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Vehicle Upgrades: Space Shuttle Main Engine (SSME)

In the Orbiter Processing Facility bay 1 at NASA's Kennedy Space Center, a Hyster fork lift (left) holding Space Shuttle Main Engine (SSME) closes in on position number 1 for installation in Atlantis.
In the Orbiter Processing Facility bay 1 at NASA's Kennedy Space Center, a Hyster fork lift (left) holding Space Shuttle Main Engine (SSME) closes in on position number 1 for installation in Atlantis. Overall, an SSME weighs approximately 7,000 pounds. Three engines provide the thrust, along with the two Solid Rocket Boosters, for liftoff. After about 2 minutes, the two boosters are spent and are separated from the external tank. The SSMEs continue firing for about 8 minutes.

The Space Shuttle Main Engine is the most reliable and highly tested large rocket engine ever built. The SSMEs have achieved 100 percent flight success with a demonstrated reliability of over 0.999. 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 512,950 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. 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 Main Engines are being upgraded to incorporate the Large Throat Main Combustion Chamber (LTMCC) to further improve the reliability of the engine systems. In conjunction with the LTMCC, the Main Injector is redesigned to maintain the high specific impulse output of the engines. This upgraded SSME configuration was launched in January 1998.