The development of solid oxide electrolysis cell technology has progressed to a level that allows for construction of a three-person breadboard system. This paper addresses the design, fabrication, and testing of the breadboard, and the data base obtained for future electrolysis systems that have application for planetary manned missions and habitats. The breadboard contains sixteen tubular cells in a closely packed bundle for the electrolysis of carbon dioxide and water vapor. Palladium diffusion tubes are arranged in the bundle parallel and symmetrical with the electrolyzer tubes for removal and separation of hydrogen from the process gases. Basic information on energy requirements, volume, and weight, are described. The operational characteristics related to measurement of the reactant and product gas compositions, temperature distribution along the electrolyzer tubular cells and through the bundle, and thermal energy losses are assessed. The reliability of individual cell performance in the bundle configuration is examined. The effects of long-term testing on the mechanical and electrical stability of the ceramic cells of the breadboard as compared to isothermal single cell testing is also examined. Performance goals are defined and discussed.