>>12408032I basically said what you're saying. The only useful thing to do with RS-25 right now is to point at it and say "see that? Don't do that". FRSC with hydrolox is fine, RL-10 is not powerful enough for large stages and BE-3U lack efficiency due to using a combustion tap-off cycle (basically the same thing as a gas generator, except the main combustion chamber is the only combustion chamber, and they add extra hydrogen to the tap-off gasses to lower its temperature before it hits the turbine). If Raptor proves anything it's that complex high performance engines can still be relatively cheap, and engine complexity is just an excuse to charge more money for oldspace companies.
In my opinion it will make sense to develop another high performance hydrolox engine once we're doing manned missions to Jupiter, because hydrolox ISRU becomes the most practical option. Granted, the Jovian moons have pretty low gravity, but that doesn't mean we should scale down the engine size we select, it means we should scale UP the surface to orbit shuttle vehicles we consider. Seven 1000 kN hydrolox engines can lift 3750 metric tons of mass in ~1.6m/s^2 gravity with a TWR of 1.16. Since we only need ~2000 m/s of delta V to achieve orbit launching from Ganymede, we only need a launch propellant mass fraction of 40%, which would be trivial to attain even with hydrolox propellant. If the actual structural wet-dry mass ratio sans payload is ~72.7%, and we reserve enough propellant that once the payload separates we're left with ~2500 m/s delta V for deorbit and landing, we can launch 1,000,000 kg of payload to orbit with every launch.
Anyway I got a little autistic there but my point is, yes, get rid of the RS-25, it's optimized for all the wrong things due to being developed as part of a shitty LV design. However, using the RS-25 as a cautionary tale, develop a new hydrolox FFSC engine and use it on reusable vehicles of whatever description.
