I. Introduction
During the last decade, small satellites (too small to be the standalone payload) have become a relevant fraction of the spacecraft launched every year and continue to increase. A total of 244 new nanosatellites were successfully launched in 2018, and more than 400 were announced for 2019. Furthermore, the number of launched nanosatellites is expected to reach 700 in 2023 [1]. The main reason behind this success is a great cost reduction, which makes space-based commercial and scientific activities an actual possibility for many new actors that previously could not afford them. This cost reduction is achieved by means of miniaturization, which also implies a large reduction of mass and standardization of components. The power subsystem is a typical example of standardized parts and components. In almost every small satellite, this subsystem is composed of solar panels (see Fig. 1), a battery, a cable harness, and a printed circuit board used as power distribution control system [2]. It is obvious that an adequate knowledge of the solar panels’ behavior is key to efficient power management. Nevertheless, it should be underlined that proper knowledge of the solar panels’ performance is equally important for the thermal modeling of the small satellite, something which is usually left aside in the design of this type of mission, because a simplified model is used [3]. This relationship between power generation and thermal effects represents a coupled problem, as the electric power delivered by a solar panel depends on its efficiency which, in turn, depends on the operating voltage V, the solar irradiance G, and the temperature of the solar cells T [4]–[7].
Selex-Galileo SPVS 5-cell modules composed of Azur Space 3G28C solar cells (top-left). UPMSat-2 satellite [8]–[10] TVAC (Thermal VAcuum Chamber) testing at IDR/UPM Institute (bottom-left). UPMSat-2 during integration tasks at the Centre Spatial Guyanais of CNES (Kourou, French Guiana, February 2020) (right).