[Spaceships] SM+35 Toroid Station?
 

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? :)

Re: [Spaceships] SM+35 Toroid Station?
 

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

Re: [Spaceships] SM+35 Toroid Station?
 

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.

Re: [Spaceships] SM+35 Toroid Station?
 

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.

Re: [Spaceships] SM+35 Toroid Station?
 

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.

Re: [Spaceships] SM+35 Toroid Station?
 

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

Re: [Spaceships] SM+35 Toroid Station?
 

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 .)

Re: [Spaceships] SM+35 Toroid Station?
 

Stone armor isn't nanotubes. Aside from that, the big problem is that spaceships uses the wrong scaling law for a lot of things, and when you use the correct scaling law you wind up with something nonsensical.

For example, 1 EP appears to be about 100 W/kg, or 5e+21W in your case. The upper limit of solar panels is about 1 kW/m^2 and realistic value is about a quarter of that, so we need 5e+18m^2 of solar panels, or about a 1.2 million kilometer radius. Radiators have a similar limit.

Re: [Spaceships] SM+35 Toroid Station?
 

Stone armor isn't fire extinguishers or airlocks, either; as far as I can tell, Spaceships abstracts away structural supports as just being there anyway.

(Edit: Well, mostly; the current draft spends $300 quintillion on its "spin gravity".)


By EP, I'm guessing you mean a Power Point?

With a bit of GIF-fiddling, the amount of surface-area a Gaea station has to face the sun is about 1.4M km^2. (Including both mirrors to reflect sunlight, and panels to absorb power.) Which is undoubtedly less than your listed numbers.

But since I'm only buying a SM+35 Solar Panel to power the SM+35 Factory to get +1 HP, if that's a problem, I'm willing to nuke both in favour of a couple more Open Spaces, and just have some SM+31-or-smaller panels, factories, and the like.

Re: [Spaceships] SM+35 Toroid Station?
 

Spaceships assumes that the armor functions as structural support.
Try SM+22 (you have about 1/3,000,000 the area you need). Note that solar panels are in fact cinematic even in the normal size range given in Spaceships.

Re: [Spaceships] SM+35 Toroid Station?
 

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.

Re: [Spaceships] SM+35 Toroid Station?
 

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.

Re: [Spaceships] SM+35 Toroid Station?
 

Not really. A ship can be built with as little armor as you want - including no armor at all - and still be assumed to have structural supports. What Spaceships assumes is that each component has enough structural support for itself, and the ship as a whole has enough structural support for all of it's components.

Re: [Spaceships] SM+35 Toroid Station?
 

Can do. :)


If it's that important for verisimilitude, then I can always make the 13th system of armor Nanocomposite instead of another Stone. (Looks like it'll add 700k dDR, and $150 quintillion; though I'm slashing the budget by a lot more than that by dropping the SM+35 factory.)


And that brings us into the station's actual design goals.

The original builders' purpose was to create what's effectively an offline backup system for their civilization, by placing a selection of stations in various out-of-the-way points in the galaxy; each of which could maintain itself, independently, for x million years, and maintain a population of baseline humans (or near-human equivalent) for the duration. I'm assuming that simply keeping an offline set of records of DNA and some vatfacs prepped doesn't meet their criteria. I'm trying to take some of the lessons of Biosphere 2 into account, and that keeping an active biosphere working for a long time requires more redundancies than is immediately obvious to account for various complex interactions. I'm also assuming that there are issues in most forms of active management of any such collection of ecosystems, so it all has to mostly run itself. (Plus or minus the occasional automated nudge, such as vatfaccing up some individuals of a species that's undergoing too much genetic drift; and with at least one release valve for any human-equivalents who are too curious to avoid poking their fingers into dangerous pies; and with a set of systems to rapidly increase the inhabitants' tech-level if galactic society vanishes for too long.)

Put another way, the purpose of the station isn't maximizing industry, or energy, or even population; it's maximizing absurdly-long-term ecological stability. There are plenty of arguments that could be had about the trade-offs between structural strength and biosphere acreage, but a Varleyian Gaea seems to both be possible without superscience and to provide a plausibly large area, so seems a good starting point.


For example, if I wanted to get a similar amount of acreage with a SM+34 station, I'd need at least 10 of the systems to be Open Spaces (and with fewer armour systems, the radiation protection would be roughly halved); and couldn't do it at all with a SM+33 station, even with all twenty systems being Open Space.


:thumbs-up:

Re: [Spaceships] SM+35 Toroid Station?
 

You only need 10 metric tons of shielding per square meter to provide shielding similar to the Earth, so 1 km of air at 1 atm would provide sufficient shielding. A shell of carbon nanotubes 1 km thick would provide more than enough additional protection to stop asteroid impacts. Even a TL 12 civilization would balk at the cost of a SM+35 ark and would probably rather go for 100,000 SM+27 ark.

If we assume an overall density (including static structural elements and static armor) of 1 metric ton per 14 cubic meters, an SM+27 ark will have a volume of 42 trillion cubic meters. If we assume a cylinder with a length 4 times the radius (and nonrotating armor and structural elements), you would end up with a length of 220 km, a rotational radius of 55 km, and a projected area of 2 million square kilometers. With 100,000 of them, you end up with a total projected area of 200 billion square kilometers. Even if only 50% of the projected area is habitat support, that gives you a total of 250 Earths in surface area.

Re: [Spaceships] SM+35 Toroid Station?
 

Are you sure that's right? If the radius is 55 km, the circumference is about 345 km; and the cylinder's surface area would be 220 * 345 = 76,000 km^2. Am I missing something?

Re: [Spaceships] SM+35 Toroid Station?
 

As Earth has a lot more than 1km of air, that doesn't follow.

Re: [Spaceships] SM+35 Toroid Station?
 

I've seen other estimates for the 10 tons per square meter for radiation shielding. If air is 1.225 kg / m^3, then to get 10 tons worth, you need a depth of 7.4 km of such air. (This doesn't include air getting less dense at higher altitudes.)

Re: [Spaceships] SM+35 Toroid Station?
 

The scale height of the atmosphere is a bit above 8 km. Remember, it gets thinner as altitude increases, so the total mass isn't linear in the height of the atmosphere.

A fairly simple proof for this: air pressure at sea level is 101 kPa. The source of pressure is the weight of the atmosphere above you. The weight of atmosphere is mass * G, so the mass is 101 kPa/9.8N/kg = 10,300 kg/m^2.

Re: [Spaceships] SM+35 Toroid Station?
 

Sorry, I tend to layer my habitat designs and went back to an old design that had fifty-five habitat shells, each with 1 km of thickness It ends up being a effective projected area of 2 million square kilometers.

Re: [Spaceships] SM+35 Toroid Station?
 

I think you're running into flaws with how Spaceships handles radiation shielding, it's a fairly trivial problem on truly large scale habitats. Other than that, I would probably not even try to use Spaceships for this, because it's just really far away from the sort of thing Spaceships is designed for.

Re: [Spaceships] SM+35 Toroid Station?
 

Ah, now I get what you meant.

Hrm... it looks like Spaceships' "Open Spaces" don't really match up with this approach, as their rated acreage comes nowhere close to what you describe. So, presumably, all those spaces would be built as Habitats; a SM+27 Hab system with total life support would house 10 billion people, and cost $3 quadrillion. Which /could/ work...

... though I'm still hesitant to try this approach, given how many things can go wrong with actively-managed life-support systems in a single century, let alone a hundred-thousand centuries. I admit that I'm heading into territory Spaceships doesn't come close to touching with this requirement, but I think I'd need a bit more persuasion to abandon my current 'self-correcting ecosystems' approach.



True, but where Spaceships /can/ stretch this far, it's offering some interesting insights, such as how viable any particular drive-system might be to nudge such a ridiculously-large body's orbit. (Eg, the rocket equation is less of an issue than flying enough fuel-mining robotic craft just to feed a SM+29 mass driver; the fuel for which costs $3 quadrillion to provide 0.00003 mps of delta-v to a SM+35 station. (Which is cheaper than any other non-superscience drive in the books, usually by orders of magnitude.))

Re: [Spaceships] SM+35 Toroid Station?
 

Unless you have some sort of active management system, a habitat would probably destabilize within a thousand years or so regardless of the size as artificial structures need repairs since they cannot depend on gravity to keep everything together. For example, even a relatively small asteroid impact (~10 m radius) would imbalance the spin gravity system by subtracting mass from somewhere, which would result in the entire system decaying within a few days without load shifting (0.2 rotations per minute is still a rotational velocity of more than 20 km/s). Since a 10 m radius S-type asteroid masses ~10,000 metric tons, it would hit with an average energy of ~400 kilotons of TNT, probably fragmenting off a few billion metric tons of stone armor.

Re: [Spaceships] SM+35 Toroid Station?
 

I suspect that such external astronomical events would be the main reason to switch from passive management to active intervention. (Another such possible trouble could be a Carrington-level CME.) How far could a SM+31 Enhanced Sensor Array, with an Array Level of 32, pick up any such bodies? My notes on detecting a SM-10 piece of junk is that at 50,000 miles, the modifiers to the roll are -10 (SM), -46 (extreme range, 50,000 miles), +32 (telescopic vision), +10 (in plain sight), +24 (silhouetted against deep space), for a total of +10, automatic detection. A 10-metre rock is, what, SM+6 (SM+4 for dimension, +2 for sphere shape), meaning rolls to detect it are 16 higher than that; so it would be auto-detected at, what, 20 million miles out? (Even further, if the station takes extra time for a scan: 150 million miles, with the +5 bonus for a half-hour scan.) Even at orbital velocities, an AU and a half seems a good enough distance to launch a staged series of countermeasures. (Though I'm still poking around with numbers to figure out if any of the reaction engines would let a Gaea move far enough to avoid such a strike, after detection.)

Re: [Spaceships] SM+35 Toroid Station?
 

Reaction engines are completely unrealistic at the size. The waste heat alone would vaporize the engines because their volume to area ratios would be so high. You have a BDO that cannot maneuver any better than any other large asteroid.

Re: [Spaceships] SM+35 Toroid Station?
 

So I've noticed. (A SM+29 Orion drive system would use up 1,500,000,000,000,000 tons of drive-units to provide a whopping 6.4 metres/second of delta-v. Which would be enough to move the station its own width in roughly 10.8 hours.)

Since Spaceships doesn't handle sails above SM+12, I'm currently looking into (ie, googling) an option for selectively altering the craft's albedo, to see if I can figure out how much of a change in impetus that might provide; and then I plan on reading up on magnetic fields, such as the ones around gas giants, for any other options.

And once I get my fill of figuring out how one BDO works... I get to start thinking about /lots/ of BDOs in various places. (I don't know if GURPS can handle any sort of description for a Kardashev >2 precursor society, but I'll be willing to give it a try.)

Put another way, I'm trying to use Spaceships more as a springboard and less as a straightjacket. :) )

Re: [Spaceships] SM+35 Toroid Station?
 

I recommend not trying to do either one. Spaceships is designed for quick and dirty, not accuracy.

Re: [Spaceships] SM+35 Toroid Station?
 

Say, could I get some help with some damage numbers here?

For a SM+35 craft, I get dST/HP of 200M; with 12 systems of stone armour and 1 system of nanocomposite armour, with Pyramid 34's armour-volume rule-tweak, I get an average of dDR of 780k for fore, central, and aft. Does that look right?

And to figure out what sort of rock can actually dent the stuff (before the 23 HP/second Self-Healing kicks in)... assuming typical orbital velocities of 10 mps, and assuming an average roll on the formula on SSp61, it looks like I'd need a rock with at least 1200 dST, which would be SM+16... is that anywhere near right? (Even a 100 megaton nuke only averages 700,000 d-Damage, and a 3 PJ beam 21,000 (and even with a (10) armor divisor, it's facing dDR of 78k).)

Is there any reference for damage levels for solar events stronger than the "a few times a decade" flares mentioned in SS5p40?

Re: [Spaceships] SM+35 Toroid Station?
 

"He's heading for that large space station."
"That's no space station. It's a moon."

Sorry, I was looking up something to compare SM+35 to, saw that Mimas fell right into the correct mass, and couldn't help but make that joke.

Re: [Spaceships] SM+35 Toroid Station?
 

The effective gravity was given as 0.2g, and the diameter 650km, so the rotational period is about 2530 seconds, or ~0.024 rpm. The rotational velocity of the rim would be about 800 m/s.

Re: [Spaceships] SM+35 Toroid Station?
 

It's debatable whether a ring configuration makes sense. The general virtue of a ring type configuration is that the atmospheric pressure can be supported the inside of the ring rather than along the entire radius of the spin compartment, reducing the amount of mass you need for atmospheric containment, but this effect is reduced if there is a pressure difference between top and bottom of the chamber.

Judging from the diagram, the outer torus has a height of around 150 km. At 0.2G and 20C, the scale height of the atmosphere is roughly 40 km, so the pressure at the top is 2-3% of the pressure at the base, and you're barely saving anything.

A cylinder with length 650 km and radius 250 km (i.e. just reversing the dimensions) has the same projected area but lower structural mass. It would rotate a bit faster (period about 26m instead of 42m) but has lower velocity, and is probably simpler to construct.

Re: [Spaceships] SM+35 Toroid Station?
 

Radius 650 km, not diameter; the canonical rotation period for the original Gaea is 61 minutes and 3.5 seconds, and with a circumference of a hair over 4,000 km, a rotation speed of 1,114 m/s.


I thought the main virtue of a ring was that it's much simpler to set up passive sun-mirrors to light up the interior, without needing to install a large electrically-powered lighting system.


In Varley's source material, the spokes have valves at top and bottom, and have a regular cycle to pump air up three spokes at a time and down the other three.

Edit: With a ground-level atmospheric pressure of 2 bars, wouldn't that mean the atmospheric scale height is 80 km, so that at ~160 km, the "natural" pressure without pumping would be about 13% (or a quarter of a bar)?


In Spaceships terms, I think this would count as being built as SM+34 with 10 Open Space systems, instead of SM+35 with 5.

Thinking about it, it... has potential. The first choice I'd have to make is lighting, since the first options I can think of lead to different shapes. Eg, doubling the cylinder's surface area, making three sections transparent with long mirrors angled to shine down; or an electric sun-line down the middle; or go umbrella-style, with a large mirror focusing light down along a similar sun-line using mumble-mumble optics to distribute it down the whole length.

I can think of several reasons for this approach, and the only reasons I can think up against it are backfilled justifications involving handwaved long-term effects. (Well, plus the "reason" of the pure style of having a toroid the stars can be seen from. Maybe the sun-facing endcap of the cylinder could be a transparent hemisphere?)

Re: [Spaceships] SM+35 Toroid Station?
 

That wasn't mentioned in the design, but I have some doubts about the passiveness.
Scale height doesn't depend on pressure, though the pressure at the top is proportional to the pressure at the bottom.
The rotational axis of the station, whatever configuration you use, is going to be parallel to the orbital axis, so neither end will be sun-facing.

Re: [Spaceships] SM+35 Toroid Station?
 

Passive lighting is an issue. The best way would be to have an array of shades that rotate slower than the habitat and the have the habitat perpendicular to the orbital plane (the Sun being always 'above' the habitat). With the rotating shades, you can block out the sunlight for an artificial night. If you want, you can have an array of rotating mirrors behind the habitat to give more light during the 'day'.

Re: [Spaceships] SM+35 Toroid Station?
 

Anyone good at mechanical physics calculations, especially for gravity-gradient stabilization and tidal locking?

I can figure out that for a station with a mass of 10e15 tons, and a length of 650 km, then a long cylinder of a station pointing at the sun would experience about 467 giganewtons of tidal force; and pretending it's a simple rod, it would have a moment of inertia around 3.19e29 m^2*kg. But I'm having trouble googling up any comprehensible equations to see if that would allow for the station to be tidally-locked to the sun.


Edit:
I'm fine with 24-hour lighting, for this particular station. As soon as I figure out what direction it's pointing, I can decide whether to have one mirror, umbrella-style, or a large mirror at each end at 90degrees pointing to a smaller mirror at each end-cap.

Re: [Spaceships] SM+35 Toroid Station?
 

That's easy. No, by definition it can't be tidally locked. A tidally locked objects rotates once per year, and this object rotates a bit more than once per hour. There are no stable solutions for 'spinning around an axis that is pointed at the sun'.
If you want it to not wobble a lot, it's pointing along the same axis as its orbiting.

Re: [Spaceships] SM+35 Toroid Station?
 

You could have counter rotating habitats connected by a stable structural element. You would need such an element anyway to anchor solar panels, shades, mirrors, etc.

On a more serious note, do we need a hollow object that is 95% trace atmosphere? If you constructed multiple levels, you could have g's ranging from .1 to 1.0 without difficulty. You could have each with 20 km separation and just have a rotational radius of 200 km. You could have four counter rotating habitats, each with a rotational radius of 200 km and a length of 1,000 km, each with ten levels connected, all connected by a static structural element.

In that type of setup, you would end up with an effective projected area of around 27 million square kilometers. The counter rotation would keep everything pointed in the right direction. Of course, that would be more complex than the first design.

Re: [Spaceships] SM+35 Toroid Station?
 

Yes, but it's unclear what benefit you get out of it, since your primary limit is that you can saturate your available energy and heat dissipation with a very small number of layers.

If you don't care about horizons, though, you can save a lot of weight by making the outer shell have a low ceiling. With no ceiling, that 2 bar surface pressure corresponds to an atmospheric mass of 100 tons per square meter, or 10^17 kg for the entire million square kilometers of habitat. Put a 1 km ceiling on the world and you reduce that to 2.4 tons.

Note that this requires a much different design than previously suggested, because the natural shape of an inflated torus is round, and with a 250 kilometer width, that's ridiculous. Fortunately, we already know how to make a flat inflated object: it's called an air mattress. Somewhat counter-intuitively, this also saves us on structural mass, because most of the atmospheric pressure is supported by internal struts (support length 1 km) instead of the belt of the torus (support length 650 km); the only stuff that has to be supported by the belt is now the static mass, which at 10 tons per square meter (plenty for a dirt belt) is still only around a tenth of the atmosphere.

The drawback is that you have considerably shortened sight lines and a bunch of pillars limiting line of sight (using the same sorts of materials as you'd need for the general case, you need something like a 3 meter pillar every kilometer).