Space Shuttle Main Engine

Aerojet Rocketdyne's Space Shuttle Main Engine (SSME) is the world’s most reliable and highly tested large rocket engine ever built, and operates at greater temperature extremes than any mechanical system in common use today. The SSME has achieved 100 percent flight success with a demonstrated reliability exceeding 0.9996 in over 1,000,000 seconds of hot-fire experience.

The SSME is a reusable, staged-combustion cycle engine. Using a mixture of liquid oxygen and liquid hydrogen, the SSME can attain a maximum thrust level (in vacuum) of 512,300 pounds which is equivalent to greater than 12,000,000 horsepower. The regeneratively cooled engine also features high performance fuel and oxidizer turbopumps that develop 69,000 horsepower and 25,000 horsepower, respectively, within compact envelops.

Ultra-high-pressure operation of the pumps and combustion chamber allows expansion of all hot gases through a high-area-ratio exhaust nozzle to achieve efficiencies never previously attained in a production rocket engine. These advantages allow a heavier payload to be carried without increasing the launch vehicle size.

The Space Shuttle Main Engine was upgraded to extend system robustness and reliability with the incorporation of the Large Throat Main Combustion Chamber (LTMCC). In conjunction with the LTMCC, new high pressure turbopumps and a redesigned powerhead were introduced as the SSME Block II configuration which launched in July 2001. The final upgrade to the Block II, introduced as the Advanced Health Management System (AHMS) and flown active in June 2007, would culminate into a factor of four improvement to engine safety when compared to earlier configurations.

Incredible Facts

  • The SSME operates under temperatures ranging from -423º Fahrenheit to +6000º Fahrenheit.
  • The maximum equivalent horsepower created by the three SSMEs is just over 37,000,000 horsepower.
  • The energy released by three SSMEs is equivalent to the output of 13 Hoover Dams.
  • Although not much larger than an automobile engine, the SSME high-pressure fuel turbopump generates 100 horsepower for each pound of its weight, while an automobile engine generates about one-half horsepower for each pound of its weight.
  • Even though the SSME weighs one-seventh as much as a locomotive engine, its high-pressure fuel pump alone delivers as much horsepower as 28 locomotives, while its high-pressure oxidizer pump delivers the equivalent horsepower for 11 more.
  • If water, instead of fuel, were pumped by the three Space Shuttle Main Engines, an average family-sized swimming pool could be drained in 25 seconds.
  • The SSME high-pressure fuel turbopump main shaft rotates at 37,000 rpm compared to about 3,000 rpm for an automobile operating at 60 mph.
  • The discharge pressure of an SSME high-pressure fuel turbopump could send a column of liquid hydrogen 36 miles in the air.



Thrust (109% Power Level)

Specific Impulse


Fuel: H2
Oxidizer: LOX

Vacuum: 512,300 lb.
Sea Level: 418,000 lb.

Vacuum: 452 sec.
Sea Level: 366 sec.
Area Ratio: 69:1
Chamber Pressure: 2,994 psia
Engine Mixture Ratio: 6.0
Throttle Range: 67–109%

Length: 168 in.
Diameter: 96 in.
Weight: 7,775 lb