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supermarket
2004-Apr-26, 07:38 AM
26.04.04

Hi,

Aritificial gravity: does anyone know of any credible theories or even workable ideas by which AG might/can be generated? I'd be grateful for any links/info/ideas anyone was able to offer.

Thanks,

supermarket

GOURDHEAD
2004-Apr-26, 12:55 PM
Acceleration works for some applications.

Littlemews
2004-Apr-26, 04:06 PM
I thinkn F=ma also works as well...
hope this link hel[
http://curious.astro.cornell.edu/question....n.php?number=65 (http://curious.astro.cornell.edu/question.php?number=65)

Fraser
2004-May-03, 07:08 PM
If you're talking about Star Trek-type artificial gravity, though, I'm not aware of any realistic research that proposes anything that could generate a gravity field.

In Babylon 5, the Omega-class ships had a rotating section that would produce artifical gravity. The rest of the ship was weightless.

http://www.tp2b.de/earth_ocd.html

That's about the only time I've ever seen it considered in science fiction.

ASEI
2004-May-03, 07:14 PM
Well, you could have rotating sections of a spacecraft. If you're really cheap, you could reel out an elevator on a cable and swing it around until an astronaut is done getting his daily g-allowance. I suppose on any planetary surface where you wanted more gravity you could build a spinning centrifugal gym or something to exercize in an enhanced gravity environment.

Sphinx
2004-May-07, 01:34 AM
I've heard people talk about generating Artificial Gravity on a number of occasions but never in-depth. Everyone makes it sound like you just rotate some kind of mass to generate the equivelant of some kind of g-field, even if it is extremely small. I'm sure it is not as simple as just spinning the space ship...or is it? What are out current limitations and how much AG can be generated as well as the practicle application of this amount?

ASEI
2004-May-07, 03:04 AM
Well, spinning the ship doesn't generate a gravitational field at all. The spinning of the ship merely accelerates the objects radially outward from the axis of rotation in the rotating reference frame. It is called "centrifugal force", though in a stationary non-rotating reference frame it goes to zero and the force can be explained by other means.

Suppose you have a ring with radius r, and a point that spun with tangental velocity v. The effective acceleration the point would feel in the rotating reference frame is a=v^2/r, like any physics book would tell you. It's nothing exotic like gravity, it is similar to the effect you would get on one of those banking roller coasters. Since the acceleration is distributed differently, it would feel different than normal gravity, and there would also be a coriolis effect to go with it (another force tangent to your radial velocity) that could get pretty dizzying on smaller disks. But on long space voyages, being spun would provide mass proportional force that should keep your body from decaying like it does without gravity.

That's about as layman as I'm willing to get. You've probably heard other things involving gyroscopic effects and "anti-gravity", but as far as I can tell, it is just principles of angular momentum and centrifugal force being mis-applied.

The three pseudo-forces in a rotating reference frame compared to a non-rotating or accelerating reference frame are as follows:

w = angular momentum
wdot = angular acceleration
v = velocity vector
a = acceleration vector
r = radius vector
x is for the cross product of vectors

coriolis = 2wxv
centrifugal = wx(wxr)
euler = wdotxr

These are the most general forms of what goes on in rotating systems.

Sphinx
2004-May-07, 03:15 AM
ah...so a very unpleasant experience. Probably make you feel like your stomach was dropping out the back end. We don't feel this on earth because earth is so large compared to us. As for the purpose of generating this unpleasant feeling, it would merely be for practicle purposes. We want our astronauts to be able to walk when they get to their destinatin. Correct?

Thanks.

Calibre
2004-May-07, 03:27 AM
A couple of off the cuff questions and ideas?

1) Is the Graviton not a particle that could be created and held in a field, probably in a slab or cylinder within a space craft or habitat? As a slab above and below would both use the same slab as the floor, this would make outside a ship up and inside a ship down. While as a cylinder; inside and out would both use the cylinder as a floor. A large cylinder would have that advantage that if the gravity field degraded then the ship/station could be rotated to at least provide centripetal gravity to the inside surfaces.
2) OR is the gravity an inherent property of all matter and energy over a threshold? Know that photons react to gravity masses such as stars. If this is the case could there could still be a partical with a stronger property that could be used to make nice “star trek” like gravity fields?

If centripetal gravity using rotating rings and disks or things stuck on cables is the only practical method to provide the gravity that keeps us strong and keeps bone matter dense then this adds significantly to the difficulty of long space flight and habitation. Guess it means we will first explore and inhabit the gravity well of moons and planets near to Earths Gravity values, such as Mar’s and the Jovian Moons.

During flight/habitation centripetal systems need to be at least 200m wide to emulate decent gravity that does not upset and make people feel sick. Imagine living on a merry go round, sleeping in particular. The problem being if the circle is too small it feels wrong to the inner ear which provides our sense of balance as the direction of the gravity even feels different from one human ear to the next. A 200m circle puts a much straighter line through a standing humans head than a 10m circle does.

Guess this would reinforce the need for a deep sleep which halts bone and muscle attrition. Ideally drug controled cryogenic sleep would be an answer – the metabolism might be reduced even lower by approaching freezing point. Freezing gets difficult – ice crystals piece human type cells soon after freezing and literally mince our structure.

A few animals (-a cricket and frog-) have cells which either have an antifreeze and probably heal and regenerate quickly. Drugs or massive Genetic Modification of human could steal these abilities. Though by this stage you may as well use that medical technology to produce a strain of people that don’t degrade in no gravity or repair the damage quickly?

So really I’m suggesting that the main alternatives are cryogenics and genetic modification to avoid or mitigate the bad effects of no gravity.

Maybe on par with trying to make a field of gravity, a field of frozen time – stasis – would be just what is needed to allow voyages beyond the moon.

zephyr46
2004-May-07, 04:55 AM
UT forum EM and Gravity (http://www.universetoday.com/forum/index.php?showtopic=2795&st=0&#entry26606)

UT Forum Gravatons What might they be (http://www.universetoday.com/forum/index.php?showtopic=3072)

UT forum Artificial Gravity (http://www.universetoday.com/forum/index.php?showtopic=3011)

This subject is a recurring one. Just reading about the Coriolis Effect is making me feel sick, and I am doubting that I would be able to stand spaceflight !

I thought with centrufugal force, when you spin a bucket over your head and the water stays in was because you build up enough momentum as the bucket comes down, the water sticks to the bottom of the bucket at the top because it's inertia is being carried forward by the momentum of the arc/circle and is built back up by gravity on the downswing, equilizing the effect of gravity, sharing it. So in space you would need an existing mass of gravity, to create any sort of artificial gravity you would need to add momentum, as for feeling ill in space though, it would depend on seeing the stars rushing past or the center of mass before you would feel sick, somthing to do with the brain equalizing input from eyes and ear drums (balance)

I have seen a recent mars/saturn or Nova (I think that was it, rescue ship goes to blue gian that is about to explode, to rescue ex boyfreind of crew member, turns out to be a pirate stealing somthing from mining colony type) movie where the ship had two rotating blocks that were rotating around the core of the ship, balanceing two sources of centrifugal force, oh yeah, where does centrapedal force fit into the standard model? Just momentum or somthing like that?

Tom2Mars
2004-May-07, 05:05 AM
Asei-Those are very good descriptions!

Also, here is an interesting site(Japanese?) that describes many rotating, artificial gravity designs. It includes some improvements on the original O'Neill torus, such as the need for a counter-rotating mass(to cancel out gyroscopic action which would cause an initial solar orientation to miss the mark as the station moved in its orbital path around the Sun).

Rotaters (http://www.dyarstraights.com/msgundam/frontier.html)

Calibre-
During flight/habitation centripetal systems need to be at least 200m wide to emulate decent gravity that does not upset and make people feel sick

My space station design is just under 200m. I'm glad to see some feedback that supports my "gut-feeling".

zephyr46
2004-May-07, 05:58 AM
Great Site :)

ASEI
2004-May-07, 02:49 PM
I've never thought it would have to be that big. I figure if people can get used to zero gravity, they can probably get used to an ambient coriolis force. It would just take some time to adjust.

Tom2Mars
2004-May-11, 02:38 AM
I agree! I keep seeing these references to "well, we know what 1-G is like and we know about 0-G(or, microgravity), but we just don't know about anything in-between", or, "we just don't know if the people can handle the coriolis effect at 'X' rotation rate".

I remember a story- Before the first train to go over 20 miles/hour started its run, the "experts" had predicted that the passengers would die or explode or something crazy like that. At a time when folks had gone faster on horseback!

Well, let's just get a rotator up into space and find out what will happen for sure.

PS-Most of the references I've run across seem to suggest that 2 rpm or under is OK. If we think we want to go to Mars, we might as well try 0.37G and find out for sure. The 200m station can test that, and while it seems big, it is actually designed to pack down into a single shuttle cargo bay(or unmanned payload vehicle, or several smaller vehicles).