The rapidly growing orbital population has substantially increased collision risks in Low Earth Orbit (LEO). Over 36,500 objects are currently tracked, with the European Space Agency issuing over 100,000 conjunction warnings in 2022 alone. Conventional collision-avoidance maneuvers rely on propulsive systems that consume finite propellant reserves, limiting mission lifetimes and operational flexibility. Recent advances in solar-sail technology demonstrate orbit-control capabilities through Solar Radiation Pressure (SRP) alone, presenting a compelling propellant-free alternative. Mission concepts such as those utilizing solar sails for active debris removal may operate in congested orbital regimes where collision-avoidance capability becomes essential. However, existing literature on solar-sail collision avoidance is limited to altitudes above 1000 km where atmospheric drag can be ignored, leaving a knowledge gap for lower orbital regimes between 400 and 800 km where atmospheric drag becomes non-negligible.

This work develops and evaluates a simulation framework to assess the collision-avoidance capability of solar sails using locally optimal control laws driven by both SRP and atmospheric drag. The control laws maximize the instantaneous rate of change of an orbital element. The dynamical model incorporates perturbations caused by Earth’s oblateness, SRP, and atmospheric drag using the high-fidelity NRLMSISE-00 empirical model. For SRP-dominant scenarios, analytical control laws provide closed-form solutions while for drag-dominant environments, a hierarchical grid-search employing coarse-to-fine refinement is implemented to optimize the combined acceleration effects. Synthetic orbital uncertainties are generated through regression analysis of real Conjunction Data Messages, with collision risk assessed using both collision probability and Mahalanobis distance metrics to address dilution effects.

Results reveal significant variability in optimal maneuver durations, ranging from 5 minutes for high area-to-mass ratio sails at very low altitudes to over 6 hours for low area-to-mass ratio objects at high altitudes. These durations are substantially shorter than those found in previous work focused on altitudes above 1000 km, primarily due to the exponential increase in atmospheric density at lower altitudes, enabling effective use of semi-major axis minimization control laws with face-on orientations relative to the velocity vector. The aspect angle, which defines the orientation of the orbital plane relative to the sunlight direction, shows strong correlation with control law usage, with semi-major axis control laws being utilized more frequently at large aspect angles and Right Ascension of the Ascending Node control laws being more effective at small aspect angles. The effects of eclipse and conjunction separations on the maneuver duration are also investigated for different orbital scenarios.

The findings indicate that solar sails can perform effective collision-avoidance maneuvers with durations significantly shorter than previous estimates; however, careful consideration of environmental, physical, and orbital parameters is essential for practical implementation. The effect of atmospheric drag displays clear trends across different altitudes, aspect angles, and physical parameters, but practical viability is constrained to altitudes above 500 km during average solar weather conditions. The sensitivity of performance necessitates the consideration of solar cycle effects on maneuver duration. The results demonstrate that locally optimal control laws provide an effective framework for propellant-free collision avoidance, offering insights for future solar-sail missions operating in LEO where multiple conjunctions may be encountered during extended mission operations.