After deciding on Clarke's 1948 short story "The Sentinel" as the starting point, and with the themes of man's relationship with the universe in mind, Clarke sold Kubrick five more of his stories to use as background materials for the film. These included "Breaking Strain", "Out of the Cradle, Endlessly Orbiting. . . ", "Who's There?", "Into the Comet", and "Before Eden". Additionally, important elements from two more Clarke stories, "Encounter in the Dawn" and (to a somewhat lesser extent) "Rescue Party", made their way into the finished project. One other element (crossing vacuum without an intact pressure suit) is from the short story "Take a Deep Breath".