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View of the heat exchanger's oxygen coils.

Picture 2 of 2.

The circular tube at the extreme top of the heat exchanger (well, this is actually the bottom of the heat exchanger, as it is sitting on its inlet) appears to be an internal structure to support the tubes of the coils.

The oxygen was expanded via a pack consisting of of four separate coils of tubes. Visible here are four tubes at the extreme top (bottom) which lead to either the supply or return port (although it seems logical for the LOX to enter at the bottom of the heat exchanger and GOX to exit at the top, I am uncertain as to the direction of the oxygen flow through the heat exchanger).