I like both of the "ifs"Halidon wrote: if[1] so I'd definitely put that as being in the high end of an "upgraded Astute" range rather than a new design. If the pressure hull's diameter need to be increased and/or [2]new reactor is used you're pretty much in a "new design" space.
- as for the [2], could one safely assume electronics minituarisation having some effect also around the core that provides the actual propulsion power?