But principles are long since known, and prototypes are coming more and more often. Delta-Cliper, Space Ship One, New Shepard, unmanned Dragons, first stages of

But principles are long since known, and prototypes are coming more and more often. Delta-Cliper, Space Ship One, New Shepard, unmanned Dragons, first stages of F-9, aerodynamic tests in wind tunnels - all of them contribute, to various degrees, to the technologies needed.