A number of companies are working on suborbital flight with Blue Origin, Virgin Galactic and XCOR being among the most recognized today. I don't ask here about what actual plans different companies have, but at first look a plausible strategy could be to start out with a suborbital launch system with the aim of developing an orbital launch system out of it.
Is suborbital flights a natural stepping stone to orbit? (In our time, the early space race is a bit OT). Can the same engines, whole stages, crew capsules be used both in and sub orbit? Or are there difficult compromises which risk leading to both the suborbital and the orbital systems becoming suboptimal? For Virgin Galactic and Virgin Airline (suborbital and airlines) the synergies are not obvious to my mind, maybe the step to orbit is as big.
Sub-orbital systems which are up and coming, if they become successful, are mostly crew oriented (while sounding rockets with science payloads and ICBM's are well established and less commercial). So a strategy to begin with sub-orbital flights seems to me to require crewed flights, if the sub-orbital business leg is to generate a profit of its own. If that is correct then I suppose my question is whether it is basically rational to approach crewed orbital launches from crewed sub-orbital launches, and maybe even building on airline experiences. Will sub-orbitals get important advantages over those who go for orbit directly, or are they suboptimizing by trying to do two different things?
Airborne launches (like VG is planning), VTOL and winged spacecrafts and parachutes into the ocean and whatnot are all plausible technologies. I don't want to directly address them per se in this question about the synergies and differences in going from (or via) sub-orbital to orbital. Could for example the same launch pad and ground operations be used?