Low g

It’s clear that zero gravity is bad for you. What about low (nonzero) gravity: say 0.376 or 0.166 of Earth gravity? The only way I can see to find out would be raising mice, long-term, in a centrifuge on the ISS. Has this been done?

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55 Responses to Low g

  1. Cloudswrest says:

    I’ve wondered this myself. Also how would “weightless” animals like fish fare in free fall. How would birds adapt. How about taking a pet parakeet to the ISS.

  2. Cloudswrest says:

    This got me speculating on a design for a zero-g fish tank. How about a half meter diameter sphere of transparent, water repellent plastic. If the water doesn’t wet the walls it would pretty much just hang around as a bubble inside the tank, occasionally bouncing off the sides, sort of like a lava lamp.

    • pollux says:

      Not really. Water-repellent plastic doesn’t generate an anti-water force field; it’s better thought of as holding the water up on poles like a canopy. Your plan would pretty much just result in a normal, but spherical, fishtank that happens to be really easy to clean.

  3. masharpe says:

    Sounds like an interesting experiment. And for those wondering…

    0.376g: Mars gravity
    0.166g: Moon gravity

    The effect of living long-term in Mars gravity seems very relevant for Mars colonization.

  4. Glen Kissel says:

    Actually gravity at the altitude of the ISS is just under 90% of what it is on the surface of the Earth.

  5. melendwyr says:

    Well, we understand at least some of the ways in which microgravity is bad for us. Quite a few of them come about because our bodies are designed to spend as few resources as possible, so they calibrate repairs to the amount of physical stresses placed on the relevant systems. For example, astronauts tend to lose bone density because they’re not experiencing the constant low-level stress of pushing against the ground to move. Astronauts exercise with elastic belts to push them against treadmills, but this doesn’t compensate for the elimination of experienced gravity very well – it’s better than nothing, but a far cry from normality.
    Experiencing small fractions of normal gravity would also be a far cry from the normal state.
    Although some low-gravity changes cause immediate problems (having large amounts of calcium freed in the body from disintegrating bones is surprisingly toxic) many of them only become ‘bad’ when we go back to Earth conditions.

    • pauljaminet says:

      The problem is more fundamental than that. On the cellular level, basic functions depend on the presence of gravity, notably formation of the cytoskeleton and cytoskeletal rearrangement in processes like migration and cell division. Wound healing is impaired in microgravity and it is not clear that embryos can form or develop properly.

      • melendwyr says:

        There’s also the problem that radiation shielding on the ISS or a hypothetical Mars mission is necessarily less than optimal. It’s not so bad in low Earth orbit, where the planet’s magnetic field screens most of it.

        On a tangential note, it seems to me that geomagnetism is the key feature that makes Earth unusual – all of its other peculiar features, including the presence of life, are dependent on it. (Maybe its being so metal-rich isn’t, but life is probably possible on a poorer world – as long as it has a magnetic field.)

  6. TWS says:

    I saw a film of a cat in the cockpit of a jet in freefall. The cat and pilot were not happy.

      • TWS says:

        If they could get their claws into anything they would have held on like grim death.

      • jb says:

        A cat doesn’t even really need a parachute. Their terminal velocity is pretty low, and if they land on a soft surface they are likely to be just fine.

        • Jim says:

          Wikipedia says that they reach a terminal velocity of about 60 mph. it also says that in addition to orienting themselves to land on their feet they instinctively relax. I had polio as a child and have often fallen (one of my roommates once told me that he thought falling down the stairs was my normal way of descending them) without much serious injury. One of my doctors told me that polio patients are so used to falling that they relax when they fall instead of tensing up like other people which transmits more shock to the skeleton.

  7. pauljaminet says:

    The key experiment would be whether embryonic development can occur successfully in microgravity. To date, no mice have reproduced in space. https://www.engadget.com/2017/05/23/mouse-sperm-space-reproduction/

  8. KM32 says:

    Have any of you read The Integral Trees, by Larry Niven?

  9. Robert says:

    Interesting to think of natural selection and how it would work things out in environments of differing gravity. What would be favored vs not?

  10. Having grown up on air bases, as an Air Force brat, and having pursued an extremely health-conscious and mostly vegetarian lifestyle since the 1960s, I’ve followed this matter with some interest. It is certain that airline pilots die younger than the general population, as has been confirmed by serious studies. It’s no surprise, considering the stress, interference with sleep patterns, heavy dosages from off-planet radiation and questionable lifestyles (eating, alcohol, exercise).
    That the human organism is poorly adapted to long-term space travel also seems to have been confirmed, by the major powers committed to orbital ventures. We are terran organisms, evolved over millions of years to fit certain conditions. This does not include zero, or reduced, gravity. An analogue would be the varied impairments deep-sea divers are subject to.
    Linky to retired pilot deaths: http://articles.latimes.com/1990-04-13/business/fi-1324_1_pilot-retirement

    • ohwilleke says:

      My first intuition would be that airline pilots are dying prematurely mostly from trauma related to risk seeking behavior, rather than exposure to radiation, higher than average stress or sleep pattern disruption. Anecdotally, a retired airline pilot I lived with as an exchange student once had a serious need for speed while driving and pursued risk-seeking hobbies.

  11. Abelard Lindsey says:

    The only way I can see to find out would be raising mice, long-term, in a centrifuge on the ISS. Has this been done?

    Of course not. Has NASA ever done any research that could be useful for large scale space colonization?

  12. whyteablog says:

    They had that idea before the ISS launched.


    Their/your centrifuge idea has been executed to look at hypergravity.


    And they’ve looked extensively without a centrifuge.


    Haven’t found any with 0 > g > 1. Which… well, you know. That ought to be a thing. I haven’t looked all that thoroughly, though.

    Someone made a project of this idea but it failed to launch.


  13. whyteablog says:

    Also, regarding the title of your post, I think it’s rude to talk about Africa that way.

  14. Zach Cochran says:

    The ISS module is in the parking lot of the Tsukuba Space Center in Japan. Never got launched. https://en.wikipedia.org/wiki/Centrifuge_Accommodations_Module

  15. Dave Pinsen says:

    Kim Stanley Robinson described 0.38g as the perfect gravity for humans in his novel 2312.

  16. Nigel Seel says:

    I’m surprised no-one has mentioned the high-tesla levitating frog.

  17. Greying Wanderer says:

    astronauts should sunbathe imo – vitamin D ftw

  18. engleberg says:

    @ It’s clear that zero gravity is bad for you.

    So, why aren’t we building centrifuges for weightlifters?

    • pauljaminet says:

      We evolved in 1 g and there’s every reason to think our biology is optimized for that. Higher gravity might have short-term benefits for weightlifters, but long-term effects of living in higher g would undoubtedly be harmful.

    • Because it’s a lot easier just to add more weight to the barbell?

    • engleberg says:

      I’m thinking of a passage in Pournelle’s A Step Farther out when he mentions an experiment where hamsters in a 4-G centrifuge lived longer and bounced around healthily. I’m not a steroid queen, and I’ve read ‘On Being the Right Size’, so I don’t say I’d start with 4-G. Maybe 1.5 for yoga and 1.1 for lifters. But, ‘undoubtedly be harmful’? Compared to the strange crap bodybuilders do? And barbells don’t stress the whole bod.

      • Bies Podkrakowski says:

        So this may be source of planet Sparta in Pournelle’s CoDominium series. Sparta was bigger than Earth and colonist there were healthier and longer living thanks to increased workout. I remember this because it seemed strange then. The SF writers’ consensus was that lower gravity is better because it puts less stress on the cardiovascular system.

        There were even some popular science articles about space hospitals for heart patients. Zero g was deemed ideal for convalescence after heart surgery. Of course there was one author that noticed that potential patients have to survive travel and acceleration first.

  19. Dave says:

    Are centripetal force and acceleration due to gravity the same? I mean, they have different causes, does stuff behave exactly the same under both? Could you tell the difference? Could your cells tell the difference?

    • Jalfrezi says:

      Watch some youtube videos on the equivalence principle, it’s logically beautiful. As far as we know there’s no difference between the gravitational “force” and the forces due to acceleration (linear or centripetal).

      • Dave says:

        Apparently there would be differences with coreolis effect. Centripetal force would be different at your head and toes. And if you ran fast enough in the right direction, you could outrun artificial gravity! And presumably get heavier if you ran in the other direction.

        I don’t know if organisms would be able to detect these differences.

        • Steven C. says:

          That’s why such rotating structures would need a large radius. Early designs for rotating space stations involve a tube in a ring around, and attached to, a central hub. The pseudo-gravity in the hub would be much lower than in the outer ring. Said structure would have to be several hundred feet across; much larger than the ISS!

  20. Greying Wanderer says:

    looking at it the other way what would zero g be medically good for?

    orbital burns unit?

  21. Reziac says:

    It may not be the zero or low G that’s bad for you. The symptoms from long-term living on the Space Station are entirely consistent with low-grade thyroid damage (to be expected if cosmic radiation is affecting iodine) — which is typically not picked up by a TSH test, probably the only thyroid diagnostic being run on returning astronauts (since the utterly wrong but prevailing wisdom is that TSH is the only diagnostic you need). Really need to do a full panel including T3 conversion and uptake, and it wouldn’t hurt to check parathyroid too (actual hormone output, not just blood calcium levels).

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