The rotation thing introduces a whole new dimension. The analogy of a car on the surface of the earth was not intended to suggest rotation was the end result. However, the analogy is significant indeed.CaptainBeowulf wrote:Does the universe have a rotational angular momentum? No (at least assuming Mach's Principle is true).
The above analysis is a purely 1D analysis - all momentum change in the same line. One can instead think of a long geared track in space of considerable mass, along which a geared cart accelerates. Same things apply, no rotation.
But if the CoG of the ROTU is, indeed, not in line with the direction of acceleration of a propellantless thruster then that thruster would gain rotational momentum wrt ROTU if it were to accelerate. Conservation of momentum would dictate that the ROTU would then have to acquire rotational energy.
if momentum is transferred from a prospective propellantless thruster to the ROTU,
if the acceleration of the thruster is not inline with the CoG of the universe
if the ROTU cannot rotate
the thruster cannot accelerate, because the only solution that satisfies the above statements is zero rotational momentum change in both ROTU and thruster.