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Agena Engine
Agena Engine -

Credit: Bell. 24,273 bytes. 397 x 248 pixels.

Oxidiser: Nitric Acid. Oxidiser Density: 1.51 g/cc. Oxidiser Freezing Point: -42.00 deg C. Oxidiser Boiling Point: 86.00 deg C.

Drawing on the German World War II Wasserfall rocket, nitric acid (HNO3) became the early storable oxidiser of choice for missiles and upper stages of the 1950's. To overcome various problems with its use, it was necessary to combine the nitric acid with N2O4 and passivation compounds. These formulae were considered extremely secret at the time. The propellant combinations WFNA/ JP-4 and later IRFNA/JP-4 were the first storable systems given serious consideration in the United States. Problems which caused the abandoning of these propellants were the absence of reliable hypergolic ignition and unstable combustion. IRFNA/UDMH and IRFNA/JP-X finally did prove satisfactory.

By the late 1950's it was apparent that N2O4 by itself was a better oxidiser. Therefore nitric acid was almost entirely replaced by pure N2O4 in storable liquid fuel rocket engines developed after 1960. The composition of propellant-grade nitric acids is covered by Military Specification MIL-N-7254. The nitric acids are fuming liquids which vary from colorless to brown, depending on the amount of dissolved N2O4. The vapours from these acids have a characteristic pungent odour. They are highly corrosive, toxic, oxidising agents and attack most metals. They react with most organic materials violently enough to cause fire. The acids are soluble in water in all proportions, with an accompanying evolution of heat. They cannot be made to explode. Approximately 90 per cent of the nitric acid is made by the catalytic oxidation of ammonia with air or oxygen to yield nitric oxide (NO). The latter is oxidised to N2O4 which, when treated with water, yields nitric acid (HNO3) and may be concentrated by distillation with sulphuric acid. Red fuming nitric acids may be produced by passing gaseous N2O4 into nitric acid, a slight modification of the above process. Production of nitric acid was estimated at 3 million tonnes in 1959. The price of RFNA was $ 0.20 per kg in drum lots; IRFNA was slightly higher. The varieties of nitric acid propellants include:

Fuel: UDMH. Fuel Density: 0.79 g/cc. Fuel Freezing Point: -57.00 deg C. Fuel Boiling Point: 63.00 deg C.

Unsymmetrical Dimethylhydrazine ((CH3)2NNH2) became the storable liquid fuel of choice by the mid-1950's. Development of UDMH in the Soviet Union began in 1949. It is used in virtually all storable liquid rocket engines except for some orbital manoeuvring engines in the United States, where MMH has been preferred due to a slightly higher density and performance. Unsymmetrical dimethylhydrazine (UDMH) is 98 to 99 per cent pure and is described by Military Specification MIL-D-25604. The normally expected impurities are dimethylamine and water. UDMH is a clear, hygroscopic liquid which yellows on exposure to air. It absorbs oxygen and carbon dioxide. UDMH is a toxic volatile liquid. It exhibits the sharp ammoniacal or fishy odour which is characteristic of organic amines. It is completely miscible with water, ethanol, and most petroleum fuels. It is not shock sensitive. The vapours are flammable in air over 2.5 to 95 per cent concentration range. UDMH can be produced commercially by nitrosation of dimethylamine, to N-nitro-sodimethylrtmine, followed by reduction of the intermediate to UDMH and subsequent purification. UDMH can be prepared, also, by a modification of the Raschig process (see discussion of hydrazine), in which the chloramine intermediate is with dimethylamine rather than with ammonia. The price in 1959 for tank-car quantities was under $ 1.00 per kg. Engineering studies indicated a price of $ 1.00 per kg with large scale sustained production. But due to its toxic nature, production and transport costs soared in response to environmental regulations. By the 1980's NASA was paying $ 24.00 per kg.

Engines Using Nitric acid/UDMH

Eng-engineslink Thrust(vac)-kgf Thrust(vac)-kN Isp-sec Isp (sea level)-sec Designed for Status
RM-100B 45   283      
KDU-414 200 1.96 272   Upper Stages Out of Production
Isayev DOS-3/4 400 3.92     Upper Stages Out of Production
KTDU-35 417 4.09 280   Upper Stages Out of Production
KTDU-53 417 4.09 280   Upper Stages Out of Production
KTDU-66 417 4.09 280   Upper Stages Out of Production
KTDU-417 1,929 18.92 314   Upper Stages Out of Production
RD-851 3,310 32.48 279 243 First Stages Out of Production
AJ10-118D 3,436 33.70 278 160 Upper Stages Out of Production
AJ10-118 3,447 33.80 271 150 Upper Stages Out of Production
AJ10-101 3,500 34.30 270 240 Upper Stages Out of Production
AJ10-104 3,579 35.10 278   Upper Stages Out of Production
AJ10-118E 3,579 35.10 278   Upper Stages Out of Production
AJ10-118F 4,218 41.40 306   Upper Stages Out of Production
AJ10-118H 4,427   319      
AJ10-118G 4,427   314      
RD-852 4,920 48.25 255   Upper Stages Out of Production
Bell 8048 7,031 68.90 276   Upper Stages Out of Production
Bell 8081 7,257 71.20 285   Upper Stages Out of Production
Bell 8096 7,257 71.20 300   Upper Stages Out of Production
Nodong 14,718 144.00 255 232 First Stages In Production
11D49 16,060 157.50 303   Upper Stages In Production
YF-2A 31,218 306.10 268 241 First Stages In Production
Von Braun-3 40,000 392.30 286 230 Upper Stages Study 1952
Von Braun-2 47,058 461.50 286 230 Upper Stages Study 1952
RD-853 47,682 467.60 301   Upper Stages Developed 1960-63
U102-000 47,723 468.00 307   Upper Stages Out of Production
AJ10-33 52,000          
RD-215 88,100 864.00 291 248 First Stages Out of Production
RD-217 88,200 865.00 289 246 First Stages Out of Production
RD-219 89,950 883.00 293   Upper Stages Hardware
RD-225 90,653 889.00 294 251 First Stages Out of Production
RD-220 109,518 1,074.00 306 270 First Stages Developed 1960-
RD-221 114,004 1,118.00 318   Upper Stages Developed 1960-
RD-222 166,622 1,634.00 302 272 First Stages Developed 1960-61
RD-223 173,046 1,697.00 314   Upper Stages Developed 1960-61
RD-216 177,400 1,728.00 291 248 First Stages In Production
RD-224 181,306 1,778.00 294 251 First Stages Out of Production
S5.45 200,000 1,961.00 267   Upper Stages Out of Production
RD-218 266,000 2,592.00 289 246 First Stages Out of Production
Von Braun-1 311,764 3,057.30 286 230 First Stages Study 1952

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