The Brayton Power Conversion Unit (BPCU) is a fully integrated power conversion system including turbine-alternator-compressor (TAC), recuperator, and gas cooler with a 62.7% Xenon and 37.3% Helium (83.8 g/mol) working fluid designed for operation up to 2 kWe. The heat source used in the test was an annular finned heat exchanger containing a series of silicon-carbide electrical resistance elements that raised the working fluid temperature to over 1000K, simulating a fission reactor heat source. A commerical chiller with a pumped ethylene glycol cooling loop provided waste heat rejection, simulating a space radiator system. Multi-Foil Insulation (MFI) covers the high temperature components to minimize heat loss in the rough vacuum test environment. The BPCU was the first closed Brayton cycle to be coupled with an ion propulsion system and was used to examine external mechanical vibration characteristics and responses. It has been used for validation of a BPCU computer model built using the Closed Cycle System Simulation (CCSS) design and analysis tool.