I wonder about this......

with a shuttle like vehicle on the top of the stack, ad no solids. plus the ability to launch very heavy loads when desired.

the 2nd skylab could of been put in orbit, ISS could of been built with fewer larger modules

no solids to have leaky joints, no foam loss damaging TPS.

and we could of slowly done more apolo applications missions.

was the shuttle ever cheaper to operate than apollo