In Tom Godwin's short story "The Cold Equations," Marilyn's jettison from the ship is inevitable, and Barton has no choice but to do so. To be jettisoned does, indeed, mean to be thrown overboard a "vessel of aircraft" to lighten its load (Random House Dictionary). Marilyn's jettison is inevitable because the continuation of her one life aboard the Emergency Dispatch Ship (EDS) will cost the lives of many others.
Godwin's futuristic science fiction story is set in outer space, and mankind is in the process of colonizing the various planets in the galaxy. Since the colonies on the various planets are very far apart from each other, the chances of man's survival in the colonies are slim without some method of emergency transportation. EDSs were designed to be lightweight to reach their destinations and fulfill their emergency missions as quickly as possible. Since they need to be lightweight, they can only carry the precise amount of fuel needed to reach their destination, and fuel is calculated based on mass and distance. The additional weight of a stowaway changes the mass, and the ships do not carry enough fuel to be able to reach their destinations with additional mass. Therefore, authorities have issued the regulation that all stowaways must be jettisoned to ensure the EDSs reach their destinations and save the lives they set out to save. As the narrator explains, "It was a law not of men's choosing but made imperative by the circumstances of the space frontier."
By the end of the story, Marilyn perfectly understands there is not enough fuel to carry her weight and accepts her choice has led to consequences she did not anticipated. After writing her goodbye letter to her parents and talking with her brother on the radio, she is prepared to accept her fate; she steps "into the air lock" and tells Barton, "I'm ready." Barton then performs the necessary actions to jettison her. Although Barton knows he has no choice but to take Marilyn's life to ensure the lives of others are saved, he grieves over her death, still feeling her presence and hearing her words long after she is gone.