## Comment Re:so is there a good theory? (Score 1) 470

* With the only known reactionless drive we have, the photon drive,*

First of all the term "reactionless" makes no sense. You mean: "without reaction mass".

Secondly: the photon drive has a reaction mass, they are called "photons".

Of course a "normal" rocket is no PM, and neither is a EM drive, that was my point.

Your point seemed to be that my maths works equally well for a rocket and EM drive, so if it were correct, both would have been allowing PM. As it is already known that normal rockets do not allow PM, my maths must be incorrect.

My point is that my calculations only take into account what happens on the engine side. In the EM drive, the engine is all there is to it. It converts energy and produces work all by itself. In a normal rocket, what used to be part of the system is now expelled as reaction mass. So the calculations are complete for an assumed reactionless EM drive, but incomplete for a rocket engine. It may be the case that my maths are not correct for Em drive either, but your point for its incorrectness is not valid.

I am not saying EM drive is PM, nor am I saying that it cannot work. I am saying that it cannot be an engine that converts energy into propulsive power without interacting with any kind of matter, as assuming that allows an impossible construct, a PM machine. We just don't know where its reaction mass comes from.