Ary Sternfeld (* 14 May 1905, Sieradz in Poland, then in Kalisz Governorate of Russian Empire – † 5 July 1980, Moscow, Russia) was co-creator of the modern aerospace science.
He was a Polish engineer of Jewish origin, who studied in Poland and France.
From 1935 until his death he worked in Moscow.
He was the first person to describe the bi-elliptic transfer technique of changing orbits, in 1934.In 1934, Sternfeld won the Prix REP-Hirsch (later known as the Prix d'Astronautique) of the French Astronomical Society for his book Initiation à la Cosmonautique.
He is thus credited with introducing the word cosmonautics in the language of science and engineering.