The beauty of novel space is that it's boundless in a way real space could never be. I mean, think about 'The Hitchhiker's Guide to the Galaxy'—Douglas Adams packed entire civilizations into a single spaceship, and the Vogons destroyed planets for bureaucratic paperwork! Real space exploration is shackled by physics, budgets, and the slow crawl of light-years. But in books, you can zip through wormholes, meet telepathic aliens, or stumble upon a sentient nebula by chapter three.
That said, there's a weird kinship between the two. Both require imagination—scientists dreaming up warp drives, authors sketching dystopian Mars colonies. Real astronauts train for years to float in zero gravity; novelists spend months researching orbital mechanics to make their zero-g fight scenes feel authentic. But only one lets you have a talking spaceship with existential dread, like in 'Ancillary Justice'.