Barrier of the Unknown (Russian: Барьер неизвестности, romanized: Barier neizvestnosti) is a 1961 Soviet science fiction film directed by Nikita Kurikhin.The film tells about the creators and testers of the Soviet piloted hypersonic airplane "Cyclone". In the USSR, there were many such programs which were left unfinished, but all the characteristics of the Cyclone (speed, altitude, etc., except for "radioactive combustion accelerators"), including flight characteristics (launch from a carrier aircraft) are exactly borrowed from the North American X-15.