<i>11% of the energy output of the US...I don&#x27;t doubt the theoretical possibility, I doubt the economic and experimental reality.</i><p>If we&#x27;re going to be doing space travel on time scales where decades don&#x27;t come into the picture, we&#x27;re going to need devices with this kind of energy. Access to that kind of energy isn&#x27;t ridiculous if your infrastructure is already in space, so it&#x27;s only ridiculous in our current context.<p>The notion of creating a web of railway networks across an entire country was completely impractical before the Bessemer steel process.<p><i>I haven&#x27;t even gotten into dispersion of a laser beam.</i><p>Also, diffraction lenses of ridiculous size become practical in micro-gravity so diffraction isn&#x27;t an issue either, so long as your infrastructure is already in space. This is precisely how Planetary Resources will eventually make their giga-fortunes; by pioneering entirely new forms of infrastructure for an entirely new context of civilization. (This new context may not have much to do with earthly civilization, or even with humans.)