 In reaction to this trend, hard science fiction began to be distinguished as a separate subgenre, but paradoxically Heinlein is also considered a seminal figure in hard science fiction, due to his extensive knowledge of engineering and the careful scientific research demonstrated in his stories.Heinlein himself stated—with obvious pride—that in the days before pocket calculators, he and his wife Virginia once worked for several days on a mathematical equation describing an Earth-Mars rocket orbit, which was then subsumed in a single sentence of the novel "Space Cadet".Heinlein is often credited with bringing serious writing techniques to the genre of science fiction.