"In Viagens Interplanetarias, Sprague’s interstellar travel takes place in Earth's backyard, so to speak; among stars, that is, within a reasonable number of light-years from the sun. Further, his concept of interstellar travel has . This makes the stories harder to write. I once asked him why he did this and he explained that since travel faster than the speed of light was impossible, it would take far too long to reach the really distant stars. I pointed out that if he used “hyper-space” as most writers did, that wouldn’t matter. (Hyperspace is a mythical term among s.f. writers and can be used in a vague and foggy way to excuse any speeds up to infinity.) Sprague said he didn't believe in hyperspace. I said neither did I but I used it. He just put his pipe in his mouth and shook his head. "If I don’t believe a thing is possible," he said, "I don't use it.""