Meanwhile, having engines that have higher specific impulse helps quite a bit as well. That is to say: a nuclear engine needs less propellant to provide the sam

Meanwhile, having engines that have higher specific impulse helps quite a bit as well. That is to say: a nuclear engine needs less propellant to provide the same amount of delta V (actual work). Since the majority of a rocket's mass is in the propellant, this scales non-linearly. A nuclear rocket is a big improvement over chemical rockets already.