People gloss over things like building a turbine engine as easy - it is not - it's been done, yes, but for these guys to build, qualify, validate and get an eng

People gloss over things like building a turbine engine as easy - it is not - it's been done, yes, but for these guys to build, qualify, validate and get an engine flying on passenger planes is a HUGE undertaking even ASSUMING this critical piece of tech was perfect. To also then build the plane? I'm curious to see what their re-entry technology looks like - feels pretty critical path to me. What are these applications and industries that will be revolutionized? I'm serious - I've heard this will revolutionize hypersonic cars. OK. The plane concept itself required a closed loop normal rocket engine - so you've got to have that AND the Sabre AND are doing single stage to orbit. I shudder to think of the mass fractions - how does carrying all this extra around make sense just from the physics - do you save that much in terms of LOX?