Space development enthusiasts typically explain the significance of their favorite very large space projects-whether constructing orbital colonies or cities beneath the surface of the Moon, terraforming Mars or Venus, or launching interstellar spacecraft-in terms of their promise to produce vast new wealth, open frontiers to serve as social "safety valves" for the ambitious or the dissenting, generate the novel problems that drive dramatic advances in science and engineering, provide new sources of natural resources, and permit population dispersal to assure the long term survival of our species. Without question, these are all laudable reasons for the adventure of space and any very large space project would probably meet several of these objectives. However, if the economic and social promise of these projects is so extraordinary, and if the social losses which result from failing to undertake them are so large, why haven't humans embarked on them? Why aren't we even close to beginning one of these great enterprises? Given the assertion made by many space development enthusiasts that the basic technology needed for their favorite projects already exists or can be developed from the available science, asking these questions is entirely fair. The answers must be found in political economy, some rudimentary understanding of which will be necessary before realistic planning for any very large space project can begin.