The idea of using a large gun to send humans into space is as impossible today as it was a century and a half ago, when Jules Verne wrote From the Earth to the Moon and Around the Moon. Yet he went to great lengths to persuade readers it wasn't impossible - not through arm-waving and made-up technobabble, but using real physics and astronomy. No one had done anything like that in fiction before - and even today it's unusual to see so much "real science"...