An exotic space propulsion system

I have not blogged about the EmDrive before although I have followed it for years. It seems far-out - a space propulsion system which is propellantless. It seems to violate the law of momentum. Many still regard it as impossible and there is no generally accepted explanation of how it works. However careful tests, some by NASA, have found that it does seem to produce a small steady thrust.

Remember that effects have many times been pronounced impossible before but later accepted. I am posting an item about the EmDrive as an example of such.

NASA is publishing a paper describing tests they have been conducting, as reported by NextBigFuture.

An article in DigitalTrends gives an overview:
"The issue is, the entire concept of a reactionless drive is inconsistent with Newton’s conservation of momentum, which states that within a closed system, linear and angular momentum remain constant regardless of any changes that take place within said system. More plainly: Unless an outside force is applied, an object will not move."

So how does it work? it uses microwaves - read the article to find out.