Doesn't anyone remember Gerard K. O'Neill and "The High Frontier" published back in the mid 70's? The whole idea was that building powersats in space would be far more efficient. We would need a mass launcher on the moon, and space colonies at L5. This could be the path to large-scale settlements in space.
In any case, they did a bunch of up-front research into microwave transmission, space-based manufacturing techniques and whatnot. A fun read.