# Artificial gravity in a rotating space station

## Main Question or Discussion Point

It is often proposed that gravity could be simulated on a space station by rotating around an axis, such that the astronaut experiences the centripetal force of the space station wall, analogously to gravity. It is usually mentioned that the radius of rotation must be very large to avoid significant Coriolis effect being experienced by the astronaut. My question is this:

Could Coriolis effects be cancelled by some weird tumbling or precessing program of spin? I imagine this could be accomplished with a constant expenditure of thrust, but what about something inertial, even if it required gyroscopes or whatever?

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sophiecentaur
Gold Member
some weird tumbling or precessing program of spin?
Wow, what a strange environment you are suggesting. Actually, the occupants would be far more likely to learn to cope with a very predictable effect like a moderate Coriolis, once they get their sea / space legs. When they return to Earth they are just as likely to fall over without the effect - 'the sways' is a common experience that people get when they return from a few days at sea and stand in their kitchen whilst washing dishes etc..
And I agree with @A.T. of course!

anorlunda
Mentor
jrmichler
You can study this yourself by riding the Gravitron. Just sit up and move your head around.

And Wikipedia: https://en.wikipedia.org/wiki/Gravitron. I know for a fact that Coriolis effects forced me to lay down on the grass for an hour after one ride, while my then 12 year old daughter rode it continuously for hours. Google motion sickness centrifuge for lots of good information.

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sophiecentaur
Gold Member
You can study this yourself by riding the Gravitron. Just sit up and move your head around.
View attachment 232128

And Wikipedia: https://en.wikipedia.org/wiki/Gravitron. I know for a fact that Coriolis effects forced me to lay down on the grass for an hour after one ride, while my then 12 year old daughter rode it continuously for hours. Google motion sickness centrifuge for lots of good information.
I can feel quite nauseous enough after a few rotations of the little roundabout in my granddaughter's local kiddies' playground. I think it's the mucus in my 'tubes'. I definitely no longer have the 'right stuff'. Also, when tacking on my sailboat, Coriolis used to spoil my sense of direction as I tried to change sides in the cockpit and found I was moving diagonally.

Look at the formula:
https://en.wikipedia.org/wiki/Coriolis_force#Formula
Can you make it zero for all values of v, by changing Ω over time?
My ability to work with vectors is poor I'll admit, but the simple answer seems to be no, right? It is not possible to make Ac zero by changing the angular velocity over time. And would this take into account the possibility of rotation around a separate axis, such as spinning around the radius of the primary rotation? I suppose such an additional rotation would introduce an additional Coriolis acceleration...

You can study this yourself by riding the Gravitron. Just sit up and move your head around.
View attachment 232128

And Wikipedia: https://en.wikipedia.org/wiki/Gravitron. I know for a fact that Coriolis effects forced me to lay down on the grass for an hour after one ride, while my then 12 year old daughter rode it continuously for hours. Google motion sickness centrifuge for lots of good information.
The Gravitron is a fixture from my county fair childhood- just the thought experiment of moving around in there makes me queasy. I never had the right stuff. I remember hurling from it, though thankfully not inside the gravitron itself- my lunch came up on the cool down lap on the pirate ship!

A.T.
And would this take into account the possibility of rotation around a separate axis, such as spinning around the radius of the primary rotation?
You still get one net Ω.

You still get one net Ω.
That's the fundamental insight I was missing. I can see why it is the case. Thanks!

.Scott
Homework Helper
The real problem is not the corriolis effect but simply the angular velocity.
The higher that angular velocity, the bigger the problem astronauts will have when they change the orientation of the head. For example, they may acclimate to running around with the spin of the station. But then sitting down at a desk and facing in a different direction will take some recovery.

Here is a good article:

From https://flightsafety.org/hf/hf_jul-aug95.pdf

DaveC426913
Gold Member
Also, when tacking on my sailboat, Coriolis used to spoil my sense of direction as I tried to change sides in the cockpit and found I was moving diagonally.

I have this image of you diving for the port gun'le and instead finding yourself below, sprawled across the dinette.

"I think I made a wrong toin at Albaqoickie..."

sophiecentaur
Gold Member

I have this image of you diving for the port gun'le and instead finding yourself below, sprawled across the dinette.

"I think I made a wrong toin at Albaqoickie..."
Haha. Its could happen if I were not hanging onto the tiller! Fact is, the part of the boat that my brain was aiming at and which my body control was using is not there any more. I reckon that's how we could describe the (fictitious) Coriolis Force. Physics was not uppermost in my mind at such times but I guess a really competent helms person would be doing those sums automatically during all manoeuvres. It's part of getting your sea legs, I suppose.

sophiecentaur
Gold Member
You still get one net Ω.
True but there is also an unexpected translation. That's related to Coriolis even when you are moving your head to change view of the inside of the cabin. I think that the condition where these effects come is could well be related to differences between what's experienced by each sides of our balance mechanism. I hesitate to use the phrase 'what's really happening' . . . . . but there's an explanation in there somewhere.

A.T.
The real problem is not the corriolis effect but simply the angular velocity.
And how exactly does angular velocity cause a problem?

Here is a good article:

From https://flightsafety.org/hf/hf_jul-aug95.pdf
According to the article, human sensory organs detect angular accelerations, not constant angular velocity.

.Scott
Homework Helper
And how exactly does angular velocity cause a problem?
According to the article, human sensory organs detect angular accelerations, not constant angular velocity.
I addressed this in my original post.
People will soon adapt to a constant angular velocity (in less than a minute according to the article).
But every time they reposition their head, the clock starts over. So if you walk in a straight line for 1 minute, you're OK. But before you start a turn to the left or right, you may want to close your eyes and keep them closed well after the you have completed the turn.

But the problem is not just a matter of discomfort. The motion information is used with eye movement - so when you're "dizzy" from turning, everything seems to be moving. Your eyes will not properly track stationary objects - like a control panel or computer terminal.

For pilots, this falls under the category of vertigo and spacial disorientation - and is often fatal. It may not be fatal for the space station occupant, but there is a technique that can be borrowed from pilots to deal with this. If you shake your head vigorously, you can scramble your inner ear balance mechanism and temporarily shut it down. This will give you back your vision.

anorlunda
Mentor
For pilots, this falls under the category of vertigo and spacial disorientation - and is often fatal. It may not be fatal for the space station occupant, but there is a technique that can be borrowed from pilots to deal with this. If you shake your head vigorously, you can scramble your inner ear balance mechanism and temporarily shut it down. This will give you back your vision.
Wow, thanks for sharing that. I was never taught that in my pilot training. It sounds very sensible.

A.T.
People will soon adapt to a constant angular velocity (in less than a minute according to the article).
Yes, the fluid in the inner ear canals stops flowing after a while. So when your head keeps a fixed orientation w.r.t to the rotating station you don't perceive the rotation.
But every time they reposition their head, the clock starts over.
But why exactly is it different from turning your head in a non-rotating station? It is because the fluid in the inner ear canals starts flowing in a different way, than it would in a non-rotating station. And from the frame of the rotating station this difference is attributed to the Coriolis force, which affects the fluid, as soon it starts moving w.r.t to the station due to the head rotation.

Your original statement that the Coriolis effect is not the problem, doesn't make much sense to me. It's a matter of the chosen reference frame what you attribute the sensory difference to.

jbriggs444
Homework Helper
2019 Award
But why exactly is it different from turning your head in a non-rotating station?
If you turn your head in a rotating station, Coriolis can cause an unexpected circulation in the fluid at right angles to the rotation you initiated. If you turn your head in a non-rotating station, this does not occur.

sophiecentaur
Gold Member
If you turn your head in a rotating station, Coriolis can cause an unexpected circulation in the fluid
Also, the two sides of your head can have different radii of rotation about the ship's axis. The two different degrees of Coriolis Force would certainly be "unexpected".
If you shake your head vigorously, you can scramble your inner ear balance mechanism and temporarily shut it down.
I suspect this accounts for how dancers can avoid vertigo by 'spotting' at a fixed spot during each rotation.

jbriggs444
Homework Helper
2019 Award
Also, the two sides of your head can have different radii of rotation about the ship's axis. The two different degrees of Coriolis Force would certainly be "unexpected".
But radius does not appear in the formula for Coriolis force. $F=2mv \times \omega$

.Scott
Homework Helper
But why exactly is it different from turning your head in a non-rotating station? It is because the fluid in the inner ear canals starts flowing in a different way, than it would in a non-rotating station. And from the frame of the rotating station this difference is attributed to the Coriolis force, which affects the fluid, as soon it starts moving w.r.t to the station due to the head rotation.

Your original statement that the Coriolis effect is not the problem, doesn't make much sense to me. It's a matter of the chosen reference frame what you attribute the sensory difference to.
Let's say that you begin by facing the same direction as the rotation of the spaceship. You are now have perpetual pitch-up angular velocity. After a minute or two, you will acclimate to this. Then you turn around 180 so you are looking back opposite the direction of rotation. This is a perpetual pitch down angular velocity - the opposite of what you have adapted to.

This is not Coriolis affect. This is an attempt by you inner ear to estimate angular acceleration and velocity - to assist with walking and seeing.

When I did the pilot physiological training at Andrews AFB (decades ago), one of the exercises was a simulated and enclosed cockpit that turned in one direction. There was no visual reference to anything outside of the cockpit. Initially the turning was somewhat noticeable, then not noticeable at all. But then we would be given an instruction to squawk a code - which required that we turn our head down towards the floor to operate the transponder. Upon lifting my head back up again, I had the very strong feeling that I was now in a stiff right turn. So I prepared for a correcting maneuver by focusing on the pitch indicator for feedback. Of course, that indicator correctly showed that I was still in straight and level flight.

Here's the link to that same article. It's only four pages long: https://flightsafety.org/hf/hf_jul-aug95.pdf

One of the many points made in that article is this:
It takes about one degree per second per second of acceleration to stimulate the semicircular canal sensory organ. In other words, in order to keep stimulating these canals with turning, one has to increase the acceleration to two degrees per second by the end of the second second and three degrees per second by the end of the third second and so on.
If the angular acceleration ceases, and a constant rate of turn occurs, the semicircular canals will cease to detect the constant angular velocity.
This is important information related to the OP. If the station if turning at 1 degree per second and an occupant turns 180 degrees - he will be changing his angular velocity from +1deg/sec to -1deg/sec. Thus we should expect he will fully recover in about 2 seconds. But that would require a diameter of more than 6 Km to generate 1G.
From an engineering perspective, that 2 second period puts a limit on what the inner ear will detect. With a little compromise, we could probably make due with 5deg/sec and 0.8Gs - getting our diameter down to about 1Km. But I would do some experiments before building such a monster.

jbriggs444
Homework Helper
2019 Award
This is not Coriolis affect. This is an attempt by you inner ear to estimate angular acceleration and velocity - to assist with walking and seeing.
I believe that this is the Coriolis effect -- acting on the fluid in the inner ear, creating the perception that you report.

.Scott
Homework Helper
I believe that this is the Coriolis effect -- acting on the fluid in the inner ear, creating the perception that you report.
It may be. But we are talking about a fluid running through an enclosed circular path - not the usual setup for the Coriolis Force.
To put this in terms of the Coriolis Force, we would be considering the inner ear fluid as the recipient of this force. But there is no possibility for that fluid to follow a "Coriolis trajectory" since it is fully confined. The force applied to walls of the canals is not what is measured. And the velocity of the fluid along the circular path is affected by the net Coriolis Force integrated around the entire circuit - which as a first order approximation would tend to zero out any Coriolis effect.

I don't doubt that this could still be described as a Coriolis Force, but given the overall mechanism, it is more directly the work of angular acceleration, friction, and the sensor response.