 His most famous work, "" ("Issledovanie mirovikh prostranstv reaktivnimi priborami", or "The Exploration of Cosmic Space by Means of Reaction Devices"), was published in 1903, but this theoretical work was not widely influential outside Russia.Spaceflight became an engineering possibility with the work of Robert H. Goddard's publication in 1919 of his paper "A Method of Reaching Extreme Altitudes", where his application of the de Laval nozzle to liquid fuel rockets gave sufficient power for interplanetary travel to become possible.This paper was highly influential on Hermann Oberth and Wernher Von Braun, later key players in spaceflight.