Oort Cloud Colonies

Comets are largely ice, and ice makes a good cosmic ray shield.   Moreover, the bulk of the space colony's mass is the radiation shiled.

This drawing is not to scale.  If one foot equals one kilometer, a 100 foot thick multi-decked shell would only be  0.367 inches thick.  The ice will only be 15 to 20 feet thick, so we could build alot of subsurface dwellings without shrinking the "outside" areas in the sphere.  Perhaps the best thing to do with subsurface levels, would be farming.  I envisioned a domed farm strip running abound the equator of the Bernal sphere in which conditions were controlled for maxium crop yeilds.  A humid, CO2 enhanced atmosphere would be great for plants but not for people.  If we move the farms below, the equator could have a little river instead.  The sulfur lamp does not have to burn as brightly for people as it would for plants, but there will be vegetation; trees, flowers and shrubs, on the inner surface for the sake of beauty.

The passive radiation shield will amass about 63 million tons.  If we budget 100 million tons for the colony, we have more than enough left over.  A one million ton fusion powerplant would not seem outlandish.  The ITER will amass 10,000 tons and generate 500 MWe.  Our plant could generate 50,000 MWe.  That much power could illuminate 50 square kilometers as brightly as the Sun does on Earth.  Since plants don't need full sunlight, this would be more than enough for farming under lamps and powering the colony.  Future fusion reactors will be much more efficient and they will tap energy from protium-normal hydrogen.  There is plenty of protium in the universe.  Thus, it seems as if humanity can survive in the farthest regions of the solar system.

Sunlight can be harvested with huge reflectors in the outer solar system, but EK Belt and Oort Cloud dwellers will need to use fusion.  A deuterium-helium 3 TOKAMAK might be hundreds of feet in diameter, but there will be limited qtys. 3he in deep space but plenty of normal hydrogen-protium, in the water ice of trillions of comets and frozen atmospheres of rogue planets and brown dwarfs.  To fuse protium some enormous machines will be needed like the one above.  These monsters would not be economical in the inner system where plenty of cheap solar energy is available or even in the realm of Saturn where plenty of 3he is available and solar energy if one builds big enough reflectors.     Giant protium reactors would be built with cheap robot labor.  In space, there will be no need for vacuum pumps, high strength structures and obtaining super cold for super conductivity will be easy out beyond Pluto in the interstellar abyss. These factors will contribute to the feasibility of protium fusion powerplants as long as they produce more power than they consume.      Protons will be accelerated to near light speed and collided in the intense positive electrostatic field of the reactor vessel.  Helium will form and be vented into space or captured and stored.  Gamma ray energy from the fusion of quadruplets of protons will heat the reactor vessel and its working fluid (water, ammonia, helium?) to drive turbo-generators.  Power will be beamed to various colonies in the colony cluster surrounding a comet.  All of space will become habitable to humanity and not just the warm space near stars.  Given that most stars are red dwarfs and most of these are flare stars erupting X-ray bursts with thousands of times the energy of a flare on Sol, much of the territory near stars is undesirable.  The widely dispersed riches and cold  of the vast interstellar cometary clouds becomes less frightening.  Mag-sailing ships will ride beams between comet clusters at high speeds, knocking down the average 20 A.U. separation barrier. Giant protium powerplants will power the propulsion beams for 2,000,000 kph mag-sailing inter-cometary space ships of the Oort Clouds.  Ignited brown dwarfs and rogue Jupiters that have been slammed with relativistic iron projectiles propelled by RAVENs (Relativistically Accelerated Vehicle Energizing Nodes-complexes of solar collectors and particle beams that propell mag-sailing spacecraft) to generate chunks of neutron matter than then consume matter and release energy to create artificial stars in the interstellar abyss might supply power to small RAVENs that power starships of the comet dwellers. Mag-sailing vessels will brake in the interstellar medium, thus it will be possible to travel from the inner system in spacecraft accelerated by propulsion beams and brake at destinations in the Oort.  See: Charting the Oort Cloud

Interior of a Stanford Torus by Don Davis