The Space Shuttle Main Engine (SSME) is an engineering marvel: the most efficient liquid fuel burning rocket engine, with variable thrust control and the ability to be reused for multiple launches. This upclose photo of the powerhead (where fuel flow and combustion are controlled) shows the preburner oxidizer pump in the center.

The Space Shuttle Main Engine (SSME) is an engineering marvel: the most efficient liquid fuel burning rocket engine, with variable thrust control and the ability to be reused for multiple launches. This upclose photo of the powerhead (where fuel flow and combustion are controlled) shows the preburner oxidizer pump in the center.