> A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet.
What are you basing this on? NERVA was for getting off the planet. It had a thrust of ~250 kN. In comparison, a SpaceX Merlin engine has a thrust of ~900 kN, while ion drives have <1 N of thrust.
High fixed (non propellant) drive weight compared to chemical rockets makes it pretty inefficient due to the gravity well - thrust/weight ratio vs time matters a lot when you’re quickly climbing out of the well. And it is very difficult to do that quickly with nuclear without exceeding our materials science abilities and causing a nuclear accident.
Additionally, atmospheric density and friction matter a lot in these situations, and getting out of high density atmosphere and ‘up’ as quickly as possible pays large dividends.
Once you’re in a very low friction environment and ideally already moving near orbital or extra orbital velocities, taking your time is all good, and maximum end-to-end efficiency and power density matters more - you can have as much time as you want.
What are you basing this on? NERVA was for getting off the planet. It had a thrust of ~250 kN. In comparison, a SpaceX Merlin engine has a thrust of ~900 kN, while ion drives have <1 N of thrust.