ABSTRACT:  As telecommunications payloads shrink, there has been a recent push to develop aircraft that can provide long-endurance (days to weeks) persistent aerial coverage. These aircraft present a complicated systems engineering problem because of the multifaceted interaction of various requirements, such as endurance, wind speeds, operational capability, and coverage footprint. We use a rapid form of convex optimization, geometric programming, to explore trade-offs between solar-electric and gas powered architectures for long-endurance aircraft . While solar-electric powered aircraft can theoretically fly for months, they are operationally limited by reduced solar flux during the winter and wind speeds at higher latitudes. Gas powered aircraft, on the other hand, are limited in their endurance by the amount of fuel that they can carry, but are shown to have operational capability across a wider range of latitudes, seasons, and wind conditions.  We present a detailed trade study to evaluate which architecture is best suited to meet a given set of requirements, and what is the optimum size and endurance of that platform.