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131 Mircea Pfleiderer and Paul Leyhausen worried that passengers might suffer a crippling loss of technological knowledge during the long flight. Papagiannis took a more upbeat view, commenting that our own Earth is a colossal spaceship that orbits the Galaxy in about 250 million years; nobody seems to mind this grand trip. O’Neill-type space colonies would make the colonization of the Galaxy much easier and much more complete, because their inhabitants will prefer to live in space habitats rather than search for planets with Earth-like atmospheres. Your present author and others have proposed interstellar colonization strategies built around such artificial biospheres.** British starflight visionary Anthony Martin concluded that “the most likely transport would be ponderously slow world ships with city-sized cargoes of individuals, probably grouped into nation-sized fleets.” French scientist Maurice de San foresaw a long-term outcome: a nomadic culture living between stars.* The Interstellar Shuttle Stimulated by the idea of periodic alien visitations to our solar system, RW. Moir and W.L. Barr of the Lawrence Livermore National Labora- tory proposed cycling interstellar ships that would connect several systems. In this scheme, a world ship would exploit the gravitational slingshot effect of each star to send itself on to the next sun in its closed path. Once initiated, this approach would use a minimum of propulsion energy. There is one catch; the minimum time for a 16-light-year trip around three stars would be about 41,000 years.*° How do we reconcile these long journeys with the human life span? One approach is to maintain humans in a kind of suspended animation during much of the voyage. Don Wilcox suggested “cryo-sleep” in his 1940 story “The Voyage that Lasted Six Hundred Years.”*’ That idea later became a staple of science fiction films such as “2001” and “Alien,” although its fea- sibility has not yet been proven. Another approach is to extend individual human life spans. “For a being with a life span of 3000 years a voyage of 200 years might seem not a dreary waste of most of one’s life,” said astronomer Michael Hart, “but rather a diverting interlude.”* There have been more exotic proposals. Clarke suggested in 1968 that we send only germ cells, fertilizing them 20 years before landing and having cybernetic nurses raise the babies. Others proposed that we simply send information on desirable nucleotide sequences that the starship would convert into living beings. A probe might even prepare an environment on a suitable planet so that Earth organisms can survive and support the introduction of machine-nurtured humans.” Human Voyages