Twin Spin

It’s 2118, September 29.

I may have forgotten to mention that we’re working on a typical twin cylinder space habitat, a minimal “Island Three” O’Neill style colony with the following dimensions : 5 mile (8 km) diameter, 20 mile (32 km) length, a limit based on 1970s material science. Unlike the colonies described in his book, “High Frontier,” these cylindrical vessels are not open, but divided into concentric decks.
To further enhance the environment, the decks are subdivided into concentric cylinders, that are spun at different rates to simulate gravity in a range.
Instead of only the outermost shell having the ideal “earth normal” gravity, multiple concentric shells allow for repetition of the 1g to 0.7g range.
. . . .
5 mile diameter ship has a radius of 13200 feet (4023 meters).
For a range of G = 1.0 to 0.7, 9 shells + 1 hub
. . . . .
Shell 1, Deck 1, . .  G=1.0,  0.470 RPM, 443.13 MPH
Shell 1, Deck 398, .G= 0.7,  0.470  RPM, 309.85 MPH

Shell 2, Deck 1, . . .G=1.0,  0.562 RPM, 369.95 MPH
Shell 2, Deck 275, .G=0.7,  0.562 RPM, 259.20 MPH

Shell 3, Deck 1, . . .G=1.0,  0.672 RPM, 309.28 MPH
Shell 3, Deck 192 . G=0.7, 0.672 RPM, 216.72 MPH
(and so on)

There is a 20 foot (2 deck) gap between each concentric cylinder. And of course, the central hub (1000 feet / 304 meter diameter) is not spun, since it is used for docking vessels, and bulk storage.

Overall there are 1252 decks under spin, providing a maximum surface area of 206,943.84 square miles per cylinder. (For comparison, the surface area of California is 163,696 sq mi)
Our twin cylinder colony has a maximum surface area 413,887.68 sq. mi. The optimized maximum carrying capacity is 60 people per square mile, or 24,833,260 people. Of course, the initial crew are a fraction of that capacity, allowing for expansion room as the generations double.

Working backwards, from the optimax of 24.8 million, 12.4 million, 6.2 million, 3.1 million, and 1.5 million – our current target goal of charter crew members. Based on a 60 year doubling rate, the colony is good for 240 years. But the current practice is to either “bud” off a daughter colony, keeping in the same orbit, or claim an empty, crew it, stock it, and “surf gravity” to a new orbit. . . long before optimax is reached.

As usual, the order of the day is to work hard, play hard, enjoy the fruits of our labor, and live the good life, building prosperity, one space ship at a time.

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