Ary Abramovich Sternfeld (1905–1980) was a Polish-Soviet pioneer of theoretical astronautics. Born in Sieradz (Poland, then part of the Russian Empire) into a Jewish family, he studied in Krakow and Nancy before defending a foundational doctoral thesis at the Sorbonne in 1934, titled Initiation à la cosmonautique. That same year, the Paris Academy of Astronautics awarded him the international Esnault-Pelterie–Hirsch prize. In 1935 he emigrated to the USSR, where he worked at the RNII (Reactive Scientific Research Institute) alongside Tikhonravov and Glushko. A prolific author, he published in 1937 Введение в космонавтику (Introduction to Cosmonautics), a foundational theoretical treatise, followed by a series of widely read popular works (Polyot v mirovoye prostranstvo, 1949 ; Artificial Earth Satellites, 1956 ; From Artificial Satellites to Interplanetary Flight, 1959) that shaped a generation of Soviet scientists and future cosmonauts. He computed optimal interplanetary trajectories and popularized several neologisms (cosmonaut, cosmodrome, cosmonef). Sidelined under Stalinism, he received belated recognition after the launch of Sputnik.