A rocket propels itself rectilinearly through empty space by emitting pure radiation in the direction opposite to its motion. If u is its final velocity relative to its initial rest frame, prove that the ratio of the initial to the final rest mass of the rocket is given by M M C+U C-U 1/2 A rocket propels itself rectilinearly through empty space by emitting pure radiation in the direction opposite to its motion. If u is its final velocity relative to its initial rest frame, prove that the ratio of the initial to the final rest mass of the rocket is given by M M C+U C-U 1/2