Crabylon Six

If humans were reproducing so that they doubled every 50 years, the total population of humans in 2257 AD might be 187 billion.
(2020-2257 = 237 years; 4.74 doubling cycles; 2^4.74 = 26.72 factor; times 7 billion = 187,059,693,952, or 187 billion)
To sustain that number on terrestrial planets would be impractical. Whereas massive cylindrical space habitats could support that many. Acclimated to living in artificial habitats, humans could exist in any stellar system, as long as there was plenty of raw materials to construct more colonies… and a friendly neighborhood fusion reactor.

An “Island Three” O’Neill colony might consist of (2) 5 mile diameter by 20 mile long cylinders.
https://en.wikipedia.org/wiki/O%27Neill_cylinder
Radius = 13200 ft. (4023.4 m)
Each cylinder could hold 1319 “floors” of concentric cylinders, with a total surface area of 207188.04 square miles (536614.56 square kilometers).
Combining both cylinders, the net result is 414,376.08 square miles (1073229.12 square kilometers).

(For comparison, the surface area of California is 163,696 sq mi or 423970.69 sq km )

If the population density was 100/ sq.mi.(6.4 acres per person), a space colony could contain a maximum of 41,437,608 passengers.

To house 187 billion humans, would require only 4,514 mega-colonies in 2257. Of course, the construction rate would have to be doubling at a faster rate than humanity – say 20 to 30 years to construct a colony. And if each new colony has the “job” of building another colony, the rate of construction would exceed the rate of human population growth.

As for raw material, there’s plenty in the Solar system.

Scientists think the M-type (metallic) asteroid 16 Psyche is comprised mostly of metallic iron and nickel similar to Earth’s core.
https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/16-psyche/in-depth/
https://en.wikipedia.org/wiki/16_Psyche
16 Psyche (asteroid) mass : (2.23±0.36)×10^19 kg

From this one asteroid, one could build 546,256,494,080 battleships of the Iowa Class.
IOWA class battleship weighs 45,000 tons (40,823,313.3 kg, or 40,823 metric tonnes)

{Of course, we’d rather build autonomous space colonies, instead of armored dreadnoughts in space.}
An O’Neill cylinder 5 miles x 20 miles, 1319 decks, holding approx. 10.36 million crew (nominal) 20 million (max).
Massing 26,742 megatonnes per colony
Estimated 833,895 space colonies could be constructed from just that one asteroid.

Most efficient means to construct the infrastructure is to use autonomous robot factories (“Queen ants”) which are seeded upon a multitude of celestial bodies. Each “queen” builds tools (myrmidons?), that build the bigger tools, that build the shells, hulls, tanks, and habitats necessary for space colonization. When finished, they could be shipped via the Interplanetary Transport Network, to a Lagrange point near Earth, for commissioning with crew and supplies.

Once the rate of new colony construction far exceeds the rate of population growth, there will be innumerable opportunities for staking a claim on an “empty” and setting off, to new orbits, or even new star systems, utilizing solar powered laser satellites to propel these colonies outfitted with massive solar sails.

Star systems may be colonized by first sending robot scouts / factories to investigate and begin construction of infrastructure, vessels, and laser propulsion systems. Then launch an armada (i.e., serial packets) of colony transport habitats, via laser propulsion (0.1g acceleration requires 354 days to reach 0.1c), to the neighboring star systems. The continuous long chain of ships, 0.1 light year apart, provide a communications link. One year from destination, decelerate using the laser systems previously built, and then crew, provision and commission the habitats and vivariums awaiting their arrival. (Low acceleration is more practical when living within a 1g spinning habitat.)

Repeat the process, and expand life outward to new star systems, filling the galaxy in half a billion years or so.
By then we might have a means to reach other galaxies.


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