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Why no Artificial Gravity ??

Just thinking said:
Basically, why are there no plans to create near future spacecraft with some sort of artificial gravity? No -- not the Star Trek / Hollywood type, but the simple rotational 2001: A Space Odyssey type.
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Well, currently the first problem is it costs roughly $10,000 per pound to launch something into space.

http://www.stanford.edu/~klynn/mars_paper.htm

Obviously this ship would have to be put together in space, made of components manufactured on Earth. So you are going to have to launch all that "junk" up into space.

Some side effects due to this are:

The Coriolis effect produced by rotation could cause dizziness, nausea and disorientation. Experiments have shown that slower rates of rotation reduce the Coriolis forces and its effects. It is generally believed that at 2 rpm or less no adverse effects from the Coriolis forces will occur, at higher rates some people can become accustomed to it and some do not, but at rates above 7rpm few if any can become accustomed. It is not yet known if very long exposures to high levels of Coriolis forces can increase the likelihood of becoming accustomed. The nausea-inducing effects of Coriolis forces can also be mitigated by restraining movement of the head. Head restraints are perhaps practical for exercising in artificial gravity (an artificial gravity gym), but not for much else.

Gravity gradients: Artificial gravity levels vary proportionately with the distance from the center of rotation. With a small radius of rotation the amount of gravity felt at one's head would be significantly different from the amount felt at one's feet. This could make movement and changing body position awkward. Again, slower rotations or larger rotational radii should not lead to such a problem.

Angular movement: As noted high angular velocities produce high levels of Coriolis forces, angular momentum would require a propulsion system of some kind to spin up (or spin down). Also if parts of the spaceship are intentionally not spinning, friction and similar torques will cause the rates of spin to converge (as well as causing the otherwise-stationary parts to spin), requiring motors and power to be used to compensate for the losses due to friction. Angular inertia can also complicate spacecraft propulsion and attitude control.


Their are also significant engineering problems associated with a ship that rotates.

The engineering challenges of creating a rotating spacecraft are comparatively modest compared to any other proposed approach. Theoretical spacecraft designs using artificial gravity have a great number of variants with intrinsic problems and advantages. To reduce Coriolis forces to livable levels a rate of spin of 2 rpm or less would be needed. To produce 1g the radius of rotation would have to be 224 m (735 ft) or greater, which would make for a very large spaceship. To reduce mass, the support along the diameter could consist of nothing but a cable connecting two sections of a spaceship, possibly a habitat module and a counterweight consisting of every other part of the spacecraft. Eugene F. Lally of the Jet Propulsion Laboratory proposed this concept in the early 1960's in a paper titled, "To Spin or Not to Spin". It is not yet known if exposure to high gravity for short periods of time is as beneficial to health as continuous exposure to normal gravity. It is also not known how effective low levels of gravity would be to countering the health effects of weightlessness. Artificial gravity at 0.1g would require a radius of only 22 m (74 ft). Likewise at a radius of 10 m about 10 rpm would be required to produce earth gravity (at the hips; gravity would be 11% higher at the feet), or 14 rpm to produce 2g. If brief exposure to high gravity can negate the health effects of weightlessness then a small centrifuge could be used as an exercise area.

The Gemini 11 mission attempted to produce artificial gravity by rotating the capsule around the Agena Target Vehicle which it was attached to by a 36 meter tether. The resultant force was too small to be felt by either astronaut, but objects were observed moving towards the 'floor' of the capsule.

The Mars Gravity Biosatellite will study the effect of artificial gravity on mammals. An artificial gravity field of 0.38g (Mars gravity) will be produced by rotation (34 rpm, radius of ca. 30 cm). Fifteen mice will orbit Earth for five weeks and land alive.



http://en.wikipedia.org/wiki/Artificial_gravity
 
There is no gravity. There is only the Down Fairies. You a-fairieists just don't understand that it's the Down Fairies' job to keep us on Earth and punish us if we leave.
 
RenaissanceBiker said:
I think the next step will probably be a moon base, with it's natural gravity. A spinning space structure with artificial gravity may be the next step after that, but where will such a station be needed? Orbitting Mars? That step is a doozy.
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I want a Ringworld. And I want it now.
 
"Alex, I'll take "spacecraft design" for $1600."

"And the answer is: 'Communication antennas, solar panels, cameras, docking ports, and thrusters.'"

"What are five things that work better when they're not spinning around?"

"Correct!"

Of course, you can attach those things to a non-spinning portion, but then you need a coupling. This presents all sorts of problems, especially if a pressurized path through the coupling has to exist (for instance, if access to a non-spinning dock is required).

Respectfully,
Myriad
 
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If we could cheaply mine the moon then a large mission to Mars may be a lot cheaper than getting everything from the bottom of a very deep well ie Earth.
 
Certainly, the tethered counterweight method is the most practicable. Or at least, a useful space wheel has to be extremely large to get low enough rpm, and to avoid problems like people moving around will shift the center of gravity.

Of course, antennas, external sensors (including camaras), thrusters, etc. get much more complicated but technology can solve most of the problems.

The real question is: Is there really a need? It should be much easier to arrange for sufficient training to keep astronaut's bones from de-calcifying. One possibility is a running barrel, which could just be a ring-formed track somewhere in the craft. All the astronauts would have to was learn to start running around it, and they would provide their own private "gravity" just like a motocycle-drome. To avoid upsetting the equilibrium of the craft, one or several counterweights could be rotated and electronically synchronized to their movement. Experiments in space have already shown that a limited time of weight-bearing training every day is enough to keep bones healthy.

Hans
 
Well, there are a number of things that become much easier even in a low gravity field.

1) Eating.

2) Going to the potty.

3) No need for elaborate methods to reduce muscle and bone atrophy.

4) Nothing will be floating around -- such as dirt, liquids, debris, etc.

5) Things basically stay put.

6) Familiarity with everyday actions/reactions.
 
A rotating object does not accurately reproduce gravity. Gravity is a constant force downwards. Whether you are sitting, standing, jumping, flying, whatever, there is always the same force pulling you in the same direction (from a human-scale point of view). A rotating ring does not do this. If you jump, no force, if you lift your arm, nothing pulling it down, if you drop something, it doesn't fall. The problems adapting to this kind of artifical gravity would be at least as great as the problems adapting to micro-gravity, and there would be very few, if any, advantages.
 
Cuddles said:
A rotating ring does not do this. If you jump, no force, if you lift your arm, nothing pulling it down, if you drop something, it doesn't fall.
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That's not true. There is already a cite to an experiment done on Gemini that demonstrated that objects fell to the floor in even a very low spin test.

The only real difference is that one is a linear radius relationship and the other is radius squared which isn't really going to be a practical difference.
 
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Cuddles said:
If you jump, no force, if you lift your arm, nothing pulling it down, if you drop something, it doesn't fall.
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Well sort of right but not really. If you drop something it continues moving in a straight line, but the floor and you are not so it will hit the floor as the floor is pulled into its path by the centripetal acceleration.

It might not fall straight down but at a weird angle but it would fall. I need to find my old advanced mechanics books and look at these equations again.
 
ponderingturtle said:
Well sort of right but not really. If you drop something it continues moving in a straight line, but the floor and you are not so it will hit the floor as the floor is pulled into its path by the centripetal acceleration.
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Yes, but only if the rotation of the spacecraft brings the floor into the object's path. If you drop the object at the exact center of rotation, for example, in theory it'll never fall. In practice, the movement of the air will probably push it to a point where it'll hit the floor eventually, but it certainly wouldn't be "falling" in the sense we're all familiar with.

Rotation is a pretty good way of simulating gravity, but it can produce some very counterintuitive effects, especially when the radius is small.
 
toddjh said:
Rotation is a pretty good way of simulating gravity, but it can produce some very counterintuitive effects, especially when the radius is small.
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A comparable situation exists for gravity. If you were on an extremely dense object with a very small radius you'd experience noticable counterintuitive effects also. (Things not falling straight, substantial difference of gravity with altitude).
 
Imagine this. You have a hollow torus in space that is not rotating. You place an object in the torus so that it is not in contact with the walls. Now start the torus rotating so that the object stays out of contact with it. What happens to the object?

Absolutely nothing. It stays happily floating there. Hence, not gravity.
 
Yes, but that's not comparable to the situations you described. Your example is simply saying "things that aren't accelerating aren't accelerating" and the situation you describe will only be relevant when spinning up the station.
 
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Cuddles said:
Imagine this. You have a hollow torus in space that is not rotating. You place an object in the torus so that it is not in contact with the walls. Now start the torus rotating so that the object stays out of contact with it. What happens to the object?

Absolutely nothing. It stays happily floating there. Hence, not gravity.
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Bolding mine. But if the object (or astronaut) is attached to the wall as the torus is sped up, once the torus stops accelerating and rotates at a constant rate, from the astronaut's point of view, things will feel similar to a gravitational field.

It won't be exact. If he drops an object from his hand, it will fall to the ground a bit quicker than what he would expect under a normal gravitational field. It will also not fall straight down. However, the differences between a normal gravitational field and what the astronaut experiences get smaller and smaller as the radius of the torus increases.
 
RecoveringYuppy said:
Yes, but that's not comparable to the situations you described. Your example is simply saying "things that aren't accelerating aren't accelerating" and the situation you describe will only be relevant when spinning up the station.
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An interesting side note about being in a rotating torus -- assume you are feeling normal gravity as you stand in one position on the floor, your head pointed toward the center of rotation. If you decided to start running in the opposite direction of rotation, you would start to experience less G's -- and this might enable to run even faster. If you could go fast enough to match the linear speed of the torus (but in the opposite direction) you would become weightless. You would float -- and the body of the torus would now spin relative to you. You would fly through the compartments (hopefully without hitting anything) as if you were Superman.
 
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Cuddles said:
Imagine this. You have a hollow torus in space that is not rotating. You place an object in the torus so that it is not in contact with the walls. Now start the torus rotating so that the object stays out of contact with it. What happens to the object?

Absolutely nothing. It stays happily floating there. Hence, not gravity.
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But the problem is that you are moving with the torus in your earlier note. Well you might have removed all rotation from your arm, and have it floating past you at many miles per hour.

That is really throwing something backwards fast enough to negate the rotation not droping it.
 
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