energies Review Power Bus Management Techniques for Space Missions in Low Earth Orbit Luigi Schirone 1, * , Matteo Ferrara 1 , Pierpaolo Granello 1 , Claudio Paris 2 and Filippo Pellitteri 3   Citation: Schirone, L.; Ferrara, M.; Granello, P.; Paris, C.; Pellitteri, F. Power Bus Management Techniques for Space Missions in Low Earth Orbit. Energies 2021, 14, 7932. https://doi.org/10.3390/en14237932 Academic Editors: Yitao Liu and Ching-Ming Lai Received: 18 October 2021 Accepted: 23 November 2021 Published: 26 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Scuola di Ingegneria Aerospaziale, Sapienza University of Rome, 00138 Rome, Italy; matteo.ferrara@uniroma1.it (M.F.); pierpaolo.granello@gmail.com (P.G.) 2 Centro Ricerche Enrico Fermi, 00184 Rome, Italy; claudio.paris@cref.it 3 Dipartimento di Ingegneria, University of Palermo, 90128 Palermo, Italy; filippo.pellitteri@unipa.it * Correspondence: luigi.schirone@uniroma1.it Abstract: In space vehicles, the typical configurations for the Solar Array Power Regulators in charge of managing power transfer from the solar array to the power bus are quite different from the corresponding devices in use for terrestrial applications. A thorough analysis is reported for the most popular approaches, namely Sequential Switching Shunt Regulation and parallel-input Pulse Width Modulated converters with Maximum Power Point Tracking. Their performance is compared with reference to a typical mission in low Earth orbit, highlighting the respective strengths and weaknesses. A novel solar array managing technique, the Sequential Maximum Power Tracking, is also introduced in the trade-off and was demonstrated able to boost energy harvesting, especially in the presence of mismatching in the solar array. It also can achieve top levels of reliability using a rather simple control hardware. Its operation was verified both by a Matlab–Simulink model and by an experimental breadboard. Keywords: satellite power sources; solar array regulation module; battery charge/discharge regula- tion module; maximum power point tracking (MPPT); sequential switching shunt regulation (S 3 R); power conversion unit 1. Introduction Electrical power systems for space applications are highly demanding in terms of reliability: the related constraints of component screening and Single Point Failure Free (SPFF) circuitry set severe limits on available design solutions. Therefore, specific circuitry and regulation architectures were developed, quite different from those normally in use for stand-alone applications in the terrestrial environment, taking into account the other unique constraints of mass budget, electromagnetic compatibility, and not-convective heat exchange. In addition, even the operating environment is quite different from terrestrial applica- tions [1]. Spacecraft are exposed to a severe radiative environment that affects both solar cells, via crystallographic damage mainly related to absorption of energetic particles, and electronic components, that are also affected by the secondary radiation generated as a byproduct of the interaction between cosmic rays and spacecraft materials. Sunlight is also different as, unfiltered by the atmosphere, it is richer in photons in the visible and ultraviolet (UV) range, up to the UV-B spectral region (AM0 spectrum). Solar irradiance is 1367 W/m 2 , with ±3.5% seasonal variations for eccentricity of the Earth’s orbit around Sun, plus some minor random fluctuations related to solar activity. Spacecraft periodically undergo eclipses with characteristics dependent on orbit geometry: in the most common Earth orbits the time spent in darkness ranges between 30 and 70 min, and sunlight time between successive eclipses varies from 1 h to some months. Energies 2021, 14, 7932. https://doi.org/10.3390/en14237932 https://www.mdpi.com/journal/energies