In defense, it's being built right now. AFAIR SpaceX tested engines for it recently.
It's engineering. When you have a design validated "on paper" you're likely already 80% done - the rest is to actually assemble and fix problems simulations didn't catch.
It's engineering. When you have a design validated "on paper" you're likely already 80% done - the rest is to actually assemble and fix problems simulations didn't catch.