RHOK-SAT: Investigating Perovskite Solar Cell Performance and Degradation in Low Earth Orbit Through a 1U CubeSat

RHOK-SAT is a 1U CubeSat scheduled to launch in September 2025 aboard a resupply mission to the International Space Station (ISS) through NASA’s CubeSat Launch Initiative (CSLI) program. Its mission is to characterize the performance and degradation of six experimental perovskite solar cells in low Earth orbit for 12 months. Characterization consists of current-voltage measurement taken by one dedicated microcontroller per solar cell. Measurements are performed when the cells are in direct sunlight, determined via a quadrant photodiode. A silver-alloyed copper indium gallium selenide (ACIGS) solar cell serves as a reference for comparative analysis due to its well-characterized behavior. Each solar cell is also equipped with a resistance temperature detector (RTD) to provide complementary thermal data to every measurement. RHOK-SAT’s payload is mounted using two printed circuit boards (PCBs), with the solar cells mounted beneath a non-conductive anodized top plate featuring apertures. The satellite’s flight software (FSW), running on FreeRTOS, manages experiment execution, data management, communications, and system health. Supported by a full-duplex transceiver on board, the software defines a robust communication pipeline for experimental data downlink through an acknowledgment system with the commanding ground station. Additionally, interrupt-driven timers allow experimental data downlink to be automated and received by ground stations across the globe. As a fail-safe mechanism, the FSW can also be updated in flight, providing further tolerance against unanticipated behavior. To monitor system health, RHOK-SAT periodically transmits telemetry data, including battery level, tumbling rate, and solar panel temperature, which can be visualized on a Grafana dashboard. RHOK-SAT relies on two ground station systems. The primary, commanding ground station, located at Rhodes College, is equipped to transmit commands to the satellite and receive data. Additionally, RHOK-SAT is part of the SatNOGS network, a global open-source satellite ground station system. Through SatNOGS, ground stations worldwide can be utilized to receive data, significantly increasing downlink capability. RHOK-SAT is a collaborative project involving Rhodes College, the Photovoltaic Materials and Devices Group (formerly at the University of Oklahoma, now at the University at Buffalo), the National Renewable Energy Laboratory (NREL), and the Aerospace Corporation.