The thin line between science fantasy and fact all but vanishes in this lively account of how Earthlings can find Lebensraum Out There. A Lebensraum, moreover, which promises ideal climate, no bugs, and an unlimited supply of free energy, courtesy of the sun. That same solar power converted to electricity and relayed back to earth via microwave would not only solve the energy crisis here, but also help defray the cost of the extraterrestrial establishments. Acknowledging his debt to such prophetic writers as the Russian, Konstantin Tsiolkowsky, Princeton physicist O'Neill describes in great detail the design of spheres or cylindrical islands in space. Each would have cosmic-ray shielding, a self-contained atmosphere, gravity induced by rotation, climate and day-night cycles determined by solar reflecting mirrors, and so on. The first ones would be built from lunar stuff, later ones from asteroids. What is surprising is that no exotic technology is involved--the calculations and costs are based on the current state-of-the-art (with perhaps a little dream factor in the notion of ""mass-drivers"" and ""magnetic levitation planes""). Advocates of small-is-beautiful or deceleration in growth may question the morality of planetary sprawl. What they may no longer question is the possibility. O'Neill's text makes it clear that this is no pie-in-the-sky dream but a program that might appeal to present-day pilgrims or prospectors out to make a new world.