Breakthrough Propulsion Physics Project

The Breakthrough Propulsion Physics Project (BPP) was a research project funded by NASA from 1996 to 2002 to study various proposals for revolutionary methods of spacecraft propulsion that would require breakthroughs in physics before they could be realized. The project ended in 2002, when the Advanced Space Transportation Program was reorganized and all speculative research (less than Technology readiness level 3) was cancelled.

Source: Wikipedia — Breakthrough Propulsion Physics Project (CC BY-SA 4.0)