Artificial Gravity Theory

[TheCanadianVendingMachine]

Hello all, I come up with a theory here. Now, as we all know artifical gravity seems to be some sci-fi stuff. But as we also know, spinning and centrifugal force can make you stick to a wall. So, what about a spacecraft with a slightly smaller spacecraft inside that spins at human gravity? Something like this -

So, now here's the part where people criticise. I am no major in any degree, but I come up with many theory's in my mind. Please do tell me why this is/isn't wrong

[dharak1]

I think the problem with small diameter rings is the Coriolis effect. I don't know what problems it creates but I think it makes something happen in your bodily fluids.

[lajoswinkler]

What's the point of rotating something in something that's not rotating? To appear motionless to outside spectators?

[TheCanadianVendingMachine]

Well, with the spinning inside, it can be a motor that spins it with electricity, instead of anything else. And with the coriolis effect, I do not know as for I have not studied that yet.

[lajoswinkler]

But why the stationary part? What does it do?

All I see is already developed concept with a motionless cover over it. Kind of like putting a box over a blender to avoid looking at its rotating blade.

[Awaras]

Well, with the spinning inside, it can be a motor that spins it with electricity, instead of anything else. And with the coriolis effect, I do not know as for I have not studied that yet.

Spinning the inner ring with electric motors will make the outside ring and anything connected to it spin in the opposite direction, forcing you to use RCS or some other means of propulsion to stop it spinning. Then you might as well spin the whole ship and avoid all the extra mass of equipment you would need to make the inside ring.

As for the coriolis forces, basically they mess with a person's sense of balance causing them to feel dizzy every time they move, with prolonged exposure causing nausea and stuff like that. Think of the dizziness you feel after riding on a merry-go-found and imagine living on one for weeks or months at a time...

Since this effect decreases as the diameter of the spinning habitat increases, according to this, the minimal diameter of the ring needs to be larger than 40 meters with the spin rate of no more than 4 revolutions per second to avoid the worst effects. This gives you around 1/3 G of artificial gravity inside the ring. If you want more gravity, you must build a bigger ring to avoid the effect.

Edited September 18, 2013 by Awaras

[KOCOUR]

Coriolis effect:

http://abyss.uoregon.edu/~js/glossary/coriolis_effect.html

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml

http://en.wikipedia.org/wiki/Coriolis_effect

[M.Wolfy]

if you were in a spacecraft like that...

you can't be %0.01 claustrophobic, and you will have to rely on instruments for berthing/docking, no windows... windows help a lot.

[Nuke]

What's the point of rotating something in something that's not rotating? To appear motionless to outside spectators?

if you have a ship with both artificial and zero gravity sections, this eliminates the need for rotating pressure seals between those sections. you can then have a non-sealed gravity deck in a static pressure hull. this would be preferable in a large space freighter, where its easier to keep cargo in zero-g. you can also reduce the mass of a centrifuge greatly if it doesn't need to perform radiation shielding and pressure bulkhead functions.

now if it was a lightweight ship, such as something used for a round trip to mars, spinning the whole thing on the long axis will work fine. id hate to have to design the attitude control system though.

[Mekan1k]

dharak1- Partly right. However, the biggest problem would be the acceleration gradient.

Imagine, if you will, you spun this device up so that the resultant force of artificial gravity is effectively 1 g. Now, the human body is sensitive to acceleration gradients of 1/100th of a g, or 0.0981 meters per second (This was tested by the nazis on rather unfortunate test subjects), and although this would TECHNICLY work, it would have problems with the internal acceleration gradients. If the gradient is too high... We experience rather violent involuntary dis-assembly, as the softer tissues tend to give way.

Now, we will run some numbers on this.

First: conceptualize the problem

We are assuming that you are 'standing' with your head pointing in the direction of the center of rotation, with your feet on the inside surface of the circle. This would generate 'artificial' gravity for the person standing, as they would feel a centripetal acceleration in a vector pointing perpendicular to the surface of the circle, away from the center of rotation.

If you are 2 meters tall, and the module you are in has a radius® of 4 meters (of inside space, so you have 8pi*the length of the cylinder to stand on{as per the equation As = Cs*height}), that means that the capsule's floor has a speed of

v = sqrt(a*r)

With a being equal to g, the earth gravity at sea level, the velocity would be 6.264 meters per second, or ~4 seconds per rotation.

6.246 meters/sec is 22,485.5 meters per hour, or 22.5 km/hr. This, kind sir, is really ****ing fast- if you jumped from a moving car at that speed you would probably hurt yourself.

Now, that is generating a velocity of 6.264 meters per second at your foot level, to generate the artificial gravity at foot level. Now lets go to your torso.

Now, I am going to be a bit biologically ignorant, but lets assume your belly button is 1 meter off the ground, making the relative radius 3 meters rather than 4. (We have to assume that your spine is strong enough to keep you upright)

T (Period) = 2*pi*r/v , therefore v = 2*pi*r/T

The velocity is 4.71 meters per second.

a = V^2 /r, therefore the acceleration your belly button is experiencing is 7.3947 m/s^2, or roughly 3/4 of gravity. {a = (pi^2 * 4 * r)/(T^2) }

(A general assumption is that as you get get farther away from the center of rotation, the acceleration is doubled every time the radius is doubled.)

Now, you head, having a radius only 2 meters away from the center of rotation, is not hitting anything as you whiz around this insane little cylinder.

The period is 4 seconds, and with a radius of two meters we can use the equation a = (pi^2 * 4 * r)/(T^2) to calculate the acceleration.

The acceleration the top of your head is experiencing is 4.929 meters per second per second. Your eyes are experiencing an acceleration of roughly 5 m/s^2, assuming you are built like most humans.

The difference in acceleration between your eyes and your feet is a 4 m/s acceleration.

YOU WILL FEEL THAT.

Anything at eye level will be roughly half times the weight it will be at foot level, and your blood will be having trouble as you are in a semi-imposed artificial gravity.

Now, onto acceleration gradient:

Humans have been known to survive a 170g acceleration (all-bet he broke his legs and spine, but he lived). Most people die from that. The acceleration gradient is the measure of acceleration change per meter.

The man who survived went from free-fall to 1g in 2 meters. This is an acceleration gradient of 169g/2 meters, or 84.5g's/meter. To put that in perspective, that means that your foot and knee, being 1/2 an inch apart, are experiencing a difference in acceleration of 42.25g, or 414.4725 meters/sec^2.

To put this another way, if your foot was held by a brace in zero-g, then the knee would be being accelerated at 414.47 meters/sec^2.

The disembodied knee would be ripped from the foot, and it's ankle would probably tear like a spare actor from a zombie movie.

Your body inside that cylinder would be experiencing an acceleration gradient of 2.4g/m, which, while not fatal, would be unpleasant.

You would feel light-headed, and unbalanced when you walk.

To prevent the acceleration gradient from being a problem, the radius should be equal to the height of the area you want to have be moving at 1g * at least a hundred. So if you want to have your whole body feel like it is being accelerated at 1g like at earth on sea level, your radius (for a 2 meter tall human) would need to be at least 200 meters. (I would recommend 220 meters, because it is a nice margin of error of 10% in case someone wants to jump a bit.

This would make your module large enough to put the ISS inside it 4 times and still have room for a 747 jet (just based off radius).

Now, a solution to not being required to make macro-structures that size but to still have a solution is to build for people lying down- a person lying down is what- 10 cm? That's 0.1 meters.

The radius of the centrifuge for this would be 22 meters, meaning it could be feasibly built.

In theory.

Oh, and your diagram needs a method of holding the outer surface from moving.

[Nuke]

heres a really good calc for testing hypothetical ring configurations:

http://www.artificial-gravity.com/sw/SpinCalc/