Building Your Ringworld

robject · Aug 30, 2015

Ecological Niche: Between O'Neill Cylinders and Dyson Spheres.
Size Ranges: 1600 km to 300 million km diameter (and up).
Population Digits: typically 9 to 12 (and up). Billions and trillions (and up).
TL Range: TL 10 (ring stations), TL 16 to TL 27 (ringmoons), TL 27 (ringworlds)

Using some quick math, as opposed to perfectly correct math, I come up with this rule of thumb:

Population of a Ringworld:

Population (billions) = Dk x Dk x P(r) / 300.

Dk = Diameter in kkm (thousands of kilometers).
P(r) = Width of floor, as a percentage of Dk.

Of course, max population will vary based on the ring's design.

Earth Masses:

M(Earth) = Dk x Dk x P(r) / 100,000,000.
Dk = Diameter in kkm (thousands of kilometers).
P(r) = Width of floor, as a percentage of Dk.

P(r) typically shrinks as the ring's diameter grows.

Code:

LaGrange Habitats: use Size Codes 1 through V.
Ringmoons: use 200x Size Codes 1 through T.

Size Code TL Type                Diameter     Pr    Mass(e)  Pop
--------- -- ---------------- -------------- ------ -------  ---      
  1 - F   10 Ring Station      1.6 - 24 kkm  1+24/D    -     6-8
  L - V      Ring Station      32 - 288 kkm  1+10/D    -     8-9
    W     12 Ringmoon 1         0.32 mkm      1      = D/200   
    X                           0.4 mkm       1      = D/200  
    Y         Ringmoon 2-9     0.6 - 2.9 mkm  1      = D/20  
    Y     16  Ringmoon A-F     3.2 - 4.8 mkm  1      = D/20  
    Y     20  Ringmoon L         6.4 mkm      1      0.4      
    Y         Ringmoon M         9.6 mkm      1      0.9      C
    Y         Ringmoon N         12.8 mkm    0.9     1.5      
    Y     27  Ringmoon P         16.0 mkm    0.8     2.0      
    Y         BD Ring/RMQ        19.2 mkm    0.8     3.0      
    Y         Ringmoon R         22.4 mkm    0.8     4.0      
    Y         Ringmoon S         25.6 mkm    0.8     5.0      
    Y         Ringmoon T         28 mkm      0.8     6.5      
    Y         Ringmoon U         32 mkm      0.7     7.0      
    Y         Ringworld 0.3 AU   9.6 mkm     0.5     46        
    Y         Ringworld 0.7 AU   22 mkm      0.5    250        
    Y         Ringworld 1.0 AU   30 mkm      0.5    462       F      
    Y         Ringworld 1.4 AU   48 mkm      0.5   1152       G

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Habitats typically orbit worlds or sit at LaGrange points of worlds.
Ringmoons are built around worlds.
Ringworlds are built around stars.
'BD Ringworld' is a ringworld built around a Brown Dwarf star.

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Scratches · Aug 30, 2015

Hmmm, how easy would it be to detect a ringworld by size and distance of ring vs sensor TL?

I may try to figure that out, not tonight though!

robject · Aug 30, 2015

Examples: Poseidon Ring, Niven Ring

EXAMPLE - Poseidon Ring

The Poseidon Ring is a ring around a small (Size M, 30,000 miles in diameter) gas giant.

Diameter. The gas giant's diameter, in metric, is 48,000 km. A ring around this planet at just under 100D radius is 9.6 million kilometers in diameter. This makes it a Ringmoon Type M.

Floor Width. The typical P(r) width of the floor of a Ringmoon Type M is 1.0. This corresponds to 1 percent of the diameter, or 96,000 kilometers. Using a standard 1000 km mapping hex, this means the ring width would be 96 hexes tall.

In this case, however, I'm creating a thin ring, with a width of 25,000 kilometers. This is about 0.52 percent of the radius; P(r) is therefore 0.52.

Earth Surfaces. Earth-surface equivalents is Dk x Dk x P(r) / 50,000 = about 958 Earths.

Population. I will use the Small Ringworld formula:

Pop(billions) = Dk x Dk x P(r) / 5000
= 9,600 x 9,600 x 0.52 / 5000
= 9,584

This Ringmoon can sustainably support 9.5 trillion human-equivalent sophonts.

EXAMPLE - Niven ring

The Niven Ring is a ring at 1 AU around a G2 or G3 V star.

Diameter. A ring at a radius of 1 AU has a diameter of 2 AU: that is, very approximately 300 million km.

Floor Width. The typical P(r) width of the floor of such a large Ringworld is 0.5. This corresponds to 0.5 percent of the diameter, or about 1.5 million km.

Earth Surfaces. Dm x Dm x P(r) x 20 = 300 x 300 x 0.5 x 20 = about 900,000 earths.

Pop (trillions) = Dm x Dm x P(r) / 5 = 9,000.

This Ringworld can sustainably support 9 quadrillion human-equivalent sophonts.

robject · Aug 30, 2015

Detecting a Ringworld

Scratches said:
Hmmm, how easy would it be to detect a ringworld by size and distance of ring vs sensor TL?

I may try to figure that out, not tonight though!

A 1.6 kkm diameter orbital habitat is a Size 12 object, which is detectable from Deep Space ranges (30 light minutes), but not from the outer system.

Space ranges often represent 30x magnitude changes. Assuming this holds true, then detection ranges for typical starship sensors would be:

a 1.6 kkm habitat at S=12 (30 light minutes),
a 48 kkm habitat at S=13 (83 light minutes),
a 1.4 mkm habitat at S=14 (40 light-hours),
a 42 mkm ring at S=15 (10 light-days),
a 120 mkm ring at S=16 (one light-month), and
a 300 mkm ring (e.g. one around Sol at 1 AU) at S=17 (one parsec).

As far as TL goes, a surface mounted sensor at TL 12 would take a couple days before fully learning about the 1.6 kkm habitat at 30 light minutes. On the other hand, at attack range it would take maybe 2 or 3 hours to pull out all the information the sensors would be capable of finding out.

On the other hand, a Scout beagle with TL 16 sensors in Large Bays would do better, cutting the scan time in half.

robject · Sep 1, 2015

What's the approximate volume of a 1,600 km diameter ring station, with a width of 400 km, and a thickness of 100m? (Pretend the walls' volume is factored into these numbers).

Width = 4 x 10^5 m.
Circumference = appx 5,000 km, or 5 x 10^6 m.
Volume = appx 5 x 10^6 x 4 x 10^5 x 10^2 = 2 x 10^14 cubic meters

Assuming mass is very roughly the same density as asteroids (it isn't, but I'm being very loose here), this station requires raw material equal to an asteroid with a length of 10^5 meters. 100 km long. That's a big asteroid. There are perhaps 200 of these in our own solar system.

In short: if you want to build one of these stations, you had better really need it.

robject · Sep 3, 2015

Here's the smallest ring stations, and the approximate size of the asteroid needed to build each, given an assumed floor width of course.

Also included is the ring's usable surface area, in "Earth Surfaces". For the sake of simplicity, assume this number directly represents a sustainable population in billions. So 0.004 means the ring station sustainably supports 4 million people.

Code:

Diameter, km    Floor Width, km Asteroid size, km   Surf, earth
1,600           384             110                 0.004
3,200           736             200                 0.015
4,800           1,056           230                 0.032
6,400           1,344           280                 0.054
8,000           1,600           310                 0.080
9,600           1,824           350                 0.110
11,200          2,016           380                 0.142
12,800          2,176           410                 0.175
14,400          2,304           430                 0.208
16,000          2,400           460                 0.241
17,600          2,464           475                 0.272
19,200          2,496           490                 0.301
20,800          2,496           500                 0.326
22,400          2,464           515                 0.347
24,000          2,400           520                 0.362

Aramais · Sep 9, 2015

robject said:
Here's the smallest ring stations, and the approximate size of the asteroid needed to build each, given an assumed floor width of course.

Also included is the ring's usable surface area, in "Earth Surfaces". For the sake of simplicity, assume this number directly represents a sustainable population in billions. So 0.004 means the ring station sustainably supports 4 million people.

Code:

Diameter, km Floor Width, km Asteroid size, km Surf, earth 1,600 384 110 0.004 3,200 736 200 0.015 4,800 1,056 230 0.032 6,400 1,344 280 0.054 8,000 1,600 310 0.080 9,600 1,824 350 0.110 11,200 2,016 380 0.142 12,800 2,176 410 0.175 14,400 2,304 430 0.208 16,000 2,400 460 0.241 17,600 2,464 475 0.272 19,200 2,496 490 0.301 20,800 2,496 500 0.326 22,400 2,464 515 0.347 24,000 2,400 520 0.362

I more or less draw the line at ringworlds. They are huge, wasteful of material, and essentially vanity construction. It becomes inconceivable that a population of human-sized beings needs 362 billion beings worth of space and air. To my intuitive view, at least, humans could never manage to have that many people without devastating social issues -- constant war and competition. Non-humans...well, the giant, intelligent ants can build whatever they want.

savage · Sep 9, 2015

Aramais said:
I more or less draw the line at ringworlds. They are huge, wasteful of material, and essentially vanity construction. It becomes inconceivable that a population of human-sized beings needs 362 billion beings worth of space and air. To my intuitive view, at least, humans could never manage to have that many people without devastating social issues -- constant war and competition. Non-humans...well, the giant, intelligent ants can build whatever they want.

Perhaps, but a xenophobic culture with a grim future and time on their hands/claws/paws/hoofs/tentacles may prefer this route.

The commercial interest is another twist, but i don't see the land wars. Laid out correctly it would end the argument. If a society found itself with a need to ship food from a central location, it may stunt its growth and find this unlikely fix.

Or, for example, "The discovery of other sophonts caused a xenophobic reaction in K'kree society. The realization that intelligent carnivores might exist..." from the Wiki. So, what if the Ancients Ring world was intended for the K'Kree genetic experiments and not the Ancients. A useless assumption since it was never finished, but still. And, what would the K'Kree do if they thought it was a solution?

Ulsyus · Sep 9, 2015

savage said:
Perhaps, but a xenophobic culture with a grim future and time on their hands/claws/paws/hoofs/tentacles may prefer this route

But unless it was a means of escaping some sort of genocidal/extinction event, wouldn't it be a case of putting all their eggs (or larvae or embryos, etc) into one basket?

savage · Sep 11, 2015

Ulsyus said:
But unless it was a means of escaping some sort of genocidal/extinction event, wouldn't it be a case of putting all their eggs (or larvae or embryos, etc) into one basket?

Yes, but if they can build a ring world, it might not be a concern. Isn't it the Lemur that suffers from dramatic (even fatal) separation anxiety? A culture may have no other acceptable alternative, if interdependence is extremely high.
Now this may be a rare case, but it only takes one determined culture.

robject · Sep 11, 2015

Aramais said:
I more or less draw the line at ringworlds. They are huge, wasteful of material, and essentially vanity construction. It becomes inconceivable that a population of human-sized beings needs 362 billion beings worth of space and air. To my intuitive view, at least, humans could never manage to have that many people without devastating social issues -- constant war and competition. Non-humans...well, the giant, intelligent ants can build whatever they want.

Those small ringworlds topped out at 362 million, not billion, but I hear what you're saying.

And Greg, that just means you're slightly on the Simulationist side of things, regardless of what you think about personal combat.

As for the small ringmoons: given sufficient technology, I think a human Size 6 world (for example) with 40 billion people could easily be ringed by a single structure.

And for the BIG ringworlds: I am already on record as saying that it's quite reasonable and consistent to say that strange things go on once you're up at TL 27.

rancke · Sep 11, 2015

robject said:
As for the small ringmoons: given sufficient technology, I think a human Size 6 world (for example) with 40 billion people could easily be ringed by a single structure.

Muan Gwi has one IIRC.

Hans

robject · Sep 11, 2015

rancke said:
Muan Gwi has one IIRC.

Hans

I think there's one in Deneb as well. IIRC as usual.

rancke · Sep 11, 2015

robject said:
I think there's one in Deneb as well. IIRC as usual.

Umm... Didn't you write the sourcebook on Deneb? I just playtested Rim of Fire.

Hans

RandyB · Sep 11, 2015

Tangent to current discussion, but relevant to thread in toto:

I once had a concept for a ringmoon that had beanstalk "spokes" from the planet's surface to the ringmoon. As I lack the intellectual chops to work out the details, the idea probably violates physics to hell and gone, though.

robject · Sep 11, 2015

RandyB said:
Tangent to current discussion, but relevant to thread in toto:

I once had a concept for a ringmoon that had beanstalk "spokes" from the planet's surface to the ringmoon. As I lack the intellectual chops to work out the details, the idea probably violates physics to hell and gone, though.

Probably, but what the heck.

robject · Sep 11, 2015

rancke said:
Umm... Didn't you write the sourcebook on Deneb? I just playtested Rim of Fire.

Yeah. I must have blocked that out of my memory.

shaunhilburn · Sep 11, 2015

RandyB said:
I once had a concept for a ringmoon that had beanstalk "spokes" from the planet's surface to the ringmoon. As I lack the intellectual chops to work out the details, the idea probably violates physics to hell and gone, though.

The centrifugal gravity would be low assuming the planet, spokes, and ring are all coupled and revolve together as a single unit.

A ring constructed at the Earth's geostationary distance would have around 0.02G of centrifugal acceleration. To produce useful acceleration on the ring interior you would need to greatly increase the ring radius or the planetary rotation.

aramis · Sep 11, 2015

RandyB said:
Tangent to current discussion, but relevant to thread in toto:

I once had a concept for a ringmoon that had beanstalk "spokes" from the planet's surface to the ringmoon. As I lack the intellectual chops to work out the details, the idea probably violates physics to hell and gone, though.

Not really, provided that the ring moon is at geosynchronous orbit.

With gravitic tech, you don't even need to worry about spin-grav.

RandyB · Sep 11, 2015

shaunhilburn said:
The centrifugal gravity would be low assuming the planet, spokes, and ring are all coupled and revolve together as a single unit.

A ring constructed at the Earth's geostationary distance would have around 0.02G of centrifugal acceleration. To produce useful acceleration on the ring interior you would need to greatly increase the ring radius or the planetary rotation.

aramis said:
Not really, provided that the ring moon is at geosynchronous orbit.

With gravitic tech, you don't even need to worry about spin-grav.

Geosynchronous orbit was exactly my thought.

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