Encyclopedia Astronautica
Lox/Ammonia



xlr99.jpg
XLR-99
Credit: USAF
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. Ammonia (NH3) is a colourless gas and liquid with a strong irritating characteristic odour.

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.

It is a relatively high-boiling gas with a vapour pressure of 8.7 bar at 20 deg C. Ammonia. is toxic, and will dissolve easily in water. It will form flammable and explosive mixtures with air. Although ammonia itself is toxic, the exhaust gases from the combustion of ammonia and oxygen are not. Ammonia is produced by a Haber-Bosch process, in which the elements, nitrogen and hydrogen, are united at a temperature of 500 to 600 deg C and a. pressure of approximately 200 bar in the presence of a promoted iron catalyst. It is estimated that 4 million tonnes of anhydrous synthetic ammonia were produced in 1959 in the United States, at which time the price of tank-car quantities of refrigeration-grade anhydrous ammonia was $ 80 per tonne.

Oxidizer: LOX. Fuel: Ammonia. Propellant Formulation: LOX/Ammonia. Optimum Oxidizer to Fuel Ratio: 1.4. Temperature of Combustion: 3,090 deg K. Ratio of Specific Heats: 1.23. Density: 0.89 g/cc. Characteristic velocity c: 1,785 m/s (5,856 ft/sec). Isp Shifting: 294 sec. Isp Frozen: 285 sec. Mol: 19.80 M (64.90 ft). Oxidizer Density: 1.140 g/cc. Oxidizer Freezing Point: -219 deg C. Oxidizer Boiling Point: -183 deg C. Fuel Density: 0.604 g/cc. Fuel Freezing Point: -78 deg C. Fuel Boiling Point: -33 deg C.

Location: 1785.
Specific impulse: 343 s.
Specific impulse sea level: 294 s.

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Associated Spacecraft
  • D-558-3 American manned rocketplane. Flown 1954. The D-558-3 was a US Navy/Douglas counterpart to the X-15, which would have kept the Navy in the 'space race' and Douglas in the running for future manned spaceplanes. More...
  • X-15B American manned spacecraft. Study 1958. North American's proposal for the Air Force initial manned space project was to extend the X-15 program. The X-15B was a 'stripped' X-15A with an empty mass of 4500 kg. More...
  • X-15A American manned spaceplane. 174 launches, 1959.06.08 (X-15 Flight 1) to 1968.10.24 (X-15 Flight 199). The X-15 was the first USAF and NASA project for manned spaceflight, initiated years before Mercury. More...
  • X-15A-3 American manned spaceplane. Cancelled 1962. It had been proposed that X-15 number 3 would be reworked to install a delta wing and designed to reach Mach 8. More...
  • X-15A-2 American manned spaceplane. Study 1965. The crash-damaged X-15 number 2 was rebuilt to attain even higher speeds. The body frame was stretched, and two drop tanks were added, increasing propellant load by 75%. More...
  • Mini-shuttle American manned rocketplane. Study 1972. In August 1972 it was proposed to test a subscale version of the shuttle to test the aerodynamics. The 13,750 kg vehicle would be 11 m long and have a wingspan of 7 m. More...

Associated Engines
  • LR30 Reaction Motors Lox/Ammonia rocket engine. 222.6 kN. D-558-3. Capable rocket engine planned for use in D-558-3 and X-15. Cancelled in favour of XLR-99. More...
  • XLR99 Thiokol Lox/Ammonia rocket engine. 262.4 kN. Out of production. Isp=276s. The first large, man-rated, throttleable, restartable liquid propellant rocket engine, boosted the X-15A. First flight 1959. More...

Associated Stages
  • X-15A-2 Lox/Ammonia propellant rocket stage. Loaded/empty mass 16,069/7,766 kg. Thrust 262.45 kN. Vacuum specific impulse 276 seconds. More...
  • X-15A Lox/Ammonia propellant rocket stage. Loaded/empty mass 14,184/5,158 kg. Thrust 262.45 kN. Vacuum specific impulse 276 seconds. More...

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