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astronautix.com N2O4/MMH





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: MMH. Fuel Density: 0.88 g/cc. Fuel Freezing Point: -52.00 deg C. Fuel Boiling Point: 87.00 deg C.

Monomethylhydrazine (CH3NHNH2) is a storable liquid fuel that found favour in the United States for use in orbital spacecraft engines. Its advantages in comparison to UDMH are higher density and slightly higher performance. Monomethylhydrazine (MMH) is 95+ per cent pure, while the normally expected impurities are methylamine and water. MMH is a clear, water-white hygroscopic liquid which tends to turn yellow upon exposure to air. MMH is a toxic, volatile liquid which will react with carbon dioxide and oxygen. MMH has the typical sharp ammoniacal or fishy odour of amines. It is completely miscible in all proportions with hydrazine, water, and low molecular-weight alcohols. MMH is not sensitive to impact or friction; it is more stable than hydrazine on mild heating and similar to hydrazine in sensitivity to catalytic oxidation.

Monomethylhydrazine may be produced by a modified Raschig process; methylamine is substituted for ammonia in the reaction with chloramine. In general, substituted hydrazines may be prepared by the reaction of an alkylsulfate or halide with hydrazine. In 1959 the price for MMH was $ 15 per kg. It was projected that this would be reduced to $ 2.00 per kg in mass production. By 1990 NASA was actually paying $ 17.00 per kg due to stringent environmental protection regulations.

Engines Using N2O4/MMH

Eng-engineslink Thrust(vac)-kgf Thrust(vac)-kN Isp-sec Isp (sea level)-sec Designed for Status
Aerojet 2 0 0.00 265   Upper Stages In Production
RS-45 0   300      
RM-1-1 0   245      
RM-1-2 0   238      
RM-05 2   238      
RS-43 2   284      
Aerojet 21 2 0.02 285   Upper Stages In Production
MRE-5/Compton Observatory 3 0.02 240   Upper Stages In Production
KEW-1 3   266      
R-6C 3 0.03 290   Upper Stages In Production
Aerojet 62 6 0.06 287   Upper Stages In Production
RS-1403 8   230      
RS-1402 10   259      
RM-25 11   286      
RM-25-1 11   300      
SE-6 11   277      
R-1E 11 0.11 280   Upper Stages In Production
RESA-2 22          
KEW-2 22   275      
SE-7-1 32   274      
SE-8 42   274      
RS-42 45   305      
KEW-3 45   283      
RM-100A 45   301      
Aerojet 445 45 0.45 309   Upper Stages In Production
R-4D 49 0.49 312   Upper Stages In Production
OMV Variable Thrust Engine 58 0.58     Upper Stages In Production
DMT-600 MMH 61 0.60 306   Upper Stages In Production
RS-2101C 136   294      
RS-2101A 136   287      
RS-32 142   288      
RS-14 142   315      
KEW-4 226   235      
RS-28 272   220      
R-40A 394 3.87 306   Upper Stages In Production
RM-900 408   309      
LR-101-NA-7 525   251      
PSLV-4 714 7.00 308   Upper Stages In Production
RESA-5 725   280      
RS-51 1,178   315      
RS-34 1,200   308      
RS-41 1,220   320      
XLR-132 1,700 16.70 340   Upper Stages Out of Production
Transtar 1,700 16.70 328   Upper Stages Out of Production
General Technology 1,813   295      
Liberty-2 1,814 17.80 300 200 Upper Stages Developed 1982-1988
Press Fed 1,814 17.80 300   Upper Stages Design concept 1960's
ATE 2,039 20.00 347   Upper Stages Developed 1990's
RS-23 2,720   313      
OME 2,721 26.70 316   First Stages In Production
L7 2,800 27.40 320   Upper Stages In Production
RS-72 5,650   338      
RS-36 5,670   281      
RD-0242M 10,003 98.10 336   Upper Stages Design concept 1998-
RD-0242M1 10,003 98.10 343   Upper Stages Design concept 1998-


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Last update 3 May 2001.
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© Mark Wade, 2001 .