It's been a long long time since I read the books, but I'm pretty sure that the Dune universe takes place many years after some sort of apocalyptic war, the end result of which is computers/AI are banned. So interstellar travel in Dune is only possible through use of the spice by guild navigators to fold spacetime. In later books I think there is a sort of race of aliens (Tleilaxu, of whom the mentats such as Piter come from) who use forbidden technology and do manufacture a spice type analogue.
Also highly recommend the documentary Jodorowsky's Dune, what surely would have been an even more outlandish and bizarre movie than the Lynch version. Salvador Dali as the Emperor, Orson Welles as the Baron, Mick Jagger as Feyd. Pre-Alien HR Giger and Dan O'Bannon....would have been rad. Documentary is stellar, and maybe will also help flesh out some plot points for you as well, though Jodorowsky's treatment took a lot of liberties with the story.
Also highly recommend the documentary Jodorowsky's Dune, what surely would have been an even more outlandish and bizarre movie than the Lynch version. Salvador Dali as the Emperor, Orson Welles as the Baron, Mick Jagger as Feyd. Pre-Alien HR Giger and Dan O'Bannon....would have been rad. Documentary is stellar, and maybe will also help flesh out some plot points for you as well, though Jodorowsky's treatment took a lot of liberties with the story.