Per the arxiv paper "...Thus, at some point, the kinetic energy of the device-driven mass exceeds the energy input, and if this energy is collected via decelerating the mass (via regenerative electromagnetic braking, for example), then there would be a net gain in energy."
So, first of all, the author of the paper certainly acknowledges the simple priniciples that make EM drive propulsion function. The author is simply arguing how feasible the technology would be for achieving any significant acceleration.
He doesn't claim that EM drive is in principle a perpetual motion machine, rather that 'ar some point' [during acceleration] the energy input to achieve any signiificant acceleration to make the technology feasible would require output energy greater than the possible energy input aboard an engine of a given mass (a statement which is certainly dependant on the efficiency of the 'power conversion' of the system, which can be improved with, for example, more efficient conductors/resonator cavities, etc.).
The paper is fine IMO; it's the comment that cited the paper that is inacurrate.
To quote from the abstract: "any device with a thrust-to-power ratio greater than the photon rocket would be able to operate as a perpetual motion machine of the first kind, and thus should be excluded by the First Law of Thermodynamics" seems pretty categorical to me.
The problem is, when you look at an object with a given velocity v, it has a kinetic energy proportional to v^2. To accelerate it from 0 to v, you must have put in all that kinetic energy (ie, v^2 energy). But reactionless drives give you velocity directly in proportion to energy. At some point, the v^2 and v lines will cross, and your object will have more kinetic energy then you put into it in the first place.
For every unit of energy you pump into the drive, the velocity goes up by a unit, but since the kinetic energy of the object is proportional to v^2, at some point the kinetic energy you get out will be more than the electric energy you put in. The problem goes away with photon drives because that crossing point turns out to be at the speed of light.
This is the argument the paper is making: If you can generate velocity directly from energy, you will eventually end up generating more energy than you started with.
So, first of all, the author of the paper certainly acknowledges the simple priniciples that make EM drive propulsion function. The author is simply arguing how feasible the technology would be for achieving any significant acceleration.
He doesn't claim that EM drive is in principle a perpetual motion machine, rather that 'ar some point' [during acceleration] the energy input to achieve any signiificant acceleration to make the technology feasible would require output energy greater than the possible energy input aboard an engine of a given mass (a statement which is certainly dependant on the efficiency of the 'power conversion' of the system, which can be improved with, for example, more efficient conductors/resonator cavities, etc.).
The paper is fine IMO; it's the comment that cited the paper that is inacurrate.