Design and experimental validation of an autonomous electrical power system (EPS) for CubeSats

CubeSats have emerged as an enabling technology for a new generation of space missions, offering relatively low cost and rapid development opportunities for scientific, educational, and technology demonstration. The reliable operation of a CubeSat depends critically on its electrical power system (EPS), which serves as the primary energy backbone for all onboard subsystems and payloads. Several studies have indicated that EPS as a subsystem is most susceptible to failure in the satellite missions, as it is under tight power, volume, and reliability constraints exposed to harsh and variable orbital conditions. In this context, this paper proposes the design, hardware implementation and experimental validation of an autonomous EPS architecture to enhance the operational lifetime of CubeSats. The proposed EPS autonomously manages energy to deal with solar irradiance variations in the low earth orbit (LEO). It combines maximum power point tracking (MPPT), battery management system (BMS), regulated power distribution and sensor based telemetry based on a microcontroller unit (MCU) controlled system. A real time decision making algorithm autonomously monitors the photovoltaic (PV) array voltage. The supervisory algorithm implements a three mode graduated control strategy, i.e. normal, moderate, and power-down. It is governed by two discrete PV voltage thresholds, enabling more precise and graduated load management compared to binary single threshold schemes reported in prior work. When nominal irradiance level is regained, the system returns autonomously to desired operational mode with no interference needed from the ground station. The modular design of the system allows to upgrade its components easily without the need to redevelop entire architecture. A detailed power budget analysis yields a total system load of 1,460mW, divided between telemetry (22mW), payload (1,400mW) and communication subsystems (38mW). The deployed EPS uses a Li-ion 3-cell battery pack (11.1V, each cell 1,800mAh) and PV panels of (12V, 2,100mW). Experimental tests validate the acquisition of data from various sensors and importantly accurate mode transition from normal to power down mode and vice-versa under fluctuating irradiance conditions. Furthermore, dynamic experiments involving controlled variation of PV voltage are also conducted to evaluate both degradation and recovery behavior of the system. The results demonstrate stable, repeatable, and threshold consistent mode transitions under varying input power scenarios. The results collectively demonstrate that autonomous mode transition and load management can be achieved using low cost commercial off the shelf components (COTS), making the proposed EPS a practical, reproducible, and scalable testbed for academic and small mission CubeSat platforms.