5 ms·

I think it would be impossible for humans to walk around at more than ~1.5 g of acceleration for extended periods of time, and even that is asking a lot. Take

I think it would be impossible for humans to walk around at more than ~1.5 g of acceleration for extended periods of time, and even that is asking a lot. Take the g-force and multiply it by your body weight. That would be how heavy you feel when standing. If you are 70 kg (154 lbs) and under 1.5g of acceleration that is an extra 35 kg (77 lbs) of weight, which is about what we ask a modern soldier to carry. But the soldier gets to set their pack down when they rest, and the weight isn't applied to their internal organs. Perhaps gradual introduction of the acceleration over weeks would allow people to build conditioning, if all the crew is young and very fit. Go higher and it gets even less plausible. 2.0g is like carrying your twin. Surely this is impossible to sustain for more than an hour or two without some kind of acceleration couch—setting cardiac health aside entirely—and injury would be very likely if you were active.

hoseja 4y ago
Acceleration-added weight is carried better than a backpack. It's better distributed, the same way the rest of your normal weight is distributed, just more of it.
ginko 4y ago
>Go higher and it gets even less plausible. 2.0g is like carrying your twin. FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Will people be able to perform at peak physical level? No. Will they probably manage for a couple of days? I'd say so.
- TremendousJudge 4y ago
  It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.
  - hammock 4y ago
    That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough.
    - KineticLensman 4y ago
      Then you have to toughen up the internal tissues so that blood vessels aren't ruptured by high-pressure blood (which can cause strokes, permanent vision loss if retinal arteries are affected, etc). High blood pressure also affects kidney and liver function, amongst other things.
    - tablespoon 4y ago
      > That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough. Isn't that basically a g-suit, like fighter pilots already wear? https://en.wikipedia.org/wiki/G-suit https://en.wikipedia.org/wiki/G-suit Also, from that page: > The resting g-tolerance of a typical person is anywhere from 3–5 g depending on the person.
      - marcosdumay 4y ago
        Yes, but that tolerance is for seconds of exposition, not days.
      - ksaj 4y ago
        This is akin to the landing impact when you jump from something low enough that you won't die from it. You wouldn't survive it in a sustained manner, but the brief jolt, while maybe causing your innards to ache, is tolerated.
    - nradov 4y ago
      Athletes already use compression boots which apply pulsed pressure to the lower legs as a sports recovery modality. But those are only used for maybe an hour at a time. I doubt whether they would compensate for the physiological stress of sustained high acceleration.
- sneak 4y ago
  > FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Those people have been training for months/years to carry that weight.
  - ksaj 4y ago
    Indeed. It's also not pulling down with that same weight on each of their internal organs.
ghusbands 4y ago
You could discount a lot of extra weight over time (physiological adaptation), especially as you're not carrying it in your arms or over your shoulders, but tripping up would suddenly become a lot more fatal. Everyone's reactions and instincts are tuned for 1g.
foxyv 4y ago
You are completely right. I guess 15-30 minutes or so is the limit unless there is some new technology that can allow for long term gravity exposure. https://www.newscientist.com/article/dn2076-hypergravity-experiment-in-a-spin/ https://www.newscientist.com/article/dn2076-hypergravity-exp... > “The experiment will not progress very far, because loads of 1.5 to 2G can only be tolerated for about 15 minutes and even then it severely impacts on sensory systems, like balance,” Elmann-Larsen told New Scientist. “People can withstand forces of even 3.5G, but the time length is absolutely crucial.”
kqr 4y ago
To some extent there's a more direct comparison: a pregnant woman gains somewhere around 10--20 % bodyweight. This cannot be set down and it applies pressure to internal organs. I can't imagine making it 50 %!

hoseja 4y ago

Acceleration-added weight is carried better than a backpack. It's better distributed, the same way the rest of your normal weight is distributed, just more of it.

ginko 4y ago

>Go higher and it gets even less plausible. 2.0g is like carrying your twin. FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Will people be able to perform at peak physical level? No. Will they probably manage for a couple of days? I'd say so.

TremendousJudge 4y ago
It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.
- hammock 4y ago
  That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough.
  - KineticLensman 4y ago
    Then you have to toughen up the internal tissues so that blood vessels aren't ruptured by high-pressure blood (which can cause strokes, permanent vision loss if retinal arteries are affected, etc). High blood pressure also affects kidney and liver function, amongst other things.
  - tablespoon 4y ago
    > That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough. Isn't that basically a g-suit, like fighter pilots already wear? https://en.wikipedia.org/wiki/G-suit https://en.wikipedia.org/wiki/G-suit Also, from that page: > The resting g-tolerance of a typical person is anywhere from 3–5 g depending on the person.
    - marcosdumay 4y ago
      Yes, but that tolerance is for seconds of exposition, not days.
    - ksaj 4y ago
      This is akin to the landing impact when you jump from something low enough that you won't die from it. You wouldn't survive it in a sustained manner, but the brief jolt, while maybe causing your innards to ache, is tolerated.
  - nradov 4y ago
    Athletes already use compression boots which apply pulsed pressure to the lower legs as a sports recovery modality. But those are only used for maybe an hour at a time. I doubt whether they would compensate for the physiological stress of sustained high acceleration.
sneak 4y ago
> FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Those people have been training for months/years to carry that weight.
- ksaj 4y ago
  Indeed. It's also not pulling down with that same weight on each of their internal organs.

ghusbands 4y ago

You could discount a lot of extra weight over time (physiological adaptation), especially as you're not carrying it in your arms or over your shoulders, but tripping up would suddenly become a lot more fatal. Everyone's reactions and instincts are tuned for 1g.

foxyv 4y ago

You are completely right. I guess 15-30 minutes or so is the limit unless there is some new technology that can allow for long term gravity exposure. https://www.newscientist.com/article/dn2076-hypergravity-experiment-in-a-spin/ https://www.newscientist.com/article/dn2076-hypergravity-exp... > “The experiment will not progress very far, because loads of 1.5 to 2G can only be tolerated for about 15 minutes and even then it severely impacts on sensory systems, like balance,” Elmann-Larsen told New Scientist. “People can withstand forces of even 3.5G, but the time length is absolutely crucial.”

kqr 4y ago

To some extent there's a more direct comparison: a pregnant woman gains somewhere around 10--20 % bodyweight. This cannot be set down and it applies pressure to internal organs. I can't imagine making it 50 %!