The EM Drive, which I am still extremely sceptical of, was tested in a hard vacuum a few weeks ago. One possible model of operation, that it worked against the frameless background noise of virtual electron/positron pairs, agrees with some of the data collected.
I am not prepared to accept a drive without reaction mass, but a test in a hard vacuum is much more interesting than a test in a sealed chamber full of air, when you are heating things with microwaves.
http://www.nasaspaceflight.com/2015/04/evaluating-nasas-futuristic-em-drive/
http://nextbigfuture.com/2015/02/update-on-emdrive-work-at-nasa.html
Note specifically the Progress Update section on the NASA link which I attempt to summarize: On April 5, 2015, NASA Eagleworks created a new computer model of the EM Drive’s thrust as a three-dimensional magnetohydrodynamic flow of electron-positron virtual particles. They explain why in NASA’s experiments it was necessary to insert a high density polyethylene (HDPE) dielectric into the EM Drive, while the experiments in the UK and China were able to measure thrust without a dielectric insert. The reasons include China/UK using magnetrons for their testing. The model makes testable predictions. One should be cautious about accepting these results, but even if the model is wrong, anomalous thrust remains even when tested in hard vacuum, and until that can be explained, further testing is justified.
It then goes on to talk about possible space-time warping effects, and on that I am much more cynical.
I think warp issues are worth considering, but first let us deal with the anomalous thrust. Even if that alone works, it will free us of the tyranny of reaction mass based rocketry. With an EM drive at sub light speeds you can still explore the universe, it just takes a long time. With rockets you effectively cannot explore much outside the solar system.
For three years they have been conducting experiments to find out if you can measure, with an interferometer, a distortion of spacetime produced by EM drives. If you can, it means warp drives could work, and a spacecraft traveling at conventional speeds could achieve effective faster than light speed by contracting space in front of it and expanding space behind it. The experimental results so far had been inconclusive.
During the first two weeks of April of this year, NASA Eagleworks believe they may have finally obtained conclusive results. This time they used essentially an EM Drive, with much higher electric-field intensity, aligned in the axial direction. The interferometer’s laser light goes through small holes in the EM Drive. Over 27,000 cycles of data they obtained a power spectrum that revealed a signal frequency of 0.65 Hz with amplitude clearly above system noise. Four additional tests were successfully conducted that demonstrated repeatability.
The NASA team considered refraction of the air as a cause, but felt it unlikely because the experiment’s visibility threshold is forty times larger than the calculated effect from atmospheric heating of air.
Encouraged by these results, NASA Eagleworks plans to next conduct these interferometer tests in a vacuum.
