Investigation of the space weathering rate of the geostationary satellites’ surface materials using BVRI photometry

Our study explores space weathering and aging through the extended observation of geostationary satellites, especially those in long-term operational orbits employing the methods of multi-passband photometry using standard Johnson/Cousin’s photometric filters. Geostationary satellites, crucial for communication, offer a unique opportunity due to their consistent visibility. Employing dual-spin or three-axis stabilization systems, these satellites maintain their orientation and allow for the investigation of artificial material color changes over time. The color index, influenced by the most reflective material, remains stable throughout the year, while the varying satellite illumination is attributed to Earth’s motion. The long-term monitoring campaign was launched in 2019 and led to the observation of 18 GEO satellites. The target selection criteria included operational status and attitude stabilization. The observations, conducted during stable weather conditions and around the new moon, provide valuable data for understanding the structural changes of artificial material in the space environment. This comprehensive campaign extends until the summer of 2023, and the results showed overall trend of the positive changes in the investigated color indices i.e., $B-V,R-I$ and $B-I$. The average change values measured were $0.1\mathrm{mag}/\mathrm{year}$ in $B-V,0.5\mathrm{mag}/\mathrm{year}$ in $R-I$ and $0.21\mathrm{mag}/\mathrm{year}$ in $B-I$. The major focus of our study is to look for the darkening and reddening effect induced by space weathering and aging on single geostationary satellites and satellites with similar platforms. The published results contain color index measurements and their year-to-year variation rates.