P herein is a review of systems which can be utilized for the generation of secondary and/or propulsion power for advanced space vehicles. The power systems considered are: Chemically-fueled power supplies; open and closed cycle. Solar power supplies, closed cycle. Nuclear power supplies, closed cycle. Thermionic and thermoelectric power supplies. Solar photo-voltaic and solar recycling fuel cell power supplies. Included also in the review are the results of an initial program relating to the optimum temperature ratio, collector and radiator size for general power systems when used with nuclear, chemical or solar energy sources. The performance of the conversion devices per se as a function of the collector or radiator environment is not included. Descriptions are presented of a number of typical power systems. An attempt is made to describe the general physical construction as well as to indicate the limitations of the system. Analyses and estimates have been prepared in order to determine the system weight as a function of power level and duration. Comparison of some of the systems studied is presented. Weights and sizes of the significant components are tabulated for 1and 100-kw systems. Variation of system weight with time and power level is plotted to determine the optimum system from a weight standpoint for various applications. System selection for various missions is summarized, and the role of turbomachinery in space vehicle power systems is noted.