ah.clem and infodragon write:
This story from a Wired article: NASA is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on. Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion. British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.
NASA states... "Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma"
Ok, now that I'm at work I've had a chance to read through the paper. The quote is valid, though to be fair it is in the description of the vacuum chamber capabilities, which is not necessarily the same as the setup used in the test. However, nothing in the paper suggests they did not, so either it's a gross omission, or they did tests at vacuum.
In either case, they are planning a new design that they expect to be an order of magnitude better (0.1 N per kW), with an added feature to rule out another possibility I hadn't remembered to consider:
The [new] tapered thruster has a mechanical design such that it will be able to holdpressure at 14.7 pounds per square inch (psi) inside of the thruster body while the thruster is tested at vacuum topreclude glow discharge within the thruster body while it is being operated at high power.