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

  1. #1
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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
    Last edited by grant hutchison; 2018-Oct-01 at 09:41 AM.
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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!
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    Mark Twain, Life on the Mississippi (1883)

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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
    Last edited by grant hutchison; 2018-Oct-01 at 02:11 PM.
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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.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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