The diagram is from NASA Publication SP-413, Space Settlements: A Design Study. "An upper limit to the speed of growth of space colonization is estimated by assuming 3 years for the duplication of a habitat by a workforce equivalent to 12 percent of a habitat's population. Only 56 years are required at this rate for the construction of communities in space adequate to house a population equal to that of the Earth today." (Quote from page 175)

Source URL: http://www.nss.org/settlement/nasa/75SummerStudy/Design.html archive copy at the Wayback Machine

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