Back in 6th grade when I read my very first SciFi book – Have Space Suit, Will travel (Robert Heinlein) – I don’t think I was aware of the potential in combining sex  and science fiction.
But In 1955, Isaac Asimov wrote “The Portable Star“, a story he considered so bad, so sexy, that he forbade it ever being collected or reprinted. For fifty-four years, it has been forgotten. Until now. More on io9 Isaac Asimov’s Lost Story Of Sex And Telepathic Energy Beings