The rapid increase in space debris poses a major threat to sustainable space operations and underscores the importance of understanding long-term drivers of orbital decay. Because debris objects do not perform station-keeping maneuvers, their orbital evolution directly reflects variations in thermospheric density, unlike that of operational satellites. This makes space debris an effective natural testbed for examining the long-term influence of solar activity on atmospheric drag. This study analyzes the impact of solar activity on the decay of 17 LEO debris objects across solar cycles 22, 23, and 24 using Two-Line Element (TLE) data. TLE-derived decay profiles, combined with sunspot numbers (SSN) and the F10.7 index, reveal a threshold: decay rates rise sharply when SSN exceeds ∼ 67%–75% of its cycle peak, corresponding to increased Extreme Ultraviolet (EUV) fluxes, thermospheric density and atmospheric drag. Peak decay rates declined progressively from cycle 22 to 24, reflecting reduced solar activity. Decay profiles for cycle 24 - predicted using ballistic coefficients from earlier cycles and MSIS 2.0 atmospheric densities - match observations well after applying a scaling factor. However, two high-inclination objects showed significant deviations, suggesting possible MSIS limitations at high latitudes, while lower-inclination objects aligned closely. Moreover, geomagnetic activity indices such as AE and Dst show little correlation with long-term orbital decay rates, suggesting a comparatively weaker role at the timescales examined, for Joule heating and particle precipitation than for solar EUV forcing in driving sustained orbital decay. Overall, the findings support solar EUV-driven thermospheric variability as a primary factor influencing long-term orbital decay and emphasize the need to refine atmospheric models, particularly for polar regions, to improve reentry predictions and satellite mission planning.
Ashruf et al. (Wed,) studied this question.