/sci/ - Science & Math

>>15130438
Instead of having elevators to get into your apartment, the building should just move your alartment down to meet you. Then when you want to get out it brings your apartment back down again

>>15130463
if you want to bisit a friend it brings your apartments together at the door. If you get married it can permanently join your 2 apartments. a system like HyperLink could connect apartments from all over the world

>>15130438
just make the torus, OP

>>15130524
People will need somewhere to live while they build it.

>>15130438
I think big spheres in space is likely how we're going to build propellant depots in space, initially in low earth orbit and eventually everywhere. I envision filling up the depots will happen in 2 ways: 1: dedicated tankers. 2: excess capacity will always be filled with propellant (or materials for the prop depot). For example, if starship has a capacity of 150 tonnes, and is launching a 100 tonne satellite to LEO, the ship would fill the remaining 50 tonnes with propellant to top up the depot.

Spherical tanks would be best because they give the most volume per surface area. A way to make these would be to bring up lots of standardized sections (such as a bunch of triangles to make a 20-sided-die shape, an isocahedron). These triangle pieces would be welded by robot into the correct shape -- the robot would have multiple arms, some with electromagnets to hold the pieces at the correct angle while welding. After the isocahedron is assembled, it's filled with an incompressible fluid and a small explosive charge. The explosive is set off, popping out the steel into a perfect sphere. https://www.youtube.com/watch?v=96yhdnhPxAw

The sphere could then be covered with additional layers for micrometeor protection-- could be overwrapped with fiberglass/carbon, or additional shells of welded steel.

Multiple spheres could be joined into one massive structure, at least one sphere per type of propellant. These spheres would be sandwiched between 2 parallel planes: the sun-side would have solar panels to shade the tanks and generate power. The shady side would have heat exchangers to keep the propellants cool.

There are several possible ways to pump the propellant. A system of this size can't easily use ullage burns, so spinning the tanks and collecting the fluid using centrifugal scoops might work. Another way would be to have a bellows that inflate inside the tank and squeeze the fluid out.

please keep the /sfg/ content in the /sfg/ thread

>>15130848
And: how to stop leaks, specifically from micrometeorids?

One method is to have balloons filled with some kind of sealant in them, floating around inside the propellant tanks. If a leak happens, a balloon gets sucked to the hole and partially get sucked through, popping in the process. The balloon fabric plus the slimy sealant inside harden and seal the leak-- the hardening would be caused by exposure to hard vacuum, or exposure to the propellant.

Alternatively, the gap between layers of the concentric shells of the tank could be filled with a sealant, like self-sealing fuel tanks.

I don't think spinning the whole depot would be necessary or a good idea. If the method of tapping the propellant is with centrifugal force, then spinning the tanks individually would be superior to the whole depot spinning. You wouldn't need to worry about a wobbling/unbalanced massive torus if a tank is fuller than another. Another advantage to having the tanks themselves spinning is they could be spinning in different axes, so they'd essentially act as really big reaction control wheels, so you could rotate the depot using only electrical power.
Having the depot stationary would also make space walks FAR safer -- if an astronaut got flung off a spinning station, he would need a serious rocket with a lot of delta v to go rescue him. Compared to a fixed station where an accidentally untethered astronaut could get back with just a few m/s delta v in a small package like the MMU/SAFER.

>>15130868
>>15130884

ok I reposted to SFG

So after receiving no response yesterday (which was in itself a response) I did some research and the largest vacuum chamber is owned by NASA and it is only 30m across. The largest mobile vacuum chamber is going into ITER and is only 20m across.

>>15130524
I put some extra thought into this and it really is easier to make plates than spheres. Especially if you are trying to do things affordably.

>>15130848
>>15130884
There's some really nice food for thought in these posts. Thanks.

>>15130438
you can just do the math for this to see if its possible
keywords for research: "pressure vessel" "hoop stress"
try to design a thickness that steel/titanium/nanofiber shit can hold

>>15133261
I've looked into it before but I'm not capable of the math required so I can't work out things like tonnage which is pretty important data really.

Iron is probably the most accessible material. I don't want to use steel because steel will not vacuum weld cleanly like a pure metal will. I was intending to rely upon vacuum welding to seal the plates that make up the rotating ring once they have all been clamped together. Then coat the inside with a baked on ceramic with a glaze. The outside may benefit from electroplating but I'm putting that in the too hard basket. It doesn't seem necessary.

A few rails for electromagnets also need to be fixed to the habitation ring to produce spin by interacting with the outer shielding ring.

I can't advance very far because I can't do the math so I can't work out mass, energy requirements etc to learn if what I intend is actually even possible at all or if I need to scale down to something of a much more depressing size.

>>15133283
Hoop stress around the equator of the sphere:
300m diameter
101000 N/m^2 pressure for air
thats pi*150^2 = 70700 m^2
101000 N/m^2 * 70700 m^2 = 7140700000 N = 7.1 * 10^9 N
lets use some steel thats 400 * 10^6 N/m^2 maximum strength
area of the hoop would have to be 7.1 * 10^9 N / (400 * 10^6 N/m^2) =17.75 m^2
strung around a 300m circumference 17.75 m^2 / (300 * pi) = 2mm thickness

hey, seems like the air pressure isn't an issue, on its own

>>15133308
>=2mm thickness

That's big data to me, thanks. I'll have a look at the numbers and try to understand them but I have little hope.

>>15133328
Next calc would be seeing if a structure might be able to hold all the artificial weight
Im not doin that one

>>15130438
>>15133261
>>15130884
I did some calcs on strength, volume and weight of a stainless steel tank of radius 100m. It's really big!
>>It has a volume over 6 times larger than the Knock Nevis, the largest oil tanker ever.

For the internal pressure of the sphere, I used 123 PSI (8.5 bar) which is what Starships' tanks are tested to. I'm sure that the optimal pressure for orbital depots is different from rockets but I couldn't be bothered to figure out the optimization.

I used the first stainless steel tensile strength and density I could find.

These three constants drove the design: a shell of 8.05cm would hold the requisite pressure. Then I just figured out the mass of the shell and the mass of the propellants.

>>It would take ~829 starship trips to deliver all the steel
>>It would take ~223 starship trips to fill the tank with methane
>>It would take ~461 starship trips to fill the tank with oxygen

Maybe my math is off somewhere because the sphere seems REALLY heavy-- the sphere weighs 82,849 tonnes but only can hold 22,300 tonnes of methane or 46,120 tonnes of oxygen.

>>15133332
Yea. Your work shows that the pressure vessel itself is not the primary limiting factor. Which is great news to me because then it comes down to how much stress you can get away with placing on the magrails and flooring.

Internal volume is great but it's better when you can actually build stuff inside it. From here the math gets way more complicated and is unsolvable until there is a design anyway.

But it's a big step forward and I think it's going to be achievable to provide sufficient energy to spin the pressure vessel.

>>15133348
>>15133328
>>15133308
Yeah I got 8 cm thickness needed from this internet calculator: https://www.omnicalculator.com/physics/hoop-stress.. I'm not an engineer so I have no clue what the right equations to use are.

>>15133348
Interesting numbers. It's frightening how difficult space industry is to kick off. Realistically I'm hoping to have the metal plates necessary mined and manufactured on the moon and boosted into orbit from there. It will require a lot fewer starships.

These big spheres will be like jugs of fuel getting thrown around the solar system. Till pirates.

>>15133357
Also thanks for confirming and the link. I've been relying on spincalc to help me with spin requirements.

>>15133376
I could see using the moon to build the plates. The moon surface has a lot of useful materials: Alumina (Al2O3) is between 15% and 24% of the lunar surface. If you heat alumina up enough, it will release pure oxygen and you'll have pure aluminum. (On Earth we use a more complicated but far less energy-intensive process called the Hall-Heroult process, but that needs a lot of mass of reagents. Potentially it'd be cheaper to do direct smelting if building bigger power plants have less mass than the megatons of cryolite needed for the Hall-Heroult process). It might even be possible to bootstrap the system with solar furnaces -- use mirrors to convert alumina --> aluminum, use the aluminum to make more mirrors, etc.

I assume that the majority of the propellant depot would be oxygen, then methane, then water, and finally noble gasses [argon, krypton, xenon, etc.] for ion thrusters, etc. The reason oxygen is the most massive portion of the depot is because the stoichiometry of the chemical equation of burning methane:
>>CH4 + 2 O2 --> CO2 + 2 H2O
A mol of methane weighs 16g and a mol of oxygen weighs 32g, thus you need 64g oxygen per 16g methane (4 times as much mass of oxygen as methane). It's really handy that the moon has so much oxygen!

To get the aluminum plates (and oxygen) to the pressure tanks in LEO, you could use a really big mass driver (many km long). Potentially you could use the aluminum to precisely aerobrake/skip off the Earth's atmosphere to get to the station without using very much propellant.

>>15133348
>8cm thickness
That seems far more than necessary. Starship isn't that thick surely so why should your tank be that thick to hold the equivalent pressure?

>>15130545
They live in it while the build it.. the first pieces would function like a space station, and more pieces would be added by those aboard until complete.

>>15133498
Two parallel discussions have been taking place. One is about habitable pressure vessels. The other has mentioned compressed hydrogen storage.

>>15130524
>>15130848

torus > anything

what if we put big coils in some arrangement, could we use it to slowly re-orient the station without igniting our propelant for slow manuvers,

>>15130438
Im of the opinion that all pressure vessels are inherently dangerous and most of them will probably explode. Its only with careful maintenance and sound engineering that they can be used at all without instantly bursting, and even then they can fail at an unknown moment. This is why I replaced my water heater with a tankless design and I make sure there are no high pressure objects in my home (not even bug spray)

This idea of having humans live INSIDE a pressure vessel, basically a bomb waiting to kill everyone there sounds catastrophic and foolish

>>15133638
These are usually modular systems combined into a larger form, so if any of the mods does “explode” the other mods will seal themselves or something to prevent catastrophic losses

>>15133638
Lol what kind of schizo shit is this?
We’re talking about building submarines but the polar opposite pressure wise.
It might be best to make spikey balls, or concave cubes, however you want to call it, with a large metal frame to reinforce the corners it would hold up better to negative pressure, if the cube doesn’t work scale up your corner points to 8 but keep the concave walls.
The answer to the fuel tank problem and the habitation problem is spikey balls.

>>15130438
>Is it currently possible to construct spherical pressure vessels with an internal diameter of 300m which can resist the vacuum of space?
They have to resist one atmosphere of internal pressure. Vacuums do not suck.

We can't yet make anything close to that size in orbit, but there are no particular huge breakthroughs we'd need to achieve in order to do it. Of all the issues to be faced, holding a paltry 1 atmosphere (or less, really, space habitats can be under-pressurized) is probably the least difficult.

>>15134605
That doesn't sound like a small problem at all, the material has to resist 14 pounds of pressure pushing outward on every square inch of material. Lets say this 300m diameter sphere mentioned in the OP is used
that's an internal surface area of slightly less than 282,743m depending on the thickness of the sphere. 11131614.2 square inches gives us a staggering 155,842,596 pounds of pressure the sphere would have to resist! 150 MILLION pounds of pressure!

Can you think of any everyday material that could stand up to this kind of pressure?

You can create any complex shape with piramidal shapes.
Even modular space ships. You can even deflect radar with it.

I would pile a bunch of rocks to replicate it if I saw one shit like that floating in the sky and then after that I would get home and take my meds

>>15135271
My human flesh is resisting 14 pounds per square inch in atmospheric pressure right now, and I... I... Feel totally okay.

For sure though I am not designed to contain that much pressure in a vacuum. Only to withstand that pressure from an external source.

>>15133348
So the steel + methane + oxygen would take about 1513 trips. If a starship can launch once per day, it would take 4 starships to get that much stuff to orbit in 1 year. 1513/365 ≈ 4

>>15133466
I wrote a massive post but it disappeared while I was looking for this image so you get the brief version. Maybe that's a good thing.

I don't know a convenient method of seperating the aluminium from the lunar dust. Aluminium has some advantages though and it does need to be a pure metal, not an alloy or metaloceramic (which is what I think steel kind-of is).

Lunar activity is currently focusing on the Aitkin basin. Just as easily the north pole could have been chosen instead but the south pole is more interesting.

One reason for that is an anomaly beneath this crater is believed to be the pure metallic core of the asteroid which ended up lodged deep in the moon's crust.

So really a lot of options may yet open up on the moon. Maybe abundant nickel or titanium. I'd like to find out soon.

>>15135271
>14 pounds of pressure pushing outward on every square inch of material. Lets say this 300m diameter sphere mentioned in the OP is used
This is the meaningful number.

>that's an internal surface area of slightly less than 282,743m depending on the thickness of the sphere. 11131614.2 square inches gives us a staggering 155,842,596 pounds of pressure the sphere would have to resist! 150 MILLION pounds of pressure!

This is a meaningless set of numbers just chosen to sound big. The PSI is all that matters.

Tires in your car hols about 30 PSI overpressure. Spray cans hold up to 100 PSI overpressure. 14 is child's play, a trivial challenge. The challenge is building latge structures in orbit at all. But all that takes is learning techniques.

>>15130438
Why don't you study physics and materials science and figure it out for yourself? You can find books for free if ya really want to, anon.

>>15130438
If you don't even know how to start with a shell thickness calculation I'm not sure this thread will be helpful to you as opposed to picking up Hibbeler.

Anyway 1 atmosphere is not a huge pressure difference and you can pressurise them to be even lower. The rotation you want to do is actually the more important tensile stress. For pressurised gas though the optimal design would likely be much small diameters otherwise the required material thickness becomes too big. It's a pretty simple optimization problem to crunch if you want to be more explicit about what you want to do.

>>15136945
>The challenge is...

I intended to address this point earlier when it was first raised. Even the methods of construction are not difficult although they are untried and astronauts have admitted that it is physically extremely challenging to perform construction tasks during a spacewalk. I digress.

In my mind the greatest challenge is the engineering behind making any habitat spin. In the design I am considering I plan to use some form of magnetic axle. Either around the whole equator of the ring or a spoke design with a central hub.

The spoke and hub design is probably most feasible because it would reduce energy transmission losses potentially although having a larger surface area for magnets to interact along the equator is potentially more possible than a smaller surface area of much more powerful electromagnets.

>>15135271
CONCAVE CUBES OR “>>15134594
SPIKEY BALLS” DISPERSE THE PRESSURE PER UNIT
Sorry caps lock was on and I’m too lazy to retype

>>15135271
You retards, build the containers to push inward to resist the vacuum and handle the pressure correctly. You need spikey balls with concave surfaces to disperse the outward force.
The disadvantage is that in the end your spikey ball will need framework around the outside to reinforce all the points. Also I will note these are extremely easy to make out of steel, and cheap.

>>15137634
>>15137644
Take for instance the egg in the hand challenge, thin ass egg shells can withstand the full force of your grip because of the shape of the egg, in the egg example the pressure is going into the egg, but in space fuel tanks the pressure is inside trying to go out, so round the faces to resist pressure, even if just to be able reduce the material thickness and weight. A ball is the absolute worst shape you could possibly come up with.

Just wanted to show that 300m is not entirely an arbitrary number. Also posting picrel for reference. Some caveman math to follow later.

>>15137651
>A ball is the absolute worst shape you could possibly come up with.

Possibly, just not for the reasons you describe.

>>15137765
Diameter versus radius error. Been years since I looked at these numbers. Anyway more mistakes to follow.

So for a sphere 600m in diameter made from 2mm thick steel would weigh around 1,570 tons and would take 3Mw of consistent energy to spin constantly. Give or take. Very rough figures but I did use the maximum figures given for power consumption. You could build a lot inside, and a magnificent support manifold tied to the magnetic rails and spin it for less than 10Mw.

Or am I off by a factor of ten?

>>15137915
You’re failing to account for my giant spikey balls

Would you rather
>Live in a boring dumb sphere (like any other planet)
>Live on a donut

>>15137965
I did some research a while back and the result of that research disagrees with you so I was waiting to see if anyone else had anything to say.

My understanding is that regardless of shape, the outward pressure is the same at all points. The sphere simply maximises internal volume per unit of surface area.

>>15137966
Yea at 600m I'm leaning towards donutville in space but I don't know how to calculate the weight of the pressure vessel when the shape is a torus. I really like the idea of looking up and seeing the rooftops of the structures on the other side of the sphere. In a showdown between practicality and romance though practicality wins in the early game.

Internal volume is nice to relieve claustrophobia but you still have almost 2km of main street running the entire circumference and the view from an upper story unit balcony down that street will be pleasant and open, with a relatively open set of tree'd paths and cycleways.

Torus is winning out for habitat for several reasons honestly.

>>15138014
>the view from an upper story unit balcony

I spent more time in the Netherlands than I would have chosen. Generally, the design of their thoroughfares appeals to me. A straight vertical barrier between internal and external living space with plenty of greenery and convenient ways of getting around. I have a love/hate relationship with the place. Picrel was one of my favourite streets to walk along.

Anyway, I think it can be improved upon as a model of semi-dense urban development but there is good inspiration there. The place is still claustrophobic but not overwhelmingly so.

It would be nice to do something larger, more open, natural and wild. Like Berlin. It's just a bigger project for down the road.

>>15137644
Spiky ball would make sense if you needed compressive stress eg making your ship out of concrete.
For something that is strong in tension ie steel, make a convex ball.

>>15138014
It’s not about the pressure being distributed evenly or not it’s about making a structure that can handle it, the spikey ball with reinforced grid on the outside.

>>15139565
I don't understand which advantage overrides the added engineering challenges of such a design.

>>15133308
>hey, seems like the air pressure isn't an issue, on its own
Id be more worried about bits and pieces hitting the sphere than the atmosphere differential pressure.

I guess the good news is you wont need inert gas to weld the sphere together from plates.

>>15136089
Separating metals can have large mass requirements but it's absolutely possible. Humans have figured out how to separate ores on Earth, so there's no reason those methods won't work on the Moon. Some methods:

>>different melting point.
>>different density (once pulverized or once melted)
>> different magnetism
>>different chemical reactivity (i.e. some things dissolve in certain acid etc.

Also, the lunar crust is even richer than many Earth ores.

>>15130438
>Is it currently possible to construct spherical pressure vessels with an internal diameter of 300m which can resist the vacuum of space?
For 1 atmosphere? Easily.

>>15133283
Spacecraft aren't made out of iron, dingus. They're made out of aluminum or titanium. Rarely stainless, when somebody is being quirky.

>>15134594
You're insane, the most effective pressure vessels are all round.

>>15133283
>I was intending to rely upon vacuum welding to seal the plates
HA

No way, not to get air-tight welds. You'd have to have each surface perfectly lapped to even have a remote chance of that working, there's no way.

Just get robots to weld it the normal way. In space you don't even need a shielding gas.

>>15140337
The whole spinning object needs to be contained within a protective shell. This shell would need some serious gyroscopes to keep stable. You run the risk of debris from inside hitting the pressure vessel (which is rotating at almost 200km/hr) however small objects probably won't cause massive decompression but a slow leak instead. The whole structure would be made up of individual pressure vessels really.

>>15140436
Best idea I have for seperating aluminium from moon dust is sifting by particle size and a centrifuge but I am no chemist. Still there may not be enough water available for chemical leeching plus that method is slow.
>>15140555
This thing is pretty big so will be built from whatever is abundant and easy to mine and process. I haven't looked into moon dust for a while so I'm not sure what's in it. A little titanium and aluminium depending on the area is what I remember.

>>15140594
You mean like picrel on the end of a canadarm?

>>15140628
>picrel

>>15140633
Essentially yes, except you don't need the shielding gas when you're in a vacuum. Good welders can weld upside-down so microgravity isn't an issue.

>>15140628
>full metallurgical industry in space as your prerequisite
okay, so you're talking about a science fiction scenario you'll never live long enough to see..

>>15140639
It could be possible but the issue is that it's a long term goal which is difficult to keep a public with a short attention span interested in long enough to keep funding going.

People like me go around pointing out how possible it is to do these things. Because it's so expensive that nobody can afford to do it on their own. I think a lot of people see projects like Artemis and don't really see the point of them or where they are leading to. I do.

>>15130438
Are pressure vessels really the answer to fuel storage and transportation? Sure, Ceres is the best place to get huge amounts of water ice. Then you can split the water to the hydrogen and oxygen you need.

But the asteroid belt is much darker than Mars and not really suitable for solar energy. You would need a lot of very expensive nuclear power plants to split all the water into fuel.

Wouldn't it be simpler to lift massive chunks of ice from the surface, insulate them to reduce losses and then push these ice block toward a refinery in the inner solar system? Venus orbit receives almost twice as much energy from sunlight as the earth.

Comparatively, on Ceres, sunlight is only 15% as powerful as on Earth.

This makes Venus a much more suitable location for splitting cerusian water than the asteroid belt or Earth.

>>15130438
I forgot how insufferable this board is, this is literally just filled with high school and college kids who have just been introduced to physics or engineering. It's like a machine that constantly produces stereotypical first year student content. Stop trying to satisfy your egos and get a job where you could actually apply your knowledge instead of wanking yourself off to how smart you are.

Look at this shit hahahahaha:
>>15133348
>>15133308
>>15130884
>>15130848
aahahahahahah, is this the same boy who showed his excel calcs for how the length of a Giraffes neck was supposedly an impossibility? loool