Tonka

Tonka (also TONKA-250 and R-Stoff) is the name given to a German-designed rocket propellant first used in the Wasserfall missile, and recently used by North Korea. It was used in the Soviet Union under the name TG-02, for example in the engine designs of the A.M. Isayev Chemical Engineering Design Bureau. Its name is a reference to the tonka bean. Being invented during the Second World War, it has no connection to the similarly named toys. Its composition is approximately 50% triethylamine and 50% xylidine, most commonly used with nitric acid or its anhydrous nitric oxide derivatives (classified as the AK-2x family in the Soviet Union) as the oxidiser; the combination is hypergolic and has a maximum practical specific impulse of approximately at sea level, with the latter figure stated as a specification for the R-21 Submarine Launched Ballistic Missile, first fielded in 1963. The Soviet Union reverse-engineered the Wasserfall missile and investigated the use of hypergolic propellants for the eventually abandoned Burya ICBM project. It put TG-02/AK-2x fuelled engines into service with the Kh-22 cruise missile and the S5.4 de-orbit engine used on the Vostok and Voskhod spacecraft and the Zenit satellite.