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Walk-around of the forward end of the engine, including its combustion chamber, valve package assembly, and propellant lines.

Picture 4 of 7.

The top line is the oxidizer (nitrogen tetroxide) duct and the fuel (Aerozine 50, or a 50/50 blend of hydrazine and unsymmetrical dimethylhydrazine) duct is at bottom.

During engine development, the engine suffered from hard starts; it was discovered that this could be solved by admitting the oxidizer into the combustion chamber before the fuel. Rather than change the timing on the valves or otherwise modifying the engine start sequence, engineers added the bulbous reservoir to the end of the fuel duct, delaying the fuel's entrance into the combustion chamber.