From 1947 through 1958, Heinlein wrote twelve novels for the juvenile market. In this series, he introduces the gamut of SF conventions: lunar exploration, interplanetary travel, colonization of Mars, interstellar travel (both at the Einsteinian speed limit and faster), and many others. Through these novels (which comprised one of the most successful juvenile series in SF) Heinlein reached, and continues to reach, generations of readers.
The heroes, always male, are inevitably spunky and clean-cut juveniles (usually about high school age) who can be counted on to run afoul of oppressive rules. These books are well-written, and many readers (juvenile as well as adult) find them delightful.
Red Planet (1949) is an example of Heinlein’s excellence in that series. A Mars novel, Red Planet is not much outside the usual conventions of planetary SF. Old and arid, Mars has an unimaginably ancient indigenous civilization that lingers on, its survivors usually in some state of contemplation. The Martians have enormous powers (which becomes an element late in the plot), but they don’t seem much concerned that the earth people are colonizing their planet. Earth, though, very much needs the room because of dangerous over-population on the home planet.
Mars is the new frontier for the people hardy enough to survive the harsh environment. But even on this new frontier, an officious and, finally, bungling bureaucracy tries to make things difficult for the true Martian colonists—humans who wish to make Mars home. In typical fashion, the young heroes, Jim and Frank, foil the plans of the villains (and at one point escape capture by ice-skating the frozen Martian canals).
It is an exciting story, especially as Heinlein manipulates the plot in order to deliver enjoyable—and finally, moral—entertainment for young readers. Heinlein gains suspense with a method that is usual in popular fiction. We know, and the author knows, that the protagonist (the “good guys”) will win. In order to bring suspense, the author stacks the conditions greatly against the protagonist. The reading enjoyment then shifts to figuring out how the protagonists can win against such extraordinary odds.
So, of course, the forces of decency prevail, and in something like a second American Revolution, the Martian colonists gain a measure of self-autonomy. The self-reliant loners win out against the system; this is a theme that runs through all of Heinlein’s fiction, adult and juvenile.
Heinlein’s career in juvenile fiction came to an end with Starship Troopers (1959), a novel that his publisher would not include as part of the juvenile series. The publisher objected to the militarism of the novel, which depicts a future in which only those who have served in the armed services are entitled to full citizenship. It is a world that seems constantly on military alert (finally justified by the fact that earth is attacked by a species of especially nasty spider creatures).