the density of the ring material.
So, if you wanted an ocean of 1000m in a carbon nanotube ring with earth's gravity, it could only be 3 km in radius or 6 km in diameter.
The average depth of earth's oceans is 3.5 km, and max depth is 10.5km

Anonymous

Anonymous Mon 07 Sep 2020 05:24:27 No.12093847 Report

Quoted By: >>12093876

>>12093809
BUT WAIT
There are more theoretical materials with even higher tensile strengths than carbon nanotubes, they are Graphene with a tensile strength of 120 GPa, and Carbyne with a tensile strength of anywhere between 270 GPa and 393 GPa which is about as strong as normal matter can possibly be since it's the strength of chemical bonds.
A regular graphene ring with 50% safety margin and no other material could be almost 9000 km in diameter. How big of an ocean can fit on this?
Well you cant fit a full 10km deep ocean on it, but you CAN get up to 2.5km deep, but that's also equal to the radius, so it would be ENTIRELY filled with water, which from a certain point of view would make it 5 km deep but gravity flips halfway down.

Anonymous

Anonymous Mon 07 Sep 2020 05:40:28 No.12093876 Report

Quoted By:

>>12093847
If you go to the absolute limit of chemical bonds with Carbyne, with a whopping 393 GPa of tensile strength, and build in a 50% safety margin, you can get a max depth of 4 km, and have 2 km of sweet sweet air above you.
Now, this has all been assuming Earth gravity, but the human body can live in gravity as low as .7g indefinitely, so we'll go with that. At .7g, and with Carbyne walls, and NO safety margin, you could get an ocean depth of 7 km, and a total radius of 8.2km.
That's it, that's the absolute limit of normal matter and human physiology.
To be fair, while 7 km is 3 km or almost 2 miles shallower than the Mariana's Trench, it's still so unfathomably deep that every mountain on earth save the top 50 tallest would be underwater in this habitat.
Also, if you filled this habitat with air instead of water, you could have a rotating habitat with a diameter of almost 58000 km, or 4.5 times WIDER than the Earth, water is just that fucking dense.

In short, if you want disgustingly deep oceans, supramundane planets or just pure water planets are your only way of getting them, unless you can get a material that doesnt use chemical bonds for its strength.

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