Worth noting in relation to the JIMO story above (and for the broader issue of generating power for deep space probes): “A Power Conversion Concept for the Jupiter Icy Moons Orbiter,” by Lee S. Mason (Journal of Propulsion and Power Vol. 20 No. 5, 1 September 2004, pp. 902-910). From the abstract: “An analytical study was performed to compare design options for a reactor power system that could be utilized on a Jupiter Icy Moons Orbiter mission employing nuclear electric propulsion.”