*In January of 2004, President of the United States George W. Bush introduced “A Renewed Spirit of Discovery: The President’s Vision for U.S. Space Exploration”. European, Canadian, Asian and Russian responses have varied widely. Internal to the United States, public reaction has been mixed. One factor underlying the caution demonstrated by virtually all respondents is the issue of cost; such an effort is beyond the resources of a single country and will require international cooperation, i.e., investment. The second factor is the difficulty of “ensuring sustainability” through multiple U.S. Administration and Congressional shifts. This paper briefly reviews the history of human space flight in light of the factors which have driven expenditures in the past and posits that the current initiative may fail unless one of the following conditions is met: (1) The emergence of a political imperative sufficient to spur international governments to reprogram funds while garnering cross-generational public support, or (2) the development and implementation of a economic model that enables cost-sharing among international governments, private industry, commercial interests and the public to a degree previously unprecedented in human space flight. The paper concludes with some high-level requirements for a cost model necessary to meet the second condition, a speculative discussion of the type of “transformational event” to meet the first, and some suggestions for approaching the issue of program sustainability.