http://www.sen.com/news/architects-project-for-esa-is-out-of-this-world.html
http://www.hq.nasa.gov/office/hqlibrary/pathfinders/colony.htm
http://www.space.com/813-space-colonization-quiet-revolution.html
http://www.dailygalaxy.com/my_weblog/2009/10/space-colonization-human-species-future-or-fanatsy.html