In normal play, you are expected to be able to build the Personal Fusion Reactor before launching a rocket. So, within the 10ish hour mark.
In SE, it takes 10 times longer to access it, if not more.
As such, any mod that assumes that they will unlock early ends up locking it's recipes/technologies way later than intended.
This mod fixes it by automatically replacing the Personal Fusion Reactor as a tech prereq/recipe ingredient with either RTG 1 or 2, based on the mod setting.