Like low-energy nuclear energy generation, the "reactionless EM drive" (aka the "Cannae Drive") involves tantalizing experiments, a dedicated and very hopeful fan base, a mixed record of publications, and an incredibly skeptical community of scientists.
As summarized in this recent story, the tantalizing experiments involve putting radiation in a cavity and finding that – somehow – this creates a net force on the cavity.
There is no extant credible theory for how this can be possible given that quantum field theory conserves momentum, and should be perfectly adequate to describe this system. (And the two papers listed in the story do not appear to this author to violate this statement.)
Nonetheless, there are a number of independent experiments claiming to see this effect, and it is not obvious what accounts for the results.
It is difficult to get a clean resolution criterion on this type of matter, but the new story, suggesting that a Cannae drive might be put into orbit, makes it possible! We ask:
By start of 2019, will a "reactionless EM drive" (broadly construed) be launched on a rocket?
To resolve as positive, the drive need not make it to orbit, deploy, work, etc. The question only concerns whether the financing and "will" shall be assembled to put one on a launch pad and fire it up.