[Spaceships] SM+35 Toroid Station?

[DataPacRat]

I'm planning on doing some plots within a rotating space station based on John Varley's "Gaea": radius 650 km, width 250 km, centrifugal gravity 0.2G, air pressure 2 bars, many more pictures at http://ammonra.org/gaea/index.html . ( http://ammonra.org/gaea/sizes.html shows its size compared to some other space-things, http://ammonra.org/gaea/art/download...1_1152x864.jpg is an interior view, http://ammonra.org/gaea/jmweiss.html shows some interior structure.)

Right now, I'm seeing what I can learn by building it as a SM+35 vessel in Spaceships; I'm picking that size because it seems to match both its diameter and a back-of-the-envelope estimate I made of Gaea's mass. 12 systems of armor and 5 systems of Open Space seem to cover the essentials (eg, 250M acres of floorspace); and throwing in a biotech Robofac for the HT boost, a Solar Panel to power the Robofac, and the last SM+35 system split into hordes of SM+31-and-smaller systems seems to fill out the details. (Eg, a SM+31 Enhanced Sensor Array can auto-detect a SM-10 piece of space-junk at 50,000 miles out, giving plenty of time for some point-defense systems to shoot it down.) Include the Design Features of Spin Gravity, Self Healing, and Stealth Hull; and the Design Switches of Exposed Radiators, Living Ship, Slower Industrial Systems, and Pyramid 34's Armor Volume; and lots of Total Automation to avoid needing trillions of workspaces; and things seem to work out.

Of course, the total price is on the order of $2.6 sextillion, but that was paid millions of years ago, with all the current such stations being descended therefrom. (It looks like it takes the SM+35 robofac 5 years to create a station-egg, if it dedicates itself entirely to that task.)

But I'm only moderately familiar with the standard Spaceships rules, and stretching the tables this far beyond their norms opens up all sorts of possibilities for going wrong. So before I get into some nitty-gritty of figuring out which reaction engines might be handy for ever-so-slowly shifting orbits, I thought I'd pop over here and ask if anyone has any advice on the build. So - is there anything obvious that I might be missing? :)

[Michael Thayne]

60% armor by mass is a lot of armor. What's the reason for deciding on that approach?

[DataPacRat]

Originally Posted by Michael Thayne

60% armor by mass is a lot of armor. What's the reason for deciding on that approach?

The original novels said that under the 4000km*250km habitable surface area was a 30km depth of rock. My quick estimate of only 50% of that volume actually being solid gave me a mass estimate of 5e19 kg, which is slightly more than the 30 quadrillion tons Spaceships gives for a SM+35 craft. So using up that much mass on stone armour is at least in the right ballpark, it's dandy at shielding from radiation (PF 3M, 3k vs cosmic rays, 60M vs solar flares, twice those in a core space), stone is cheap, and I couldn't think of anything better for those spaces.

The top alternative I was thinking of was to swap one or two armour systems for more Open Spaces, given the toroid's ceiling is on the order of 100 km above its ground, and the wheel-station's large spokes include living space for arboreal-type fliers.

I'm open to being nudged in any direction there's a reason for.

[Anthony]

Spaceships has its realism problems, and you're hitting some of them, but the realistic answer is "you can't actually build something like that", so I assume you don't care about realism.

[DataPacRat]

Originally Posted by Anthony

Spaceships has its realism problems, and you're hitting some of them, but the realistic answer is "you can't actually build something like that", so I assume you don't care about realism.

Deep time gives a /lot/ of room for robofactories to Von Neumann themselves up to at least sextillion-dollars-per-millennia levels, which would have been enough to make the first such station. I'm trying to think of what sorts of evolutionary pressures might have nudged variants of the basic design one way or another, but I'm still hesitant on even just finalizing that initial design, let alone trying to work out how to spread their offspring from one star system to another, let alone working out what resources would most likely be limited enough for those offspring to compete over.

[Anthony]

Originally Posted by DataPacRat

Deep time gives a /lot/ of room for robofactories to Von Neumann themselves up to at least sextillion-dollars-per-millennia levels

Not talking about the economics. It's physically impossible to construct a station like that out of ordinary matter.

[DataPacRat]

Originally Posted by Anthony

Not talking about the economics. It's physically impossible to construct a station like that out of ordinary matter.

What's the physical limit you're thinking of?

I've seen proposals for McKendree cylinders that are 1,000 km in radius (as opposed to this station's 650), which are supposedly the limits for carbon nanotubes; and this station is only rotating fast enough to generate a fifth of a gee, which should offer even more leeway.

(Edit: McKendree's paper can be seen at http://www.zyvex.com/nanotech/nano4/....html#RTFToC17 .)

[Agemegos]

Originally Posted by DataPacRat

I'm planning on doing some plots within a rotating space station based on John Varley's "Gaea": radius 650 km, width 250 km, centrifugal gravity 0.2G, air pressure 2 bars

I calculate that you'll need a structural material about twelve times as strong as, and one-quarter the density of, high-tensile steel for that structure to resist the tension generated by its own rotation. You could build it out of a polymer reinforced with carbon nanotubes. But not stone.

And that's not counting the 15km of stone as a passive load, that's leaving it out altogether. With 33,000 tones per square metre of load you'd need an 8-km-thick band of nanotube-reinforced polymer, or 1.5-1.7 km of flawless diamond or continuous nanotubes above and below to support the stone.

[AlexanderHowl]

15 km thick armor seems...excessive for a habitat, as is any production of power points for industrial purposes (just use vast amounts of minifacs). In addition, such a habitat is a massive waste of resources, as you could use the same resources to make 1,000 habitats one-tenth the dimensions each that would have a total surface area ten times as large, allowing them to support ten times as many people. Such a complex of habitats could be connected through static structures that could support solar panels and radiators, and could support any industry that truly needed power points.