This is my first post but I saw this and thought a few people here would find it interesting. In 2009 a team of Chinese scientists took a design for a closed container propulsion drive designed by a Roger Shawer, built it and it worked. Producing a small amount of force 720 millinewton which is enough to make a thruster.Nasa have now made a similar engine which also works, exciting stuff.
I will not try and go into detail writing is not a strong point for me. Here are the sources I looked at.
http://sploid.gizmodo.com/nasa-reveals-new-impossible-engine-can-change-space-t-1614549987?utm_campaign=socialflow_gizmodo_facebook&utm_source=gizmodo_facebook&utm_medium=socialflow
http://ntrs.nasa.gov/search.jsp?R=20140006052
http://www.theverge.com/2014/8/1/5959637/nasa-cannae-drive-tests-have-promising-results
It's interesting stuff. There's been talk of EM drives for years, but I was unaware that they have had positive results from practical tests yet. From what I know, it's in a similar class to ion propulsion, it terms of thrust. The difference being that it requires no fuel , and has significantly less mass when constructed (so it has better thrust to weight, er, mass ratios). So while it's not going to replace liquid or solid fuel rockets for launches or anything that requires high acceleration, it can be very useful for long range space travel or for orbital adjustment/maintenance.
The math and science behind it is still a little fuzzy, and as such it's unclear how it will scale up... but it is promising. If it pans out on the large scale, you could combine this with an electromagnetic launch system and remove (or greatly reduce) the need for rockets in traditional space launches. Space travel could go green lol.