GURPS O'Neill Cylinder Design

[AlexanderHowl]

Well, 8 Flora would be the ideal location for such mines, as it is the closest of the large asteroids at 2.2 AU, meaning that it could supply the entire Inner System with industrial minerals. 20 TW of energy production would require 60,000 square kilometers of solar arrays, which would be 60 million metric tons of materials. At $10 per kilogram of industrial materials, the industrial materials would generate $600 billion in revenue during the 25 years of production.

[Johnny1A.2]

Originally Posted by cptbutton

I think the argument was that if you don't get out into the open air in the big outdoors sometimes it cause Bad Things to happen to your mental health. And that at scale, this would be cheaper than having to fly your workers down to Earth for a month twice a year or whatever.

Would it be, though?

To make SPS work at all requires substantial reduction in launch costs, even assuming Lunar materials. If you can get the launch costs down that much, I'm not sure the cost of rotating your crews is all that prohibitive.

Further, the classic O'Neil plan concept was that the 'colonists', for want of a better word, built SPS systems to provide power to Earth which pays for the construction and maintenance of the habs. The trouble (well, one of several troubles) with the idea is that the resources and time spend building new habs are resources and time not going into building powersats. From an investor POV, it almost certainly makes more sense to focus the full energy of the effort on the powersats directly.

(Which is a separate question from whether powersats make sense on their own terms.)

Originally Posted by martinl

After digging around a little to figure out the trade offs between diffuse space microwaves and land-based Solar, I'm still pretty skeptical about this approach, but it's fine for gaming.

Orbiting gigawatt blasts are better for gaming mind you.

Realistically, the powersats probably don't compete with ground-based solar. Even the analyses that show they do tend to make a lot of highly optimistic assumptions that wouldn't apply in reality.

The advantage of space-based solar is 24 hour sunshine without atmospheric interference. But if you want 24 hour sunshine you need high orbits, LEO gets lots of interruptions. In fact, convenience wise you want geostationary orbit, but that's pretty high and makes power transmission more expensive. It also adds to the cost of servicing and construction and protection. SPS systems would be very vulnerable to attack, basically big kilometer-wide masses of solar cells or the equivalent, and they'd need to be insured, and maintenance costs are not firmly locked down because we don't have enough information to do that. There are also a whole mess of ownership and national jurisdiction issues that would arise.

Ground-based solar gets only half a day of power at a time, and the atmosphere soaks up a good chunk of the energy before it reaches your collector. But offsetting that is ease of construction, ease of maintenance, relative ease of protection, ease of access to the power grids, relative ease of protection, minimum of unknown technology required, etc.

An SPS system requires a very massive infrastructure to build and maintain. That same infrastructure can be used to built big power collection arrays on the ground. When you consider the amount of land needed for a rectenna array, you could use that same land for solar collectors and get a lot of power.

Whenever you see any suggestion that something done in space can be done for cost 'x', you should usually mentally triple it. Space is expensive, and the proposed ways around that (Lunar mines, for ex) have a tremendous amount of expensive engineering and R&D work still to be done before anything definite can be said about their cost.

Originally Posted by AlexanderHowl

The primary economic advantage of SPS is you need a 1/5th as much solar gathering capacity, plus you do not need the storage capacity for 4x the hourly production as on the surface. In essence, 50% of the time is night and, for the day, you average 50% production, as solar intensities waxes and wanes throughout the day, plus you have cloud cover and storage inefficiencies, meaning that a nation like the USA would need 140,000 square kilometers of solar panels and 80 million metric tons of lithium ion batteries. Since the materials for lithium ion batteries cost $7,500 per metric ton, the material costs alone for
the batteries would be over $600 billion, and that it before prices increase due to increased demand.

That calculation, though, assumes solar vs. solar. In practice, you'd have to make the economic evaluation based on a mix of energy sources. Coal, oil, natural gas, hydro, wind, uranium/thorium, all compete with solar in space or on the ground, and a workable cost projection has to be based on the presence of them all, and it has to take into account the legal and political factors, not just the technical ones.

[AlexanderHowl]

Nothing beats SPS cost for cost when you get the launch cost down to $150/pound to LEO and set up the lunar/asteroid mines. You are talking about $10/MW-h without the government subsidizes of nuclear, surface solar, or wind, and, unlike surface solar or wind, it is always available and never needs battery storage. Unlike coal, natural gas, or oil, it does not release greenhouse gases, so it does not cause climate change. On every level, it is the best energy technology until we figure out fusion, which would only be better if it did not depend on tritium or imported helium-3.

[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.