The jury is still on for exotic propulsion schemes like EmDrive, Mach Effect Drive (MEGA) etc., but if they work they could open a cheap road to the planets and tomorrow the stars.

My last article about that published in Motherboard and CNET:
https://motherboard.vice.com/en_us/article/zmzmpa/emdrive-nasa-impossible-propulsion-system-explained

Especially relevant to Building Blocks:
Some exotic propulsion research today is inexpensivegarage sciencethat doesn't require multi-billion dollar investment, and can even be self-funded. EmDrive enthusiasts can now 3D-print EmDrive parts and start doing independent experimental research.