Arkady Aleksandrovich Kosmodemyansky (7 March 1909 – 8 December 1988) was a Soviet physicist and mechanician, professor at Lomonosov Moscow State University. A Doctor of Sciences in Physics and Mathematics, Stalin Prize laureate, and twice recipient of the Order of Lenin (1956 and 1957), he was the leading Soviet authority on Konstantin Tsiolkovsky's scientific legacy in the postwar decades. A specialist in theoretical mechanics and hydrodynamics, he devoted part of his career to the history of aeronautical and space sciences. From the 1950s onward he published several monographs on the father of cosmonautics, including Konstantin Tsiolkovsky: His Life and Work (Moscow, 1956, Foreign Languages Publishing House, translated into English and French) and a major scientific biography published by Nauka in 1976. His dual grounding as a practising mechanician and accessible writer allowed him to explain the mathematical significance of the Tsiolkovsky rocket equation and the theory of interplanetary travel to an international audience.