Encyclopedia Astronautica
Lox/UDMH



rd119.jpg
RD-119
Credit: © Mark Wade
Liquid oxygen was the earliest, cheapest, safest, and eventually the preferred oxidiser for large space launchers. Its main drawback is that it is moderately cryogenic, and therefore not suitable for military uses where storage of the fuelled missile and quick launch are required. 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.

Liquid oxygen, as normally supplied, is of 99.5 percent purity and is covered in the United States by Military Specification MIL-P-25508. High purity liquid oxygen has a light blue colour and is transparent. It has no characteristic odour. Liquid oxygen does not burn, but will support combustion vigorously. The liquid is stable; however, mixtures of fuel and liquid oxygen are shock-sensitive. Gaseous oxygen can form mixtures with fuel vapours that can be exploded by static electricity, electric spark, or flame. Liquid oxygen is obtained from air by fractional distillation. The 1959 United. States production of high-purity oxygen was estimated at nearly 2 million tonnes. The cost of liquid oxygen, at that time, ex-works, was $ 0.04 per kg. By the 1980's NASA was paying $ 0.08 per kg.

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.

Oxidizer: LOX. Fuel: UDMH. Propellant Formulation: LOX/UDMH. Optimum Oxidizer to Fuel Ratio: 1.67. Temperature of Combustion: 3,615 deg K. Ratio of Specific Heats: 1.24. Density: 0.97 g/cc. Characteristic velocity c: 1,865 m/s (6,118 ft/sec). Isp Shifting: 310 sec. Isp Frozen: 296 sec. Mol: 21.30 M (69.80 ft). Oxidizer Density: 1.140 g/cc. Oxidizer Freezing Point: -219 deg C. Oxidizer Boiling Point: -183 deg C. Fuel Density: 0.793 g/cc. Fuel Freezing Point: -57 deg C. Fuel Boiling Point: 63 deg C.

Location: 1865.
Specific impulse: 363 s.
Specific impulse sea level: 310 s.

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Associated Engines
  • RD-115 Glushko lox/udmh rocket engine. 1726 kN. ICBM stage 2 (stage 1 was RD-114). Developed 1961-65. Upper stage version of RD-114 with larger nozzle. Isp=357s. More...
  • RD-109 Glushko lox/udmh rocket engine. 101.6 kN. Developed 1957-60. Isp=334s. Intended for second stage of Lox/UDMH 8K73 version of R-7. Abandoned because of Korolev's refusal to use such a toxic fuel. Later basis for RD-119 used on the Kosmos space launcher. More...
  • RD-119 Glushko lox/udmh rocket engine. 105.5 kN. Kosmos 1 stage 2. Out of production. Isp=352s. Derived from RD-109 motor originally intended for the second stage of a Lox/UDMH version of the R-7. First flight 1961. More...
  • RD-113 Glushko lox/udmh rocket engine. 1138 kN. ICBM stage 2 (stage 1 was RD-112). Developed 1960. Upper stage version of RD-112 with larger nozzle. Isp=360s. More...
  • RD-112 Glushko lox/udmh rocket engine. 1089 kN. ICBM stage 1 (stage 2 was RD-113). Developed 1960. Isp=344s. More...
  • RD-114 Glushko lox/udmh rocket engine. 1653 kN. Used in ICBM stage 1 (stage 2 was RD-115). Developed 1961-65. Isp=341s. More...

Associated Stages
  • S1 Lox/UDMH propellant rocket stage. Loaded/empty mass 8,595/840 kg. Thrust 105.51 kN. Vacuum specific impulse 352 seconds. More...

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