Which neatly answers the question of why we've collectively done very little to advance any "real" aerospace barriers in the last 40 years or so.
FFS, it took c. 65 years from the first powered flight by an aircraft to putting a man on the moon. They didn't worry about the impossibility of it all, they just f'ing went ahead and did it anyway. In the 40 years since, the western world has been sitting on our hands, slowly falling into a pit of introversion, cynicism and self-loathing. Concorde? The X33? How on earth can the proposed STS replacement be an advancement on the Space Shuttle?
Today's can't-do attitude must be a gut reflex reaction to the can-do baby boomer generation.
End of rant.