> The upper limit for speeds you can reach approaches the speed of the exhaust - which tops out around 50 km/s for current ion drives, about .0002C. That is no

> The upper limit for speeds you can reach approaches the speed of the exhaust - which tops out around 50 km/s for current ion drives, about .0002C. That is not correct. The delta-v of a rocket (i.e., the maximum speed it can reach) depends on the effective exhaust velocity and on the mass fraction of its propellant; see [1]. For example, a rocket which is initially 90% propellant, can reach a velocity ~2.3 times its effective exhaust velocity. [1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation