The Space Exploration Initiative (SEI) will need a wide variety of manned systems with requirements significantly different than those for existing systems. This paper discusses the need for a space power utility concept, and examines the impact of this concept on the engineering of space power systems. Almost all existing space power systems distribute low voltage direct current. Although they have been very successful, increasing power system requirements in recent years have exposed their inherent limitations and led to the proposal of a number of alternatives including high voltage dc, and ac at various frequencies. This paper, drawing on the experience gained from Space Station Freedom and SEI systems studies, discusses the factors that may affect the choice of frequency standards on which to build such a space power utility.