We all know the pictures of the astronauts on the ISS floating around. We also suspect that a lack of gravity is bad for the body as the muscles go weak and such.
Why don’t spaceships just rotate to cause the effect of artificial gravity through centrifugal forces?
As some have already mentioned - coriolis forces. But why not build bigger so coriolis forces aren’t an issue? Because spinning up anything of sufficient diameter to even come close to 1G would need some kind of unobtainium to be strong enough to keep the spinning object intact. Say 5 tons of mass at 0 G is just mass, but now accelerate it and you need to figure out how to support 5 tons.
1 rpm for 1 G is going to need almost 1km radius. 2 rpm is ~400m.
You can see that the numbers, size, and engineering get pretty ridiculous to keep people from being sick when spun.
lol did you just watch Project Hail Mary?
Because it would be less fun
Basically, the spinning diameter has to be really long so the spinning doesn’t make you puke long-term (Coriolis force is a bitch). There were NASA tests and studies about it, which range between a 100 and a 1000 meter diameter.
So, the ship has to be built for it from the design phase, be it with a rotating ring or a tether approach. Which we didn’t have yet a usecase for (for only a few days or months):- For a future Mars mission, would slow acceleration and deceleration be more viable.
- Only real fitting usecase is a orbital space station with permanent crew.
usecase
Not a word, my dude. When your spell check wants to put a hyphen or space in, let it.
That’s the wonderful thing about a living language, if enough people start using a new word or a variation on the spelling of an existing one, it can simply become correct at a point.
The compound variant ‘usecase’ is often used in tech and refers to a very specific means in which a system is utilized.
Here is a great video on spin gravity. It covers an important detail that another comment mentions but most over look. Spinning fast enough to create gravity-like centrifugal force causes real dizziness at small diameters. 5 or 6 rpm is about the maximum we can stand.
We just need to breed two or seven generations of humans in tiny ship orbit and they will adapt.
That’s why you split the ship in two and spin the habitation module around the heavier part of the ship¹, connected by a tether, as in Project Hail Mary (which the video says is still too fast… so just make the tether longer).
- Well, around their common barycentre, but you know what I mean.
Yeah, a good idea. You run into some material strength issues, but I think this is the way.
Because the constant rotation complicates things a lot.
Specifically talking about the International Space Station, its main mission is a microgravity laboratory. We put it up there so we can learn about microgravity. Why go through all the expense of putting it up there and then spinning it to make gravity when we get it for free down here on the surface?
As for other craft? We have yet to develop manned spacecraft that can do the duration where it would be worth doing. Even the longer Apollo missions were in space for a whopping two weeks and 2/3 of the crew still landed, got out and stretched their legs. It hasn’t been worth the engineering hassle to do it.
And it is an engineering hassle, because…
-
The ship has to be designed to handle it. It’s under additional stresses, so it’s got to be built tougher to handle it. That’s added weight, and just typing that sentence made at least three rocket scientists cringe to death.
-
Humans actually aren’t great at living in a spin gravity environment. The smaller the radius of the spin, the worse it gets. For one thing, in a centrifuge, there’s a pretty steep gradient in centrifugal/centripetal/pedantic force, the farther toward the rim you are the greater the gravity. For very small distances that can be significant enough to cause problems on its own. But also, spinning humans isn’t good for their vestibular systems. Each of your inner ears has three semi-circular canals filled with fluid, and little hairs that can detect the movement of that fluid. This allows you to sense rotation around three axes, kind of like a gyroscope sensor. This evolved in an environment that rotates a 1 rotation per day, functionally stationary. Spin a human at several RPM and that constant rotation is enough to start throwing off balance, causing nausea etc. So the bigger the radius of the spin, and the slower, the better. That takes more weight, and there go three more rocket scientists.
-
It makes the spacecraft a pain to handle. You need to be able to orient spacecraft in space to point engines, windows, instruments, docking adapters etc. in various stable directions. A constant roll complicates that. “point in this direction and fire the engines” becomes a pain because, say you’re constantly rolling, and you need to change the direction your long axis points. What thrusters do you fire in what combination to steer the ship? Or do you stop the roll, maneuver/use your telescope/dock/whatever, then start rolling again? So now you’ve got to deal with gravity starting and stopping variously throughout the journey. Or, do you design the ship to have sections that do roll and sections that don’t? First, look up “gyroscopic precession” on Wikipedia. Second, wiring, plumbing etc. is a pain in the ass to handle via slip ring, let alone crew access. Third, that adds weight, which…I should probably stop saying that, rocket scientists aren’t cheap to train and that’s nine we’ve killed just in this list.
In conclusion, look what you made me do.
on point 3, long distance communication invariably uses highly directional antennas, which means these need to be aimed precisely, which means special automated gimballed antenna set that would drop signal anyway probably
also you definitely don’t want to deal with rotating gas seal that is also under pressure and fail-deadly, these already wear out quickly with sporadic use on earth. if there are two sections, one spinning and one not, both would have to be sealed
That was worth every second it took to read.
For number 3 and the slip ring. I have always thought, just make the stuff on the end self sufficient. Essentially make two spacecraft. One to run all the experiments in zero ish g. And the other to be like living quarters. You can even make them suit up to commute. But you would need one heck of a long arm to make the 2 palatable. Maybe 3 craft, two way the hell out there attached to some crazy long tethers. One in the middle. Then some kind of speed sled thing to get a person from the outside in or something. Probably need to worry about balancing out the change of weight due to the sled (and person) moving from outside in and such.
“point in this direction and fire the engines” becomes a pain because, say you’re constantly rolling, and you need to change the direction your long axis points. What thrusters do you fire in what combination to steer the ship? Or do you stop the roll, maneuver/use your telescope/dock/whatever, then start rolling again? So now you’ve got to deal with gravity starting and stopping variously throughout the journey.
according to the hohmann transfer orbit
you only do one burst at the beginning of the journey, then drift for 6 months before entering the atmosphere of the target planet to slow down.
So there’s 6 months where you don’t need to fire any engine. My plan is to first do the acceleration burn, then install solar panels on the outside of the ship (attach them via some kind of cord and cable) they fly outward due to centrifugal force so they get constant sun exposure, and then put the ship into rotation. So you don’t need to do any work on the outside anymore, until you’re shortly before landing, then you stop rotation, get in the solar panels, enter the atmosphere, do landing burn, and land.
Humans have flown a total of ten manned missions that involved a Hohmann transfer: Apollo 8, Apollo 10-17, and Artemis 2. All ten flew to the Moon. On a typical Apollo mission, the outward bound coast leg is about 72 hours, between TLI and LOI, during which time they had to do the release-turn around-dock-extract maneuver with the lunar module and do at least one course correction.
We’ve been wasting tax payer dollars for more than half a century now designing and redesigning manned Mars missions that aren’t ever going to fly. Some of the various “artist’s conceptions” over the decades have included various centrifugal gravity solutions, be it the wagon wheel type or the bolas type or whatever. I don’t believe any actual hardware has even begun construction. Before you start worrying about that, you’ve got to 1. have a society healthy enough to fly manned deep space missions, and 2. figure out how to shield the crew from radiation first. Neither of which we have figured out at the moment.
-
The ISS is primarily designed to research the effects of microgravity and other space environment issues. Hard to study zero g manufacturing when your station has artificial gravity.
True
We haven’t done anything worthy of the effort to build a ship that’s capable yet, basically.
Small ships would have to rotate really fast to make 1G, and it’s not worth the trouble if nobody lives there permanently.
Even if a small ship rotates fast that would ‘t work. If you have a small diameter then there would a huge difference between the perceived ‘gravity’ at your head vs at your feet.
Not to mention the coriolis effect wreaking havoc on your inner ear.
Not a problem when you’re sleeping lying down.
no, but the force of the rotation squeezing most of your blood into your head or feet might be a problem for you
Why? It’s still just 1G.
Do you faint when descending in an elevator?
Elevators don’t cause a pressure differential within your body.
Why? It’s still just 1G.
what is this data based on?
https://ntrs.nasa.gov/api/citations/20070001008/downloads/20070001008.pdf
At body motions or centrifuge rotation rates that are small in magnitude, the effects of the Coriolis force are negligible, as on Earth. However, in a centrifuge rotating at several rpm, there can be disconcerting effects. Simple movements become complex and eye-head movements can be altered: turning the head can make stationary objects appear to rotate and continue to move once the head has stopped. This is because Coriolis forces also create cross-coupled angular accelerations in the semicircular canals of the inner ear (see Figure 4-01) when the head is turned out of the plane of rotation. Consequently, motion sickness can result even at low rotation rates (<3 rpm), although people can eventually adapt to higher rates after incremented, prolonged exposure (see Chapter 3, Section 3.1).
You said force of rotation but the chart is talking about RPM.
Still only 1G.
Everyone is doing a terrible job of explaining, but they’re right.
Gravity, 1G, is described on terms of an acceleration. 9.81m/s2.
What is an acceleration? Is is the rate of change of a velocity. If a velocity changes slowly, it means the acceleration is low. If the velocity changes quickly, the acceleration is high.
Now, imagining a record player. Or cd player. Or your spinning wheel of choice:
You know that points farther away from the center are moving faster in absolute terms compared to points closer to the center.
Because the points farther from the center have a larger velocity, that means after some rotation, the total change of velocity for the outer points must be larger than the change of velocity for inner points. So, points farther away must have greater acceleration.
So, the apparent acceleration changes according to how far things are from the center point. This is why it really isn’t the case that it would be 1G everywhere. 1G is a specific acceleration, if if we’ve established that acceleration isn’t constant across the radius, then it can be 1 G only at one spot, not all.
You said force of rotation but the chart is talking about RPM.
yes, you have forgotten to take into account the Coriolis force and the effect it would have on your astronauts.
https://ntrs.nasa.gov/api/citations/20070001008/downloads/20070001008.pdf
At body motions or centrifuge rotation rates that are small in magnitude, the effects of the Coriolis force are negligible, as on Earth. However, in a centrifuge rotating at several rpm, there can be disconcerting effects. Simple movements become complex and eye-head movements can be altered: turning the head can make stationary objects appear to rotate and continue to move once the head has stopped. This is because Coriolis forces also create cross-coupled angular accelerations in the semicircular canals of the inner ear (see Figure 4-01) when the head is turned out of the plane of rotation. Consequently, motion sickness can result even at low rotation rates (<3 rpm), although people can eventually adapt to higher rates after incremented, prolonged exposure (see Chapter 3, Section 3.1).
in other words, the higher the RPM needed to generate 1g, the worse the effect of the Coriolis force on the astronauts.
Im not really sure what you mean by lying down? You’re not always lying down. Surely gravity is less relevant when you’re lying down anyway.
… I dont have a good understanding of physics but sci-fi novels suggest a few problems on small ships.
The first problem is the difference in gravity between your feet and your head. In a small command capsule like Artemis 2, your head might be near the centre at 0g while your feet are at the outside at 1g or even 2g. How hard does your heart need to pump blood? Would this create some kind of blood pressure problem?
The next problem is how it would “feel”. Is it called the Coriolis effect?
In a small ship you might experience 1g, but it would feel like you’re being spun around in a washing machine. Your ears would tell you that you’re constantly changing direction and it would 100% fuck you up. In sci-fi the spinning thing needs to be large enough that some g-force is produced without you feeling that sense of motion, or at least for ot to be small enough that you get used to it.
Another problem I just made up is that if there’s no gravity then 100% of the inner surface area can be terminals and readouts and equipment. If you create gravity then you need a floor to walk on which will use a heap of surface area.
There was recently a “design proposal” (more of a published thought experiment) I read (posted on lemmy) where the authors had figured out the diameter required such that the gravity differential from feet to head wouldn’t be weird. It was quite large if I recall.
I guess thats why, in sci fi it’s only used on ring shaped objects. A ship with a ring around its mid section, or a space station, or the expanse has a barrel shaped ship.
interestingly bigger ships would have to rotate faster than small ships to achieve 1g btw
this is due to smaller ships having a larger curvature so less velocity is needed
edit: no wait i just did the maths again and you’re right. smaller ships need lower absolute velocity of the outside walls, but angular velocity is higher.
Yes, but the smaller the ship, the worse the Coriolis force will be. Imagine a 10m corridor with opposing gravity on each end, and no gravity in the middle. Travelling across would be extremely disorienting.
i think that would be so much fun!
Now I’m thinking about how much force you would need to be able to jump high enough to hit escape velocity on your side, do half a flip, and land on the other…
I did the calculation somewhere else in this thread, the outer walls of the spaceship (diameter 9m) would rotate with 24 km/h, so if you run really fast, you can outrun the rotation and start to float.
Edit: a healthy adult should be able to sprint 100 m in 15 seconds, which is precisely 24 km/h. Source.
Ooh! I didn’t think about outrunning the rotation! Seems like there’d be a curve to your speed there as each bit of acceleration would make you lighter, making it easier to run… Like the rig they used in the marvel movies to make Captain America outrun everyone.
lol you’re right actually :p
You would need a pretty large radius to generate stable rotational gravity. If the radius is too small, the speed of rotation would make standing or walking nearly impossible. The larger the radius, the more imperceptible the rotational effects would be.
ok so i did some calculations:
If your ship is 9 m in diameter (just chosen at random, not because Starship is by chance 9 m in diameter)
that means x = r*cos(omega*t) and x’’ = r*omega^2*-cos(omega*t) = 1g for t = 0 implies r*omega^2 = 10 m/s², r ≈ 4.5 m, omega ≈ 1.5 rad/s
so the ship would have to rotate with roughly 0.24 rotations per second or 14 rpm. seems doable to me. the outer walls would move with 6.7 m/s or 24 km/h.
14 rpm. seems doable to me
LOL of course it is doable to create rotation. But is it no good if living there is still unbearable.
I recommend you do some sea traveling, just a few months on a cargo ship on several oceans.
Doable, not practical. Another major concern is the induced dizziness and general discomfort from such a small circumference. If you stand up straight, your head moves significantly slower than your feet. There are more effects that humans don’t do well with.
In addition keep in mind that this implies significant mechanical complexity the moment you don’t rotate the whole craft, but only a section or ring. If you do rotate all of it, simple tasks like taking a photo become… cumbersome.
Also like others have said, it’s not a permanent residence for anyone, and the main goal of the ISS is the study of low- or micro-gravity.
Have you ever been in one of these?
You can easily sit on the wall while it’s spinning, and it actually feels pretty normal. But, if you try and stand up and walk around…you’re going to have a very bad day.
For some reason your link didn’t work for me - in case it helps anyone else, here’s the link again:
Thank you.
actually i have been, and i have attributed it to the device not providing consistent centrifugal forces. instead, gravity interferes and makes it inconsistent. which would not happen on a spaceship.
It helps reduce the problems mentioned if you lessen the target goal. We don’t need 1 G of force just like we don’t need a full 1 atm or pressure or 80% of nitrogen mix in the air to breathe. Less gravity force, less RPMs for the same diameter.
But scale is still the better option, making something a few kilometers wide and with only 0.7 G means less stress, less effects from the rotation, etc. That’s still in the category of megastructures though, so while not impossible to build, not going to happen at our current level.
yeah 200 mbar of oxygen should be fine, also 0.3g if we’re gonna land on mars eventually we might as well get used to the gravity level.
the one in space odyssey did.
Currently because math. The amount of mass and length required to simulate gravity is to expensive to get into space.
The answers here are very scientific, but I always wondered if having a magnetic shoe sole could fake gravity? Is there a ‘floor’ to stand on in these ships?
Not really, magnets only really pull when they are close enough and would only really fake gravity in helping you maintain one orientation, that could be easier to achieve with velcro shoe soles.
It wouldn’t be enough. Sure you could use magnetic boots to keep you “attached,” to the outside of a magnetically affected spaceship’s outer hull, though I would imagine that with the lack of atmosphere and magnetic field to protect you from space radiation we may be inclined to use materials that aren’t necessarily magnetic in nature.
All that was to say, yes it would possibly work as a backup tether, but since nothing is pulling on the rest of your body it wouldn’t simulate gravity as much as simulate a tether rope that keeps you from floating away.
Inside the ship it is easier to pretend to be a parkour expert than having magnetic shoes.
For clarity: I don’t know for certain. I am not involved in the community, not an engineer.
Opinion: It’s incredibly difficult to do. A spinning station needs to be designed to do such a thing. It needs to be balanced and have thrusters positioned in such a way to both spin up and maintain the rotation as it goes. The ISS has been built and expanded over decades by tons of new science modules over time as new breakthroughs happened.
Spinning objects can behave in strange ways and having a regularly shifting center of mass can be a challenge by itself, and that’s before you start planning for yet uncertain experiments to bring aboard.
In addition to this, it would be an ENORMOUS challenge to dock with a station that is spinning, and the added danger to do this (or increased fuel consumption of spinning down and then spinning back up) just isn’t worth it. The alternative of maintaining a central core that is static relative to the spin wastes power and creates a massive risk (more moving parts, especially those which might create friction against metal aren’t easy to maintain in space).
Also, a small spinning station is much harder than a massive spinning station because it would have extremely noticeable differences from normal gravity to the people on board. Your head and feet would likely be moving at noticeably different speeds, which by itself is disorienting, but moving either towards or away from the direction of the spin would feel different (dropping an object would mean it falls away from the direction of spin).
Lastly, maintenance would mean that every single EVA either wastes a tremendous amount of fuel to spin down/up again, or risking flinging a person into space every time they exit.
Realistically, on a much larger station, artificial gravity via spinning might be a fantastic idea, especially for longer-term living aboard, but for the ISS, given its history, its goals, and especially where it’s at, it’s just not a great idea.
increased fuel consumption of spinning down and then spinning back up
wastes a tremendous amount of fuel to spin down/up again
I think a flywheel mechanical energy storage system could both serve as a way to store energy and as a way to manipulate the rotation while preserving rotational energy. To slow down the rotation, transfer the rotational energy to a flywheel, and then transfer it back when you need to go back to speed. That adds some mechanical complexity but it creates a more efficient way to control rotation. Plus with electric motors and solar panels, that should be possible to manage without using any propellant fuel.
I wasn’t sure if a flywheel would be good for something like this given just how much mass needs to move and how fast it needs to move to produce close to 1G of force. If it can manage something like that, that would be a super good solve for this.
That said, even if it wasn’t a good solution for the actual ring, it might be a perfect solution for the core’s movement. Given that it can be much less mass as it’s pretty much exclusively used for docking, it could basically just be a pressurized tunnel with attachment points for the ring. Spinning that up and down with a flywheel seems super reasonable.
Could you not solve the spinning-ring-friction problem via magnets? The same way maglev trains work.
It doesn’t change that this isn’t really a great idea for the ISS, but that’s an obvious solution to the problem of having a static central core.
This is already quite a bit beyond where I have any definite knowledge, but I guess if you had a core completely separated by magnets that might work, but you’d still need points of connection for people who docked to join the actual ring from.
If you did that, the core would also need its own propulsion system to spin down and spin up so that anyone docking could actually go out into the ring.
It’s worth noting here, too, that the inner core would need to spin like crazy fast for a small station to have anywhere close to 1G in the ring, so that would be its own fun thing in the core.
