The proposed innovation builds on the successes of the Phase I program by integrating our direct oxidation membrane electrode assembly (MEA) into a monolithic solid oxide fuel cell stack (SOFC) capable of long-term operation on methane or syngas. This innovation is significant because it will contribute to durable, cycle-able simple SOFC systems to meet the needs for NASA and commercial customers. ITN's Phase II strategy addresses the technical hurdles that limit the long-term durability and thermal cycling of state-of-the-art SOFCs operating on methane fuel, including • Matching stack components for coefficient of thermal expansion • Reducing stack mass • Stack sealing • Reducing anode degradation, and • Reducing operating temperatures. With this innovation, we project that the proposed SOFC stack will be capable of operating without degradation for more than the targeted 2500 hours and will operate without power density degradation after 50 start-up and shut-down cycles. By utilizing the direct-oxidation membrane electrode assemblies developed in the phase I program, the thermodynamic efficiencies from fuel source to DC output should exceed 70%. Higher efficiencies translate to lower cooling requirement as obtained by way of conduction through the stack to a radiator exposed to space and/or by anode exhaust flow.