>>9657233The center core is a Shuttle external tank with modifications.
Actually, everything below the second stage on SLS is modified or legacy Shuttle hardware, and there's also some Shuttle hardware going into Orion (they actually robbed a water tank out of one of the Shuttle orbiters to install into Orion a while back).
The second stage of Block 1 is a modified Delta IV second stage.
What they should have done is start the core stage from scratch, because modifying an existing drop-tank design into a core stage that needs to take more thrust while carrying an entire second stage plus payload on top is more trouble than it's worth.
They also should have either not used solids or should have developed both a solid booster and a liquid booster, so that unmanned launches could use cheaper solids while manned launches could use the more expensive but safer liquid boosters. Or just say fuck it and drop solids all together.
Instead of using legacy RS-25 engines that actually flew on Shuttle vehicles before they should have skipped straight to the upgraded design that reduces part count by 90% and offers higher performance because the engine doesn't need to be reusable anymore. Either that or just develop an entirely new engine, ideally a FFSC hydrogen engine, which would get a better thrust to weight ratio and higher Isp than the RS-25 anyway.
Lastly the second stage should have been the final one to begin with, obviously, and if we had built a new engine for the first stage there's no reason we couldn't have a vacuum optimized one for the second stage, which would give it a much better thrust to weight ratio and higher performance because of fewer gravity losses.
If you keep the same basic design architecture but get rid of the Shuttle hardware you can make SLS into a pretty decent rocket. Unfortunately SLS only exists to feed Space Shuttle job districts so divorcing SLS from Shuttle is impossible.
Oh, and we should have started decades ago.
