1. James A. Van Allen, “Myths and Realities of Space Flight,” Science 232 (30 May 1986): 1075–1076; letters responding to this article are given in Science 233 (8 August 1986): 610-611, I described Van Allen’s views briefly in Space 2000, pp. 324-327.
2. See Shipman, Space 2000, pp. 72ff; and A. C, Clarke, Ascent into Orbit; A Scientific Autobiography (New York: Wiley, 1984).
3. The White House, Office of the Press Secretary, Fact Sheet on the President’s Space Policy, released February 1988.
4. See, for example, Henri Pirenne, Economic and Social History of Medieval Europe, trans. I. E. Clegg (New York: Harcourt, Brace, and World, 1937), pp. 142–146.
5. The role of spices in medieval and Renaissance Europe is described by Frederic Rosengarten, Jr., The Book of Spices (New York: Pyramid, 1973), pp. 60–65.