Encyclopedia Astronautica
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.

The engine used in Shuttle Orbiter Orbital Maneuvering System (OMS). The Shuttle Orbiter carried two OMS pods (name coined by Aerojet), each housing a single Aerojet OM Engine for orbit insertion, maneuvering, and re-entry initiation. The astronauts had great faith in these engines, unlike other shuttle hardware, due to their simplicity. This did not stop NASA studying several times replacing them with complex pump-fed or cryogenic engines in order to get (unnecessarily) improved performance.

The engines never failed and never required replacement during the life of the shuttle program. They were designed to be capable of 100 missions and 500 starts in space. Rocketdyne built the shuttle SSME main engines which were supposed to have similar reliability. They didn't come close, and Rocketdyne was rewarded with billions of dollars over the decades in SSME repair, refurbishment, and improvement contracts. Aerojet's engines didn't need any of that, and the reliable designs required no further suport.

First Flown: April 12th, 1981, on the Orbiter Columbia. Mounting: gimballed ( 7 degrees yaw, 6 pitch by two electromechanical actuators for thrust vector control. Engine Cycle: pressure-fed (improvement underway for pump-fed). Oxidizer: 6743 kg nitrogen tetroxide in each pod (pods can be cross-linked). Fuel: 4087 kg of monomethyl hydrazine in each pod (pods can be cross-linked). Mixture Ratio: 1.65:1. Cooling Method: fuel regenerative for chamber, radiative for nozzle. Burn Time: qualified for 500 starts, 15 hr/100 mission life, longest firing 1250 sec, de-orbit. burn typically 150-250 secs.

Engine: 118 kg (260 lb). Chamber Pressure: 8.62 bar. Area Ratio: 55. Thrust to Weight Ratio: 23.0635593220339. Oxidizer to Fuel Ratio: 1.65. Coefficient of Thrust vacuum: 1.5638169936685.

Status: Study 1972.
Unfuelled mass: 118 kg (260 lb).
Height: 1.96 m (6.42 ft).
Diameter: 1.17 m (3.83 ft).
Thrust: 26.70 kN (6,002 lbf).
Specific impulse: 316 s.
Burn time: 1,250 s.

More... - Chronology...


Associated Countries
Associated Spacecraft
  • 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...
  • 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...
  • 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...

See also
Associated Launch Vehicles
  • Saturn Shuttle American orbital launch vehicle. A winged recoverable Saturn IC stage was considered instead of solid rocket boosters after the final shuttle design was selected. More...
  • IHLLV American orbital launch vehicle. Same concept as Shuttle C. Shuttle orbiter replaced by recoverable pod with shuttle main engines and payload cannister. Quick way for US to obtain heavy payload capability and reduce shuttle cost per kg to orbit by 3 X. More...
  • Shuttle LRB American winged orbital launch vehicle. Shuttle with Liquid Rocket Boosters in place of Solid Rocket Boosters. More...
  • Shuttle C American orbital launch vehicle. NASA Marshall design for a cargo version of the shuttle system. The shuttle orbiter would be replaced by an unmanned recoverable main engine pod. The same concept was studied earlier as the Interim Heavy Lift Launch Vehicle (IHLLV) and as the Class I Shuttle Derived Vehicle (SDV). The Phase I two-SSME configuration would have a payload of 45,000 kg to low earth orbit. Design carried to an advanced phase in 1987-1990, but then abandoned when it was found the concept had no cost advantage over existing expenable launch vehicles. More...

Associated Manufacturers and Agencies
  • Aerojet American manufacturer of rockets, spacecraft, and rocket engines. Aerojet, Sacramento, CA, USA. More...

Associated Propellants
  • 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. More...

Bibliography
  • Kudryavtseva, V M, ed., Zhidkostnikh Raketnikh Dvigatley, Visshaya Shkola, Moscow, 1993.
  • Mullane, Mike, Riding Rockets, Scribner, New York, 2006.

Associated Stages
  • 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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