Re: GURPS O'Neill Cylinder Design
 

You should probably do something like this in your base design for radiation protection, especially from GCRs over decades-long exposure.

Re: GURPS O'Neill Cylinder Design
 

The shielding is included in the 10 billion metric ton figure. The shielding cannot rotate at the same rate as the shell anyway, it is usually made from slag and lacks the structural strength, so it must usually rotate independently. Even at 10 billion metric tons though, the density is 0.0062 grams per cubic centimeter, so it is mostly empty space (47 cm of steel for the shell).

Re: GURPS O'Neill Cylinder Design
 

That works out to ~3.6 t/m2. The 1977 NASA/Stanford study (NASA SP-413) recommended (p. 43-46) a minimum of 4.5 t/m2. If anything, our increasing understanding of radiation hazards in space since then suggests that this is too low, not too high.

Re: GURPS O'Neill Cylinder Design
 

Well, the thick atmosphere and the dirt would provide additional shielding. I would personally not mind tripling the mass to provide additional stuff, so SM+23 would not be unreasonable (30 billion metric tons). Anything less than SM+22 would be asking for trouble though.

Re: GURPS O'Neill Cylinder Design
 

Put a layer of factory farms under the main land surface. More production, upper land freed for parks, radiation shielding. Yeah you get some mutated crops or animals, but what could go wrong?

Re: GURPS O'Neill Cylinder Design
 

How are you getting light to your farms?

In general I would not recommend trying to emulate a classic O'Neill cylinder and instead design an O'Neill-inspired cylindrical habitat, there are some known issues with the classic O'Neill cylinder.

Re: GURPS O'Neill Cylinder Design
 

I have started using the term "Oberth cylinder" for more general sense, because a lot of people reasonably take "O'Neill" as implying a lot of the specifics of Island Three, such as there being two cylinders, using precession effects to keep sunlight coming in through windows, etc. After all, Island Three is what they read about if they try to look up "O'Neill Cylinder" in Wikipedia for background.

One thing that I recommend not trying to emulate about Island Three is the windows. I calculate that you have to make nearly full used of the strength of steel to support the structure against the centrifugal effect; I don't think it would be practical to either fit windows that bore the radial strain or to support ones that didn't. If you want natural light I think you have to pass it in through the end-caps. Otherwise use artificial light.

Re: GURPS O'Neill Cylinder Design
 

Of course, if you aren't using the windows, there's no good reason for the cylinder design in the first place, you're probably best off with a torus or multi-torus configuration, as that vastly reduces the amount of material strength you need to resist internal pressure.

Re: GURPS O'Neill Cylinder Design
 

It makes it clearer that you're building apartment complexes in space rather than whole suburbs though. That seems so much less revolutionary. Probably also that your stucture's inhabitants are temporary too. Neither are what the O'Neill people want.

Re: GURPS O'Neill Cylinder Design
 

One problem with the whole concept for fictional/gaming purposes is 'why'. That is, why would whoever is putting up the money build this immense flying parkland, when high-density urban is more cost efficient? It's possible to think of reasons, but they're likely to involve a vastly wealthier and more advanced society than most of the O'Neil enthusiasts envision.

The classic O'Neil concept of the habitats building power satellites to pay for themselves is of course nonsensical. Solar power sats probably don't make sense on their own terms, and if you're going to build them, you don't need O'Neil habs, you need the space equivalent of a line shack or an oil rig. For comparison, you don't build a chain of mansions on site if you're starting a mine in a remote region, you build efficient living modules or something along those lines, if the workers are lucky, something less if they're not. It's cheaper.