Yeah, I did notice that the original NTR plans arose from the wish to upgrade Saturn V with its limited "throw weight" at third stage separation (http://www.ast

Yeah, I did notice that the original NTR plans arose from the wish to upgrade Saturn V with its limited "throw weight" at third stage separation (http://www.astronautix.com/s/saturnc-5n.html http://www.astronautix.com/s/saturnc-5n.html). It doesn't seem to make a lot of sense to design a propulsion unit for a sixty year old mission architecture today, though.