GURPS O'Neill Cylinder Design

[Fred Brackin]

Originally Posted by AlexanderHowl

A classic O'Neill Cylinder is going to mass around 10 billion metric tons when you account for atmosphere, habitation, structure, and shielding, so it will be a SM+22 structure by mass (volume does not really matter for Spaceships).

Yes, there is no such thing as volume-based SM in Spaceships. It confuses people enough that SM in Spaceships is different from SM in Basic. I would rather not see you inventing a new kind of SM.

[dataweaver]

Originally Posted by Fred Brackin

Yes, there is no such thing as volume-based SM in Spaceships. It confuses people enough that SM in Spaceships is different from SM in Basic. I would rather not see you inventing a new kind of SM.

That's not quite true. In David Pulver's Alternate Spaceships article (I forget which issue it was; August 2011), there's an “Armor and Volume” option for adjusting a spacecraft's surface area (in the form of a dDR multiplier for its armor) and its Target SM based on a lot of its systems being high-density. Normally, only armor systems would count, and only high-density ones at that. But I could see, say, a Singularity Drive counting as multiple high-density systems for this purpose.

And bringing it back to the topic at hand, I could see Open Systems having the opposite effect, potentially forcing armor systems to cover a higher-than-normal surface area, reducing the effective dDR they provide and increasing the ship's Target DR. You'd need to extend the chart into the “negative Armor systems” range, with each Open Space counting as -x armor systems for the purpose of the overall effect on the spacecraft's surface area. I would design an O'Neill habitat using almost exclusively Open Spaces, taking other systems only when absolutely necessary.

There's also rules for Spin Gravity, though they assume that the craft has the gear to quickly spin up or down at will. It tells you have much gravity you can have at a given SM (which would be the Target SM as described above). If the craft is set into rotation by tugboat-like spacecraft instead of on-board gear, there's no need to pay for the Spin Gravity design feature.

[AlexanderHowl]

In larger objects, the initial spin requires delta-v rather than gearing, so the cost is still applicable in realistic settings.

[Tyneras]

Thanks for the reminder on the Spin Gravity option, I'd forgotten about it.

Radiation was mentioned before, so I figured I would take a stab at it.
Normal background radiation is 0.15 to 0.35 rads per year, so lets use that as our goal.

Cosmic rays are 1 rad/week, or 52 rads per year and divide PF by 100. a PF of 20,000 gets us to our goal without special anti-cosmic ray shielding.

Solar flares from Spaceships 5 (page 40) come in a variety of flavors, with small ones up to once every 2 months and big ones every few years. Flares are also fairly non-penetrating, multiplying PF by 20. For the small ones, a total of 900 rads (at Earth orbit) would be reduced to 0.1 rads by a PF of 450. For the big ones, a 6000 rad flare would be reduced to 0.1 rads by a PF of 3000.

Now, the radiation protection table on Spaceships 5 page 41 starts following the standard GURPS log progression but then abruptly changes pace and I don't recognize the new progression. So sticking with the standard progression, the O'Neill cylinder in the OP would have a PF of 7,000 per system, giving the inhabitants 3 systems worth of protection in each system between hull armor, dirt and remaining customizable systems, a total of 21,000 PF.

Our intrepid space colonists need not worry about glowing in the dark from cosmic rays or solar flares.

It was mentioned that the science of space radiation has advanced, so maybe they still need to worry about glowing in the dark. I'm far from up to date on that topic.

Side note, I'm assuming the sudden change to progression on the protection factor table is not just a typo, but I don't think I've ever seen it anywhere else so I can't follow it past the edge of the table. If you've seen it elsewhere, let me know.

[Tyneras]

Woops, I forgot to factor in that the PF would be smeared out over a much larger area, just like the armor would. This reduces the PF of the inhabitants to 210. They are going to need a nice thick shell around their O'Neill cylinder, good anti-rad drugs or maybe a good artificial magnetic field to protect them.

But as far as a nice rocky shell goes, a SM +26 rock shell with the O'Neill cylinder as the "upper stage" spread out as 2 systems from each section rather than all in one section gives it 4 systems of 'free' rock as radiation shielding. This gives you 50,000 PF and 1500 dDR per system. You even have 2 core systems left, good place to subdivide into smaller systems for docking areas and other exposed necessities.

[AlexanderHowl]

At SM+26 (which is 1 trillion tons), two armor systems per section gives a PF 51,200 (800 for SM+14, doubled for every +2 SM, for a total of six doublings), which gives over 1 million PF against solar flares and 512 PF against cosmic rays. That leaves you with 12 hull systems and 2 core systems and, if you gave the spaceship 4 habitat components and 4 open space components, you would have 24 billion cabins, allowing you to easily support 4 billion people in a single colony. Of course, this makes sense because a SM+26 O'Neill has a spin radius of 20 km and a length of 200 km.

[Tyneras]

I'm not quite sure I follow you, AlexanderHowl. This is a SM+21 station, inflated to SM+25 due to it having a density more like a beach ball than a warship, with a SM+26 shell of rock (or more likely a mix of rock, ice, and other useful raw materials.) around it.

Unless you are just pointing out that once the cylinders get large enough, the need for a rocky shell goes away due to sheer bulk.

[DangerousThing]

Or you could have 12 billion luxury cabins, which would closer approximate a home environment, I believe. That would support 24 billion people on an SM+26 station.

Of course, you'd have to have some services which would lower the number of people (sick bays, offices, that sort of thing).

It's still a boatload of people, no pun intended.