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(09-30-2015, 02:19 PM)antred Wrote: Hmm, but how would you position such a centrifuge in an environment that already has a low but not negligible gravity component? If you make it spin around a vertical axis then people we still get pulled "down" at 0.38 G. If you make it spin around a horizontal axis, then "gravity" as felt by people living in the thing would vary from 1 G - 0.38 G = 0.62 G at the top to 1 G + 0.38 G = 1.38 G at the bottom of the centrifuge. Or have I completely misread your comment?
Picture something like disc-like building sitting on flat ground at Mars. Then envision the outer ring of the building able to rotate around the disk on a track. The floor in this outer ring as inclined to the ground, such that, when the outer ring is spun around the disk, the combined acceleration of the natural Martian gravity and the spin to equal exactly one Earth G, with the two force vectors combining to be exactly perpendicular to the floor. Thus the feeling would be exactly as if one were standing inside a building on Earth.
So there are a lot of mechanical issues to deal with in a system such as this, and maybe some problems with Coriolis effects. But if the inhabitants spend most of their time in this area, then they should not suffer the ill effects of reduced gravity.
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(09-30-2015, 02:19 PM)antred Wrote: Hmm, but how would you position such a centrifuge in an environment that already has a low but not negligible gravity component? If you make it spin around a vertical axis then people we still get pulled "down" at 0.38 G. If you make it spin around a horizontal axis, then "gravity" as felt by people living in the thing would vary from 1 G - 0.38 G = 0.62 G at the top to 1 G + 0.38 G = 1.38 G at the bottom of the centrifuge. Or have I completely misread your comment?
You would have to angle the floor. But not very much; I looked at this once for Mars, and it turns out that to get 1G, you end up having to spin nearly as fast as you would in space; that 1/3 G to the side just doesn't end up contributing that much. So the floor would be almost parallel to the spin axis.
I'm not aware of any paper that has analyzed that idea in any detail... I keep meaning to do it, but you know, I've been busy. 
If anybody knows of one I've missed, please let me know!
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(09-30-2015, 10:14 PM)hanelyp Wrote: The long term effect of fractional G is a point where we really don't have enough data.
Absolutely right. This is one of the key points I'm trying to make in my talk later this month.
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10-03-2015, 02:30 PM
(This post was last modified: 10-03-2015, 02:40 PM by Pye-rate.)
My physicist friend tells me from what he has read in professional journals that in Mars gravity one would need only spend about fours a day at one-G to maintain health. He agrees that not enough is known about partial-G enviroments to be certain.
My idea for cosmic rays, a Faraday dome. An inflatable translucent dome with embedded wires to create a magnetic field. Build settlement, cover with dome, inflate with Mars air, 1.5 Mars atmospheres should be enough.
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(10-03-2015, 02:30 PM)Pye-rate Wrote: My physicist friend tells me from what he has read in professional journals that in Mars gravity one would need only spend about fours a day at one-G to maintain health. He agrees that not enough is known about partial-G enviroments to be certain.
My idea for cosmic rays, a Faraday dome. An inflatable translucent dome with embedded wires to create a magnetic field. Build settlement, cover with dome, inflate with Mars air, 1.5 Mars atmospheres should be enough.
Yes, if your physicist friend has read that, I guarantee the author he was reading has made a wild-ass guess. I've researched this pretty extensively, and the actual space medical community hasn't the foggiest idea what the long-term effects of 1/3 G would be (especially developmental effects, i.e., gestation, infancy, and childhood).
A Faraday cage/dome will not stop cosmic rays. We're talking about massive ions (e.g. iron) zipping along at relativistic speeds. They wouldn't even notice such a puny magnetic field. A strong magnetic field causes their paths to slowly bend, and over hundreds or thousands of km, you can get a shielded area in the middle... but this requires a magnetic field that extends hundreds or thousands of km.
An extremely strong field could bend their paths in a shorter distance, of course, but now we're talking about things like giant superconducting electromagnets, and it's all theoretical.
A couple meters (5-10 tons/m^2) of matter is certainly cheaper and easier for any permanent colony. Electromagnetic shielding, if we can ever get it to work, might make more sense for ships though, where every gram counts.
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Actually he was reading a physics paper making calculations based on known factors in physics and medicine. You are right that without testing we cannot be certain. The calculation can be used as a baseline for testing, if it right well and good, if not keep testing.
Would the Faraday dome be adequate for plants/farms?
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Well if you can get a reference to that paper, I'd very much like to read it.
And the Faraday cage won't make any difference for anyone, but I do think you can grow crops without worrying about cosmic rays. Plants don't generally live long enough to get cancer, and if you increase the mutation rate, well, that will just help you breed varieties better adapted to the local conditions.
For this reason, some have proposed that agricultural areas don't need as much shielding as the living areas. But I'm not buying it. You're going to need people going up and down those rows of crops on a regular basis. Even with robotics and automation, there is always maintenance to be done, and no better/cheaper/faster way to do it than to have a person in there with bare hands, working the problem. And we don't want those maintenance workers getting cancer (or any of the other medical problems cosmic rays are likely to cause).
So, I think our agricultural areas will be just as shielded as the rest... or more likely, they'll be inside the main living areas, perhaps on a higher deck (since I do think reduced gravity is fine in this case).
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