Solid oxide fuel cell (SOFC)/ gas turbine hybrid power systems (HPSs) have been recognized by federal agencies and other entities as having the potential to operate at unprecedented levels of performance for terrestrial applications (e.g., 70% power generation efficiencies with significantly mitigated criteria pollutant and noise emissions). An innovative approach is proposed for leveraging competencies in high temperature fuel cell stack and system simulation/validation and manufacturing, in conjunction with robust aeronautical sub-system/system design capabilities, to optimize these promising systems for novel aerospace propulsion and power applications. NASA GRC?s ?Protect the Environment? and ?Explore New Aerospace Missions? initiatives are addressed via the proposed technical contributions to both alternative non-combustion and alternative fuels/combustion aeronautical power generation. SOFCs, the non-combustion alternative, serve as a promising fuel infrastructural bridge; because the technology engenders practical efficiencies between 45-60%, and it is amenable to a variety of fuel feeds (including hydrocarbons and hydrogen). The inclusion of the SOFCs into modified Brayton cycles also enhances combustion-based power/propulsion via its byproduct enhancement of the fuel quality and heating value upstream of the combustor. A rigorous conceptual design/validation study is proposed for Phase I, corresponding proof-of-concept enabling hardware development for Phase II, and NASA/non-NASA commercialization efforts for Phase III.