The engine is flexible enough that the only difference is the dataset--
you have vegastrike.config that tweaks all sorts of constants (like is warping or autopilot allowed, what is the rate of energy usage for shields, etc)
and then you have a table with shields and weapons stats in units.csv--
really most scifi games are only different in their data, the code can work for anything
check out Vega Trek, another game built on the very same codebase