Hi A simple thought experiment: A line of inertial space stations at 10 ls intervals stretching indefinitely into the distance. Two spaceships A and B located at adjacent stations. For simplicity dont consider proper acceleration, just assume identical ships and propulsion sytems and mechanically identical fuel feed etc. In this question it is only important that the accelerations be exactly equal. Disregard contraction of the ships themselves, as relative to the spatial separation this is irrelevant, vanishingly small. SO distance between will be measured from the center of the ships. Simultaneity of blastoff is not an issue as they are both starting out in the same inertial frame with conventionally synched clocks all around. So the question is simple: 1) In the frame of the stations does the distance between the ships remain the same or does it contract??? 2) In the frame of the ships does the distance remain the same or does it expand???