Design of small hand‐launched solar‐powered UAVs: From concept study to a multi‐day world endurance record flight

Abstract

We present the development process behind AtlantikSolar, a small 6.9 kg hand-launchable low-altitude solar-powered Unmanned Aerial Vehicle (UAV) that recently completed an 81-hour continuous flight and thereby established a new flight endurance world record for all aircraft below 50 kg mass. The goal of our work is to increase the usability of such solarpowered robotic aircraft by maximizing their perpetual flight robustness to meteorological deteriorations such as clouds or winds. We present energetic system models and a design methodology, implement them in our publicly-available conceptual design framework for perpetual flight-capable solar-powered UAVs, and finally apply the framework to the AtlantikSolar UAV. We present the detailed AtlantikSolar characteristics as a practical design example. Airframe, avionics, hardware, state estimation and control method development for autonomous flight operations are described. Flight data is used to validate the conceptual design framework. Flight results from the continuous 81-hour and 2338 km covered ground distance flight show that AtlantikSolar achieves 39 % minimum state-of-charge, 6.8 h excess time and 6.2 h charge margin. These performance metrics are a significant improvement over previous solar-powered UAVs. A performance outlook shows that AtlantikSolar allows perpetual flight in a 6-month window around June 21 st at mid-European latitudes, and that multi-day flights with small optical-or infrared-camera payloads are possible for the first time. The demonstrated performance represents the current state-of-the-art in solarpowered low-altitude perpetual flight performance. We conclude with lessons learned from the three-year AtlantikSolar UAV development process and with a sensitivity analysis that identifies the most promising technological areas for future solar-powered UAV performance improvements.

Fully autonomous micro air vehicle flight and landing on a moving target using visual–inertial estimation and model‐predictive control

“…Our work on the control synthesis is closely related to previous work of Darivianakis et al () and Papachristos et al () that has been successfully implemented on similar multirotor platforms and Oettershagen et al (), () that has been deployed on fixed wing platforms.…”

Robotic technologies for solar‐powered UAVs: Fully autonomous updraft‐aware aerial sensing for multiday search‐and‐rescue missions

“…Our previous work presents its design and initial flight results as well as first aerial sensing missions . More recently, a comprehensive description of the UAV's conceptual design, detailed design, and flight results—including an 81 h continuous solar‐powered flight that represents the current world record in flight endurance for all aircraft below 50 kg total mass—has been published . The reader is referred to the above literature for an in‐depth design review.…”

“…The aircraft flew autonomously except for launch and landing, carried no payload, and only had 5.8% of battery energy remaining at the end of the night. More recently, we have presented the 81 h continuous flight of the 7 kg AtlantikSolar AS‐2 UAV—the current unofficial flight endurance world record for all aircraft below 50 kg total mass—in our own work . The UAV operated autonomously except for launch and landing and had 39% of reserve power (6.8 h of reserve time) remaining.…”

“…Our previous work has focused on the platform design and low‐level flight autonomy required for energetically reliable solar‐powered perpetual flight. The goal of the research presented in this paper is to increase the ease‐of‐use and effectiveness of such solar‐powered UAVs in real‐life aerial sensing missions.…”

“…The individual research and technological contributions that were motivated by and developed for this specific SAR flight, but with the greater goal of increasing both ease‐of‐use and effectiveness of solar‐powered UAVs in similar applications, are as follows: Day/night‐capable SAR‐payload with automatic human detection capability : The development of a lightweight, power‐efficient yet day/night‐capable SAR payload consisting of a color camera, an infrared (IR) camera, an onboard computer, and WLAN for persistent data downlink is presented. Results from applying our existing human detection algorithms during the 26 h SAR flight are discussed. Platform optimization for perpetual flight with the SAR payload : Our previous work suggested the feasibility of perpetual flight with the aforementioned payload and assessed the theory behind adapting the solar‐powered UAV's energy‐storage system to the specific payload weight and power consumption. This paper applies and verifies these methods using the 26 h flight. Autonomous launch and landing framework : The existing control structure is extended with an automatic launch and landing framework that addresses the fragility of solar‐powered UAV platforms through preventive features (e.g., flare before touchdown) and a hierarchical chain of safety checks and contingency measures (e.g., go‐around on wrong landing altitude). Autonomous thermal updraft tracking framework : As the paper's main theoretical contribution, a framework to optimize the power consumption by automated tracking of thermal updrafts is developed.…”