Could people survive at two gravities?

[Qadgop_the_Mercotan]

@Jurph

You’re assuming an equivalent oxygen percentage in the air (which seems reasonable). But at 1.6g, the atmosphere would be at a higher pressure, and might contain more oxygen per cubic meter – the same phenomenon experienced by Denver athletes in Miami, for example. If the air has more oxygen, then the blood doesn’t have to move as quickly to accomplish its mission, and the heart can continue pumping at its accustomed volume & speed. Think this would offset the effects any?

Oxygen is only one vital component that blood carries. It must also carry glucose, and sheer fluid volume under adequate pressure to perfuse the tissues. And a stronger gravity field would certainly change the dynamics of those latter two items.

[Chronos]

If memory serves, one of the major causes of fatal car accidents is tearing of the aorta due to sudden deceleration. It seems to me that this would be a major problem in a higher g environment than what we’re used to. Am I right?

Yes and no. The accelerations involved in a car crash are tens of gees, which can indeed kill a person instantly, but they don’t last very long. For such short periods of time, up to about five gees will do no damage at all to a healthy human (many amusement park rides get up to about 5). This sort of problem wouldn’t be any worse for an extended time than for a few moments: It wouldn’t take long for an aorta to tear. The effects we’re more concerned about here would take at least a few hours to manifest, and probably days or years.

[Jurph]

Given that the trip would take ten years at lightspeed, it’s bound to take longer than that at conventional speeds. What if the ship were designed to accelerate at 1.5G for most of the trip, and then at some predetermined point, spin around in the middle and go to 1.75G? Or better yet, slowly increment up from 1.10G up to 2G, so that the crew (and their progeny) are continually becoming accustomed to heavier gravity? Would stretching the effects out over decades make any difference?

[Sapo]

Also a problem for the hypotheticals without the benefit of a magical teleporter (i.e. the generation ship crew), is that they would have spent most of their lives in zero g. So it is not just a doubling of gravity we are talking about here.

Of course, if they have a way to generate their gravity on ship, then they should have spent the trip ramping up to the destination g.

[thirdname]

@Jurph

Given that the trip would take ten years at lightspeed, it’s bound to take longer than that at conventional speeds. What if the ship were designed to accelerate at 1.5G for most of the trip, and then at some predetermined point, spin around in the middle and go to 1.75G? Or better yet, slowly increment up from 1.10G up to 2G, so that the crew (and their progeny) are continually becoming accustomed to heavier gravity? Would stretching the effects out over decades make any difference?

I read some impressive figure that indicated that a ship that could accelerate a 1G would be incredibly fast. Of course it’s limited to below c, but the time dialation makes it faster for the crew. I read something about a ship that accelerates at a constant 1 g could circumnavigate the galaxy in a few years or decades to the people onboard, or something like that. That might be too optomistic, as something that could accelerate at 1 G for years couldn’t be a chemical rocket, it would at least have to be some sort of nuclear rocket or an Orion ship if even that is enough.

[Der_Trihs]

@Canadjun

Has anyone ever stuck animals in a centrifuge for very extended periods of time? That’s the only way I can think of to test what would happen (and even there I would remain a little dubious if four footed critters were used for testing - there’s less lift required if you’re essentially horizontal then if you’re vertical).

Yes. Besides the previously mentioned rats, it was done with chickens, although I don’t recall how high they went with the G’s. The result was more muscular chickens. I read about it in Great Mambo Chicken and the Transhuman Condition by Ed Regis and Edward Regis; the title refers to the chickens in question.

[Quartz]

Also - and hopefully - 581c might not be just a planet, but a planet and moon, so the gravity of the main body might be even closer to Earth’s.

[Chronos]

I read some impressive figure that indicated that a ship that could accelerate a 1G would be incredibly fast. Of course it’s limited to below c, but the time dialation makes it faster for the crew. I read something about a ship that accelerates at a constant 1 g could circumnavigate the galaxy in a few years or decades to the people onboard, or something like that.

In one of those fortuitous coincidences of physics, the speed of light divided by one year is almost exactly 1 g. This means that after 1 year of acceleration at a constant 1g, your ship will be going at a proper speed of 1, relative to the frame where it started. Of course, a proper speed of 1 isn’t a true speed of c (proper speed is true speed times gamma, the relatavistic factor), but it’s still pretty darn fast. For the specific calculation of how long (in the ship’s frame) it’d take to circumnavigate the Galaxy, you can actually ignore the relativistic effects: They all cancel out. So if we take a figure of 300,000 ly for the circumference of the Galaxy, and plug into the Newtonian kinematic formula x[sub]t[/sub] = x[sub]0[/sub] + v[sub]0[/sub]t + 1/2 a t[sup]2[/sup], with v[sub]0[/sub] = x[sub]0[/sub] = 0, we get that t = 770 years (if you want to stop at the end, it’s four times that). This is a bit longer than the “few decades” you were thinking of, but a lot shorter than the 300,000 years you’d get without the time dilation.

That might be too optomistic, as something that could accelerate at 1 G for years couldn’t be a chemical rocket, it would at least have to be some sort of nuclear rocket or an Orion ship if even that is enough.

In principle, any sort of rocket can maintain any acceleration for any amount of time, if you’re willing to have a large enough ratio of fuel to payload. In practice, though, the required ratio grows impractically large, very fast. This is a problem even for nuclear rockets: Even with a 100% efficient fusion rocket (which an Orion drive isn’t), you’d still need thousands of times your payload mass in fuel to sustain a g for a year.

[Der_Trihs]

@Der Trihs

Yes. Besides the previously mentioned rats, it was done with chickens, although I don’t recall how high they went with the G’s. The result was more muscular chickens. I read about it in Great Mambo Chicken and the Transhuman Condition by Ed Regis and Edward Regis; the title refers to the chickens in question.

Oddly enough, this book came up on another board today, and someone had a quote :

There was the hyper-G work done on chickens, for example, by Arthur Hamilton (“Milt”) Smith in the 1970s. Milt Smith was a gravity specialist at the University of California at Davis who wanted to find out what would happen to humans if they lived in greater-than-normal G-forces. Naturally, he experimented on animals, and he decided that the animal that most closely resembled man for this specific purpose was the chicken.

Chickens, after all, had a posture similar to man’s: they walked upright on two legs, they had two non-load-bearing limbs (the wings), and so on. Anyway, Milt Smith and his assistants took a flock of chickens – hundreds of them, in fact – and put them into the two eighteen-foot-long centrifuges in the university’s Chronic Acceleration Research Laboratory, as the place was called.

They spun those chickens up to two-and-a-half Gs and let them stay there for a good while. In fact, they left them spinning like that day and night, for three to six months or more at a time. The hens went around and around, they clucked and they cackled and they laid their eggs, and as far as those chickens were concerned that was what ordinary life was like: a steady pull of two-and-a-half Gs. Some of those chickens spent the larger portion of their lifetimes in that goddamn accelerator.

Well, it was easy to predict what would happen. Their bones would get stronger and their muscles would get bigger–because they had all that extra gravity to work against. A total of twenty-three generations of hens was spun around like this and the same thing happened every time. When the accelerator was turned off, out walked . . . GREAT MAMBO CHICKEN!

These chronically accelerated fowl were paragons of brute strength and endurance. They’d lost excess body fat, their hearts were pumping out greater-than-normal volumes of blood, and their extensor muscles were bigger than ever. In consequence of all this, the high-G chickens had developed a three-fold increase in their ability to do work, as measured by wingbeating exercises and treadmill tests.

Note what I bolded; they survived 2 1/2 gees just fine.

[Mr.Excellent]

@Der Trihs

Oddly enough, this book came up on another board today, and someone had a quote :

Note what I bolded; they survived 2 1/2 gees just fine.

Of course, chickens live much shorter lives than people. Could that make a difference? I mean, maybe they just aren’t living long enough to experience the sorts of problems that humans might develop over the course of years.

[Chasing_Dreams]

@Der Trihs

These chronically accelerated fowl were paragons of brute strength and endurance. They’d lost excess body fat, their hearts were pumping out greater-than-normal volumes of blood, and their extensor muscles were bigger than ever. In consequence of all this, the high-G chickens had developed a three-fold increase in their ability to do work, as measured by wingbeating exercises and treadmill tests.

How do I sign up for this experiment?

[Canadjun]

OK - A slightly off-topic question. A couple of people have mentioned mice and chickens being kept in centrifuges for extended periods of time. HOW are the critters fed, their cages kept clean, etc? Seems to me that regularly stopping the centrifuge to feed, water, and clean would severely impact the experiment (how do you know that any problems that arise are due to increased “gravity” and not due to variable “gravity”?)

[Darryl_Lict]

@Canadjun

OK - A slightly off-topic question. A couple of people have mentioned mice and chickens being kept in centrifuges for extended periods of time. HOW are the critters fed, their cages kept clean, etc? Seems to me that regularly stopping the centrifuge to feed, water, and clean would severely impact the experiment (how do you know that any problems that arise are due to increased “gravity” and not due to variable “gravity”?)

Couldn’t you just have a wire mesh floor that lets the poop fling out just like a chicken coop? An axially located chicken feed and water dispenser would allow gravity fed feeding and watering. I’m not sure how you would clean the nests if you wanted a continuous multigenerational system. I would think that you could still run an effective experiment even if you reduced the 2.5G environment back down to 1G for 10 minutes a day.