== Starship == 

 I think the concepts mentioned in this section need to recognize that, with the barely conceivable exception of anti-matter propulsion, no credible means of getting up to more than about 10% of the speed of light is known.  Even with nuclear fusion, the most energetic realistic form of on-board propulsion, the rocket equation poses tremendous problems for a ship that is to accelerate to say, 0.1c , possibly coast for a while, and then decelerate to the speeds of stars in the Galaxy.  Laser sailing with  beam-driven propulsion seems potentially able to achieve similar speeds, but nothing seriously approaching light speed, due to the redshift (and accompanying loss of energy and momentum in the beam) of the source, if for no other reason; and it also  has the serious problem of not being able to stop at the destination without some other means of propulsion.   

 This means we are talking about trip times of decades or a century even to reach the nearest stars.  The technology needed to build a self-sustaining colony, with a life time of a century, could well be enabling for such concepts.  Shielding against radiation would not be significantly affected by such low speeds beyond that which would be needed to protect against cosmic rays (conservatively, 1000 gm/cm², the same as provided by the Earth's atmosphere).  Interstellar dust would probably not be a serious issue either, once far from the Solar System, perhaps avoiding especially dusty regions.  The local solar neighborhood seems to have very low density of dust and gas, on the order of 0.01 protons per cm³.  Section would be more relevant and more credible if it were edited with these realities in mind.