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astronautix.com N2O4/Pentaborane





Oxidiser: N2O4. Oxidiser Density: 1.45 g/cc. Oxidiser Freezing Point: -11.00 deg C. Oxidiser Boiling Point: 21.00 deg C.

Nitrogen tetroxide became the storable liquid propellant of choice from the late 1950's. 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.


Fuel: Pentaborane. Fuel Density: 0.62 g/cc. Fuel Freezing Point: -47.00 deg C. Fuel Boiling Point: 62.00 deg C.

Pentaborane (B5H9) was considered as a high performance fuel in the US in the 1950's. Its development was pursued with some vigour by Glushko in Russia during the 1960's. But like the other fluorine and boron motors of the time, it presented too many handling and safety problems to be adopted as a flight engine. Pentaborane is a colorless, mobile liquid. It exhibits a disagreeable odour and is an extremely toxic propellant. In the presence of water, B5H9 is much more stable than diborane. Pentaborane, if pure, is not spontaneously flammable in air. However, minor concentrations of impurities cause it to be spontaneously flammable in air. Prolonged storage for several years at room temperature reveal only negligible decomposition of pentaborane with the formation of hydrogen and solid residue. It shows good solubility in hydrocarbons, cyclohexane, and benzene.

Pentaborane is produced by the pyrolysis of diborane; the conversion is not a clean-cut reaction.

Engines Using N2O4/Pentaborane

Eng-engineslink Thrust(vac)-kgf Thrust(vac)-kN Isp-sec Isp (sea level)-sec Designed for Status
RD-270M 730,000 7,159.00 365 340 First Stages Study 1962-1970


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Last update 3 May 2001.
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