The larger NERVA I rocket gradually gave way to the smaller NERVA II rocket in mission plans as efficiency increased and thrust-to-weight ratios grew, and the KIWI gradually gave way at Los Alamos to the smaller Pewee and Pewee 2 as funding was cut to lower and lower levels by Congress and the Nixon administration.
Большие ракеты NERVA I постепенно сменились в планах на меньшие NERVA II, так как эффективность увеличилась и отношение тяги к весу выросло, и KIWI постепенно сменились на Pewee и Pewee 2 по мере сокращения финансирования.