Encyclopedia Astronautica
N2O4/MMH


Nitrogen tetroxide became the storable liquid propellant of choice from the late 1950's. 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.

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.

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. By 2006 this had skyrocketed to $170.00 per kg.

Oxidizer: N2O4. Fuel: MMH. Propellant Formulation: N2O4/MMH. Optimum Oxidizer to Fuel Ratio: 2.16. Temperature of Combustion: 3,385 deg K. Density: 1.20 g/cc. Oxidizer Density: 1.450 g/cc. Oxidizer Freezing Point: -11 deg C. Oxidizer Boiling Point: 21 deg C. Fuel Density: 0.880 g/cc. Fuel Freezing Point: -52 deg C. Fuel Boiling Point: 87 deg C.

Specific impulse: 336 s.
Specific impulse sea level: 288 s.

More... - Chronology...


Associated Spacecraft
  • Gemini American manned spacecraft. 12 launches, 1964.04.08 (Gemini 1) to 1966.11.11 (Gemini 12). It was obvious to NASA that there was a big gap of three to four years between the last Mercury flight and the first scheduled Apollo flight. More...
  • Apollo Direct SM American manned spacecraft module. Study 1961. The Service Module housed the fuel cells, environmental control, and other major equipment items required for the mission. More...
  • Apollo Direct TLM American manned spacecraft module. Study 1961. Final letdown, translation hover and landing on the lunar surface from 1800 m above the surface was performed by the terminal landing module. Engine thrust could be throttled down to 1546 kgf. More...
  • Gemini RM American manned spacecraft module. 12 launches, 1964.04.08 (Gemini 1) to 1966.11.11 (Gemini 12). More...
  • Gemini EM American manned spacecraft module. 12 launches, 1964.04.08 (Gemini 1) to 1966.11.11 (Gemini 12). More...
  • Gemini Paraglider American manned spacecraft. Study 1966. The paraglider was supposed to be used in the original Gemini program but delays in getting the wing to deploy reliably resulted in it not being flown. More...
  • Gemini B RM American manned spacecraft. Cancelled 1969. Gemini was extensively redesigned for the MOL Manned Orbiting Laboratory program. The resulting Gemini B, although externally similar, was essentially a completely new spacecraft. Reentry capsule. More...
  • Spacebus 100 French communications satellite. 12 launches, 1975.08.26 (Symphonie 2) to 1994.01.24 (Eutelsat II F5). 3-axis stabilized using bipropellant thrusters (750 kg propellant - unified with apogee insertion and maneuvering propulsion) and momentum wheels. More...
  • Columbia American manned spaceplane. 28 launches, 1981.04.12 (STS-1) to 2003.01.16 (STS-107). Columbia, the first orbiter in the Shuttle fleet, was named after the sloop that accomplished the first American circumnavigation of the globe. More...
  • Challenger American manned spaceplane. 10 launches, 1983.04.04 (STS-6) to 1986.01.28 (STS-51-L). More...
  • Discovery American manned spaceplane. 39 launches, 1984.08.30 to 2011.02.24. More...
  • Atlantis American manned spaceplane. 33 launches, 1985.10.03 to 2011.07.08. The space shuttle Atlantis was the fourth orbiter to become operational at Kennedy Space Center, and the last of the original production run. More...
  • Spacebus 300 French communications satellite. 5 launches, 1987.11.21 (TVSAT 1) to 1990.07.24 (TDF 2). 3-axis stabilized using bipropellant thrusters (1220 kg propellant - unified with apogee insertion and maneuvering propulsion) and momentum wheels. More...
  • Multi-Role Recovery Capsule British manned spacecraft. Study 1987. Britain was the only European Space Agency member opposed to ESA's ambitious man-in-space plan, and the British conservative government refused to approve the November 1987 plan. More...
  • MRC DM British manned spacecraft module. Study 1987. Reusable re-entry capsule. More...
  • Endeavour American manned spaceplane. 25 launches, 1992.05.07 to 2011.05.16. Built as a replacement after the loss of the Challenger; named after the first ship commanded by James Cook. More...
  • Shenzhou Chinese manned spacecraft. Operational, first launch 1999.11.19. The Chinese Shenzhou manned spacecraft resembled the Russian Soyuz spacecraft, but was of larger size and all-new construction. More...
  • Shenzhou SM Chinese manned spacecraft module. Operational, first launch 1999.11.19. The service module, developed by the Shanghai Academy of Space Technology, provides the electrical power, attitude, control and propulsion for the spacecraft in orbit. More...
  • Ariane 5 EPS L10 German space tug. Study 2003. Upper stage / space tug - in production. Launched by Ariane 5V. 250 kg additional propellant compared to Ariane 5G version. More...
  • Messenger American Mercury probe. One launch, 2004.08.03. NASA probe, launched in 2004 with the challenging mission of comprehensively mapping Mercury from orbit between March 2011 and March 2012. More...
  • Orion American manned spacecraft. In development. NASA's Crew Excursion Vehicle for the 21st Century More...
  • CEV Raytheon American manned spacecraft. Study 2012. Raytheon's CEV was a low L/D capsule, designed for three crew, sized so that an existing EELV Heavy could send it towards L1. More...
  • Orion SM American manned spacecraft module. Orion service module. Masses estimated based on delta-V released by NASA. More...

Associated Engines
  • Aerojet 2 Aerojet N2O4/MMH rocket engine. 2 N. In Production. Mixture Ratio(O/F): 1.65. Isp=265s. More...
  • Aerojet 21 Aerojet N2O4/MMH rocket engine. 0.021 kN. In Production. Mixture Ratio(O/F): 1.60. Isp=285s. More...
  • Aerojet 445 Aerojet N2O4/MMH rocket engine. 0.445 kN. In Production. Mixture Ratio(O/F): 1.65. Isp=309s. More...
  • Aerojet 62 Aerojet N2O4/MMH rocket engine. 0.062 kN. In Production. Mixture Ratio(O/F): 1.65. Isp=287s. More...
  • Aestus Friedrichshafen N2O4/MMH rocket engine. 29 kN. In production. Isp=324s. Upper stage engine for Ariane 5 developed 1988 - 1995. Original version could not be restarted; version for EPS L10 stage for Ariane 5V allowed multiple restarts. First flight 1996. More...
  • Aestus-2 Rocketdyne / DASA N2O4/MMH rocket engine. 60 kN. Production. Restartable upper-stage engine, began test firings at Lampoldshausen in February 2000. More...
  • ATE Rocketdyne N2O4/MMH rocket engine. 20 kN. Developed 1990's. Advance technology engine for maneuvering stages. Isp=347s. More...
  • DMT-600 MMH Isayev N2O4/MMH rocket engine. 0.600 kN. Hermes. In Production. Version of DMT-600 using MMH in place of UDMH, adaptation to western market (was discussed for European Hermes space plane project). 6,000 ignitions Isp=305s. More...
  • HiPAT Redmond N2O4/MMH rocket engine. 0.445 kN. In Production. High performance liquid apogee thruster. Isp=323s. More...
  • KEW-1 Rocketdyne N2O4/MMH rocket engine. 0.029 kN. Kinetic Energy Propulsion (7 Ib thrust). Pressure-fed. ASAT Strap-down test, XSS / DICE Microsatellite, GBI Ground-Based Interceptor, THAAD Theater High Altitude Area Defense. Isp=266s. More...
  • KEW-2 Rocketdyne N2O4/MMH rocket engine. 0.215 kN. Kinetic Energy Propulsion (50 Ib thrust). Pressure-fed. ASAT Strap-down test, XSS / DICE Microsatellite, GBI Ground-Based Interceptor, THAAD Theater High Altitude Area Defense. Isp=275s. More...
  • KEW-3 Rocketdyne N2O4/MMH rocket engine. 0.441 kN. Kinetic Energy Propulsion (100 Ib thrust). Pressure-fed. ASAT Strap-down test, XSS / DICE Microsatellite, GBI Ground-Based Interceptor, THAAD Theater High Altitude Area Defense. Isp=283s. More...
  • KEW-4 Rocketdyne N2O4/MMH rocket engine. 2.216 kN. Kinetic Energy Propulsion (500 Ib thrust). Pressure-fed. ASAT Strap-down test, XSS / DICE Microsatellite, GBI Ground-Based Interceptor, THAAD Theater High Altitude Area Defense. Isp=235s. More...
  • L7 MBB N2O4/MMH rocket engine. 27.4 kN. In Production. Isp=320s. Used on Ariane 5 launch vehicle. First flight 1996. More...
  • Liberty-2 Notional N2O4/MMH rocket engine. 17.8 kN. Development ended 1988. Pressure-fed engine. Isp=300s. Used on Liberty launch vehicle. More...
  • LR101-NA-7 Rocketdyne N2O4/MMH rocket engine. 5.148 kN. Upper Stage Target Engine Systems. Pressure-fed. Derived from Atlas vernier. Isp=251s. More...
  • OME Aerojet N2O4/MMH rocket engine. 26.7 kN. Study 1972. Isp=316s. Engine used in Shuttle Orbiter Orbital Maneuvering System pods, for orbit insertion, maneuvering, and re-entry initiation. First flight 1981. More...
  • Press Fed TRW N2O4/MMH rocket engine. 17.8 kN. Design concept 1960's. 1960's designs for 'big dumb booster'. Isp=300s. More...
  • PSLV-4 ISRO N2O4/MMH rocket engine. 7 kN. Isp=308s. Used on PSLV launch vehicle. First flight 1993. More...
  • R-1E Marquardt N2O4/MMH rocket engine. 0.110 kN. In Production from 1981. Isp=280s. Thruster developed as the Space Shuttle Orbiter's vernier attitude control and orbit adjust thruster. There were six employed in conjunction with the 38 R-40 thrusters. More...
  • R-40A Marquardt N2O4/MMH rocket engine. 3.870 kN. In Production. Isp=306s. Thruster developed for Shuttle Orbiter orbit control. The orbiter had 38 long scarf, short scarf, or no scarf configurations, depending on the location. More...
  • R-40B Redmond N2O4/MMH rocket engine. 4 kN. In Production. Isp=293s. More...
  • R-42 Redmond N2O4/MMH rocket engine. 0.890 kN. In Production. Isp=303s. More...
  • R-4D Marquardt N2O4/MMH rocket engine. 0.490 kN. Isp=312s. Developed as attitude control thruster for the Apollo Service and Lunar Modules in 1960s. In production for numerous satellites for apogee / perigee maneuvers, orbit adjustment, and attitude control. More...
  • R-6C Marquardt N2O4/MMH rocket engine. 0.033 kN. In Production. Isp=290s.Derivative of Advent communications satellite thruster for Insat 1, Arbasat 1, and Olympus and HS-393 satellites. More...
  • RD-0242M Kosberg N2O4/MMH rocket engine. 98.1 kN. Design concept 1998-. Isp=335s. Proposed variant of RD-0242 engine for upper stages using MMH in place of UDMH. Reusable for 6 ignitions total. Throttling to 80%. More...
  • RD-0242M1 Kosberg N2O4/MMH rocket engine. 98.1 kN. Design concept 1998-. Proposed variant of RD-0242 engine for upper stages using MMH in place of UDMH (adaptation to western market ?). Reusable for 6 ignitions total. Throttling to 80%. Isp=343s. More...
  • RESA-2 Rocketdyne N2O4/MMH rocket engine. 0.215 kN. Pitch Control Propulsion Module. Pressure-fed. More...
  • RESA-5 Rocketdyne N2O4/MMH rocket engine. 7.109 kN. Spacecraft. Pressure-fed. Isp=280s. More...
  • RM-05 Rocketdyne N2O4/MMH rocket engine. 0.020 kN. Satellite Reaction Control System. Pressure-fed. Isp=238s. More...
  • RM-100A Rocketdyne N2O4/MMH rocket engine. 0.441 kN. Spacecraft. Pressure-fed. Isp=301s. More...
  • RM-1-1 Rocketdyne N2O4/MMH rocket engine. 4.4 N. Satellite Reaction Control System. Pressure-fed. Isp=245s. More...
  • RM-1-2 Rocketdyne N2O4/MMH rocket engine. 4.4 N. Satellite Reaction Control. Pressure-fed. Isp=238s. More...
  • RM-25 Rocketdyne N2O4/MMH rocket engine. 0.107 kN. Spacecraft. Pressure-fed. Isp=286s. More...
  • RM-25-1 Rocketdyne N2O4/MMH rocket engine. 0.107 kN. Spacecraft. Pressure-fed. Isp=300s. More...
  • RM-900 Rocketdyne N2O4/MMH rocket engine. 4.001 kN. Shuttle Orbiter Reaction Control. Pressure-fed. Isp=309s. More...
  • RS-14 Rocketdyne N2O4/MMH rocket engine. 1.392 kN. Minuteman Postboost Velocity Control. Pressure-fed. Isp=315s. First flight 1970. More...
  • RS-1402 Rocketdyne N2O4/MMH rocket engine. 0.098 kN. Minuteman Pitch, Yaw & Roll Control. Pressure-fed. Technology engine, developed, but not produced. Led to RS-14 prodution engines. Isp=259s. More...
  • RS-1403 Rocketdyne N2O4/MMH rocket engine. 0.078 kN. Minuteman Pitch, Yaw & Roll Control. Pressure-fed. Technology engine, developed, but not produced. Led to RS-14 prodution engines. Isp=230s. More...
  • RS-2101A Rocketdyne N2O4/MMH rocket engine. 1.333 kN. Mars Mariner. Pressure-fed. Derivtive of RS-14 Minuteman engine. Isp=287s. First flight 1971. More...
  • RS-2101C Rocketdyne N2O4/MMH rocket engine. 1.333 kN. Viking. Pressure-fed. Derivtive of RS-14 Minuteman engine. Isp=294s. First flight 1975. More...
  • RS-23 Rocketdyne N2O4/MMH rocket engine. 26.670 kN. Space Shuttle Orbiter Orbit Maneuvering System. Pressure-fed. Isp=313s. First flight 1981. More...
  • RS-28 Rocketdyne N2O4/MMH rocket engine. 2.667 kN. Space Shuttle Orbiter Reaction Control. Pressure-fed. Isp=220s. More...
  • RS-36 Rocketdyne N2O4/MMH rocket engine. 55.6 kN. HOE Homing Overlay Experiment Upper Stage Axial Propulsion System. Pressure-fed. Derivative of Lance propulsioon system. Isp=281s. First flight 1983. More...
  • RS-32 Rocketdyne N2O4/MMH rocket engine. 1.392 kN. Upper Stage Target Engine Systems. Pressure-fed. Derived from Minuteman RS-14. Isp=288s. More...
  • RS-34 Rocketdyne N2O4/MMH rocket engine. 11.7 kN. Peacekeeper Postboost Axial Thrust. Pressure-fed. 1 main axial thruster per postboost propulsion system. Isp=308s. First flight 1983. More...
  • RS-45 Rocketdyne N2O4/MMH rocket engine. 4.4 N. Satellite Attitude Control and Stationkeeping. Pressure-fed. Isp=300s. More...
  • RS-43 Rocketdyne N2O4/MMH rocket engine. 0.020 kN. Attitude Control. Pressure-fed. Isp=284s. More...
  • RS-41 Rocketdyne N2O4/MMH rocket engine. 11.960 kN. Axial Spacecraft. Pressure-fed. Isp=320s. More...
  • RS-42 Rocketdyne N2O4/MMH rocket engine. 0.441 kN. Axial Spacecraft. Pressure-fed. Isp=305s. More...
  • RS-51 Rocketdyne N2O4/MMH rocket engine. 11.552 kN. Axial Spacecraft. Pressure-fed. Isp=315s. More...
  • RS-72 Rocketdyne, Ottobrunn N2O4/MMH rocket engine. 55.4 kN. Isp=340s. Aestus engine enhanced with the addition of a Boeing-Rocketdyne XLR 32 turbo-pump. More...
  • SE-6 Rocketdyne N2O4/MMH rocket engine. 0.107 kN. Gemini Re-entry Control System. Pressure-fed. Isp=277s. First flight 1964. More...
  • SE-7-1 Rocketdyne N2O4/MMH rocket engine. 0.313 kN. S-IVB Stage APS Ullage Control Engine (propellant settling). Pressure-fed. Isp=274s. First flight 1966. More...
  • SE-7-100 Rocketdyne N2O4/MMH rocket engine. 0.441 kN. Gemini Orbit Attitude and Maneuvering System (100 Ib thrust). Pressure-fed. Isp=296s. First flight 1964. More...
  • SE-7-25 Rocketdyne N2O4/MMH rocket engine. 0.107 kN. Gemini Orbit Attitude and Maneuvering System (25 Ib thrust). Pressure-fed. Isp=277s. First flight 1964. More...
  • SE-7-85 Rocketdyne N2O4/MMH rocket engine. 0.372 kN. Gemini Orbit Attitude and Maneuvering System (85 Ib thrust). Pressure-fed. Isp=295s. First flight 1964. More...
  • SE-8 Rocketdyne N2O4/MMH rocket engine. 0.411 kN. Apollo Command Module Reaction Control. Pressure-fed. Isp=274s. First flight 1966. More...
  • TIROC Kayser N2O4/MMH rocket engine. 1 N. Satellite orientation. Isp=303s. Tangential Injection and Rotational Combustion, the world's smallest thruster burning monomethylhydrazine and nitrogen tetroxide. More...
  • Transtar Aerojet N2O4/MMH rocket engine. 16.7 kN. Development completed 1987. Isp=328s. Upper stage engine using injectors, chamber, and nozzle derived from the Shuttle OMS system, but pump-fed for increased chamber pressure and Isp. Tested; no production. More...
  • XLR132 Rocketdyne N2O4/MMH rocket engine. 16.7 kN. Out of Production. Isp=340s. Pump-fed high performance upper stage engine for perigee/apogee stages. as well as transfer vehicles and lunar and Martian missions. Tested extensively but no production. More...

Associated Stages
  • Ariane 5 EPS L10 N2O4/MMH propellant rocket stage. Loaded/empty mass 12,750/2,750 kg. Thrust 27.40 kN. Vacuum specific impulse 324 seconds. 250 kg additional propellant compared to Ariane 5G version. More...
  • Ariane 5-2 N2O4/MMH propellant rocket stage. Loaded/empty mass 12,500/2,700 kg. Thrust 27.40 kN. Vacuum specific impulse 324 seconds. Storable propellant, restartable upper stage for use with Ariane 5. Chamber pressure 10 bar; expansion ratio 83.0; propellant mix ratio 2.05. Empty mass without VEB payload fairing support ring and avionics is 1200 kg. More...
  • IABS N2O4/MMH propellant rocket stage. Loaded/empty mass 1,578/275 kg. Thrust 0.98 kN. Vacuum specific impulse 312 seconds. More...
  • Jarvis-3 N2O4/MMH propellant rocket stage. Loaded/empty mass 13,400/2,000 kg. Thrust 3.92 kN. Vacuum specific impulse 312 seconds. More...
  • Liberty 2 N2O4/MMH propellant rocket stage. Loaded/empty mass 2,180/180 kg. Thrust 17.79 kN. Vacuum specific impulse 300 seconds. More...
  • PBS N2O4/MMH propellant rocket stage. Loaded mass 1,000 kg. Thrust 1.40 kN. More...
  • PSLV-4 N2O4/MMH propellant rocket stage. Loaded/empty mass 2,920/920 kg. Thrust 14.00 kN. Vacuum specific impulse 308 seconds. More...
  • Shuttle C N2O4/MMH propellant rocket stage. Loaded/empty mass 36,360/34,380 kg. Thrust 6,834.30 kN. Vacuum specific impulse 313 seconds. More...
  • Shuttle Orbiter OMS N2O4/MMH propellant rocket stage. Loaded/empty mass 25,200/3,600 kg. Thrust 53.38 kN. Vacuum specific impulse 316 seconds. Two pods, mounted each side of vertical stabilizer, provide propulsion for orbit insertion, maneuver, and de-orbit. More...

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