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Comment by martyvis | Hacker News Reader

Given that lack of gravity seems to be a major risk factor for well-being I'm surprised a static structure like the ISS doesn't yet have a rotating centrifuge-like structure ala 2001: A Space Oddysey to at least ward off the effects during sleep and downtime

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There actually was a proposal for one.

https://en.wikipedia.org/wiki/Nautilus-X

There's also this issue:

"Another problem is that we do know of adverse effects that arise at high rotational rates of speed. The Coriolis Effect has to do with rotating reference frames and it can seriously screw with the inner ear. The only way to maintain a strong centrifugal gravity while keeping rotational speed low is to lengthen the system as a whole — but the ISS isn’t nearly big enough."

Source: https://www.geek.com/news/geek-answers-why-doesnt-the-iss-ha...

So in effect if your feet are moving faster than your head by just enough for the inner ear to pick it up, you are likely to look at outcomes similar to motion sickness...

Zero-G also makes people sick, but astronauts can get used to it. If you put someone in a small spinning station for six months, would they also get used to the motion sickness? What if you found someone suffering from (and that had learned to live with) permanent vertigo?

Shouldn't motion sickness only happen when you have a reference frame? i.e., if you're on the space station you shouldn't be able to tell when it's spinning?

A rotating object isn't exactly the same as gravity. There's a rotational effect that exists, so you can tell the difference between being on the ground and in a centrifuge.

If the station is large enough. In smaller centrifuges, there'sre noticable Coriolis effects.

Only for non-inertial reference frames. If the station were rotating, it would therefore be accelerating, and you would be able to feel it.

One way to make it "big enough" is to put a weight on the end of a long cable, and spin the combination. It wouldn't need to be a full g either, some should be a lot better than nothing.

With a cable, though, there might be weird problems with oscillations.

Or, alternatively, a zero-g banjo and opportunity for true space music.

Yea, I think tethers in space are still considered quite tricky.

One alternative is to replace the cable with a rigid tube, and then have living quarters at both ends. The tube is big enough for an astronaut to pass through. Sort of a one spoke section of a spoked wheel.

Real Engineering had an episode on simulated gravity through rotation. It's a great channel, though I was a little disappointed this episode talked more about fictional examples than proposals like Nautilus-X. Great watch either way though.

https://www.youtube.com/watch?v=im-JM0f_J7s

The ISS is simply too small for that. It would have to spin at a ridiculous rate in order to get to a level of gravity where the effects are no longer felt. And in this particular case that is actually a blessing because even if the space station would be able to do this the spaceship used for any interplanetary traveling would not and so no useful data for such a trip would be collected.

Since the centrifugal force for mass m, angular velocity w and radius r is mw²r, you only need w = sqrt(g/r) to reproduce Earth-like levels of acceleration. At r = 10 m, that's already less than 1 rad/s or 1/6 cycle/s. That doesn't seem ridiculously fast.

And why wouldn't an interplanetary spaceship be able to spin fast enough? You could just build it as a space station with thrusters.

The O'Neil space station designs were premised on 1 RPM. Though a 3 RPM environment might be tolerable continuously, switching between rotating and non-rotating environments suggested a lower rate. See:

http://www.nss.org/settlement/ColoniesInSpace/colonies_chap0...

To make it Earth-like, and not make people nauseous, it has to have a diameter around 200 meters. Less than one G is practical, though. As little as 0.25 G might forestall the medical complications.

Sounds like you've just described the "Graviton", a popular amusement park ride.

While a 30 second ride may be fun, I couldn't imagine living on it for months at a time. (granted, it simulates > 1G)

https://en.wikipedia.org/wiki/Gravitron

I think the problem is the difference of g between r and r-1.75 (the height of a human standing up).

Coriolis forces will make this non-feasible. You'd need to do much better than that.

Well they do have those tied-down-with-a-spring treadmills, but that only covers you for the duration of your workout. I don’t know anything about constructing things for use in a space station, but I can’t imagine creating such a rotating structure would be easy, cheap, or safe.. a problem with a structure rotating quickly in space could quickly cause major safety issues for the ISS I’d imagine.

Resistance training is certainly still possible, but you still lose the normal ambient resistance you get on earth just from walking around and holding your limbs in place against gravity. The difference between low-gravity and someone on Earth who doesn’t exercise much is probably much larger than the difference between a non-exercising Earthling and an Earthling who exercises.

Besides, that doesn’t really work for the other physiological effects of low gravity, like the heart and circulation issues mentioned in the article.

Great point about the treadmill.

I guess my point is that I just can’t imagine that all the brilliant people involved with the ISS _didn’t_ think of a rotating structure.. but even just getting a sizable non-rotating structure cost 150B.

I wonder what kind of health issues we’d see even with a rotating structure tho. Would living on such a structure really help prevent most of these issues?

Other comments in this thread have discussed it. Sounds like NASA is well aware of rotating structures, but large ones are way too expensive and small ones cause other issues due to the fast rotation required.

The ISS is, primarily, our single microgravity laboratory. Giving it gravity would make it unfit for that role.

(NASA could duplicate the radiation and confinement here on Earth relatively easily, if not for the ethical issues. These seem to not matter as much when compensated with the privilege of going to space. But making gravity on space just to hack an ethically acceptable experiment would start to get ridiculous.)

> The ISS is, primarily, our single microgravity laboratory. Giving it gravity would make it unfit for that role.

Centripetal force is not truly gravity. This is useful because a station simulating gravity by spinning can still have areas that are isolated from this force (the center).

Lack of gravity also means there will never be a permanent presence in space. Making a big station and spinning it is the only way anyone is going to survive in space for more than a few years.

I guess if the costs of sending something into space comes down this will become an option, then they just have to solve radiation shielding and everyone will be happy.

Of course no tests have been actually done so both are assumptions..

As others have stated, if you don't take a very large diameter, the Coriolis effect starts to be really disorienting. That can be counteracted somewhat by reducing the speed of rotation, but that comes at the cost of lower effective gravity.

I love that movie. The bone-space montage is so good.

One was planned, but it was cancelled due to budget overruns: https://en.m.wikipedia.org/wiki/Centrifuge_Accommodations_Mo...

Humans would not have fit.

The goal was to "Expose a variety of biological specimens that are less than 24.5 in (0.62 m) tall"

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