Shortly after World War II, a young Arthur C. Clarke penned a work of speculative documentary fiction: his account of mankind's first foray to the moon. Written in 1947, Prelude to Space has that accomplishment taking place in 1978—nearly a decade, we know now, after the real-life moonshot.
If Clarke underestimated the speed with which human beings would make it to the moon, he overestimated the speed with which space exploration would advance in subsequent decades. His book takes it for granted that the first journey to Mars will follow closely on the heels of the first lunar mission. Indeed, reaching the moon is seen as valuable in part because it offers a low-gravity launch pad from which to explore the further reaches of space. Needless to say, reality has failed to match those hopes.
