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Comment by gruez | Hacker News Reader

> vacuum cleaner-like suction device is then activated that draws fluid toward the feet, preventing it from accumulating in the head.

How does that even work? The liquid is accumulating inside the head. How would pulling a vacuum (presumably outside the body, in the sleeping bag) help? If anything the vacuum would force liquid to the head by squeezing liquid from the body.

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They've been experimenting with this on the Russian side of the station for years. Their version is semi rigid and creates low pressure around the astronaut's legs so the natural pressure in the body and the air pressure of the ISS on the upper body and face squeeze the blood into their lower extremities away from where it pools naturally in micro gravity.

http://www.astronautix.com/c/chibis.html

https://blogs.nasa.gov/ISS_Science_Blog/2015/06/02/rubber-va...

I guess it sucks on the "skin balloon" by creating low pressure around the lower body, thus "inflating" the legs (think swollen feet).

But I'm a little surprised that would work. Another way to look at it, would be that the higher pressure on the head and torso "squeezes" fluids down, like a water balloon - squeeze one end, and liquid goes to the other end?

Create low pressure around the legs, they puff up with blood which means less blood in other parts of the body. If you need a demonstration then google “penis pump”

Iirc there is a lot of debate on the minimum g level required to avoid negative effects. Spinning people tends to make them uncomfortable and nautious.

However, I'd be quite curious if the g level is actually very low. You could have a small gently rotating section of a station.

  > small gently rotating section of a station

A small rotating section near the center would have extremely uncomfortable tidal effects. You want to be as far as possible from the fulcrum to reduce the tidal effects.

You can probably just lie down and sleep though. The tidal effects would be interesting, but I'm not sure they'd be uncomfortable. Walking would be more difficult, as you'd feel you are about to fall on your face (or back) but I don't think it's something one wouldn't be able to get used to.

Wouldn't work with the 4.5 m size limit of the current ISS modules, it's barely doable with a Starship-wide module, but seems totally doable with inflatables. Bigelow was designing 12m+ wide modules and that was a limitation of the rocket fairing that was launching it. With, say, Starship, the module could be much wider.

How fast does it really need to spin? I'm not sure there have been any studies on 1/128g or less. In a 4.5 meter section 1/128g would only be 1 rotation per 30 seconds.

The issue is that at the average height of the astronaut the rotation speed at their head would be half of that at their feet given the 4-5m modules we can launch.

I don’t know what is the maximum difference that would be tolerable but it’s not 2x for sure.

So to get it down to single digit % you are looking at 200M+ or so in diameter.

If it’s just for sleeping and liquid pooling at the back won’t pose a health risk then if they are lying down the diameter can be much lower but you are still probably looking at 15-20M which might be possible with inflatable modules I think 3.5-4X expansion would be quite possible with the existing inflatable modules we have.

A 4.5 meter section rotating at 1 rotation per 30 seconds would likely suffer very noticeable Coriolis effects.

You don't need humongous modules for that. Just take two normal ones and tether them together with a long strong wire.

The tough part with making it small is the smaller the torus or device the larger the gradient of forces along a riders body which can be disorienting. Any useful G level and comfortable size would likely be larger than any existing module.

Think iron lung, not shrink-wrap.

There are veins for other liquids, just like there are for blood. The liquids don't lie around everywhere under the skin.

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