The rectangular umbilical connection for the S-shaped engine compartment conditioning duct.
The engine compartment conditioning system provided 300 to 500 pounds per
minute of gaseous nitrogen to the engine compartment to prevent hazardous gas
accumulation, formation of liquified air (due to the extreme temperatures of
the liquid hydrogen), and to maintain proper thrust structure temperature.
Swing arm 4 would attach
to the stage at this location; one of the swing arm's purposes was to supply an