The voyage duration of c. 50,000 years for the Centauri Princess is largely governed by the fact that the Alpha Centauri system is passing by our Solar System in its travels about the center of the Milky Way galaxy, and any high-mass/slow-cruising craft launched from Earth needs to get there within a reasonable time window. ] Thereafter, the system will start to recede away from us again, widening the gap and making any journeys between Sol and Alpha Centauri increasingly dis-optimised (see original discussions on this by Ahad).