John Shesta was an American rocket engineer who designed the Viking rocket propulsion system. An early member of the American Rocket Society, Shesta was one of the founders of Reaction Motors, a company responsible for building many of the engines used in American space launch vehicles and missiles. As Milton Rosen wrote in The Viking Rocket Story: "Shesta was a conservative designer; he made the [Viking rocket] chamber overly large to ensure complete combustion and he chose an injector ... that, while not the best known, was reasonably sure to work."