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So, in my sci-fi future, humanity has spread across the universe, made contact with many sentient races, and advanced technology greatly.

However, very few bases in the vacuum of space can use artificial gravity, since it takes so many materials to create an O’Neill Cylinder. This is going to be a major impediment to expansion, as humans need gravity for their biological systems to continue functioning.

But, what if the entire base was magnetic? As long as the humans on board wore metal, it would probably be the same. And anything metal would stay in position. Do you think this would be feasible for bases, larger ships, and other stuff in outer space? Or would it take too much energy?

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    $\begingroup$ the second top answer to this question: worldbuilding.stackexchange.com/questions/236980/… talks about magnetism in place of gravity $\endgroup$
    – KaffeeByte
    Oct 28, 2022 at 17:56
  • $\begingroup$ Does that answer solve your problem? If it does, we can flag this question as a duplicate. We do this just to avoid repeating answers and focus effort in a single Q&A. it is no demerit on your part to post a duplicate question and they actually help people find the answer they need. Please reply to this comment. $\endgroup$ Oct 28, 2022 at 18:03
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    $\begingroup$ Does this answer your question? Generating gravity $\endgroup$ Oct 28, 2022 at 18:03
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    $\begingroup$ To say that O'Neill cylinders are expensive in the face of the costs interstellar travel is surprising to me. The same infrastructure to build FTL ship components will be able to build habitat components. Especially considering the per capita costs. $\endgroup$ Oct 28, 2022 at 23:05
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    $\begingroup$ just look up how the ISS toilet works, and then think about what magnets would change about that. (hint: nothing) $\endgroup$
    – ths
    Oct 29, 2022 at 1:05

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Magnetism for Artificial Gravity is a Terrible Idea

Magnetism, though might sound impressive for science-fiction, is actually a really terrible idea. Especially if the world is based on real-science, then magnetism is not the first choice.

For starters, magnetizing a piece of iron, the size of the ISS, would require the energy required to power a large city (that is kind of optimistic, it might take even more energy). I am not talking about electromagnets, I am talking about permanent magnets. Even hard iron can be magnetized with electricity to produce a permanent magnet, if the current is strong enough.

And furthermore, all metals can't be magnets, at least with the current understanding of physics. Spacecraft are mostly made of light elements like aluminum to minimize mass. There is a reason why the ISS and even the Space Shuttle are made of aluminum and not iron. Even with advanced technology, you would want to minimize the payload weight as much as possible, so that they can reach space easily. Another reason why most spacecraft are compact.

And anything metal would stay in position.

That is merely an assumption that rises from the fact that we live on a large planet, which exerts enough gravity to make some things feel heavier than others. Since metals generally have a high density, on Earth, they feel "heavy" and therefore, they stay in place.

However, in the vacuum of space, there is virtually nothing to exert any substantial gravity on the metals. So, iron would be virtually weightless in the microgravity environments of space. This means that your Magnetic base can be easily budged from its place by a slow impact.

However we haven't started with the worst problem yet.

Magnetism as artificial gravity has been suggested in multiple sci-fi books (such as Tintin-Explorers on the Moon), but in reality, magnetism only exerts a force on your exterior, and not on the interior.

This means that blood will pool in the head and torso, which can result in light-headedness, and other symptoms.

Your astronauts will get easily tired as they have to constantly walk with strong magnetic clothes, which means that they are weighted down to the ground, a bit too hard.

I'd stick to rotating habitats and O'Neill cylinders.

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    $\begingroup$ The conclusion is right, but there are some factual issues here. Recent advancements is steel have gotten good enough that spaceX rockets are using iron alloys instead of aluminum now. Also, no one said you have to use electro-magnets. Passive magnetism would would fine and not require a constant source of electricity to maintain. Also the nudging thing does not make a difference. You use orbital mechanics and corrective thrusters regardless of your source of artificial gravity. $\endgroup$
    – Nosajimiki
    Oct 28, 2022 at 20:11
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    $\begingroup$ @Nosajimiki: SpaceX's Starship is made of some kind of weldable stainless steel, which is non-magnetic. $\endgroup$
    – AlexP
    Oct 28, 2022 at 20:36
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    $\begingroup$ @AlexP They are made from a 300-series stainless steel which is only "mostly non-magnetic". However, if there was a need for magnetism, there are plenty of other steels that would do. For example, a 400-series stainless steel is generally tougher and mostly ferromagnetic. It would be a bit more expensive, but could still meet all of the mission requirements plus the added need for magnets. $\endgroup$
    – Nosajimiki
    Oct 28, 2022 at 21:15
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    $\begingroup$ This answer is right to note that holding a human body to the ground with magnetic clothing will have practically zero effect on their internal biology, meaning that the health problems OP is worried about will still be a concern. (Unless the magnetism is extremely powerful, in which case it could be lethal.) $\endgroup$
    – Tom
    Oct 29, 2022 at 17:34
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    $\begingroup$ "However, in the vacuum of space, there is virtually nothing to exert any substantial gravity on the metals. So, iron would be as light as a vacuum in the microgravity environments of space. This means that your Magnetic base can be easily budged from its place by a slow impact." I don't have a clue what you're talking about here. $\endgroup$
    – J.G.
    Oct 29, 2022 at 21:44
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Magnets are not the same as artificial gravity

...as humans need gravity for their biological systems to continue functioning...

Magnets will stick you to the ground, but not pull on your insides in such a way that it helps with your biological systems. So it will not meet the health requirements of artificial gravity. Magnetic boots can be good for short duration space missions to give some stability and since of normalcy, but not good for any permeant space habitats.

... and you don't need to go big to use rotational forces

However, very few bases in the vacuum of space can use artificial gravity, since it takes so many materials to create an O’Neill Cylinder.

The reason rotational force is preferred is that it effects your whole body, but you don't need something as big as an O’Neill Cylinder. An O’Neill Cylinder was considered as the absolute biggest we could make a space colony before the angular forces would become too strong for any known material to not be ripped apart at the time. They should be seen as a near upper limit, not a lower limit (material science has come a long way since 1974, so you could go a bit bigger in diameter than he predicted if you wanted too).

With rotational gravity, you really can go as small as you like (technically speaking) but the smaller your radius, the more things like moving around and standing up cause weird things to happen. So if you are in a 10m cylinder for example. Your head will experience ~0.8G while your feet experience 1.0G which itself will be disorienting. But then as you walk your apparent gravity will change by +/- 15% depending on if you are walking with or against the rotation of the cylinder. Running gets even more weird. A decent runner could even sprint fast enough to make themselves weightless or double thier weight... so the smaller you go, the more you'll have to get used to doing things slowly and carefully.

A Sandford Torus is often considered more of an "ideal" space colony radius, designed to balance comfort and small size. They are about 800 times less massive than O’Neill Cylinder but still have large enough of a radius that its citizens could go about most of thier daily activities without noticeable gravitational perturbances... but honestly anything bigger than about 50m will probably be good enough, and be made small enough to be suitable for even a small crew

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Frame Challenge

However, very few bases in the vacuum of space can use artificial gravity, since it takes so many materials to create an O’Neill Cylinder.

You do not need an O'Neill cylinder to have artificial gravity. You can make a smaller sealed environment like the one from A Space Odyssey:

enter image description here

Being small means it needs to spin faster to generate the same amount of gravity. (Edit: But good for you the smaller habitat needs the slower speed at the rim) I would have thought it was the other way around!

In any case a 100m radius donut habitat need to to rotate about 4 times per minute. Or once every 15 seconds.

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    $\begingroup$ I built this calculator jsfiddle.net/nosajimiki/k98z2h1a/240 a while back for this question worldbuilding.stackexchange.com/questions/150259/… Using it you can see that a 100m ring spins at ~31m/s to get 1G whereas a an O'Neil cylendar needs to spin at ~198m/s $\endgroup$
    – Nosajimiki
    Oct 28, 2022 at 20:31
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    $\begingroup$ There's no rule that says 'all space stations must have exactly 1 g of artificial gravity'. It would be perfectly feasible to reduce the spin rate & hence the 'G force' of a space station down to say .7 of a G without producing any adverse long term physical effects for humans. You might want to give birth in a standard g environment but someone could for instance spend a couple of years on secondment to a low G station and be perfectly fine when they returned to Earth. They may want exercise in preparation for returning and may have sore feet for a while but their bodies would soon adapt. $\endgroup$
    – Mon
    Oct 29, 2022 at 1:31
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    $\begingroup$ @Mon also, magnets in clothing are completely unworkable, but weighted clothing to compensate for partial rotational gravity might be quite helpful. The minimum amount of gravity required to settle fluids acceptably might be lower than the minimum required to prevent weakening of the long bones. And things like holding food and drink in place don't need anything like full gravity. $\endgroup$ Oct 30, 2022 at 0:42
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    $\begingroup$ @Mon I think you meant to write "@Daron" to hail him... that said... I'm now very curious about what inspired Daron's user profile, lol. $\endgroup$
    – Nosajimiki
    Oct 31, 2022 at 19:11
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    $\begingroup$ @Brendan Currently astronauts survive extended periods of zero G for months at a time. The longest period on record is 438 days! Anyone spending more than say 6 months or in space so suffers a significant loss of bone density amongst other significant health impacts but for shorter periods of time? The astronauts recover easily and are walking around a few days later. So something like a three year assignment on a .7 G station is not going to be a problem at all. No need to breed special races of humans, rotate your staff (pun intended). $\endgroup$
    – Mon
    Nov 7, 2022 at 22:36
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Actually a space station doesn't need to have a torus shaped habitation ring likethe classic space wheel..

YOu can have habitable sections of any size. Connected by cables. The two habitable sections spin around the center point of the cable between them. There can be a zero gravity section at the center of the cable for spaceships to dock, zero gravity work, etc.

Pressurized cable cars can run up and down the cables between sections like an elevator.

Thus a space station can be built much smaller than a classical wheel shaped space stations, let alone an O'Neil cylinder.

In fact, that is a possible design for a space ship to use when coasting for long periods between periods of acceleration and deceleration. Two ends of the ship can extend a cable betweenthem and start rotating around the centralpoint of the cable to make simulated gravity in the living quarters. So that design can be as small as a space ship.

It would be a bit of a pain to start spinning when beinning to coast, and then to stop spinnng before starting to decelerate, but providing simulated gravity during long space flights might be essential for the health of the crews.

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I have contemplated this concept, and yes, it would almost certainly work, but remember this will involve laminating every blessed thing and person that enters this ship with bits of metal. We’re talking metal clothing, tools, books, TP, everything.

Do remember that the rotating habitat concept can be downsized to reduce the amount of materials needed. Downsized a lot. A ring or cylinder only 100 metres wide, spinning 5 times a second, works just as well as a 1.8 kilometre torus rotating once a minute.

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    $\begingroup$ And how would metal lamination prevent blood pooling into the upper body to cause light-headedness? $\endgroup$
    – Alastor
    Oct 28, 2022 at 18:21
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    $\begingroup$ Look at videos of iron filings around a magnet, and consider that the same will be happening to every magnetic object in the field you're trying to simulate gravity with. Objects will weirdly stick to each other or repel each other depending on how the induced fields line up, form chains, they will prefer to line themselves up with the surrounding field, etc. And it won't even sort of work for food or drink, or bodily fluids. $\endgroup$ Oct 29, 2022 at 15:07
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Actually, if you did something unbelievably cool, this could work

Taken at face value magnetism appears to not replace gravity. Folks are right. You can wear magnetic boots or don an set of iron chain mail. But as has been pointed out elsewhere, while that pulls the body to the floor, it doesn't pull on the heart, or the blood, or the brain, or a lot of other things.

But what if it could?

Behold! I give you Ferrofluids!

Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid (usually an organic solvent or water). Each magnetic particle is thoroughly coated with a surfactant to inhibit clumping.

What your advanced tech civilization has done to make cheap bases and ships is introduce a ferrofluid into everything inhabitants eat and drink. It infuses the blood and tissues of the body and, given magnetized floors, allows people to walk around somewhat normally. There are some modern-day realities that we need to ignore as solved-in-the-future:

  1. The strength of a magnet decreases with distance a LOT faster than gravity does. What this means is the strength needed to hold a person to the floor normally would be high magnetic strength at the feet and low magnetic strength at the head. That might cause some interesting blood pressure problems. However, consider that a magent can be large and powerful, but not necessarily strong.

  2. We need to ignore that the ferrofluid, no matter how technologically advanced, constitutes an increase of mass. Just as an example, consider the effects of adding 10kg of mass to your body. Again, blood pressure....

  3. While this solution explains to a level of suspension-of-disbelief holding a living creature to the floor... you'd have to make sure everything was made of materials that would be drawn in a magnetic field to the floor simulating gravity. To use current-day examples: paper and pen ink, anything made of wood or plastic, clothing. Frankly embuing everything with a ferrofluid or ferropowder seems to magically fix everything.

  4. There does come a point where an aspect of the body is too small for a ferrofluid to easily explain things. What percentage of a red blood cell is water? What percentage of a cell. is water? Eventually you get down to details that can't be embued with a ferrofluid without invoking Clarkean Magic. However, I believe that these details fall well outside the requirements for suspension-of-disbelief.

Ferrofluids my friend... invest today!

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  • $\begingroup$ Honestly, -3 without a single comment? You folks have no sense of imagination. $\endgroup$
    – JBH
    Jan 19, 2023 at 10:47

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