The video link below will give an overview:

https://www.youtube.com/watch?v=gTEMMiQXXVg

NASA has made news in recent years due to its development of the controversial EmDrive, an "impossible" engine that could make interstellar travel possible.

What are the implications of this drive and why it should, in theory, not work according to the principles forbidding the operation of perpetual motion machines? Whether or not you think the EmDrive is a real, operating engine.