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how would I generate gravity in an orbital station without spinning in a really fast circle or making it as big as a planet, or would I have to cut my losses and just moon-base my idea (I'm trying not to chuck in magical gravity creation devices, to me they feel kinda like a question-dodgy solution)

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    $\begingroup$ For clarification, why don't you want "spin in a really fast circle?" Solving that problem is likely (almost guaranteed) easier than non-centrifugal gravity generation $\endgroup$
    – automaton
    Commented Oct 20, 2022 at 18:57
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    $\begingroup$ That's the simplest solution, and the science is well-understood. You'd need a balancing mechanism to keep the weight distribution even, but that's not even as complicated as other astronautical tech. As a bonus, you get different intensities of "gravity" at different distances from the center of rotation. And none at the core, for those zero-G applications $\endgroup$
    – automaton
    Commented Oct 20, 2022 at 19:14

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or making it as big as a planet

It's not about size, it's about absolute mass. So instead of going bigger, you can go denser.

You could have a small blackhole somewhere inside the ship, supported by future technology. This is a lot more handwaving than spinning the ship, but hey, you asked for that.

A black hole as massive as the Earth would be the size of a coin. Do notice that the gravity gradient around this thing will be a pain - anyone getting even a few meters close to it, even outside the event horizon, will be spaghettified.

Alternatively you could have a small piece of the core of a neutron star, with its pressure kept by huge lasers. That would be less drastic than a black hole, but still a huge amount of handwaving.

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    $\begingroup$ This barely helps if you're trying to avoid magical solutions, but it does have the added benefit that trapped black holes could be an excellent power source if you could make them. If your ship is powered by a trapped black hole, you get artificial gravity as a free bonus. $\endgroup$ Commented Oct 20, 2022 at 7:00
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    $\begingroup$ @Michael Matter falling into the black hole will release much of its gravitational potential energy if the conditions are right. The accretion disks we observe around black holes are capable of liberating more energy for a given mass than matter-antimatter reactions. There are other (theoretical) ways too, like "make the black hole small enough that it releases huge amounts of Hawking radiation" or special cases for rotating and/or electrically charged black holes. $\endgroup$
    – Luaan
    Commented Oct 20, 2022 at 9:48
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    $\begingroup$ @Michael look up the ergosphere of a spinning (Kerr) black hole and the Penrose process. By sending objects prograde through the ergosphere and firing a mass backwards (it will still appear to move prograde to a distant observer) you can extract energy from the black hole's angular momentum. Using Hawking Radiation you can just feed mass into the black hole(s) at the same rate you extract energy. This gives you perfect mass to energy conversion without needing antimatter, but does need you to be able to confine the small black holes $\endgroup$
    – Tristan
    Commented Oct 20, 2022 at 10:57
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    $\begingroup$ If all else fails, it's the perfect waste disposal system $\endgroup$
    – Seggan
    Commented Oct 20, 2022 at 15:58
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    $\begingroup$ Magical gravity sources were ruled out, but magical power sources were not. $\endgroup$ Commented Oct 20, 2022 at 19:40
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A way of simulating gravity which I've never seen in fiction:

Have the station sub-floor/centre made of magnetite. Preferably make the station floorspace a few metres above the surface of a giant magnetite lump.

Once you've established that, you need to get the inhabitants to wear chain-mail vests and trousers/skirts or equivalent, possibly leg-warmers - or clothing impregnated with magnetic plastic fibres (For a less strong effect):

Neat mail shirt

Copyright unknown 2022, via armormadeeasy. Fair usage.

All objects would need to be in ferrite (or ferrite impregnated plastics) or magnetic metal containers, food and drink would need to contain fine ferrite powder encapsulated in plastic Nano-beads to prevent undue wear of the tooth-enamel (recoverable from waste).

Where are you going to get the magnetite? Asteroids.

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    $\begingroup$ No, no no. Fun thought, but you're ignoring the distance squared issue. Let's presume that the people just wear mail shirts. Any magnetic field strong enough to be noticeable at waist height would be too strong to stand up from if you fell over. And you'd fall over a lot, because you'd be seriously top-heavy. $\endgroup$ Commented Oct 20, 2022 at 1:05
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    $\begingroup$ Not if the magnet is below the floor. They don't need to get that near it. @RobertRapplean (OK, editing to clarify). $\endgroup$ Commented Oct 20, 2022 at 1:15
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    $\begingroup$ @RobertRapplean: That would be the fourth power of the distance. $\endgroup$
    – AlexP
    Commented Oct 20, 2022 at 6:57
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    $\begingroup$ The force with which a magnet attracts a piece of iron decreases with the fourth power of the distance. It does not behave like gravity at all. $\endgroup$
    – AlexP
    Commented Oct 20, 2022 at 6:58
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    $\begingroup$ you could use electromagnets in both the floor and roof to generate a constant magnetic field (with some squiffiness near the edges of the room). Also the fourth power is wrong. A dipole field decays like the third power, but because we're relying on induced fields the force would go like the sixth but this is from a single dipole. An infinite plane of aligned dipoles (which approximates a room much wider than it is tall with aligned dipoles in its floor) would have a field dropping off linearly, giving an inverse square force on ferromagnetic objects $\endgroup$
    – Tristan
    Commented Oct 20, 2022 at 10:45
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Two Tethered bases:

Or one with a counterweight. In space, size is relative because space is huge. But a base can be tiny while taking up a lot of room. Place your station on a long tether anchored to either a second base or a convenient counterweight (like an asteroid). The two objects can spin around each other and generate simulated gravity.

Go fast:

If your base is always moving, you will feel acceleration. While this is usually supplied by spinning, your base can always be on the move by having your base be a spaceship. If acceleration is cheap, then fly back and forth to provide simulated gravity. But this isn’t a good solution if fuel and power are in short supply.

Degenerate matter:

Why simulate gravity when you can simply experience it? If you have extraordinary means, then build your base around a blob of super dense matter. As long as the base doesn’t move, no problems.

Okay, a few. Degenerate matter is usually in the form of a dead star or the like. To enjoy anything like a normal gravity, your base needs to be BIG or you somehow need a small blob. The HOWS would be really hand-wavy.

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    $\begingroup$ "The two objects can spin around each other" I'd appreciate no spinning. :) $\endgroup$ Commented Oct 20, 2022 at 1:18
  • $\begingroup$ @erro50282069 Thought you just didn’t want fast or sup wide. I’ll add. $\endgroup$
    – DWKraus
    Commented Oct 20, 2022 at 1:27
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    $\begingroup$ This wouldn't have to be spinning in a really fast circle. The ships themselves wouldn't actually be spinning at all, just swinging on the end of a tether. For a 224 meter tether, the rotational velocity would be 2 rpm. You'd hardly notice it. $\endgroup$ Commented Oct 20, 2022 at 2:03
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Big fans.

indoor skydiving

source

Can a fan blow hard enough to oppose gravity? Clearly that is what these fans do - exert a force opposite of that produced by gravity such that people are suspended in the air.

A fan strong enough to oppose gravity can reproduce gravity if you turn it around. Fans of this sort in your station will push persons and things against the floor, which will be perforated to allow the air past to be recirculated. Persons on the station will wear silver body suits like 7 of 9, because less form fitting garments flap in the wind and get worn out fast. Hair will be worn in buns or under skinhead wigs. Chapstick will be used frequently.

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    $\begingroup$ This would make the station a really awful place to live and/or work. I want to congratulate you but I'm not sure whether it's for your creativity or your cheerful disregard for the fictional residents. Perhaps both! $\endgroup$
    – kaya3
    Commented Oct 20, 2022 at 10:32
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As far as we currently know, you can create feeling of gravity in only two ways: by acceleration (so, spinning if you want an immobile base-it's not like it is fast spinning, so it's not an engineering issue at all) or by having enough energy (usually mass, but can actually be any kind of energy) in small enough space.

As for a moon-base: you wouldn't want to stay there for a long time. Gravity there is far too small, and it would introduce physiological changes similar to those astronauts experience while living in micro-gravity. In fact, full time colonization of the Moon will probably consist of having a rotating habitat in it's orbit instead of living on the surface.

There is only one real alternative: that you bypass artificial gravity altogether. With genetical engineering you could potentially fix the issues people have with micro-gravity. Or you can have advanced medicine, so adverse effects can easily be fixed. Or you go cyborg route/mind upload, so you don't have biological bodies anymore. Or make people spend 5 hours every day exercising in a special micro-gravity supported gym, so the adverse effects come way slower. In short, you introduce a change in inhabitants of the station that makes artificial gravity unnecessary.

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The material in a neutron star is extremely dense and has a lot of gravity relative to its size. A typical density might be roughly 10^17Kg/m^3.

You could make a spherical ship that has a core made from the same dense material as a neutron star. Because of the incredible density of the core, the ship doesn't need to be very large.

For a ship with a radius of only 100m you would need a core with a radius of only 15cm to generate a regular earth gravity of 9.8m/s^2.

Obviously, the core is not going to naturally sit stably in the center of the ship. But this can be solved with an active control system that adjusts the ship position around the core to keep it centered. If the core material is magnetic, that helps a lot with centering.

Some other things to note...

  • If the core is radioactive, it could also serve as a power source.

  • When the ship is destroyed it likely implodes rather than flying apart.

  • The ship can't land on a planet, or the core will de-center and likely destroy a lot of stuff. The only exception would be if magnetic centering is used (but probably still not possible).

  • Another reason you can't land the ship is that the core would be extremely heavy. The 15cm core would weigh like 1.4 trillion Metric tons.

  • Things like steering and acceleration are going to be very gradual with that much weight. Think more like an oil tanker rather than a sports car.

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    $\begingroup$ A 15-cm sphere of neutronium doesn't have enough mass to keep itself compact, and will explode violently without super-science or sorcery. $\endgroup$
    – notovny
    Commented Oct 20, 2022 at 18:49
  • $\begingroup$ @notovny That is certainly a problem. $\endgroup$
    – user4574
    Commented Oct 20, 2022 at 19:42
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Checks question tags --> "Science-based" and "hard sci-fi" aren't listed, so this is one of several technological-themed "magic" variants:

Bend space.

From General Relativity, gravity's equivalent to the curvature of space-time, and there are a couple theoretical ways to do this that involve exotic matter and/or relativistic speeds. There's a bunch of handwavium involved in making these, but... they're at least sciency.

  • The Alcubierre drive spins large quantities of negative mass and has some strong tidal forces near the edges - but if your station was positioned in the right part of the edge, and if your "warp bubble" was big enough, you'd presumably get something that feels locally like a gravitational field. If you don't want to go traveling through space at superluminal speeds, maybe you additionally have a conveniently-placed black hole and the Alcubierre warp bubble is orbiting it. The fringe fields (tidal forces) are still going to make entry & exit problematic.
  • Put your station on the edge of a wormhole. From a distance, wormholes would look a lot like black holes (covered in other answers), but are somewhat harder to construct. Though theoretically maybe-existing, naturally-occurring ones are probably on the scale where quantum gravity is important. So yours is constructed by super-tech! Or rare! Or dates to a time right after the Big Bang when solar-scale masses were getting quantum entangled and scattered around the universes. Anyhow, falling "down" the wormhole would spit you out somewhere else.
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