An article at NasaSpaceFlight.com is claiming that the superficially reactionless EmDrive has again been tested at NASA Eagleworks, this time in hard vacuum, and the anomalous thrust is still being detected:
A group at NASA's Johnson Space Center has successfully tested an electromagnetic (EM) propulsion drive in a vacuum – a major breakthrough for a multi-year international effort comprising several competing research teams. Thrust measurements of the EM Drive defy classical physics' expectations that such a closed (microwave) cavity should be unusable for space propulsion because of the law of conservation of momentum.
With the popular explanations of thermal convection or atmospheric ionization being ruled out by operation in vacuum, and thrust thousands of times greater than expected from a photon rocket, is it time to start taking the EM Drive seriously as a fundamentally new form of propulsion, and possibly a door to new physics?
Roger Shawyer, the inventor of the EmDrive, claims that the device's efficiency will scale even further with greater levels of power, potentially enabling fast interstellar travel powered by a radioisotope thermoelectric generator or nuclear fission.
Previously: NASA Validates "Impossible" Space Drive's Thrust
Honestly, you don't need to test it in space at all. VASIMR and other ion engines were tested right here on Earth. If this thing can create 4 times or the promised hundreds of times more thrust per Watt than ion engines, it will be obvious. The vacuum testing eliminates some of the skepticism.
NASA needs to do two things: refine it to work very predictably, and investigate claims of >1 Newton of thrust per kilowatt (or the insane 300 Newtons per kilowatt). State of the art ion engines produce 0.04 Newton of thrust per kilowatt.
I think that it needs to be tested not only in a vacuum, which I'm delighted they've done, but outside the Earth's magnetosphere. I'm excited by this, but I'm not convinced that it's not following conservation principles by infinitesimally pushing-against/degrading the planet's magnetic field.