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This study examines traditional models used to predict long-term debris accumulation in low Earth orbit and reveals they may significantly underestimate collision risk when satellite constellations are organized into narrow altitude shells. By treating the LEO environment as a stochastic process rather than a deterministic one, the researchers found that narrow-shell models can predict debris populations up to 4.5 times higher than conventional models, with some simulations showing runaway growth scenarios. The discrepancy arises because random fluctuations in debris populations create nonlinear feedback effects that amplify collision rates, an effect missed by standard averaging approaches.
Why it matters
As satellite mega-constellations increasingly crowd narrow orbital bands, this research suggests current sustainability assessments may underestimate collision hazards and debris accumulation. The findings provide a more realistic modeling framework for evaluating orbital capacity limits and informing space traffic management policies.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: Deterministic source-sink models are widely used to assess the long-term evolution, capacity, and sustainability of the low Earth orbit (LEO) environment. These models propagate shell-averaged populations through ordinary differential equations (ODEs), relying on individual collision, disposal, and decay events to average out within sufficiently large altitude shells. As constellation traffic is increasingly organized into kilometer- and sub-kilometer-scale shells, this averaging assumption becomes strained. We formulate the multi-shell, multi-species LEO environment as a Markov jump process and, from this formulation, recover the conventional source-sink ODE as a large-volume limit and derive a stochastic differential equation (SDE) approximation whose fluctuations scale as V^{-1/2} in the per-shell volume V. The diffusion approximation is validated against an exact discrete-event simulation of the underlying jump process. Sweeping V at fixed spatial density over the 450-800 km band, we find that the two descriptions agree at shell volumes comparable to those used in established source-sink models but diverge as shells narrow. At the finest shell volume considered, the mean debris population reaches roughly 4.5 times the ODE prediction, with several realizations undergoing runaway growth absent from the ODE trajectory. This departure is driven by nonlinear collision terms, through which population variance and covariance raise expected collision rates, generating further debris and reinforcing the collision-debris feedback. Narrow-shell stochasticity thus both widens the outcome distribution and shifts the expected trajectory. Because the stochastic model shares its parameterization with the deterministic one, it provides a scale-consistent extension of existing source-sink models for evaluating shell configuration, collision risk, and long-term LEO sustainability.
Source: Narrow-Shell Stochasticity in Source-Sink Models of the Low Earth Orbit Environment