Generating gravity

Question

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)

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 — automaton, Oct 20 '22 at 18:57
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 — automaton, Oct 20 '22 at 19:14

The Square-Cube Law · Answer 1 · 2022-10-21T00:40:36.347

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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.

edited Oct 21 '22 at 00:40

answered Oct 20 '22 at 04:01

The Square-Cube Law

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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. – IndigoFenix Oct 20 '22 at 07:00
@IndigoFenix: How would you power anything with a black hole? As far as I understand they are a perfect energy sink, not source :D – Michael Oct 20 '22 at 09:00
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@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. – Luaan Oct 20 '22 at 09:48
@Luaan: So you mean just using it for a gravity battery? But how do you “charge” it, i.e. put all the masses in their initial places? – Michael Oct 20 '22 at 10:20
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@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 – Tristan Oct 20 '22 at 10:57
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If all else fails, it's the perfect waste disposal system – Seggan Oct 20 '22 at 15:58
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Magical gravity sources were ruled out, but magical power sources were not. – user253751 Oct 20 '22 at 19:40
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I like it. They don't even need fancy tech to tow the black hole around. Maybe they found "Planet X" and discovered it's actually a small black hole. Rather than attempt moving it, they just built a station around it, because free gravity. – JamieB Oct 20 '22 at 22:25
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@Michael The nice thing about gravity is that it always attracts; the system of "1kg ball of iron close to the event horizon of the black hole" has less energy than "1kg ball of iron far from the event horizon of the black hole". It's not energy that came from the outside - to "pay" for the energy, you'd have to take the ball out again, and nobody wants to do that :P – Luaan Oct 21 '22 at 06:07

Escaped dental patient. · Answer 2 · 2022-10-20T05:29:48.197

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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):

^{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.

edited Oct 20 '22 at 05:29

answered Oct 20 '22 at 00:56

Escaped dental patient.

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mmmm the tasty metal flavour (not sarcastic i fricking love the taste of metal) – erro50282069 Oct 20 '22 at 01:00
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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. – Robert Rapplean Oct 20 '22 at 01:05
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Not if the magnet is below the floor. They don't need to get that near it. @RobertRapplean (OK, editing to clarify). – Escaped dental patient. Oct 20 '22 at 01:15
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@RobertRapplean: That would be the fourth power of the distance. – AlexP Oct 20 '22 at 06:57
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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. – AlexP Oct 20 '22 at 06:58
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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 – Tristan Oct 20 '22 at 10:45
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note that in the same approximation gravity is a constant field, so you're still getting different behaviour from the magnetite floor. Also note that water is slightly diamagnetic meaning it is repelled by magnetic fields (cf the ignobel prize for levitating a frog) so in principle this could be used to provide gravity (in the opposite direction) without requiring clothes, but would need much larger fields (and would probably feel very strange as your muscles would pull down on your bones rather than vice versa) – Tristan Oct 20 '22 at 10:50
Just make sure all computer data storage is on solid-state, non-magnetic drives. That much magnetism would probably not be great for a traditional hard drive. You could shield it, but shielding costs weight, and weight = money when you're talking about space. (Actually that might make those chain mail suits a bit cost-prohibitive as well come to think of it...) – Darrel Hoffman Oct 20 '22 at 13:53
Second, third, fourth power of distance shoudn't matter if you can move the magnetite far enough away. Remember that the floor is "a few metres above the surface of a giant magnetite lump". Change that "few metres" to whatever you need to get a usable field. Obviously, this a) may require a lot of magnetite, b) may result in a lot of wasted space, and c) doesn't resolve any of the other problems. – bornfromanegg Oct 20 '22 at 14:22
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Using magnets for gravity won't solve many of the physiological problems (like eye swelling) that occur when the human body is not exposed to gravity. Also using the toilet is going to be just as hard as it currently is in space (watch out for floaters). – user4574 Oct 20 '22 at 15:28
@AlexP, if the jacket were properly aligned magnetite, you'd be right, but with just a ferrous material, it's the square of the distance. https://socratic.org/questions/how-does-distance-affect-magnetic-force – Robert Rapplean Oct 20 '22 at 15:47
A problem with this is that the force isn't distributed throughout the body. Gravity pulls every cell in your body equally, so there's relatively little "squashing". But here, the magnet only pulls your external garments - basically your entire body weight will be sitting on your shoulders and hips. I can support my body weight comfortably, but an equal weight sitting on my shoulders would be very uncomfortable even if my body weighed nothing. – Nuclear Hoagie Oct 20 '22 at 16:34
I agree with a couple of things which are disadvantages - I'd suggest making the force less than the full weight of the person for ease of wear, and I'm not sure about the eyeball thing, I'd need to research how astronauts/cosmonauts coped with that particular side-effect. – Escaped dental patient. Oct 20 '22 at 17:59
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All you have to do is play with some magnets for a couple minutes to see how hilariously unfeasible this idea is. The magnetic force goes from incredibly strong to essentially 0 over very small distances and there's no getting around that regardless of what you do to compensate -- at best it will still be incredibly awkward vs normal gravity. – eps Oct 20 '22 at 20:30
There's also the fact that anything other than 1 flat floor will be practically impossible as the magnets would all be interfering with each other and pulling occupants in different directions – eps Oct 20 '22 at 20:36
On top of the other issues, objects containing or made of magnetic materials would stick to each other and to the user's clothes, experience odd torques, etc. And it'd be little help in managing food and drink, or other objects that can't feasibly be made to incorporate magnetic materials. – Christopher James Huff Oct 20 '22 at 20:45
You've got a point, maybe that's one of the reasons why no-one's implemented it in fiction or real-life. @ChristopherJamesHuff I'm becoming increasingly aware that I'd not thought it through.... – Escaped dental patient. Oct 20 '22 at 21:01
@Angry Muppet. I disagree with all the criticism of this. Don't listen to it. Even with current off the shelf standard gear that every system integrator uses, plus some nice electronmagnets, you could set up a field that adjusts in strength dynamically. Machine vision system + electromagnet array = this will work. With future tech, it's a doddle. You could couple it with very, very weak (and thus cheap) 'gravity' from rotation to make sure objects don't float freely. – Oct 21 '22 at 06:31
Cover the leg warmers in pictures of traditional, Loony Tunes style horseshoe magnets. – Oct 21 '22 at 06:38
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Something similar can be seen in some iterations of the "Asteroid M" arc in X-Men. Magneto builds a whole city on an asteroid. He puts metal everywhere because he can control magnetism, and he really likes to be able to control everything. – Stef Oct 29 '22 at 08:23

DWKraus · Answer 3 · 2022-10-20T02:07:11.657

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.

"The two objects can spin around each other" I'd appreciate no spinning. :) — erro50282069, Oct 20 '22 at 01:18
@erro50282069 Thought you just didn’t want fast or sup wide. I’ll add. — DWKraus, Oct 20 '22 at 01:27
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. — Robert Rapplean, Oct 20 '22 at 02:03

score 5 · Answer 4 · answered Oct 20 '22 at 03:22

Big fans.

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.

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! — kaya3, Oct 20 '22 at 10:32

score 2 · Answer 5 · answered Oct 20 '22 at 11:56

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.

score 0 · Answer 6 · answered Oct 20 '22 at 15:20

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.

A 15-cm sphere of neutronium doesn't have enough mass to keep itself compact, and will explode violently without super-science or sorcery. — notovny, Oct 20 '22 at 18:49

score 0 · Answer 7 · answered Oct 20 '22 at 18:13

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.

Generating gravity

7 Answers7

Two Tethered bases:

Go fast:

Degenerate matter:

Linked