Satellite Drag and Sustainable Space Operations in a Dynamic Thermosphere

Abstract

Earth’s orbit has become increasingly congested and contested in recent years. The surge in launched payloads, combined with satellite failures, explosions, and collisions, has contributed to a large and growing population of orbital debris objects that can remain in orbit for decades, centuries, or longer. Meanwhile, decreasing launch costs and maturing satellite technology have created conditions favorable for rapid commercialization across orbital regimes, especially in low Earth orbit (LEO). Today, a small number of commercial entities operate the large majority of the world’s active satellites as part of proliferated LEO constellations. Sustaining productive activity in an increasingly crowded orbital environment has made satellite conjunction assessment and collision avoidance essential for safe operations. These efforts require not just accurate trajectory predictions, but also credible estimates of uncertainty. In LEO, variability in atmospheric drag is by far the dominant source of propagation error, often leading to deviations of several kilometers per day due to unpredictable solar and geomagnetic activity. Even over short timescales, trajectory prediction is challenging because existing forecasts exhibit limited predictive skill. Although forecast errors are often non-Gaussian and heteroscedastic, operational products are generally presented as deterministic, and atmospheric models rarely provide rigorous uncertainty characterization. This work introduces a new approach for probabilistic satellite drag modeling based on historical correlations between space weather drivers and satellite dynamics. Unlike traditional methods, it models satellite behavior directly without reconstructing thermospheric mass density or requiring detailed knowledge of satellite properties such as the ballistic coefficient. This end-to-end strategy offers substantial computational and operational advantages for many space domain awareness tasks. Capturing both trajectory predictions and their associated uncertainty is critical for enabling informed collision avoidance decisions, particularly during geomagnetic storms when current infrastructure frequently fails. Because the orbital lifetime of debris objects can exceed hundreds of years, population dynamics in space critically depend on long-term variability in the composition of Earth’s thermosphere. Rising concentrations of carbon dioxide and other greenhouse gases have caused warming in the troposphere but cooling and contraction in the upper atmosphere. This contraction decreases atmospheric density in LEO, reducing drag and extending the orbital lifetime of debris objects. Longer-lived debris populations pose a persistent collision hazard for all active satellites as long as they remain in orbit. Even natural events, such as a prolonged grand solar minimum, could further reduce thermospheric density and contribute to longer debris lifetime in LEO. With little ability to predict such an event, it is necessary to understand the potential consequences and to identify strategies that enable the continued safe and productive use of LEO. This work models the impact of such long-term environmental changes on limits for sustainable satellite deployments. LEO is a finite respource increasingly at risk of overexploitation. Conserving it and sharing it fairly requires that we first understand its fundamental capacity and our current occupation of that capacity. Some metrics have been proposed to measure the satellite carrying capacity of Earth’s orbit, but none have previously accounted for the potential influence of a changing space climate. This work develops new methods for defining carrying capacity as a common currency, enabling clear constraint-driven thresholds on activity and a better understanding of how existing and proposed missions consume available capacity. These new metrics provide insight into how environmental variability may affect the long-term sustainability of operations in LEO. Respecting and understanding this influence that the natural environment has on our collective ability to operate spacecraft in LEO is critical to preventing the overexploitation of this regime and protecting it for future generations.