I wager there's quite a few stories exploring this premise. I remember reading Stephen Baxter's "Voyage" in the 90s, in which Kennedy escapes his assasination,

I wager there's quite a few stories exploring this premise. I remember reading Stephen Baxter's "Voyage" in the 90s, in which Kennedy escapes his assasination, the Apollo program ends rather differently and NASA subsequently stretches/evolves the hardware to put a crewed mission on Mars, rather than building the Shuttle. It's been a long time, but I think I recall enjoying the geeking out on the equipment and little historical details. (I've since read the novel has been widely criticized as plagiarizing the Cox/Murray book on Apollo history, which I read 20 years later and is an amazing achievement.)