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A sign which, at one time, accompanied the SSME. It reads

MAIN ENGINES

Power For Lift-Off And Ascent To Orbit

The Pathfinder's three main engines are real. The two lower engines powered the first flights of Columbia in 1981. The other engine, located at top, was used in ground test firings.

At launch, the three main engines (fed liquid hydrogen and oxygen from the external tank) are ignited several seconds before lift-off. They operate for approximately 8.5 minutes of flight, drawing about 47,000 gallons of liquid hydrogen and 17,000 gallons of liquid oxygen each minute.

Shortly before separation, the Shuttle achieves orbit. The main engines shut down and maneuvering rockets fire to position the Shuttle into its final orbit. Reusable, each engine is designed for 7.5 hours of operation or to endure up to 55 starts.

Length: 14 ft.
Diameter: 7.5 ft.
Approximate Weight: 7,000 lbs.
Thrust: 393,800 lbs.
Prime Contractor: Rockwell International Rocketdyne Division