Evaluating the energy balance of high altitude platforms at early design stages

High altitude platforms, also known as pseudo-satellites, are envisioned as unmanned aircraft flying at altitudes above 15 km to provide observation, remote sensing or communication services. A challenging yet recurring requirement for such aicraft is to be able to perform long-endurance missions over multiple days or even weeks. A sophisticated onboard energy management system including solar panels and batteries is needed to achieve this. The energy balance of such an aircraft depends on many factors which should be considered in the design process. In this work, we propose a systematic approach to evaluate the energy balance of high altitude platform designs for specific mission scenarios. This approach can be employed at very early design stages and incrementally extended to follow the design process. We demonstrate the methodology with an exemplary parameter study for a generic fixed-wing aircraft. In particular, the impact and correlations of the mission latitude, wind conditions, flight trajectory optimization, sizing of the platform and solar panel coverage of the main wing was evaluated. A key result is that battery mass can be reduced significantly, especially for missions at high latitudes, by optimizing the holding pattern that is flown throughout the mission or by increasing the solar panel coverage. Generally, the results indicate that the method allows to evaluate mission-specific effects on the energy balance of high altitude platforms.