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Detail of the heat exchanger ports.

Picture 1 of 3.

On an engine ready for flight, there would be lines leading to and from these ports.

From top to bottom, the ports are

• GOX return port (the liquid oxygen having been converted to gaseous oxygen)
• Helium return port
• LOX supply port
• Helium supply port

The holes in these ports lead to coils of tubes in the heat exchanger interior, where warm turbine exhaust heats the oxygen and helium, which is then used to pressurize the propellant tanks.

Also note the gas generator just to the right of bottom center.