> The RS-25 is related to the J-2
How so? Other than sharing a fuel type, and thus surely things learned during J-2 development and operation influenced the RS-25 development and operation, so far as I know the two engines are completely different. Different cycles, different power packs (e.g. turbopump), wildly different packaging, different head pressure, different chamber pressure, throat, etc etc etc. I'm pretty sure that the J-2 did not cool the bell with the fuel, though I could be mistaken. Are the combustion chambers similar? What makes the two engines related, other than the fuel type and of course manufacturer?