Premature Reentry of the Binar CubeSats Due To Underestimation of Solar and Geomagnetic Activities and Its Implication for Importance of Medium‐ and Long‐Term Space Weather Forecasts

Abstract The rapid development of low‐Earth orbit (LEO) satellites brings increased attention to spacecraft collisions, space debris, orbital decay, and satellite reentry. Neutral density and associated drag force on the satellite orbits elevate space risks, significantly determined by space weather disturbances, particularly geomagnetic storms. On 3 September 2024, the Australian Binar‐2, 3, and 4 satellites were deployed, but their actual lifetimes were only around 2 months, much shorter than designed, only 20% that of the nearly identical Binar 1 satellite launched in 2022. For the first time, we analyze the premature reentries of the Binar‐2, 3, and 4 satellites to unveil the severe space weather impact on their lifetimes, especially the influence of accuracy of medium‐ and long‐term space weather prediction on satellite lifetime designs. Our findings reveal that the premature reentries of Binar‐2, 3, and 4 satellites were caused by enhanced neutral density due to much higher solar and geomagnetic activities than predicted. The actual satellite lifetimes align well with estimations based on observed space parameters, whereas large deviations occur when using predicted parameters. The widely used predictions for medium‐ and long‐term space weather underestimated the F10.7 index and sunspot numbers during Solar Cycle 25 (SC25), especially during the peak time, leading to discrepancies in the designed satellite lifetimes. Our results illustrate the importance of medium‐to long‐term space weather forecasting for the lifespan of LEO satellites.