Imagining my own telepathic navigators, unlike Herbert's Spice-addicted thralls, mine were free agents offering their services to the highest bidder, wearing evidence of their skill and prosperity on vestments and antennae, star-charts wrapped around their minds, and the incense of a distant world, the destination, filling their lungs, navigating using all their senses and faculties. The more skilled the seer, the more wealthy the patrons -- the penalty for a navigational mistake was horrific, lethal, so the best seers enjoy celestial prestige and command celestial fees.