The recent rise in solar activity has coincided with a marked increase in satellite reentries from low Earth orbit (LEO), particularly among Starlink satellites. A new study titled “Tracking Reentries of Starlink Satellites During the Rising Phase of Solar Cycle 25” examines how geomagnetic storms are accelerating the orbital decay of these satellites. With over 500 Starlink reentries analyzed from 2020 to 2024, the study highlights how atmospheric drag, intensified by solar-induced geomagnetic activity, is altering satellite trajectories and reducing their lifespans. This research arrives at a moment when satellite deployment and solar activity are both at historic highs.
Growth of Satellite Deployments and Reentry Concerns
Since the launch of the first Starlink satellites in 2019, the population of spacecraft in very-low Earth orbit (VLEO) has increased rapidly. Starlink’s operational model deploys large groups of satellites at low altitudes, typically around 210 km initially, before boosting them to their designated altitudes near 550 km. The study found that many of these satellites reenter the atmosphere prematurely, particularly during or following geomagnetic disturbances. Between 2020 and 2024, nearly 1,200 satellites reentered from VLEO, and nearly half were Starlink satellites.
The increase in reentry events raises safety and sustainability concerns. Low orbit altitudes are more susceptible to atmospheric drag, especially when the upper atmosphere is disturbed by geomagnetic storms. These disturbances can cause rapid increases in thermospheric density, effectively lowering satellite orbits and increasing the chance of uncontrolled reentries.
Solar and Geomagnetic Forces at Work
Solar activity is tracked through the F10.7 solar flux index, a measure of solar radio emissions that strongly correlates with ultraviolet and X-ray emissions affecting Earth’s upper atmosphere. Geomagnetic activity, on the other hand, is captured using the Dst index, which quantifies disturbances in Earth’s magnetic field. Both of these indicators were critical to the study’s assessment of satellite reentry dynamics.
The research demonstrates that during periods of elevated solar and geomagnetic activity, satellites encounter a denser thermosphere. This increase in atmospheric drag leads to accelerated orbital decay. The study confirmed that reentries occurred more rapidly during geomagnetic storms classified as moderate (Dst between –100 nT and –200 nT) and severe (Dst below –200 nT). Notably, satellites reentered an average of seven days after reaching a reference altitude during severe storms, compared to 16 days under quiet conditions.
Case Study: The May 2024 Gannon Superstorm
One illustrative case is the reentry of Starlink-2601 during the May 2024 geomagnetic storm, the most intense storm in two decades. The satellite was descending as the storm began and quickly plummeted from 276 km to 100 km in less than two days. The increase in drag was substantial, and the satellite’s reentry occurred 11 days earlier than predicted using conventional orbit propagation models.
Such discrepancies between predicted and actual reentry epochs were found to be a recurring pattern. The study revealed that prediction errors grew with the intensity of geomagnetic storms. This finding suggests that current models, which often rely on simplified propagation algorithms and outdated assumptions, struggle to account for dynamic atmospheric changes during solar storms.
Superposed Epoch Analysis and Satellite Behavior
The authors used a technique known as superposed epoch analysis to evaluate satellite behavior in response to storm conditions. A reference altitude of around 280 km was chosen to represent the final opportunity for operators to intervene before atmospheric drag becomes dominant. From this baseline, satellite altitudes and velocities were tracked over several weeks.
The analysis revealed clear patterns. Satellites encountering stronger geomagnetic conditions decayed more quickly and reached reentry velocities of approximately 7.85 km/s sooner than those in weaker conditions. Although the dataset contained a relatively small number of satellites reentering during severe storms (just 37), the findings remained consistent: greater geomagnetic intensity resulted in shorter reentry timelines and larger discrepancies between predictions and outcomes.
Implications for Reentry Prediction Models
One of the more consequential observations from the study is the limitation of current reentry prediction methods. Most models, including SGP4, do not incorporate real-time atmospheric density variations caused by space weather events. These methods instead extrapolate from existing orbital elements, leading to growing inaccuracies during active periods. As a result, operational decisions regarding collision avoidance and reentry timing become increasingly uncertain.
To address this challenge, the study suggests integrating higher cadence observational data and refined drag models that reflect changing thermospheric conditions. Doing so would improve both reentry forecasts and broader space traffic management, especially as satellite constellations continue to grow in number and complexity.
Differences in Satellite Design and Performance
Variability in satellite design adds another layer of complexity. Starlink satellites have evolved significantly since their first versions, with changes in mass and surface area affecting drag behavior. A satellite’s ballistic coefficient, which reflects its susceptibility to drag based on its shape and mass, can differ substantially across designs. As newer, more massive satellites are launched, their drag behavior may diverge from earlier models even under similar environmental conditions.
This difference has practical implications. Satellites with higher ballistic coefficients experience less drag, but are still affected by the same geomagnetic conditions. When mixed in a statistical sample, such variations introduce greater uncertainty in predicted reentry timelines. This suggests a need for satellite-specific modeling to refine forecasts.
Interactions Between Storm Intensity and Duration
Another key factor is storm duration. Longer storms can have a more sustained impact on thermospheric density than shorter, more intense events. Prior research found that prolonged moderate storms could result in more orbital decay than brief but powerful ones. The present study acknowledges this dynamic, although its dataset did not allow for detailed temporal alignment between storm onset and satellite response.
Some reentries may have occurred during extended exposure to corotating interaction regions (CIRs), which create slower and more persistent geomagnetic effects. These differ from sudden disturbances caused by coronal mass ejections (CMEs), which tend to deliver short, intense bursts of geomagnetic activity. Disentangling these effects remains a challenge for future research.
Reentry Locations and Ground Risk
The study also examined geographic data for 1,864 satellite reentries between 2000 and 2024. The reentries were distributed globally but concentrated within the orbital inclination bands of ±53°, which correspond to Starlink’s coverage area. Most reentries occurred over the ocean, but a non-negligible number were near populated land areas. This underscores the need for effective tracking and prediction to prevent damage or injury from falling debris.
Although current debris mitigation guidelines help manage these risks, unexpected reentries during geomagnetic storms can bypass planned disposal procedures. Improved modeling and response systems are needed to ensure compliance with international safety protocols and prevent unanticipated atmospheric entries.
Combining Solar and Geomagnetic Effects
Solar and geomagnetic activity often occur in tandem, but they influence the upper atmosphere in different ways. Solar flux increases ionization and causes general atmospheric expansion, while geomagnetic storms create localized heating through electric currents and particle interactions. Together, these forces drive short-term and long-term changes in thermospheric density.
The study observed that although solar activity alone does not fully explain satellite decay, it amplifies the effects of geomagnetic storms. This interaction makes forecasting more challenging. Joule heating from geomagnetic storms often outweighs the more gradual impact of solar radiation. Still, the highest prediction errors and orbital decay rates were typically seen during periods of both high solar flux and intense geomagnetic storms.
Summary
Between 2020 and 2024, during the rising phase of Solar Cycle 25, solar and geomagnetic activity had a measurable effect on the orbital decay and reentry of Starlink satellites. Key findings include:
- Satellite reentry frequency increased significantly during periods of elevated geomagnetic activity.
- Severe geomagnetic storms reduced satellite lifespans by more than half compared to quieter periods.
- Prediction errors in reentry timing widened during storm conditions, highlighting deficiencies in standard propagation models.
- Superposed epoch analysis showed that satellites accelerated toward reentry at a faster rate under storm conditions.
- Differences in satellite design and storm duration added complexity to prediction accuracy.
- Combined solar and geomagnetic activity created the most challenging conditions for orbital forecasting.
The study represents the first large-scale statistical analysis of more than 500 similar satellites exposed to a range of geomagnetic environments. As solar activity continues to increase in this cycle, and more satellites populate VLEO, the importance of robust reentry prediction systems will only grow. Addressing the challenges identified in this research will help safeguard both operational assets in orbit and populations on the ground.
