Yes there was criticism in the article suggesting evaporation as the source of the thurst However it was together with all criticisms removed censored by POV pushing editors No control for mass was done in either experiment and evaporation of order of less than microgram per second could easily explain the effect especially in the NASA case even more so if there is some moisture What you are essentially doing is microwaving the interior of a cone and surprise surprise there is a small force in the opposite direction Then you turn off the heating but your interior is still at higher temperature measure it again and there is still a force yet smaller Nothing to do with exotic physics everything to do with experimental error due to unforeseen effect of evaporation i e ablation though some moisture might play an effect especially if there are parts other than metal this is in my opinion the most likely explanation EM radiation can not cause such effect at these power force ratios that part was also removed from the article though all was sourced So if there is no some weird effect and QED effects virtual plasma included boil down to EM radiation reaction there is no violation of impulse conservation there so that is excluded too it should be reaction from some loss of mass and evaporation is an obvious source However they did not check for that Also some of experiments were done in atmosphere at atmospheric pressure even in chamber according to brief paper so other possibility is interaction with heated air However in vacuum ablation seems to be most likely explanation Why all this sourced material and all criticism was removed beats me 213 198 221 171