Scott Manley tells us (see Engadget also) that the reaction-less drive peer reviewed paper is out, and nicely explains the basics. If it works, it would violate the long-held belief that linear momentum is conserved.
A vacuum test campaign evaluating the impulsive thrust performance of a tapered radio-frequency test article excited in the transverse magnitude 212 mode at 1937 MHz has been completed.
What is a "transverse magnitude 212 mode"? Could it be a *transverse magnetic" mode actually? That's a real term, and would be written $TM212$, having three indices instead of two because it's a more complex shape than a cylinder. Or is it a new kind of resonant mode? Is this what publication in a peer-reviewed journal means? All reviewers, and the journal's editor approved this paper including the abstract?
Further, the RF amplifier is on the torsional balance, and DC power is supplied through sliding liquid metal contacts "to eliminate cable forces'. A current flowing through a closed circuit will experience a Lorenz force tending to push the loop to larger area. (See the "sliding bar problem, fig. 10.12.1) The magnitude of the force would scale linearly with current (and therefore with the RF power). I don't see any discussion of this force on the torsional balance, or estimation of it's magnitude, but it looks like when they tested reverse thrust, the sliding contacts were also moved to the other side as well. Was this force addressed in earlier publications, or did the reviewers miss this as well?
above: Example of a reactionless electromagnetic drive being tested inside a vacuum chamber, from National Geographic. Note, the drive is supposed to produce of the order of 30 to 100 micro-Newtons, which is about the weight of a few mosquito.
above: The "sliding bar" problem from here.