I apologize that I am not sure just what you are saying, but I think you are wanting to know if you can measure the velocity of a closed rocket by measuring the difference in the light intensity at the front and the back of the rocket. If that is your question then you will not be able to do it. The problem with you system is that it is a closed system and therefore will pretty much represent a single reference frame. The velocity of the rocket will not affect the transmission of the light if the reference frames of the 2 points (Cfront and Cback) are not moving with respect to each other and with respect to the light source. This would be true with either Galilean or Special relativity.
Galilean relativity assumes that all velocities are simple additional quantities, in this case the velocities, with respect to each other, are zero, so there would be no observable difference.
Special (Einsteinian) relativity assumes that the speed of light is a constant, and that the relative velocities are dependent on how close the relative velocity of the reference frames is to the speed of light. But in this case the relative velocities are zero, so once again there would be no effect.
Bill Gill
