Space

Thinking about the equivalent temperatures the aft end of the rocket must face… It probably exceeds the maximum use temperature of any material. They must use the liquid oxygen and/or fuel as part of an active cooling system as it enters the rocket engine.

I make rockets IRL.
I reserve the right to shamelessly recast for degen reasons. 
Soldier once upon a time.

Is it possible the entire bottom of that enormous rocket is composed of small welded together tubes carrying LOX? That’s a massive area!