It's not yet a real speciality, due to the fact there's no real work being done (practical work, that is) Thus, anyone thinking about the problem is probably a mathematical physicist, or a plain theoretical physicist (or an n-dimensional geometer) Astrophysicists are those who specialise in the physics, evolution, care and feeding of stars; they're like cosmologists, need a very big laboratory for their experiments, and even then, a couple of billion years before the observations show enough change to write up. (Hm, a faster than light drive would be handy for watching the evolution of stellar types, if it went fast enough)
In today's ultra-specialised world it's highly improbable (not impossible, evidently) that one person, or even a small team, would be responsible for the basic equations, the translation of these equations into a viable physical theory, and the developement of that theory into a hardware solution that engineers and technicians could translate into a prototype; a century and a half ago, this would have been the norm.
How about an n-dimensional cosmo-topologist?
but 'Astrophysicist,' would probably cover most of it. The guy who did this work on a spaceship would simply be the navigator.
