Encyclopedia Astronautica
Nitric acid/Hydrazine


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. 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. Hydrazine (N2H4) found early use as a fuel, but it was quickly replaced by UDMH. It is still used as a monopropellant for satellite station-keeping motors.

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.

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:

  • WFNA - White fuming nitric acid is based on anhydrous nitric acid (HNO3), a colourless corrosive liquid which fumes in moist air. They contain a maximum of 2 per cent water and 0.5 per cent nitrogen dioxide, and decompose to yield amounts of water, nitrogen dioxide, and oxygen which are in chemical equilibrium.

  • IWFNA - Inhibited white fuming nitric acid. Since container materials are attacked by WFNA and equilibrium products, 0.6 per cent HF is added for passivation by deposition of a protective metallic fluoride coating.

  • RFNA - Red fuming nitric acid. Since WFNA or IWFNA exhibit excessive equilibrium decomposition pressures, reaching 75 bar at 700 deg C. To suppress the high pressure through a mass-action effect, some 13 per cent N2O4 and 3 per cent H20 are added, in order to reduce equilibrium pressures to 2 bar at 700 deg C. The colour of the resulting red fuming nitric acid is imparted by N204.

  • IRFNA - Inhibited red fuming nitric acid. Addition of 0.6 per cent HF to RFNA produces inhibited RFNA (IRFNA). The IRFNA specification was published in 1954 and thereafter Russian rocket engines using the same fuel appeared.

  • AK20 - Russian formulation consisting of 80% nitric acid + 20% N2O4 (AK = Azotna Kislota = Nitric Acid)

  • AK20F - Russian formulation consisting of 80% nitric acid + 20% N2O4 + fluorine passivant

  • AK20I - Russian formulation consisting of 80% nitric acid + 20% N2O4 + iodine passivant

  • AK20K - Russian formulation consisting of 80% nitric acid + 20% N2O4 + unknown additive

  • AK27I - Russian formulation consisting of 73% nitric acid + 27% N2O4 + iodine passivant

  • AK-27P - Russian formulation consisting of 73% nitric acid + 27% N2O4 + unknown additive

Hydrazine marketed for rocket propellant contains a minimum of 97 per cent N2H4, the other constituent being primarily water. Hydrazine is a clear, water-white, hygroscopic liquid. The solid is white. Hydrazine a toxic, flammable caustic liquid and a strong reducing agent. Its odour is similar that of ammonia, though less strong. It is slightly soluble in ammonia and methyl-amine. It is soluble in water, methanol, ethanol, UDMH, and ethylenediamine. Hydrazine is manufactured by the Raschig process, which involves the oxidation of ammonia to chloramine, either indirectly with aqueous sodium hypochlorite or directly with chlorine, and subsequent reaction of chloramine with excess ammonia. Raw materials include caustic, ammonia, and chlorine; these are high-tonnage, heavy chemicals. The cost of anhydrous hydrazine in drum quantities in 1959 was $ 7.00 per kg. The projected price, based on large-scale commercial production, was expected to be $ 1.00 per kg. Due to environmental regulations, by 1990 NASA was paying $ 17.00 per kg.

Oxidizer: Nitric acid. Fuel: Hydrazine. Propellant Formulation: IRFNA/Hydrazine. Optimum Oxidizer to Fuel Ratio: 1.45. Temperature of Combustion: 3,045 deg K. Ratio of Specific Heats: 1.25. Density: 1.28 g/cc. Characteristic velocity c: 1,725 m/s (5,659 ft/sec). Isp Shifting: 283 sec. Isp Frozen: 277 sec. Mol: 20.00 M (65.00 ft). Oxidizer Density: 1.510 g/cc. Oxidizer Freezing Point: -42 deg C. Oxidizer Boiling Point: 86 deg C. Fuel Density: 1.008 g/cc. Fuel Freezing Point: 2.00 deg C. Fuel Boiling Point: 113 deg C.

Location: 1725.
Specific impulse: 328 s.
Specific impulse sea level: 283 s.

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Associated Spacecraft
  • Von Braun Passenger Ship American manned Mars orbiter. Study 1952. The first design for a manned Mars orbiter based on engineering analysis. 10 passengers would be housed in a 20-m-diameter sphere during the 963 day mission to Mars, in Mars orbit, and back to earth. More...
  • Von Braun Lunar Lander American manned lunar lander. Study 1952. Von Braun's first lunar lander design was an immense spacecraft, larger in earth orbit than a Saturn V booster. More...
  • Von Braun Landing Boat American manned Mars lander. Study 1952. The first design for a manned Mars lander based on engineering analysis. The enormous glider would have a wingspan of 153 m, and land on Mars horizontally either on skis, skids, or wheels on a prepared runway. More...
  • 1956 Von Braun Passenger Ship American manned Mars orbiter. Study 1956. The 1956 version of Von Braun's Mars design was slashed by 50% in mass, while the number of passengers was increased from 10 to 12. More...
  • 1956 Von Braun Cargo Ship American manned Mars orbiter. Study 1956. Using the same basic systems as the Passenger Ship, the Cargo Ship would substitute a 177 metric ton Landing Boat for the surface expedition in place of the Passenger Sphere and propellant for the return home. More...
  • 1956 Von Braun Landing Boat American manned Mars lander. Study 1956. The 1956 modification of Von Braun's Landing Boat design was reduced in mass by 12%, and the wingspan by 10%. More...
  • Soyuz A Russian manned spacecraft. Study 1962. The 7K Soyuz spacecraft was initially designed for rendezvous and docking operations in near earth orbit, leading to piloted circumlunar flight. More...
  • Soyuz A PAO Russian manned spacecraft module. Study 1962. Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system but with no base flange for a shroud. Equipment-engine section. More...
  • Soyuz 7K-OK Russian manned spacecraft. 17 launches, 1966.11.28 (Cosmos 133) to 1970.06.01 (Soyuz 9). Development of a three-manned orbital version of the Soyuz, the 7K-OK was approved in December 1963. More...
  • Soyuz 7K-OK PAO Russian manned spacecraft module. 17 launches, 1966.11.28 (Cosmos 133) to 1970.06.01 (Soyuz 9). Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system. Equipment-engine section. More...
  • Soyuz Kontakt Russian manned spacecraft. Cancelled 1974. Modification of the Soyuz 7K-OK spacecraft to test in earth orbit the Kontakt rendezvous and docking system. More...
  • Salyut 1 Russian manned space station. 2 launches, 1971.04.19 (Salyut 1) and 1972.07.29 (Zarya s/n 122). Salyut 1 was the first DOS long duration orbital station. More...
  • Soyuz 7KT-OK Russian manned spacecraft. 2 launches, 1971.04.23 (Soyuz 10) to 1971.06.06 (Soyuz 11). This was a modification of Soyuz 7K-OK with a lightweight docking system and a crew transfer tunnel. More...
  • Soyuz 7K-OKS PAO Russian manned spacecraft module. 2 launches, 1971.04.23 (Soyuz 10) to 1971.06.06 (Soyuz 11). Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system. Equipment-engine section. More...
  • Soyuz 7K-T Russian manned spacecraft. 23 launches, 1972.06.26 (Cosmos 496) to 1981.05.14 (Soyuz 40). More...
  • Soyuz 7K-T PAO Russian manned spacecraft module. 23 launches, 1972.06.26 (Cosmos 496) to 1981.05.14 (Soyuz 40). Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system. Equipment-engine section. More...
  • Salyut 4 Russian manned space station. 2 launches, 1973.05.11 (Cosmos 557) to 1974.12.26 (Salyut 4). Four of the initial DOS-1 versions of a civilian Soviet space station were built using converted Almaz military stations. More...
  • Soyuz 7K-TM Russian manned spacecraft. 4 launches, 1974.04.03 (Cosmos 638) to 1975.07.15 (Soyuz 19 (ASTP)). The Soyuz 7K-T as modified for the docking with Apollo. More...
  • Soyuz 7K-T/A9 Russian manned spacecraft. 8 launches, 1974.05.27 (Cosmos 656) to 1978.06.27 (Soyuz 30). Version of 7K-T for flights to Almaz. Known difference with the basic 7K-T included systems for remote control of the Almaz station and a revised parachute system. More...
  • Soyuz ASTP PAO Russian manned spacecraft module. 4 launches, 1974.04.03 (Cosmos 638) to 1975.07.15 (Soyuz 19 (ASTP)). Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system. Equipment-engine section. More...
  • Soyuz 7K-MF6 Russian manned spacecraft. One launch, 1976.09.15, Soyuz 22. Soyuz 7K-T modified with installation of East German MF6 multispectral camera. Used for a unique solo Soyuz earth resources mission. More...
  • Soyuz 7K-MF6 PAO Russian manned spacecraft module. One launch, 1976.09.15, Soyuz 22. Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system. Equipment-engine section. More...
  • Progress Russian logistics spacecraft. 43 launches, 1978.01.20 (Progress 1) to 1990.05.06 (Progress 42). Progress took the basic Soyuz 7K-T manned ferry designed for the Salyut space station and modified it for unmanned space station resupply. More...
  • Progress PAO Russian manned spacecraft module. 43 launches, 1978.01.20 (Progress 1) to 1990.05.06 (Progress 42). Derived from Soyuz 7K-OK basic PAO service module with pump-fed main engines and separate RCS/main engine propellant feed system. Equipment-engine section. More...

Associated Stages
  • Von Braun 1952-3 Nitric acid/Hydrazine propellant rocket stage. Loaded/empty mass 105,000/22,000 kg. Thrust 2,033.80 kN. Vacuum specific impulse 296 seconds. More...
  • Von Braun 1948-1 Nitric acid/Hydrazine propellant rocket stage. Loaded/empty mass 5,500,000/700,000 kg. Thrust 141,286.30 kN. Vacuum specific impulse 257 seconds. More...
  • Von Braun 1948-2 Nitric acid/Hydrazine propellant rocket stage. Loaded/empty mass 770,000/70,000 kg. Thrust 16,271.10 kN. Vacuum specific impulse 298 seconds. More...
  • Von Braun 1948-3 Nitric acid/Hydrazine propellant rocket stage. Loaded/empty mass 105,000/22,000 kg. Thrust 2,033.80 kN. Vacuum specific impulse 296 seconds. More...
  • Von Braun 1952-1 Nitric acid/Hydrazine propellant rocket stage. Loaded/empty mass 5,500,000/700,000 kg. Thrust 141,286.30 kN. Vacuum specific impulse 257 seconds. More...
  • Von Braun 1952-2 Nitric acid/Hydrazine propellant rocket stage. Loaded/empty mass 770,000/70,000 kg. Thrust 16,271.10 kN. Vacuum specific impulse 298 seconds. More...

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