Space Shuttle Main Engine Nozzle

I believe that this is a photo of the Space Shuttle's Main Engine (SSME) nozzle. It has a large bell shape and cooling tubes visible along its exterior. Rocketdyne developed the SSME in the 1970s. The engine first flew on the inaugural shuttle mission in April 1981. Each shuttle carried three SSMEs mounted in the aft compartment, which burned liquid hydrogen and liquid oxygen to provide the primary propulsion during ascent. The engines were designed for reuse, operating through multiple missions with refurbishment between flights.

The SSME nozzle expanded exhaust gases from the combustion chamber to maximize thrust efficiency. The bell-shaped nozzle had an expansion ratio of 77.5:1 and measured approximately 8 feet in diameter at its exit. The nozzle was constructed with regenerative cooling, using liquid hydrogen flowing through stainless steel tubes brazed to the nozzle wall to prevent overheating from exhaust temperatures that exceeded 6,000°F. Each SSME produced 512,000 pounds in vacuum. The engine operated at chamber pressures of 3,000 psi.