Interstellar travel
Kennedy's calculation depends on r, the mean annual increase in world power production. From any point in time to a given destination, there is a minimum to the total time to destination. Voyagers would probably arrive without being overtaken by later voyagers by waiting a time t before leaving. The relation between the time it takes to get to a destination (now, Tnow, or after waiting, Tt, and growth in velocity of travel is