Minimum Operation Altitude for Self-Sustainable Operation of Solar-Powered Fixed-Wing UAVs in Airborne Networks

Non-terrestrial networks (NTNs) play a pivotal role in advancing 6G and beyond networks by providing global coverage for backbone infrastructure, wireless access, and backhauling. In particular, fixed-wing unmanned aerial vehicles (UAVs) at tropospheric altitudes are positioned as an efficient platform to provide backhauling for ground-based base stations using high-capacity point-to-point wireless links that operate at either optical or radio spectrum. These UAVs are typically solar-powered to ensure self-sustainability for extended operation durations. Higher altitudes improve energy harvesting by bringing the UAV closer to the sun and reducing energy consumption due to lower air density. Achieving self-sustainability requires determining the minimum operational altitude at which energy harvested consistently exceeds consumption. In this paper, we derive a closed-form expression for the minimum operational altitude of solar-powered fixed-wing UAVs, ensuring a balance between harvested and consumed energy. Key factors such as geographical location, time of year, UAV mass, and solar panel efficiency are shown to significantly influence this altitude, making them critical to the system’s sustainable operation.