# How fast can a cylinder spin, with a human on its inner wall, to NOT experience motion sickness?

## Context

I'm working on an interstellar Ark made of a few (probably 3 to be more specific) layers of cylinders (modified O'Neil's concept), while trying to get the station to be as compact as possible. I want at least one layer to experience 1 g of centrifugal force and one, outer layer to experience force of 1,25 g. Both cylinders are actually one rigid object that just got divided into two, as I don't see the need to separate them, if having them welded means saving resources and costs.

## Question

Accounting for those factors, and for the fact of me trying to make the ship as thin as possible, how quickly could the cylinders rotate until humans would be unable to do any sort of a work due to chronic motion sickness?

Sidenote: if the diameter of the cylinders matter, and you need any sort of a reference, let's assume for the 1 g cylinder, the minimal radius of 250 metres and the maximal of 4 kilometres

• Huh. I started to type up an answer ("there should be no problem so long as they can't SEE that they're rotating") but it's a deeper rabbit hole than I thought: pubmed.ncbi.nlm.nih.gov/14703662 Apparently we have tested up to 23 rpm and humans have been fine. I didn't read into the details but I think one concern in a small radius ship is that your head and your feet would experience different "gravity"? Commented Mar 20, 2023 at 13:05
• 250m radius appears rather large already. At 250 radius, You'll get a speed at the outside of about 50 meters/sec , making about 32 seconds for a single rotation. I would be very confident that there is not issue with that. Even a radius of 100m still has 20 seconds per rotations. g = v^2/R Commented Mar 20, 2023 at 13:17
• This falls into my "how many angels can dance on the head of a pin? Answer: as many as wanting" category of questions. People experience motion sickness to varying degrees - vastly varying degrees. There are people (e.g. fighter jet pilots) who wouldn't get sick with a 10m diameter cylinder. There are people (e.g. a friend of mine) who get motion sickness driving in-city. I don't know of an average - but more to the point, this is the kind of detail that most authors ignore, especially when you consider that most people born in the cylinder won't experience motion sickness.
– JBH
Commented Mar 20, 2023 at 14:09
• Even an individual by themselves suffers from motion sickness in different situations. I, for example, get a lot of motion sickness in the back seat of a car but none when I'm driving/in the front seat. A friend of mine is the opposite.
– GFA
Commented Mar 20, 2023 at 14:17
• Its a bit subjective (within bounds) as it depends to some extent on acclimatization but a good source for calculation is here: artificial-gravity.com/sw/SpinCalc Commented Mar 21, 2023 at 16:16