Artificial gravity in spinning space ship conumdrum

[nuby]

I read that discussion, and almost everything makes sense to me. The thing I see making artifical gravity impractical are the issues astronauts would have with nausea, disorientation, etc. One thing confusing to me is the coriolis effect the astronauts would experience. If an astronaut was standing still in the rotating ship, why would he not experience a coriolis (not sure if this the best term) affect?

It seems since his head and feet would be moving at two different speeds (from an outside reference point), he might experience some sort of (rotating) force from that, even while not moving.

Shooting Star, if you have any more questions for me, send a private message. Since I can't say what I think here.

 

[Shooting Star]

I read that discussion, and almost everything makes sense to me.

HEAR THAT, FELLAS? One up for PF.

The thing I see making artifical gravity impractical are the issues astronauts would have with nausea, disorientation, etc.

That has nothing to do with rotating frames and inertial forces, and need not be discussed here. Many people throw up when traveling by car.

One thing confusing to me is the coriolis effect the astronauts would experience. If an astronaut was standing still in the rotating ship, why would he not experience a coriolis (not sure if this the best term) affect? It seems since his head and feet would be moving at two different speeds (from an outside reference point), he might experience some sort of (rotating) force from that, even while not moving.

The Coriolis force is given by -2wXv. This v is wrt the rotating frame, not the "stationary" inertial frame of reference. So, if an astronaut is standing still in the rotating frame, the velocities of all mass points on him is zero wrt the rotating frame. So, v is 0 for all points on his body and the Coriolis force on him is 0.

As you said, his head and feet has two different velocities wrt the IFR, but that has nothing to do with the Coriolis effect. You have to measure velocities wrt the rotating frame.

But the centrifugal force on his head and feet would be different, because they are at different distances from the rotating centre. It may not be noticeable if his distance from the centre is large compared to his height. Even on earth, out head and feet experiences different gravity.

I won't discuss anymore for fear of confusing you with something. Try to understand the Coriolis force. Read that discussion again if you have confusion. Think of something moving with uniform velocity inside a rotating shell, and what you see as st line motion becomes a spiral trajectory wrt the shell. That is what the Coriolis force basically is all about.

Shooting Star, if you have any more questions for me, send a private message. Since I can't say what I think here.

You can PM me any time.

If anybody asks you a question, and you answer honestly without expressing your own opinion, then I believe and hope that you won't get any points any more. I did not unsubscribe because at the last moment I thought you were not able to communicate properly, and also lacked some knowledge. Others will understand that too. But no more comments like in space things are different. Space is the same everywhere, at least for the purpose of our discussion.

And, remember, psychological or even technological issues are not very relevant in theoretical discussions.

 

[linton]

I read that discussion, and almost everything makes sense to me. The thing I see making artifical gravity impractical are the issues astronauts would have with nausea, disorientation, etc. One thing confusing to me is the coriolis effect the astronauts would experience. If an astronaut was standing still in the rotating ship, why would he not experience a coriolis (not sure if this the best term) affect?

It would have to be a pretty tiny spaceship if nausea was a major problem. Specifically because if they actually employed this method in the design they would increase the ring diameter so that the rotational speed would be less, to create the same centripetal force.

 

[LURCH]

Maybe this image will chaneg the way things look;

NASA's "Mars Express" plan, to get astronauts to Mars, includes a plan to spool out the capsule, in which they will spend most of the trip, on the end of a long cable. On the other end will be the final booster stage of the rocket. The two objects will be set spinning around each other (the cenetr of thwe cable will eb nearyl staionary). This will provide a downward push to keep the astronauts pressed against the floor, keeping them healthy and making many ordinary tasks easier.

Nuby, when you think of it that way, with the center of rotation outside of the capsule, does it make any difference?

 

[DaveC426913]

It would have to be a pretty tiny spaceship if nausea was a major problem. Specifically because if they actually employed this method in the design they would increase the ring diameter so that the rotational speed would be less, to create the same centripetal force.

Even in a medium-sized spaceship, the astronaut is still spinning about an axis - it just happens to be an axis that is an arbitrary number of metres over his head. You're going to feel it.

 

[Shooting Star]

It would have to be a pretty tiny spaceship if nausea was a major problem. Specifically because if they actually employed this method in the design they would increase the ring diameter so that the rotational speed would be less, to create the same centripetal force.

That is one of the most sensible comments I’ve encountered in this thread.

Even in a medium-sized spaceship, the astronaut is still spinning about an axis - it just happens to be an axis that is an arbitrary number of metres over his head. You're going to feel it.

Is this your feeling or have you got any numbers to show?

Let us take some conservative estimates and do the math.

1. Radius of the rotating space station is 100 m.
2. The angular speed w is such that the centrifugal acceleration equals 9.8 m/s² at the rim.
3. A typical astronaut is, say, 2m tall.
4. He walks at a pace of 5 km/hr = (25/18) m/s.

The difference between the centrifugal acceleration at his feet and head is 0.02 g. This is the “tidal force” when he is not moving wrt the station. I don’t think the human body can sense this variation in g between the head and the foot.

More concern has been shown here about the Coriolis effect. It is maximum when the velocity is perpendicular to the axis of rotation, that is, when he walks along a latitude of the cylinder, and the value turns out to be 0.089 g, which is less than 9/100 than g at earth’s surface. Generally, it will be less than this.

So, when he walks, he may have to compensate for this force. Remember, this is a small space station compared to what people have in minds for the future. (The ISS is around 120 m across, just for the purpose of comparison.) For bigger stations, the Coriolis force will be much less, and people will not notice it or will get habituated to it if it is small but appreciable.

Do not compare the effects of rotations in small or even big centrifuges with effects on a rotating space station.

 

[DaveC426913]

Let us take some conservative estimates and do the math.

1. Radius of the rotating space station is 100 m.

Well we were talking about a spaceship, and a spaceship of 100m diameter is anything but conservative.

That being said, there's no need to belabour it; we'll talk about space stations.

 

[blunt187]

Shooting star is the Man! or woman?

ok I'm just a college dropout who found this webpage on a humbug. Artificial graivty, or should I say mechanically produced gravity? would definitely work if the station is spining around fast enough at a steady space, as long as it is a large enough, and on a constant axis(how large I don't know, but i looked at the video link and sure enough, it seemed to be working pretty well!) . It doesn't really matter if gravity is affecting it or not becuase it is going to affect the whole thing including the people equally (unless it's like a black hole or some weird outer space thing I don't know about). Think of the carnival ride once again (I believe there is a link to it up above in this thread). Imagine that, on a giant robotic arm, it doesn't matter if they turn it upside down or sideways those people are still going to stick to that wall. Unless the giant arm turned em upside down and shook em like it was trying to get the last drop of ketchup out of a glass bottle, which i think would be cool, especially if nuby was on it. j/k :-)

 

[KenJackson]

would definitely work if the station is spining ... It doesn't really matter if gravity is affecting it or not ... Think of the carnival ride once again (I believe there is a link to it up above in this thread). Imagine that, on a giant robotic arm, it doesn't matter if they turn it upside down or sideways those people are still going to stick to that wall.

Spinning? Who says the carnival ride is spinning and not the Earth? Who nominated the Earth to be the center of the universe?

It's easy to slip into classic absolute space thinking. Though the question isn't absolutely answered yet, I'm still pleased enough by what was said earlier.

I was pleased that someone mentioned Mach's Principle, which caused me to find the wikipedia discussion on the same. I am content to learn that Einstein grappled with the issue and decided that inertia originates in a kind of interaction between bodies. That is, (as I understand it) the presence of other matter (I guess all matter in the universe) determines what is and is not spinning.

 

[atyy]

The Earth is a spinning spaceship - with artificial gravity - in the "wrong" direction! See D H's comment on how the centrifugal force affects pendulums at the equator (post #3 pf this thread):

https://www.physicsforums.com/showthread.php?p=1868564#post1868564

 

[atyy]

I was pleased that someone mentioned Mach's Principle, which caused me to find the wikipedia discussion on the same. I am content to learn that Einstein grappled with the issue and decided that inertia originates in a kind of interaction between bodies. That is, (as I understand it) the presence of other matter (I guess all matter in the universe) determines what is and is not spinning.

I think even in General Relativity, rotation is absolute, in the sense that it produces a gravitational field without a matter source. The other common absolute motion in GR texts is the uniformly accelerating rocket, which also produces a gravitational field without a matter source.

 

[Nick666]

For anyone planning to check in at the Centrifugal Space Station, remember to sit your *** and put your furniture on the far ends of the space station.

 

[Shooting Star]

Spinning? Who says the carnival ride is spinning and not the Earth? Who nominated the Earth to be the center of the universe?

It's easy to slip into classic absolute space thinking. Though the question isn't absolutely answered yet, I'm still pleased enough by what was said earlier.

It is also easy to simplify the matter to an extent where metaphysics takes precedence over Physics. Mach’s Principle, though a guiding light for Einstein, need not be last word. In addition, the principle itself indicates that nearby masses should have an appreciable effect on the motion of a body. Taking the view that the carnival ride can be described completely by considering relative rotations would be too simplistic.

I think even in General Relativity, rotation is absolute, in the sense that it produces a gravitational field without a matter source. The other common absolute motion in GR texts is the uniformly accelerating rocket, which also produces a gravitational field without a matter source.

Please remember that all these results apply to our universe, where there is a background of matter, distant or otherwise. Otherwise, what would we measure the rotation against? (Please don't say with accelerometers.) That is the whole spirit behind Mach’s Principle. We have to find a different universe and conduct some experiments before conclusively stating how much of an effect the distant or nearby matter have on the motion with respect to any frame of reference.

(As far as I remember vaguely, there are matter-free solutions to the GR Equations, though I must admit that I am not familiar with their status in accepted science.)

[About "Shooting star is the Man! or woman?", please look up my profile, which contains a single entry. However, due to the way language and society have evolved, "name_of_woman is the the woman!" doesn't quite deliver the original connotation...]

 

[atyy]

Please remember that all these results apply to our universe, where there is a background of matter, distant or otherwise. Otherwise, what would we measure the rotation against? (Please don't say with accelerometers.) That is the whole spirit behind Mach’s Principle. We have to find a different universe and conduct some experiments before conclusively stating how much of an effect the distant or nearby matter have on the motion with respect to any frame of reference.

Well, it's a bit unclear what Mach's Principle is. General Relativity respects some form of Mach's Principle in the sense that the local gravitational acceleration of a test particle is inertial (ie. an accelerometer measures zero). I'm not sure I'm recalling correctly, but I believe "General Relativity" by Hobson, Efstathiou, and Lasenby actually exclude rotated frames from being considered inertial, and call this "Mach's Principle"!

 

[schroder]

Shooting Star, Like other have explained, I think the coriolis effect will be at play in a rotating spaceship (and on earth). But, I'm wondering if the magnitude of the effect is a greater in space, and how it is calculated in space or on land (moon, earth, etc).

From reading this one cannot avoid the conclusion that there is a lot of confusion concerning gravity and centripetal acceleration. This is understandable since gravity is a centripetal acceleration, but generally when we speak of centripetal acceleration we are not speaking about gravity! Gravity, as far as we know, is not related to rotation, but is directly proportional to mass and indirectly proportional to the square of the distance. Centripetal acceleration is directly proportional to the velocity of rotation and the inversely proportional to the distance from the axis of rotation. The idea of utilizing centripetal acceleration to simulate the force of gravity does certainly have it’s merits. Since the earliest days of orbital space flight it became apparent that humans who are removed from the force of gravity as well as electromagnetic fields suffer biological consequences. The excuses which were used in the 1960’s, such as, “He slipped and fell in the shower”, for returning astronauts, are no longer offered or accepted. But a great deal more research needs to be done to determine if this form of “gravity substitute” is indeed viable, as it may well have serious long-term health consequences. The first thing to realize is that the force of centripetal acceleration due to rotation, while generating a similar force magnitude, is not the same as the force of gravity. On the surface of the earth, the force of gravity can be calculated from the equation: g = G x M / r^2 Where G is the gravitational constant of 6.67 x 10^-11, M is the mass of the Earth 5.98 x 10^24 kilograms and r is the radius of the Earth 6.37 x 10^6 meters. This results in a gravitational acceleration of ~ 9.8 m/s^2. Now, for an astronaut, or any human, who has the height of 2 meters, this gravitational force will vary along his height, from head to toe, by a factor of only one part in ten million. So essentially, there is no variation in gravity along the height/length of a human on the surface of the earth. However, the centripetal acceleration, and thus centripetal force, exerted on this same astronaut who is inside a spacecraft which employs rotational centripetal acceleration to simulate the force of gravity will experience quite a bit of variation along his 2 meter height. If we assume a spacecraft of one kilometer in length, from the axis of rotation, it will need to have an angular velocity of 0.099 rad per second to achieve a centripetal acceleration which is the same as gravity, 9.8 m/sec^2. Due to the astonauts’ height of 2 meters, the radius from the axis is now 998 meters and with the same angular velocity the centripetal acceleration will be only 9.78 m/sec^2. This may not seem to be much of a variation, but it certainly is not a trivial consideration! This represents a variation of 2 parts in one thousand, compared to the one part in ten million on the surface of the earth. No one can say what the possible biological consequences may be of this increased variation of about five orders of magnitude over a long length of time. Obviously, much more research needs to be done in this area.