Multi-megawatt class nuclear fission reactor powered closed cycle MHD single cycle for space applications using helium and xenon mixture as a working gas has been studied. System analysis was carried out. Total plant efficiency was expected to be 55.2 % including pre-ionization power. Effects of compressor stage number, regenerator efficiency and radiation cooler temperature on plant efficiency were studied. Specific mass of power generation plant was examined. Specific mass of 3 kg/kWe at the net electrical output power of 1 MWe and less than 2 kg/kWe for the output of larger than 3 MWe were expected. Three phases of research and development plan were proposed; Phase-I, Proof of Principle, Phase-II Demonstration of Power Generation, and Phase-III Prototypical Closed Loop Test.