I thought that was implied by the description of the EM drive of "X kilowatt for Y newton". But I guess the effect could indeed depend on your speed relative to

I thought that was implied by the description of the EM drive of "X kilowatt for Y newton". But I guess the effect could indeed depend on your speed relative to some special reference frame, like that of the microwave background. If that's the case, then we can do something like the Michelson–Morley experiment, to check whether the effect is different depending on the direction the Earth is moving in its orbit.