Propellentless rocket?

A NASA engineer came up with a new method of propulsion that uses electric fields, and which has no expulsion of mass. 

This was something that was believed impossible, theoretically. But yet he has developed a prototype. 

I look forward to seeing how it will work, once they share more with the public. 

https://www.thebrighterside.news/space/nasa-engineer-developed-a-propellant-less-rocket-that-defies-conventional-laws-of-physics