# Technology Identification, Evaluation, Selection, and Optimization of a HALE Solar Aircraft  
[PERSON] and [PERSON]  
1 Department of Aerospace Engineering, Sejong University, 209, Neungdong-Ro, Gwangjin-Gu, Seoul 05006, Korea; [EMAIL_ADDRESS]  
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Footnote †: journal: Applied Sciences  
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Footnote †: journal: Applied Sciences  
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-directing emergency resources [5]. In comparison to orbital satellites, \"atmospheric satellites\" would offer better observational resolution, local persistence, and the capability of reuse [6]. The first flight of a solar aircraft was Sunrise I. After that, an improved version, Sunrise II, was built and tested on the 12 th of September 1975. On the 18 th of May 1980, the Gossamer Penguin realized which can be considered as the world's first piloted, solar-powered flight. On 7 July 1981, the next version, named Solar Challenger, crossed the English Channel with solar energy as its sole power source. In 1993, the Pathfinder, with its 30-m wingspan and weight of 254 kg, was tested at low altitude [7]. In 2004, the Autonomous Systems Lab of EPFL/ETHZ launched the Sky-Sailor project under a contract with the European Space Agency. This project presents the methodology used for the global design of solar powered airplanes to achieve continuous flight on earth [7]. QinetiQ is also very active in the field of solar HALE platforms with Zephyr, an airplane that flew in July 2006 for 18 h. Zephyr was acquired and developed by Airbus and Zephyr S is regarded as the world's most advanced aircraft in terms of long endurance flight performance. In the test flight in 2018, Zephyr S set an endurance record of 25 days, 23 h and 57 min; however, the location of test flight was Wyndham in Australia, near the equator. If flown on a mission at a different latitude than the equator, it seems the aircraft would show a huge difference in its endurance performance for the different flight conditions. Thus, the location and date of the flight determine the aircraft's performance. The available power is dependent not only on the factors of wing area (solar cell area), cell efficiency, latitude, and time of year but also on the time of day [8]. Another variable with a great effect on endurance is the aerodynamic characteristics of the aircraft. In the case of solar aircraft, most drag is generated by the main wings; this can be modeled with a simple aerodynamic analysis program such as XFL85. However, inconveniently, calculation must be repeated each time a variable changes. To resolve this problem, a new aerodynamic model is designed in consideration of a configuration design variable and flight condition variable; model is then utilized as the basic equation for long endurance performance analysis by assessing flight possibility and margin value [9]. As shown above, because of solar energy the power source of solar aircrafts largely varies depending on the operating environment factors such as flight date, location, and subsystem efficiency, all of which affect the endurance, it is necessary to perform sensitivity analysis of the main design variables. Given that it is the near-equatorial areas, with maximum solar energy incidence, where solar aircraft under development across the world are tested, solar aircraft sensitivity analysis were implemented in this study in consideration of flight mission latitudes other than those near the equator. In addition, the mission profile is another important consideration. Climb rate, descent rate, and speed changes are calculated through the balance between the amount of available solar energy and the required energy. Studies on the descent are also necessary to minimize the energy required for cruise and night-time flight.