We need a Space Elevator!
Yep, another simple idea that makes space more accessible.
I’m personally not interested in interstellar flight in respect to this thread so much as I am interested in making our solar system more accessible. The space elevator combined with mining and manufacturing in space and on the moon would make space much easier.
3D printing in space is another thing that could lead to great leaps. Even rocky asteroids could be pulverized and turned into concrete for printing into massive hulls for the large ships we really need for long duration time in space. We currently send life rings to space with a couple of men when we really need aircraft carriers with crews of dozens or hundreds.
What do you make the cable out of?