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Comment by tln | Hacker News Reader

I don't get why "if [the diameter] is an order of magnitude larger, the structure won't hold together when it spins". The centripetal force is the same, 9.8N/kg, so it's kg / m^2 that matters. Right?

Wikipedia lists other design updates: https://en.wikipedia.org/wiki/O%27Neill_cylinder#Design_upda...

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Imagine cutting a cylinder in half from top to bottom, then taping the halves back together. As you spin it, the tape has to stop the two halves from flying apart. If you make the cylinder bigger and keep the centripetal acceleration the same, the tape has a harder job do because it has heavier things trying to fly apart.

Every strip of the cylinder has to keep the opposing halves from flying apart. For a big enough cylinder, the material will not be strong enough. You can make the cylinder walls thicker, but now you've made the flying-apart halves heavier too.

But if you just consider equal size strips, with the larger cylinder just having more of them, then the force on each will be the same... unless you're saying the imaginary tape have to deal with forces from other strips. I don't see why

It's similar to making a taller building. You end up supporting more weight as the structure grows in height. Diameter in this case being similar to height.

I wonder if interspersing non rotating segments could allow a larger diameter. Not sure how the bearings would work or if they could be strong enough. Magnets maybe?

One has to consider how you replace the bearings when they start to wear out. It's a moving part, it's going to wear out.

not that its practical but if you have cylinder halves of enough mass then gravity will hold them together

But then they wouldn't be rigid enough to maintain their shape under gravitational forces... and we've invented a planet :-)

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