Richard Garwin, a respected nuclear scientist, has estimated that 1,300 high-performance centrifuges would have to operate full time for three years to make the 60 kilograms of fissile material needed for a basic (“gun-type”) nuclear weapon. Accomplishing that would require an enormous sustained input of electricity, without fluctuation or interruption. Moreover, the operation of a multi-centrifuge “cascade” requires a high-powered motor with a speed twice that of a MiG-21 jet engine. North Korea cannot produce engines even for its Russian-supplied MiGs, and it has only limited, highly unreliable electricity capabilities.