Regularity and reentry basins of low Earth orbits in the J₂-solar radiation pressure problem

We investigate the long-term dynamical structure of low Earth orbits (LEOs) using the Smaller Alignment Index (SALI), a fast numerical indicator of chaos, within a closed-form averaged model that incorporates the effects of solar radiation pressure and Earth's oblateness. Our analysis reveals that the area-to-mass ratio is a key parameter governing the onset and extent of chaotic behavior in LEOs. We map the system's chaotic regions, study the behavior of reentry trajectories and characterize their temporal laws over a timescale constrained by the $25$-year mitigation guideline. Within this physically relevant timescale, we show that most of the reentry trajectories exhibit regular motion. Reentry basins, constructed according to different mitigation guidelines up to $25$ years, display fractal-like structures for less-stringent guidelines. The degree of this fractality is quantitatively assessed using the uncertainty exponent method. In most cases, for large area-to-mass ratios, reentry occurs on relatively short timescales (a few years) - short enough that no fractal behavior is observed in the basin boundaries. This numerical dynamical study offers insights into the development of dynamically informed deorbiting strategies.