10.5 reduction in Earth launch costs, either through an improved Earth launch system or a reduction in total launch mass required may significantly cut program cost as well. However, both routes to saving money trade off against each other. Savings from ~n improvement in the Earth launch system or from making part of the construction site from lunar materials may easily be lost in the discounted cost due to the increased development cost early in the program or the longer time needed to build the construction site. The lowestcost transportation and construction scenarios may differ for each colony design. The study group also concluded that, given the proposed construction scenario, the cost of a second colony would be about 15% of the first, because the reuse of the construction site already in space greatly reduces the Earth launch costs, and because a second colony program only takes 7 years. X.2 SUGGESTED RESEARCH X.2.1: General Remarks: The study group recommends that the following questions should be investigated to improve knowledge of the space colony concept. Asterisks (*) indicate priority items. X.2.2: Human Physiology: *l) Long-Term Effects of Rotation: What are the tradeoffs between spin rates and physiological and psychological problems in human beings? What is the effect of spin rates on biological processes, including pregnancy and child growth? What are the time periods and training required to adapt to spin rates, and to readapt to Earth rotation? *2) Long-Term Effects of Reduced Gravity: What are the adaptive physiological changes brought on by life at lower-thanone-g? How long are the adaptation and readaptation periods? If the changes become permanent, how long does this take? What are the effects on pregnancy and child growth?
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