Specialist (short story)
"Specialist" is a science fiction short story by Robert Sheckley. It was first published in 1953 and has appeared in various collections, including Untouched by Human Hands (1954) and The Golden Age of Science Fiction (anthology), edited by Kingsley Amis in 1981.
The Crew comprises varied members of vastly different intelligent races, all in close mental rapport known as the Cooperation, and serving specialized functions; they are known as Engine, Thinker, Eye etc. But without a Pusher, they cannot accelerate to ftl speeds. They manage to locate a planet known to be rich in primitive Pushers, Earth. They try to communicate with a man they find, but he is so violent and resistant that they are forced to bring him on board the ship to try to reason with him.
Gradually, the man begins to realize the nature of the Crew and the pleasure to be found as a part of the mental Cooperation. He agrees to join the crew. Hesitantly at first, he tries to Push and finally learns how it is done. The ship speeds away at eight times the speed of light and accelerating.