Encyclopedia Astronautica
N2O4/Kerosene


Nitrogen tetroxide became the storable liquid propellant of choice from the late 1950's. Rocket propellant RP-1, or its foreign equivalents, is a straight-run kerosene fraction, which is subjected to further treatment, i.e., acid washing, sulphur dioxide extraction. Thus, unsaturated substances which polymerise in storage are removed, as are sulphur-containing hydrocarbons.

Nitrogen tetroxide consists principally of the tetroxide in equilibrium with a small amount of nitrogen dioxide (NO2). The purified grade contains less than 0.1 per cent water. Nitrogen tetroxide (N2O4) has a characteristic reddish-brown colour in both liquid and gaseous phases. The solid tetroxide is colorless. N2O4 has an irritating, unpleasant acid-like odour. N2O4 is a very reactive, toxic oxidiser. It is non-flammable with air; however, it will inflame combustible materials. It is not sensitive to mechanical shock, heat, or detonation. Nitrogen dioxide is made by the catalytic oxidation of ammonia; steam is used as a diluent to reduce the combustion temperature. Most of the water is condensed out, and the gases are further cooled; the nitric oxide is oxidised to nitrogen dioxide, and the remainder of the water is removed as nitric acid. The gas is essentially pure nitrogen tetroxide, which is condensed in a brine-cooled liquefier. 1959 production amounted to 60,000 tonnes per year. In carload lots of one-ton cylinders, the price was $ 0.15 per kg. By 1990 NASA was paying $ 6.00 per kg due to environmental regulations.

Rocket propellant RP-1 is a straight-run kerosene fraction, which is subjected to further treatment, i.e., acid washing, sulphur dioxide extraction. Thus, unsaturated substances which polymerise in storage are removed, as are sulphur-containing hydrocarbons. Furthermore, in order to meet specification requirements of density, heat of combustion, and aromatic content, the kerosene must be obtained from crudes with a high naphthene content. RP-1 is an excellent solvent for many organic materials. The flash point is above 43 deg C. Above that temperature RP-1 will form explosive mixtures with air. The temperature range for explosive mixtures (rich limit) is 79 to 85 deg C. RP-1 is not so toxic as the JP series of fuels because of its lower aromatic content. In the United States, suitable kerosene fractions in 1960 were limited almost exclusively to the West Coast. The estimated 1956 United States production was 7700 tonnes, and the price was $0.05 per kg. By the 1980's it was typically $ 0.20 per kg. Russian formulations have typical densities of 0.82 to 0.85 g/cc, and even higher densities were achieved in the N1 and Soyuz 11A511U rockets by superchilling the fuel prior to loading.

Oxidizer: N2O4. Fuel: Kerosene. Propellant Formulation: N2O4/Kerosene. Optimum Oxidizer to Fuel Ratio: 4.04. Temperature of Combustion: 3,445 deg K. Density: 1.25 g/cc. Characteristic velocity c: 1,660 m/s (5,440 ft/sec). Isp Shifting: 276 sec. Isp Frozen: 264 sec. Oxidizer Density: 1.450 g/cc. Oxidizer Freezing Point: -11 deg C. Oxidizer Boiling Point: 21 deg C. Fuel Density: 0.806 g/cc. Fuel Freezing Point: -73 deg C. Fuel Boiling Point: 147 deg C.

Location: 1660.
Specific impulse: 323 s.
Specific impulse sea level: 276 s.

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Associated Engines
  • Otrag Otrag N2O4/Kerosene rocket engine. 27.5 kN. First and upper stages of low-cost booster. Out of production. Isp=297s. Pressure-fed, using cheapest possible propellants. Injection pressure: 40-15 bar; thrust control: 100-40 %. First flight 1977. More...

Associated Stages
  • Otrag N2O4/Kerosene propellant rocket stage. Loaded/empty mass 1,500/150 kg. Thrust 26.96 kN. Vacuum specific impulse 297 seconds. Clustered to form Otrag launch vehicles. Pressure-fed, using cheapest possible propellants. Injection pressure: 40 - 15 bar; Thrust control: 100% - 40 %; Pressurization: Compressed air 66% tank filling in blow-down mode; Injector: Radial like on like; Chamber cooling: Ablative phenolic; Material of injector, valves, bulkheads: AlMg5; Material of cylindrical tank sections: cold rolled low carbon stainless steel. More...

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