Resources for physics of artificial gravity in science fiction?

[Brian G Turner]

I'm sure we've had resources written about or linked to here previously, about the physics of artificial gravity in science fiction. I'm thinking specifically about the use of rotating space stations and what sort of limitations are imposed by using them.

For example, in my WIP I had originally imagined multiple decks within a rotating cylinder, but now I'm wondering how many I can have before changes to the radius result in significant changes to the acceleration that humans would notice. However, I'm struggling to find any online articles and equations that would provide clear answers to this.

Did we have something posted here before? If not, does anyone have any pointers?

 

[Daysman]

Oh, is it the rotational issue -- how small the radius can be, before your crew get disoriented / begin to puke?

 

[Serendipity]

If you have a constant speed of rotation then,

Centrifugal Force = mass . speed . speed / radius

where the radius is from the centre your rotation to where you are, mass is your mass and speed is in the direction tangential to the rotation.

So for an acceleration of 1g or 9.806 m/s/s you need

9.806 = speed . speed / radius

The speed and radius, within the limits of the practicalities of technology, up to you.

Hope this helps.

 

[Venusian Broon]

Have you checked out the Wikipedia article on it?

Artificial gravity - Wikipedia

It has a simple set of equations (actually it's just the same one, rearranged)

Yes, changing your position with regards to the radius will influence the force that you will experience. The acceleration is proportional to the radius, so as you travel towards the axis of rotation it will drop linearly.

The article also states that coriolis effect may induce dizziness, nausea and disorientation in humans if the rotation is faster than 2 revolutions per minute (with caveats that we may be handle more - space sickness?)

 

[Brian G Turner]

Excellent! That's the formula I was after.

I'd been through a number of Wiki articles and other websites, but I couldn't confirm whether the change in radius had a linear effect on force or not.

It looks like it is, which means the number of possible decks in a rotating cylinder will need to be limited, according to its radius, before the effects of reduced "gravity" become significant.

 

[Joshua Jones]

Brian, I was working on a similar issue in my WiP, and came to the same conclusion you did. My colonies are relatively small (4km radius), so I could only have a couple decks, but larger stations could probably have significantly more. Also, it would seem that the residents of higher decks (mine are for long term civilian habitation) would likely grow a bit taller and more slender than on lower decks, but be physically weaker unless specially trained.

I also use this effect for a moment of comic relief... my colonies use a central hub as a ship dock, and a protagonist was on an elevator to this for the first time, starts feeling lightheaded (unknown to him, due to the reduced gravity), instinctively reaches for his head... and proceeds to slap himself pretty hard in the face, as his limbs are lighter too.

Oh, the fun we can expect in artificial gravity fields...

 

[Brian G Turner]

My colonies are relatively small (4km radius), so I could only have a couple decks,

I'm going for much smaller, and figure I can get away with it.

My radius is 500m, and accounting for decks with a height of 2.5m I figure I can have 20 decks, i.e., 50m. This means an effective variation of g +/-10% across them, which I figure is an acceptable range - especially if the deck in the centre of these is my command deck and therefore at optimum g, meaning that the first and last decks would be only 5% at variance with g.

This might be enough to be noticeable, but I don't think enough to adversely effect movement. Additionally, these areas could be given over to storage or menial activities, meaning that only the lowest classes are likely to notice anything, and - in my society at least - the officers will not care if such people do experience any discomfort.

Actually, as an addendum, I figure on storage bays toward the centre would be advantageous, as heavy goods would have less weight and therefore be easier to move, plus it keeps the centre of mass nearer the actual center which I figure would be more stable.

This is all for a colony ship btw.

 

[SilentRoamer]

I immediately thought about Enders Game and found this Brian.

Artificial Gravity in Space

Might be some use to you?

 

[Brian G Turner]

Definitely good to reference - cheers for that.

I'm not sure why they suggest 4-6 rotations as optimum, though - I went for nearer 2 precisely because I wanted to avoid Coriolis effects.

The physics of it all is certainly interesting though - after reading Rendezvous with Rama I'd worried that g to r might be a square relationship and needed to check that, as if so decks would not be feasible. Thankfully it's not.