From 1947 through 1958, Robert Heinlein was primarily an author of science fiction aimed at the "juvenile" market, specifically at teenaged boys. Besides two minor novellas serialized in Boys' Life, the magazine of the Boy Scouts of America, there were twelve dazzlingly successful novels published as a juvenile series by Scribner's. These dozen novels have proved to be as popular and influential as anything Heinlein ever wrote, all going into continual mass-market reprintings, with several transposed into movie, television, and comic-strip versions. (p. 73)

[These works] form a coherent epic, the story of the conquest of space. Like the tales and sketches Heinlein was publishing in general-circulation magazines, these longer works are optimistic, expansionary, romantic, pulsing with missionary zeal for a colossal human endeavor and also throbbing with a fever to escape from the urbanized, complex, supposedly routinized and imprisoning experience of Earth. The central figures are always boys making their...