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A Stratospheric Airborne Climate Observatory System is proposed to leverage recent advancements in key enabling technologies for solar electric flight (batteries and solar cells) and enabling technologies for Earth observation (lidar, radar, laser systems, etc.). Advantages of this observation system include the ability to make in-situ measurements of the stratosphere, measure at a high spacial and temporal resolution, and direct-ablility (the trajectory can be adjusted in real-time for persistent monitoring or tracking).Although historical examples of similar solar-electric long-endurance aircraft have faced considerable technical and programmatic challenges, this effort employs several risk mitigation strategies to avoid common pitfalls such as wing structural divergence. The vehicle, mission, and operational strategy are designed in tandem, customizing each aspect of the design to best serve the mission requirements while minimizing risk (modelled by wingspan as a proxy for aero-structural risk). An integrated optimization framework is presented as a tool for aircraft sizing and the key driving parameters are explored, including technology specifications, payload mass and power, and the cruise altitude of the vehicle.Several potential climate science missions are then proposed, each where the attributes of this SACOS vehicle fill a persistent void in current observational techniques. The sizing tool is used to show the size, capability and seasonality of a SACOS vehicle designed for said application. This analysis illustrates a rich feasible space, and minimal technical risk should the SACOS vehicle operate seasonally (only in summer months where solar conditions are favorable).

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Electric short takeo and landing (eSTOL) aircraft and electric vertical takeo and landing (eVTOL) aircraft are being developed for missions where availability of ground infrastructure is a critical design driver. Because eSTOL aircraft can generate high e ective lift coe cients through the interaction of the wing, flaps, and distributed propellers they can achieve takeo and landing distances comparable with the ground footprint proposed for eVTOL facilities. eSTOL aircraft require smaller propulsion systems and less energy for takeo and landing than eVTOL aircraft, which in turn translates to reduced vehicle weight or increased payload, range, and/or speed.This paper compares the performance di erence between eSTOL and eVTOL aircraft, for both hybrid-and battery-electric propulsion architectures. Both tilt-duct and tilt-rotor eVTOL configurations are examined. For aircraft with an equivalent weight and span to proposed eVTOLs, eSTOL aircraft are able to carry 1.8-2.6x the payload at the same speed and range, depending on the eVTOL type and propulsion system architecture. This number is sensitive to eVTOL disk loading, design mission, and modeling of blown wing performance. The benefit of eSTOL arises primarily from reduced propulsion system weights and reduced energy consumption in the takeo and landing phases. This benefit varies significantly with design ground footprint and payload; and less so with range and speed.

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