Howard McCurdy and Roger Launius propose a method for assessing the financial burden that space expeditions impose on the national economy.  The method calculates the cost of the program as a proportion of the gross domestic product in the year the expedition is approved.  Excerpted from their forthcoming book on NASA Spaceflight: A History of Innovation by Launius and McCurdy, to be published in late 2017 by Palgrave Macmillan.