The kinds we read in books and see in movies like 2001: ASO all the time: a moderate-sized, rotating ring, or torus really, that would keep the astronauts pinned to the curved “floor”.
Is it too impractical to build and assemble in space or hasn’t it been done yet for other reasons? It seems at this point, humanity will have an indefinite presence in space, so why not?
Cuz it’s a bitch trying to dock your capsule/shuttle to it.
Too big and too mechanically complex. But mostly too big.
You wouldn’t necessarily need to dock to the ring, assuming the station was designed with a central, non-moving docking hub.
More mechanically complex I get; sure, it’s not as relative simple as just interlocking a bunch of modules together. But I’d argue you could have a working centrifugal ring for not that much more material used in the ISS.
But despite a bit of extra cost, wouldn’t some sort of artificial gravity be worth the investment? Wouldn’t this grant astronauts longer stays in orbit (fewer launches, unless it’s the solar radiation that’s the limiting factor) along with various other benefits?
You go into space to experience micro gravity. We can get all the gravity we want down here on earth. All the lab space would still need to be outside the centrifuge area, adding massive complexity for little benefit.
A good deal of the official rationale for building space stations is to be able to perform experiments in microgravity. If we want to do science under gravity, we can do that on the ground.
All good reasons not to build such a ring, and I’m sure these are the factual, actual reasons one was never implemented.
However, it does eventually seem like common sense to design a station with one, if at least to provide a respite and creature comforts for the crew, since a central, non-spinning hub for experiments, and a rotating ring for living quarters are not mutually exclusive, pre se.
Not a very big one, and it’s mechanically much more complex.
I would like to note you’re making some fairly large assumptions about not just how simple this would be but also some of the biomechanics involved. It’s not just “a bit” of extra cost but a ton of extra cost.
That said, there is a proposal to add a small spinning module to the ISS for experiments and to serve as sleep quarters. We’ll see if it goes through.
As for some of the technical reasons it’s hard, let’s say you only had a 10m radius ring of modules of roughly the same size as the current ISS modules. You’ve already made a station 5 times the size of the ISS. And that’s for a lousy 10m radius.
There’s a couple ways of going about the rotation. One is to build a very large station and spin it relatively slowly (1 rpm or less). That’s obviously cost prohibitive.
Another is to build a small station and spin it very fast. There are a couple issues with this. One is that you get some definite issues since your head and feet will feel very different levels of apparent gravity (a person’s height would be a significant fraction of the radius of the ring). Blood would constantly be drawn away from the head while standing. There’s also the problem of nausea. To generate sufficient apparent gravity, you’d need several RPM of rotation. That can get disorienting for anybody who has to look outside. At those speeds, you aren’t going to be doing much photography of Earth (at least if you don’t want to vomit).
Not insurmountable problems, but there’s not much benefit to spinning an entire ISS-like station either. A single spinning module (as above) as sleeping quarters would be sufficient. Less of a problem of blood flow if you’re prone, too. You wouldn’t really want to use them as living quarters, though. Radius is too small, so the crew could easily experience vertigo just from trying to walk around.
The small radius problem is, I think, what a lot of people overlook. It’s well and good to consider people point masses for calculations. But, in reality, we’re of significant size compared to a station like the ISS.
The purpose of a space station (currently) is also to explore how humans are affected by microgravity in the long term.
At some point, living on a space station won’t be an end in and of itself, and we’ll want to add creature comforts like gravity. But that is some time off.
Self-correction. This would be roughly the same size as the ISS.
It’s as the saying goes, ‘Putting the cart before the horse’. IOW it’s that both:
[ol]
[li]A rotating ring space station needs to be very large.[/li]
and
[li]A very large space station is the only kind that would really need simulated gravity.[/li][/ol]
In either case there’s little reason for one without the other…
True. A space station with artificial gravity wouldn’t be of much use unless we wanted to test the long term affects of gravity greater than micro, but less than 1G on humans. Say for a Mars mission which would involve spending at least 18 months at .4G, and almost certainly involve some form of rotation on the way.
It seems to me that a big problem (in the “mechanically complex” area) would be the need for it to be both large and massive. If the rotating station is too small, then the presence or absence of a person will easily change the center of gravity, and suddenly the whole thing is wobbling like a washing machine whose clothes aren’t evenly distributed.
As I recall, the book version of 2001: A Space Odyssey (or perhaps it was The Making Of 2001) described the construction of the large space station which Dr. Floyd stopped at on the way to the moon. They explained that opposing sections needed to be installed together, to keep it balanced.
How about this for a design : you launch the spinning section in 3 pieces. There’s the hub, which has high tech bearings and you dock it to the current ISS. Then there’s 2 modules that are the sections that are under spin, and they attach to the hub by long cables. There’s 2 hatches on the hub, and 2 hatches on the modules, and an elevator car goes between the 2.
The massive problem I can see right away with this is that with this setup, you have 4 separate pieces that are not connected to each other except by a sturdy cable. That is, the 2 elevator cars, and 2 hab modules aren’t connected. So how do you get oxygen, CO2, power, coolant, and data to these 4 separate things? Can a flexible hose that is 10-50 meters long deliver all this?
An even bigger problem is that as the hub spins and the station is kept spin free, how do you correct for the tiny amount of friction in the bearings that transfers some of the angular momentum from the spinning section to the station?
It occurs to me that if you had paired electromagnets inside the bearing, you could essentially create counter-torque to eliminate any angular momentum that transferred to the station. That is, as the bearings leak and the station begins to spin, you inject energy to speed up the spinning habitat in such a way to cancel out any spin on the station.
The flexible cable problem is probably solvable. Space doesn’t radiate heat very well, so a flexible cable made of the right kind of materials could probably send compressed air back and forth, as well as electricity, coolant, and so on. I’m thinking 1 of the modules would be for sleeping, and the other would have exercise equipment, a shower, and maybe a toilet (I bet it’s a lot easier to drop a deuce in even 1/10 of a G!)
Why build this spinning station? Because we can simulate long term exposure to Mars or the Moon in the relative safety of earth’s orbit, where supplies can be delivered monthly and the station can be evacuated at any time in an emergency.
Space stations also get power from solar arrays, which become significantly more difficult to keep oriented in a rotating ring.
Rotating stations can also cause dizziness issues because of a phenomenon called vestibular cross-coupling (or vestibular coriolis illusion). Everytime a passenger moves his head relative to the station’s rotation axis, this would activate his semi-circular canals (the part of the inner ear that detect head rotations). That would be highly disorienting and sickening as anyone moving around in the station would experience vertigo sensations with every head movement. Actually this effect is used to habituate people to motion sickness.
Here is a short explanation of this effect:
Imagine that the station rotates at x deg/s, and that an astronauts stands with his head towards the rotation axis, his feet away from it, and facing the direction of motion. A line going though his two ears is parallell to the rotation axis. The astronaut is actually rotating (pitching) upward at x deg/s.
If the astronaut suddently turns in order to face away from the direction of motion, he will reposition himself relative to the station’s rotation and will end up rotating downward at x deg/s.
This means that, as he turns, the astronaut undergoes a rapid change of angular velocity with a magnitude of 2.x deg/s. This will activate the canals who will tell the astronaut that he is rotating downward at 2.x deg/s (although his is now standing still inside the station). The sensation is similar to the vertigo that you can experience if you spin for a while: everything seems to spin around you, and the ability to stand can be severly compromised.
Imagine a station that generates 0.1G gravity with a radius of 10m. That gives x = 18 deg/s; and so movements inside this station will result in bursts of vertigo with amplitudes as high as 36 deg/s which is not very strong but already disturbing.
For a station that generates 1G gravity with 10m radius, you get x = 180 deg/s. No one would be able to move around very long with this type of velocities!
I think (but I’m not an expert) that the double-ring station partially constructed in 2001 was vastly larger than our present-day ISS. It’s proved to be so hard and expensive to keep the ISS going that the cost of a bigger place might be prohibitive.
Plus all our stations so far orbit in what’s actually the uppermost fringe of the Earth’s atmosphere (for a number of reasons). You’re not going to build a giant station that needs to be constantly reboosted to avoid a decaying orbit.
Sure. But with a non-spinning station, you just have to match X and Y as you slowly close along the Z-axis. With a spinnign station, you have to match X, Y, rotation rate, and phase angle, all at the same time, while you slowly close along the Z-axis.
Well, a solution to that would be to make a de-spun docking mechanism that once it latches on the spacecraft slowly breaks relative to the station to spin up the spacecraft until it rotates at the same rate as the station.
Of course that would take some of the angular velocity from the station, but by reversing the process to undock that would be restored, unless thrusters are used to keep a constant spin rate at all times.
In any case, not worth the trouble at the moment.