Why artificial gravity is not possible?

[wllsrvive]

What are some of the obstacles scientist face with the idea of creating artificial gravity for a space station?

 

[Yaridovich]

In order to create artificial gravity you would need to have the space station constantly accelerating in one direction so that the people inside would experience a force equal to the rate of acceleration times their body mass. This would create the illusion of weight. This is impractical because the station can't just keep accelerating; it would run out of fuel at some point. Utilizing centripetal acceleration could work, but the space station would need to be orbiting very quickly for any significant effects.

 

[Filip Larsen]

Regarding using a rotating space station to simulate gravity there is a so-called comfort zone where only some combinations of rotational radius and speed is considered applicable for human living conditions.

If you don't mind reading a bit you may find http://www.artificial-gravity.com/ a useful site.

 

[Mikeral]

If you want to create gravity in it natural state. By that, i mean attraction of two masses. you would need to place an object with the same mass as the earth, maybe a black hole, in the belly of the craft. Only problem with that is going to be moving. when you accelerate, you are going to have to move the mass of an entire planet. But by the time we are able to safely handle black holes like they were toys, i think we would be able to play around with accelerating enormous masses. But i'll leave that to the science fiction authors.
Like the two posts above me have said, the only obstacles that are faced are constant acceleration, fuel is expensive, or building a rotating station is just a question of size and maintaining the speed of rotation.

 

[Filip Larsen]

If you want to create gravity in it natural state. By that, i mean attraction of two masses. you would need to place an object with the same mass as the earth, maybe a black hole, in the belly of the craft.

Since the spacecraft would be much closer to such a black hole than the center of Earth you would only need a fraction of the mass. For instance, to get 1 g at 100 m from the black hole you would only need around 4-billionth of the mass or around 1.5*10¹⁵ kg. Still a great deal to accelerate though and there would also be some unpleasant gravity gradients.

Like the two posts above me have said, the only obstacles that are faced are constant acceleration, fuel is expensive, or building a rotating station is just a question of size and maintaining the speed of rotation.

Rotation is usually easy to maintain in vacuum since rotational momentum is conserved. If you need to "start and stop" rotation a lot you can use two or more counter-rotating rings instead of ejecting a lot of rocket reaction mass to change rotation. This way you only need energy to change rotation speed.

 

[russ_watters]

What is "artificial gravity"? Is that like artificial light?

 

[Dickfore]

In order that you provide gravitational field of the order g at distances of the order L, using Newton's Law of Universal gravitation we can deduce the necessary mass:

<br /> M = \frac{g \, L^{2}}{G}<br />

where:

G\ =\ 6.673 \times\ 10^{-11}\ \mathrm{m}^{3} \mathrm{kg}^{-1} \mathrm{s}^{-2}<br />

is the Universal gravitational constant.

Since the object surely has to be within a sphere with radius L, the density of the object has to be no less than:

<br /> \rho = \frac{3 m}{4 \pi \, L^{3}} = \frac{3 \, g}{4 \pi \, G \, L}<br />

i.e. it scales inversly proportional with the distances over which we want to create the field. Let us look at what distance a sphere with the density of water (typical density of ordinary substances plus minus one order of magnitude) will create the same field as the acceleration of free fall:

<br /> L = \frac{3 \times 9.81 \, \mathrm{m} \, \mathrm{s}^{-2}}{4 \times 3.142 \times 6.673(10)\ \times\ 10^{-11}\ \mathrm{m}^{3} \, \mathrm{kg}^{-1} \, \mathrm{s}^{-2} \, \times 10^{3} \, \mathrm{kg} \, \mathrm{m}^{-3}} = 3.51 \times 10^{7} \, \mathrm{m}<br />

Not surprisingly, this is of the same order of magnitude as the radius of the Earth. For laboratory sized distances, which are a million times smaller, one would need a material that is a million times denser than water. Fortunately, the mass scales with the square of linear dimensions. This would mean that the mass of the object would be one trillion (10¹²) times less than the mass of the Earth (M_{E} = 5.96 \times 10^{24} \, \mathrm{kg}), so only about 6 \times 10^{12} \, \mathrm{kg}. Assuming the weight of an average human to be 70 kg (between both sexes), this mass would be equal to the total combined mass of 85 billion average humans!

 

[mheslep]

At first glance I assume the OP meant the creation of artificial gravity by means of acceleration, i.e. a=g. The 'problems' then a spacecraft construction would include structural mechanics, docking dynamics, and the like.

 

[russ_watters]

At first glance I assume the OP meant the creation of artificial gravity by means of acceleration, i.e. a=g.

That's not what I concluded, because clearly, that method of creating an effect similar to gravity is possible.

 

[mheslep]

That's not what I concluded, because clearly, that method of creating an effect similar to gravity is possible.

<shrug> Maybe. OP's phrase was "what are the obstacles", which is ambiguous in its implied assumptions.

 

[cjameshuff]

Centrifugal simulated gravity is entirely possible. The radius of rotation required for comfortably low coriolis effects is large, but that can fairly easily be handled by using two sections attached by a long tether. It would be harder to dock with, but even this isn't really the biggest problem.

One of the biggest reasons to put a station into orbit in the first place is for the freefall environment...a rotating station would be rather unsuited for all the microgravity experiments we want to do. Separate rotating and non-rotating sections would be one way around this, but would be far more complex and expensive than either a rotating or non-rotating station. An ISS module containing a much smaller centrifuge was planned for doing small experiments at a variety of "gravity" levels, but was canceled due to cost overruns and lack of available Shuttle flights.

 

[nismaratwork]

I believe that we'll be genetically modifying ourselves for space LOOOONG before we bother to start moving worlds, or orbiting superdense objects. I am not including centrifugal simulation in this statement.

 

[Chronos]

Taming even a tiny black hole would be a formidable challenge. How would you make it 'sit' while building a spacecraft around it? It would be necessary to have an 'on/off' switch. The science necessary for black hole obedience school remains beyond our reach.

 

[Filip Larsen]

Taming even a tiny black hole would be a formidable challenge. How would you make it 'sit' while building a spacecraft around it?

Using (a lot of) electrical charge seems like a possibility.

 

[nismaratwork]

You see, this is why I'm thinking cybernetics and genetic modification before tame black holes.

 

[DLuckyE]

You could probably also create a very strong magnetic field to pull everything to one direction. Problem being ofcourse you won't be able to carry any ferromagnetic material since it would be pulled too hard towards the field.

But it's probably easier than creating a mini black hole ;)

 

[nismaratwork]

You could probably also create a very strong magnetic field to pull everything to one direction. Problem being ofcourse you won't be able to carry any ferromagnetic material since it would be pulled too hard towards the field.

But it's probably easier than creating a mini black hole ;)

Anything that strong would probably kill you, although I'm not sure. Certainly it wouldn't pay to have fillings... *wince*

 

[FawkesCa]

You could probably also create a very strong magnetic field to pull everything to one direction. Problem being ofcourse you won't be able to carry any ferromagnetic material since it would be pulled too hard towards the field. ;)

that would be great except the whole point to creating gravity would be so HUMANS (andthe such) could walk around. a magnetic field would only hold down metal things, not people... unless, like the nismaratwork insinuated, you had lot of fillings... or a Prince Albert... oooowwwwww

 

[utkarsh009]

Centrifugal simulated gravity is entirely possible. The radius of rotation required for comfortably low coriolis effects is large, but that can fairly easily be handled by using two sections attached by a long tether. It would be harder to dock with, but even this isn't really the biggest problem.

One of the biggest reasons to put a station into orbit in the first place is for the freefall environment...a rotating station would be rather unsuited for all the microgravity experiments we want to do. Separate rotating and non-rotating sections would be one way around this, but would be far more complex and expensive than either a rotating or non-rotating station. An ISS module containing a much smaller centrifuge was planned for doing small experiments at a variety of "gravity" levels, but was canceled due to cost overruns and lack of available Shuttle flights.

i totally agree with what cjameshuff said. scientist are looking forward to build a rotating spaceship to send people to Mars thus reducing the risk of muscle weakening or decay.

 

[DLuckyE]

that would be great except the whole point to creating gravity would be so HUMANS (andthe such) could walk around. a magnetic field would only hold down metal things, not people... unless, like the nismaratwork insinuated, you had lot of fillings... or a Prince Albert... oooowwwwww

Magnetic fields do work on everything, given they are strong enough. But I'm not sure if they would just hold you in place (like they do at the HFML) or if you could make them push you away.


You could of course also keep accelerating at 1g continuously, no idea where you'd get the fuel for that though =P

 

[nismaratwork]

Magnetic fields do work on everything, given they are strong enough. But I'm not sure if they would just hold you in place (like they do at the HFML) or if you could make them push you away.You could of course also keep accelerating at 1g continuously, no idea where you'd get the fuel for that though =P

I'm pretty sure a field that strong would interfere with your nervous system long before it was capable of producing anything like 1g equivalent for a human. You'd basically be in a non-stop EMP from hell, and by "interfere with" I mean kill horribly.

Rotational microgravity makes more sense anyway, substituting one pseudo force for another.

 

[Brett13]

couldnt you just place magnets in the floor of the station and on the bottom of your boots and on certain places of your body?

 

[nismaratwork]

couldnt you just place magnets in the floor of the station and on the bottom of your boots and on certain places of your body?

Magnetic boots would hold you to the deck, and assuming you had pressure switches to turn the magnets on your boots on and off to allow you to walk, it works. That has nothing to do with the lack of gravity on the rest of the body, and magnets on your body would simply cause local strain. Gravity is more than just "glue" keeping you on the floor.

 

[DaveC426913]

Magnetic boots would hold you to the deck, and assuming you had pressure switches to turn the magnets on your boots on and off to allow you to walk, it works.

You wouldn't need to turn the magnets on/off.
1] You'd make the floor/boots so that there was only enough attraction to hold you to the deck, easy enough to pull away from with moderate effort.
2] You wouldn't have to pull away directly, you'd use a labour saving mechanism. Consider the lowly fulcrum. Your boots (or sandals) would have a convex sole, with magnets only at the toe and heel. Rolling forward on them would pull the magnets away from the deck using a very fluid, natural motion. Once the magnets are more than a small distance from the deck, the pull is vastly reduced* (magnetic field falls off as the cube. This is why fridge magnets fall off the fridge so easily.)


*This is also why attaching magnets at various points on your body wouldn't work. A magnet attached to your elbow could be calibrated to provide a natural amount of "weight". But if your elbow for some reason were to go from a height of 3.5feet to 1.75feet, the pull on it would increase drastically - by eight times.

 

[nismaratwork]

You wouldn't need to turn the magnets on/off.
1] You'd make the floor/boots so that there was only enough attraction to hold you to the deck, easy enough to pull away from with moderate effort.
2] You wouldn't have to pull away directly, you'd use a labour saving mechanism. Consider the lowly fulcrum. Your boots (or sandals) would have a convex sole, with magnets only at the toe and heel. Rolling forward on them would pull the magnets away from the deck using a very fluid, natural motion. Once the magnets are more than a small distance from the deck, the pull is vastly reduced* (magnetic field falls off as the cube. This is why fridge magnets fall off the fridge so easily.)


*This is also why attaching magnets at various points on your body wouldn't work. A magnet attached to your elbow could be calibrated to provide a natural amount of "weight". But if your elbow for some reason were to go from a height of 3.5feet to 1.75feet, the pull on it would increase drastically - by eight times.

Good point, and even if you did simulate the weight with electromagnets on the body that altered intensity with distance from the deck, I'm not sure that it would change the effect of microgravity on the bones and organs. Needless to say, you would also be walking death for any unshielded electronics.

 

[markjohn82]

Could you then not just have part of the ship (where the crew spend most of their time) spinning to simulate gravity and then have magnetic boots for ease of travel around the rest of the ship?

 

[markjohn82]

How long does the human body need in a gravitaional environment, could the bodies needs be met during sleep time?

 

[nismaratwork]

How long does the human body need in a gravitaional environment, could the bodies needs be met during sleep time?

I'm sure that something is better than nothing, but it would be an extension, not amelioration.

Markjohn82: That's basically the idea to begin with, given a habitation ring, and then areas adapted for a microgravity environment, with the goal being something like DaveC's description of magnetic boots.

 

[DaveC426913]

...DaveC's description of magnetic boots.

Of course, we're 4 decades late for solutions to this. In 2001 A Space Oddysey, they simply used velcro - a much more practical solution than magnets.

 

[Brett13]

Mentioning 2001 reminded me of something, along with the avatar, could we put the astronauts in a hypersleep or something? They wouldn't be using their muscles so could it somehow negate the effect of the no gravity?

 

[nismaratwork]

Mentioning 2001 reminded me of something, along with the avatar, could we put the astronauts in a hypersleep or something? They wouldn't be using their muscles so could it somehow negate the effect of the no gravity?

There is plenty of research into induced hibernation, such as the use of Hydrogen Sulfide, but we're nowhere near "hypersleep".

 

[russ_watters]

How long does the human body need in a gravitaional environment, could the bodies needs be met during sleep time?

When you're sleeping your heart isn't pumping uphill and none of your other muscles are working, so no.

 

[spikenigma]

I've heard it proposed that an Elecromagnetic Field bends spacetime but can be blocked in various ways.

If you can generate a field of sufficient strengh to have a significant gravitational (bending of spacetime) component but block the field itself perhaps?

 

[DaveC426913]

I've heard it proposed that an Elecromagnetic Field bends spacetime but can be blocked in various ways.

If you can generate a field of sufficient strengh to have a significant gravitational (bending of spacetime) component but block the field itself perhaps?

But why bother? If you're going to expend this much effort to create gravity, there's a really easy resource that provides it: mass. Make your space station really massive - enough to make gravity a factor.

The energy required to power up your EMF to the point where it bends spacetime is going to be on the order of the energy involved in moving an asteroid-sized space station around anyway, so why make a Rube Goldberg device to get the same result?

 

[spikenigma]

But why bother? If you're going to expend this much effort to create gravity, there's a really easy resource that provides it: mass. Make your space station really massive - enough to make gravity a factor.

The energy required to power up your EMF to the point where it bends spacetime is going to be on the order of the energy involved in moving an asteroid-sized space station around anyway, so why make a Rube Goldberg device to get the same result?

As has been hinted at earlier in the thread, generating the field is * easier.

The energy moving an asteroid-sized space station around to generate a gravitational field of 9.8 m/s is going to be several orders of magnitude less than accellerating and decellerating a mass equivilent to planet Earth wherever you want to go.

* Nothing is "easy" about this scenario of course :)

 

[DaveC426913]

As has been hinted at earlier in the thread, generating the field is * easier.

Where?

The energy moving an asteroid-sized space station around to generate a gravitational field of 9.8 m/s is going to be several orders of magnitude less than accellerating and decellerating a mass equivilent to planet Earth wherever you want to go.

Sorry -point of order- we're mixing up ideas. My suggestion was that an asteroid-sized space station would be big enough to create sufficient real gravity (but less than Earth's gravity). If the intent is to create gravity equivalent to 9.8ms^2, then that's different.

So let's set some benchmarks. I'll go with yours. We want to make our space station have gravity of 1 Earth g.

1] Tell me why you are convinced that it would take "several orders of magnitude less energy" to produce 1g by way of an EMF than it would to simply move around an Earth-sized body. I am not convinced it would.


2] You wouldn't actually need an Earth mass body. We feel 1g because we are ~4000mles from the gravitational point source. A smaller, denser and much less massive body would accomplish the same thing. It should be calculable how small a mass you'd need.

 

[spikenigma]

Where?

Post 16, but then he went on to talk about micro-blackholes, so perhaps not!

Sorry -point of order- we're mixing up ideas. My suggestion was that an asteroid-sized space station would be big enough to create sufficient real gravity (but less than Earth's gravity). If the intent is to create gravity equivalent to 9.8ms^2, then that's different.

A space station is easier since you don't have to move it nor power your artificial gravity - whether you need to rotate it or not. I was thinking of a starship.

So let's set some benchmarks. I'll go with yours. We want to make our space station have gravity of 1 Earth g.

1] Tell me why you are convinced that it would take "several orders of magnitude less energy" to produce 1g by way of an EMF than it would to simply move around an Earth-sized body. I am not convinced it would.

I'll say from the outset that I am in no way qualified in the field we are talking about to provide calculations on this, and would happily accept them from anybody who cares to have a go in the thread.

My view is based on this:

http://www.sciencedaily.com/releases/2006/03/060325232140.htm - beware popular science magazine

http://esamultimedia.esa.int/docs/gsp/Experimental_Detection.pdf - experimental paper

Which produced a gravitomagnetic field 100 millionths that of Earth.

Obviously, the field scales up geometrically based on speed of rotation, strength of magnetic field, size of super-conductor, charge of super-conductor etc...

However, back-of-the envelope below and assuming it scales up linearly to give a fair minimum:

Let's say (perhaps erroneously) that this small lab uses a tenth of the LHC's annual 800,000 Megawatt hours running this specific experiment constantly - so 80'000 Mwh or 2.88x10^14 joules. Multiply by 10^9 is 2.88x10^23 J annually for an Earth-strength field.

CharlesP (https://www.physicsforums.com/archive/index.php/t-63459.html) seems to suggest that moving the Earth to any appriciable degree would take approximately 4.18 x 10 ^15 joules every 10 seconds for a billion years in one megaton bombs. A total of 1.3x10^31 J to move the Earth. To say nothing of deceleration or damage to the body.

2] You wouldn't actually need an Earth mass body. We feel 1g because we are ~4000mles from the gravitational point source. A smaller, denser and much less massive body would accomplish the same thing. It should be calculable how small a mass you'd need.

You'd still need to move it, would the extra-terristial mining, manufacture and moving of this body take less than 2.88x10^23 J annually? - in the null case my point still stands

 

[nismaratwork]

Why would a ship not have a rotational habitat area around a central axis?

 

[DaveC426913]

Why would a ship not have a rotational habitat area around a central axis?

Have you been following the thread? We're looking for alternate forms of artificial gravity. A centrifuge is only one method and it has its drawbacks.

 

[DrGreg]

So let's set some benchmarks. I'll go with yours. We want to make our space station have gravity of 1 Earth g.

...

2] You wouldn't actually need an Earth mass body. We feel 1g because we are ~4000mles from the gravitational point source. A smaller, denser and much less massive body would accomplish the same thing. It should be calculable how small a mass you'd need.

Dickfore has already covered this in post #7, but here's another way of putting it. A planet of half the Earth's radius but the same density would have half the surface gravity (it turns out), so to maintain the same gravity you'd have to double the density. There's a maximum density that would be possible with ordinary matter, so that puts a (pretty large) limit on the minimum sized planet with 1 g surface gravity. This makes this method practically infeasible, at least until we find a way of creating a tame mini black hole.

 

[nismaratwork]

Have you been following the thread? We're looking for alternate forms of artificial gravity. A centrifuge is only one method and it has its drawbacks.

We covered all the possibilities from miniature black holes to magnetic fields that would fricassee your nervous system. I would say the same conclusion is the substitution of the pseud-force for another. Did you read Spike's post? He specifically compared a rotation STATION with a ship, and I was pointing out that a ship need not lack a centrifugal component... do you have an alternative suggestion?

 

[DaveC426913]

... that puts a (pretty large) limit on the minimum sized planet with 1 g surface gravity. This makes this method practically infeasible...

Agreed. My point was simply that some EM force-field powerful enough to create a gravity well would likely use an equivalent amount of energy as it would take to throw a planet around. IMO.

 

[SkepticJ]

The best thing to do, in the long run, will be to alter our biology to where lack of gravity won't weaken us. That, or become machines without the weaknesses of meat.

Nearer term, just use two centrifuges spinning in opposite directions, or a smaller, high speed flywheel spinning counter to the rotation of the centrifuge. That'll take care of the pesky gyroscopic effects of the centrifuge(s).

You just have to live with the Coriolis effect, but if you make your wheel with a big enough diameter, at least it won't make the occupants sick when they move their heads around.

 

[DaveC426913]

The best thing to do, in the long run, will be to alter our biology to where lack of gravity won't weaken us. That, or become machines without the weaknesses of meat.

Gravity serves other purposes than keeping our bones strong. It keeps our feet on the floor and the butcher knife on the countertop. Either of those floating around a room can be bad. Both of those floating around a room can be double plus bad.

 

[Chronos]

Gravitational fields are carried by integer spin particles, EM fields are the product of a half spin particle.

 

[Ich]

Gravitational fields are carried by integer spin particles, EM fields are the product of a half spin particle.

Even and odd numbers, not integer and half.

 

[nismaratwork]

The best thing to do, in the long run, will be to alter our biology to where lack of gravity won't weaken us. That, or become machines without the weaknesses of meat.

Nearer term, just use two centrifuges spinning in opposite directions, or a smaller, high speed flywheel spinning counter to the rotation of the centrifuge. That'll take care of the pesky gyroscopic effects of the centrifuge(s).

You just have to live with the Coriolis effect, but if you make your wheel with a big enough diameter, at least it won't make the occupants sick when they move their heads around.

https://www.physicsforums.com/showpost.php?p=2781702&postcount=12

Yep, I agree.

DaveC: Not just objects which can be dangerous in 1g; liquids can become very hazardous or at least a terrible mess, and of course there is the issue of bacterial growth in microgravity.

 

[DaveC426913]

...of course there is the issue of bacterial growth in microgravity.

What effect does microgravity have on bacterial growth?

[EDIT] I can see it impeding bacterial growth, but I got the impression you were suggesting growth would become problematic for occupants. I could be misinterpreting.

[EDIT EDIT] Oh yeah. Impaired bacterial growth in our bodies could negatively impact our health.

 

[nismaratwork]

What effect does microgravity have on bacterial growth?

[EDIT] I can see it impeding bacterial growth, but I got the impression you were suggesting growth would become problematic for occupants. I could be misinterpreting.

[EDIT EDIT] Oh yeah. Impaired bacterial growth in our bodies could negatively impact our health.

Re: Edit Edit: Exactly!

 

[SkepticJ]

Gravity serves other purposes than keeping our bones strong. It keeps our feet on the floor and the butcher knife on the countertop. Either of those floating around a room can be bad. Both of those floating around a room can be double plus bad.

Magnets, gecko-like adhesive, velcro, clips, straps, bungee cords . . . can all secure things you don't want floating around when you're not using them.

Zero gravity is so much more useful. You get http://www.kschroeder.com/my-books/sun-of-suns/engineering-virga" that way.

You can manufacture novel materials in zero gee because liquids of different densities don't separate. You can grow large, perfect crystals without the constraint of gravity. Though with molecular manufacturing, these would probably be obsolete reasons for manufacturing materials in zero gee.