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Thread: How many gravities could human colonists withstand? Would you believe FOUR?

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    Exclamation How many gravities could human colonists withstand? Would you believe FOUR?

    Let me be perfectly clear: there ain't no gosh darn way I'm gonna live on a planet with FOUR gravities! Forget it.


    https://arxiv.org/abs/1808.07417

    Effects of exoplanetary gravity on human locomotor ability

    Nikola Poljak, Dora Klindzic, Mateo Kruljac (Submitted on 22 Aug 2018)

    At some point in the future, if mankind hopes to settle planets outside the Solar System, it will be crucial to determine the range of planetary conditions under which human beings could survive and function. In this article, we apply physical considerations to future exoplanetary biology to determine the limitations which gravity imposes on several systems governing the human body. Initially, we examine the ultimate limits at which the human skeleton breaks and muscles become unable to lift the body from the ground. We also produce a new model for the energetic expenditure of walking, by modelling the leg as an inverted pendulum. Both approaches conclude that, with rigorous training, humans could perform normal locomotion at gravity no higher than 4 g Earth.


    Astronomy link: http://www.astronomy.com/news/2018/0...ity-to-the-max
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    My poor old knees can barely function at 1g anymore..........

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    Survive, maybe. Function?

    No.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by ronin View Post
    My poor old knees can barely function at 1g anymore..........
    Im ready to move into the Lunar Elon Musk Assisted Living facility.


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    The associated question is, what's the lowest gravity we could tolerate in a colony without suffering the negative effects experienced in mciro-gravity.

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    Quote Originally Posted by Eclogite View Post
    The associated question is, what's the lowest gravity we could tolerate in a colony without suffering the negative effects experienced in mciro-gravity.
    That's a harder one to test. Higher accelerations can always be done in a centrifuge. Remember the great mambo chickens!

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    We'll get a lot better at genetic engineering by then so high gravity and low gravity won't be problems. I guess.

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    Quote Originally Posted by Noclevername View Post
    Survive, maybe. Function?

    No.
    I am very inclined to agree with you. It is one thing to spin up to 4 gees and do a couple of tests, but everyday life at 4 gees would be brutal and short. I think you'd be stressed to death.
    Solfe

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    Quote Originally Posted by Chuck View Post
    We'll get a lot better at genetic engineering by then so high gravity and low gravity won't be problems. I guess.
    In order to figure out all the long term medical effects of low gravity and how to counter them artificially, we would first have to observe those effects in humans. Which means, by having humans living in low gravity. We will learn by doing.

    In particular, we won't know how growing children will be affected by low gravity, until children actually grow up in low gravity.

    (The same is true of higher gravity but in our Solar System that is not a problem, unless you plan colonies in Jupiter's atmosphere.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Won't our new intelligent computers just simulate life in different gravities without experimenting on us?

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    Quote Originally Posted by Chuck View Post
    Won't our new intelligent computers just simulate life in different gravities without experimenting on us?
    Computer simulations are of limited utility when researching something we have little data on. Garbage in, garbage out.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    With reference to the thread title, I don't believe it for a minute.
    In the discussion, the authors hand-wave their way past a lot of significant cardiorespiratory physiology, ignoring the difference between sustained and transient loads, and revealing their complete lack of knowledge of the relevant physiology. (Physicists are notoriously poor at physiology - see Geoffrey Landis's dissertation on human exposure to vacuum for another example of a clever and knowledgeable person making terrible rookie errors outside his field.)

    We know from experience with people who have abnormal physiological loads on their cardiovascular system that our 4g colonists would have very poor respiratory gas exchange, would develop gross leg and pulmonary oedema, and would go into cardiac failure soon after.

    Grant Hutchison
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    Considering the depth of the gravity well, once colonists get to a heavy planet with 4 g's or the like, they are almost certain to STAY there. You ain't leavin'.

    See you on Ceres!
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    Quote Originally Posted by Roger E. Moore View Post
    Considering the depth of the gravity well, once colonists get to a heavy planet with 4 g's or the like, they are almost certain to STAY there. You ain't leavin'.
    On account of being dead.
    But a space elevator or space fountain might be the way to circumvent the reaction mass problem.

    Grant Hutchison
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    Quote Originally Posted by grant hutchison View Post
    With reference to the thread title, I don't believe it for a minute.
    In the discussion, the authors hand-wave their way past a lot of significant cardiorespiratory physiology, ignoring the difference between sustained and transient loads, and revealing their complete lack of knowledge of the relevant physiology. (Physicists are notoriously poor at physiology - see Geoffrey Landis's dissertation on human exposure to vacuum for another example of a clever and knowledgeable person making terrible rookie errors outside his field.)

    We know from experience with people who have abnormal physiological loads on their cardiovascular system that our 4g colonists would have very poor respiratory gas exchange, would develop gross leg and pulmonary oedema, and would go into cardiac failure soon after.

    Grant Hutchison
    In somewhat more layman terms, my initial thought too was that your heart would have to work really hard to get blood to your head, so something would give up sooner rather than later. As for just being in 4G for a short (really short!) amount of time: we know that fighter pilots still can move their hand and keep their head up in those conditions. With good exercise, you might be able to walk around. But it would be very, very uncomfortable. I've had my foot supported only half while doing a 2.5g pull, and my ankle was almost getting sprained already. I had to give my leg a serious pull to get it inboard.

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    Quote Originally Posted by Chuck View Post
    We'll get a lot better at genetic engineering by then so high gravity and low gravity won't be problems. I guess.
    I am afraid that you are probably underestimating the difficulty of genetic engineering. The way that we develop is fascinating, but perhaps not the way you might imagine. We don't have a body plan in our genetic code that says, "there is a big bone here, and make this out of this." Rather, pluripotent cells (meaning cells that can differentiate into different types) migrate through a process that involves positive and negative chemical signals, and some of them die and others live on, turning on certain receptors for example that allow them to respond to certain chemicals. So you can't simply design an organism to say have steel bones or something like that. The bones have been actually created by cells that say take in calcium and then process the calcium into structures that become bones. And we don't really make genes that just do something. Usually, what you do is (for example to make an animal that glows) fine a gene in a jellyfish that makes the jellyfish glow by creating a fluorescent protein, and then insert that gene into the animal's genes. You can't for example genetically modify an animal to produce diamonds, because there aren't enzymes that create diamonds out of carbon.
    As above, so below

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    Quote Originally Posted by swampyankee View Post
    That's a harder one to test. Higher accelerations can always be done in a centrifuge. Remember the great mambo chickens!
    A rotating space station, as envisaged by artists and SF writers before we entered space, would provide the opportunity to explore that across a range of g's. Once you got the experiment past the ethics committee.

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    Quote Originally Posted by Eclogite View Post
    A rotating space station, as envisaged by artists and SF writers before we entered space, would provide the opportunity to explore that across a range of g's. Once you got the experiment past the ethics committee.
    Building a rotating station is non-trivial. Building a high-G station is harder.
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    Quote Originally Posted by Noclevername View Post
    Building a rotating station is non-trivial. Building a high-G station is harder.
    True, but the best way to deal with humans going to that super-Earth would be a high-G generation starship. You actually don't want a fast ride there.

    Slowly spin up the torus, so that in the thousand+ years it takes to get there--you arrive with effective surface gravity, and let evolution take care of the rest.

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    Quote Originally Posted by publiusr View Post
    True, but the best way to deal with humans going to that super-Earth would be a high-G generation starship. You actually don't want a fast ride there.

    Slowly spin up the torus, so that in the thousand+ years it takes to get there--you arrive with effective surface gravity, and let evolution take care of the rest.
    A thousand years may not be enough for humans to evolve that way. And they might die out instead of adapt.

    But it's the old dilemma: If you can survive 1000 years in an artificial habitat, why would you need a planet at all?
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    Quote Originally Posted by Eclogite View Post
    A rotating space station, as envisaged by artists and SF writers before we entered space, would provide the opportunity to explore that across a range of g's. Once you got the experiment past the ethics committee.
    You could build the centrifuge on the ground. Ones in orbit would only be needed to investigate 0<=g<1.

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    I would imagine any slip or fall in 4g that would result in traumatic injuries. A person's 1-meter COG would have the same potential energy as a 4-meter fall on earth.

    Maybe near-future exoskeletons could help mitigate, but I agree with others that cardiovascular problems would commence rather quickly. Maybe a month or two wouldn't be too harmful for healthy astronauts in their 20's-30's...

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    Quote Originally Posted by VQkr View Post
    I would imagine any slip or fall in 4g that would result in traumatic injuries. A person's 1-meter COG would have the same potential energy as a 4-meter fall on earth.

    Maybe near-future exoskeletons could help mitigate, but I agree with others that cardiovascular problems would commence rather quickly. Maybe a month or two wouldn't be too harmful for healthy astronauts in their 20's-30's...
    Wasn't there a scene at the beginning of Pournelle & Niven's The Mote in God's Eye in which someone stood up while a starship was under multiple-g acceleration? And sitting down again turned out to be traumatic?

    I was picturing everyday events like dropping a cup of water (SPLAT) or wristwatch (CRASH) or tripping and falling on your kid's ball & jacks (IMPALED TO DEATH) or tripping on a crowded stairwell (LANDSLIDE).

    This is not going to work in 4 g.
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    Quote Originally Posted by Roger E. Moore View Post
    Wasn't there a scene at the beginning of Pournelle & Niven's The Mote in God's Eye in which someone stood up while a starship was under multiple-g acceleration? And sitting down again turned out to be traumatic?
    Yup. Sally. I believe it was 3 G?
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    Quote Originally Posted by swampyankee View Post
    You could build the centrifuge on the ground. Ones in orbit would only be needed to investigate 0<=g<1.
    There have been studies on the effects of hypergravity on rats. Cages apparently would be spun about for months. I'd be curious about cage design (how food and water are supplied and how it's cleaned, but maybe they just stop the things regularly.)

    Here's a Wikipedia article with links to a couple of references:

    https://en.wikipedia.org/wiki/Hyperg..._aging_of_rats

    https://en.wikipedia.org/wiki/Hyperg..._of_adult_rats

    I remember reading somewhere that hypergravity rats come to look like rattish bodybuilders, but I don't have a source for that and I don't know if the person claiming it had a good source.

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    In most of the papers I've read, it does not seem likely that a terrestrial planet's gravity will get above 2 g's; for whatever reason, most get as far as 1.4 or so. Even super-Earths or mini-Neptunes or ice dwarfs or whatever they are calling them this particular minute, those rarely get to 2 g's and up. I think we'll be okay there.

    But 4 g's, you can't even kneel down to tie your shoelaces without going into surgery afterward. To get that kind of gravity, you'd have a superdense planet probably made of something poisonous to humanity, so we'd never go there anyway.
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    Quote Originally Posted by Roger E. Moore View Post
    I was picturing everyday events like dropping a cup of water (SPLAT) or wristwatch (CRASH) or tripping and falling on your kid's ball & jacks (IMPALED TO DEATH) or tripping on a crowded stairwell (LANDSLIDE).

    This is not going to work in 4 g.
    Another problem (apart from the whole cardio-respiratory death thing) is the speed with which you hit the ground if you fall over. Half the time in which to try to break your fall, but four times the impact energy. Fit young people would fall like frail elderly people.

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    Ah. I did some math on an Excel sheet to get the surface gravity for what is supposed to be the most massive super-Earth known (yet), K2-216b,which is 7.4-8.0 M-earth and 1.75 R-earth. I get about 2.5 g. Maybe we don't have to worry about 4 g.

    We can't go to K2-216b anyway, it's fried by its star (too close), but we get the idea. 2 g, though still presents some health problems.
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    Quote Originally Posted by Jens View Post
    I am afraid that you are probably underestimating the difficulty of genetic engineering.
    Maybe so, but the difficulties associated with space colonisation are also very large.

    I have little doubt that by the time we are ready to contemplate putting colonies in Jupiter's clouds, we will have made very significant advances in genetic engineering. If you want to live in a gas-bag city floating in the atmosphere of the largest planet, you will need to have sufficiently advanced biotech to do so comfortably, because the gravity is more than twice Earth's standard. Maybe genetic engineering won't be enough - to thrive on Jupiter you might need to augment most of your biological functions. Even so, genetic engineering (or rather, gene therapy) might have a role to play, by making your tissues robust enough to tolerate constant contact with artificial implants.
    Last edited by eburacum45; 2018-Oct-25 at 02:55 AM.

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    There are plenty of large extrasolar gas giants with cloud-top gravity levels much higher than that found on Jupiter. Some people in the far future might try to colonise worlds like this- the problems would be daunting, and I doubt that the population of such a colony would look very familiar to our eyes. Whether they would be mostly biological or mostly machine is another question- it may be that the difference becomes blurred long before we even get to such locations.

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