Development and On-orbit Operation of Solar Panels for JAXA's Lunar Lander SLIM (Smart Lander for Investigating Moon)

Smart Lander for Investigating Moon (SLIM) was JAXA's spacecraft designed to demonstrate precision lunar landing technology. SLIM was launched on September 7, 2023 (JST), from the Tanegashima Space Center by H-IIA Rocket No. 47 and achieved a successful pinpoint landing on the Moon on January 20, 2024 (JST). To meet the stringent mass constraints of a small lunar lander, extensive weight reduction was implemented through the development of a lightweight solar array panel (SAP). The SAP incorporated newly developed inverted metamorphic InGaP/GaAs/InGaAs triple-junction (IMM3J) solar cells, featuring an ultra-thin flexible structure of only 13µm with initial efficiency exceeding 32%. These cells achieved more than five times the power-to-mass ratio compared to conventional InGaP/GaAs/Ge triple-junction solar cells, significantly contributing to SLIM's mass reduction goals. The SAP demonstrated exceptional performance throughout the mission, maintaining predicted power output while traversing the harsh radiation environment of the Van Allen belts. This paper describes comprehensive analysis of the SAP's development, on-orbit performance, and operational results, providing valuable insights for future lightweight space power systems.