In May 2024, Earth experienced its largest geomagnetic storm in over 20 years. This powerful solar event had wide-ranging impacts on satellite operations in low Earth orbit (LEO), revealing vulnerabilities in space infrastructure and conjunction assessment capabilities. As the population of satellites in LEO has grown dramatically since the last major storm in 2003, the effects were more pronounced and widespread than in previous events. This article examines the impacts of the May 2024 geomagnetic storm on satellite drag, orbital decay, and space traffic management, as well as the challenges in forecasting such events.

Background on Geomagnetic Storms

Geomagnetic storms occur when the Sun releases large bursts of energy and charged particles that interact with Earth’s magnetic field and upper atmosphere. These solar events are most common near the peak of the 11-year solar cycle, when the Sun’s activity is at its highest. The May 2024 storm was triggered by several X-class solar flares and coronal mass ejections (CMEs) from an active region on the Sun between May 7-11.

When the charged particles and magnetic fields from CMEs reach Earth, they can cause rapid fluctuations in the planet’s magnetic field. This geomagnetic activity leads to heating and expansion of the upper atmosphere, or thermosphere. The resulting increase in atmospheric density at orbital altitudes causes enhanced drag on satellites, potentially altering their orbits.

Forecasting Challenges

One of the key issues highlighted by the May 2024 storm was the difficulty in accurately forecasting geomagnetic activity, even in the short term. Analysis of the geomagnetic index ap, which quantifies disturbances in Earth’s magnetic field, showed that forecasts significantly underpredicted the magnitude and duration of the storm.

The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center (SWPC) releases daily 3-day forecasts of ap. However, across all forecast time horizons from 0-3 days, the initial increase in ap during the May 2024 storm was underpredicted by 100-300 units. After the storm’s peak, the 0-1 day forecast then vastly overpredicted ap levels.

These inaccurate forecasts are likely due to heavy reliance on “persistence” assumptions, which consider the most likely future value of an index to be close to its current measured value. While this approach works reasonably well during quiet periods, it struggles to capture rapid changes during major storm events.

The inherent challenges in predicting solar activity contribute to these forecasting difficulties. Coronal mass ejections can reach Earth anywhere from 15 hours to 3 days after eruption, moving at speeds between 250-3000 km/s. While telescopes can observe CMEs and measure solar wind conditions, providing useful short-term forecasts, longer-term predictions would require the ability to anticipate CME eruptions themselves.

This uncertainty in space weather forecasting has significant implications for satellite operators and space traffic management. Accurate predictions of atmospheric density changes and resulting orbital perturbations are critical for maintaining satellite safety and performing conjunction assessments to prevent potential collisions.

Atmospheric Density Enhancements

To understand the storm’s impacts on the upper atmosphere, researchers used empirical models like the Naval Research Laboratory’s Mass Spectrometer and Incoherent Scatter radar (Extended) model, or NRLMSISE-00. This model uses solar and geomagnetic indices like F10.7 (solar radio flux) and ap to compute thermosphere properties including total mass density.

Model results showed dramatic increases in atmospheric density at orbital altitudes during the storm. At 400 km altitude, density enhancements of up to 6 times the pre-storm baseline were observed, with most of the increase concentrated in the northern hemisphere. While empirical models have limitations, these estimates aligned with observations of enhanced satellite drag during the event.

Impacts on Satellite Drag and Orbital Decay

The increase in atmospheric density during the storm led to significantly enhanced drag on satellites in low Earth orbit. Analysis of two-line element (TLE) data for the entire catalog of tracked objects in LEO revealed widespread changes in orbital decay rates.

For example, one satellite (KANOPUS-V 3) saw its average orbital decay rate increase from about 38 meters per day before the storm to 180 meters per day during the peak of the event – more than a 4-fold increase. Many satellites experienced similar rapid drops in altitude over the course of just a few days.

This sudden orbital decay posed challenges for satellite operators trying to maintain specific altitudes or constellation configurations. Unplanned changes in altitude can disrupt carefully designed satellite spacing and phasing, potentially degrading service quality or coverage for some systems.

Mass Satellite Maneuvering

In response to the enhanced drag and orbital decay, thousands of satellites performed unplanned station-keeping maneuvers to maintain their intended orbits. Data showed that while only about 1000 of the nearly 10,000 active payloads in LEO were maneuvering during quiet conditions before the storm, this number increased dramatically once the effects of increased atmospheric density accumulated.

Most of this mass maneuvering activity was attributed to the Starlink constellation, which uses autonomous orbit maintenance systems that can quickly respond to perturbations. As more proliferated LEO constellations are established with similar capabilities, this type of rapid, widespread maneuvering may become more common during future storms.

The mass maneuvering activity poses challenges for space traffic management and collision avoidance processes. Typical conjunction assessment procedures consider a 7-day look-ahead window, propagating orbits forward to identify potential close approaches between objects. However, the combination of enhanced drag and thousands of unplanned maneuvers made it extremely difficult to accurately predict satellite positions even a few days in advance during and immediately after the storm.

Implications for Conjunction Assessment

The May 2024 storm revealed significant vulnerabilities in existing conjunction assessment capabilities during major space weather events. Several factors combined to severely degrade the ability to predict potential collisions:

• Poor space weather forecasts led to large errors in predicted atmospheric density and resulting orbital decay rates.
• Rapid, unpredictable changes in satellite drag made even short-term orbit propagation highly uncertain.
• Widespread unplanned maneuvers by thousands of satellites further increased orbit prediction errors.
• Reduced frequency of tracking data updates for some satellites during periods of rapid decay added to position uncertainties.

These issues made it very difficult or impossible to perform reliable conjunction assessments during the storm and in the days that followed. This temporary loss of collision prediction capability significantly increased the risk of accidental collisions or debris-generating events in the already congested LEO environment.

The challenges highlighted by this event suggest that current conjunction assessment procedures may need to be made more robust to handle major space weather disturbances. As the satellite population in LEO continues to grow, ensuring these critical safety processes can function effectively during storms will be essential for long-term space sustainability.

Debris Removal Effects

While the storm created short-term risks, it also had some positive long-term effects on the orbital debris environment. The enhanced atmospheric drag caused accelerated orbital decay for debris objects as well as active satellites. However, only operational spacecraft can perform station-keeping maneuvers to maintain altitude.

Analysis of altitude changes for cataloged objects between 400-700 km showed that while most active payloads maintained their orbits, debris objects experienced significant decay. Some debris pieces lost several kilometers of altitude over just a few days. Rocket bodies also decayed, though not as rapidly as smaller debris due to their lower area-to-mass ratios.

This accelerated removal of debris from heavily populated orbital regimes is beneficial for the long-term sustainability of the space environment. Strong solar cycles with frequent geomagnetic storms can help naturally clean up accumulating debris populations that pose collision risks to active satellites.

Operational Impacts and Lessons Learned

The May 2024 storm had wide-ranging impacts on satellite operations beyond just orbital changes. Some of the key operational effects and lessons learned include:

• Degraded GPS/GNSS accuracy: The ionospheric disturbances caused by the storm degraded the accuracy of satellite navigation signals. This affected not only users on the ground, but also satellites that rely on GPS for precise orbit determination and station-keeping.
• Communications disruptions: Ionospheric scintillation and absorption caused intermittent disruptions to satellite communications, particularly at high latitudes.
• Increased collision avoidance maneuvers: Some operators reported having to perform more frequent collision avoidance maneuvers in the weeks following the storm due to orbit prediction uncertainties.
• Need for improved space weather forecasting: The event highlighted the importance of continued investment in space weather observation and forecasting capabilities to provide more accurate and timely warnings.
• Importance of diverse constellations: Satellites and constellations with access to multiple GNSS systems were generally more resilient to navigation disruptions than those relying on GPS alone.
• Value of autonomous systems: Satellites with onboard autonomous orbit maintenance capabilities were able to respond more quickly to drag variations than those relying on ground commands.
• Need for flexible operations: Operators with the ability to rapidly adjust planned activities and resource allocations were better able to mitigate the storm’s impacts.

Historical Perspective

The research paper “Space Weather Effects on Satellites” discusses the significant detrimental effects that space weather, driven by solar activity, can have on satellites in orbit around Earth.

There have been a number of notable satellite failures throughout history that have been attributed to space weather. For example, in 1994, the Anik E-1 and E-2 satellites experienced attitude control issues and a hard failure of a momentum wheel, likely due to deep dielectric charging. More recently, in February 2022, SpaceX lost 38 of 49 recently launched Starlink satellites after they were hit by a geomagnetic storm.

Analysis of historical Starlink launches shows that space weather conditions, such as coronal mass ejections, solar energetic particles, and geomagnetic storms, are often correlated with satellite anomalies and failures. The February 2022 event, in particular, involved a solar flare, a solar energetic electron event, and a geomagnetic storm in the days surrounding the ill-fated launch.

Looking Ahead

The May 2024 geomagnetic storm provided valuable insights into the vulnerabilities of modern space systems and infrastructure to major space weather events. As we approach the peak of the current solar cycle, more frequent and intense storms are likely in the coming months and years.

To enhance resilience against future events, the space community may need to consider several areas for improvement:

• Enhanced space weather monitoring and forecasting capabilities, potentially including new dedicated solar observation missions.
• More robust and adaptable conjunction assessment processes that can handle periods of high uncertainty.
• Improved atmospheric density and drag models for more accurate orbit predictions during disturbed conditions.
• Upgraded onboard systems for satellites to enhance autonomous navigation and orbit maintenance capabilities.
• Regulatory frameworks and best practices for satellite operations during major space weather events.
• Continued research into the effects of geomagnetic storms on the LEO environment and satellite systems.

As the number of satellites in orbit continues to grow and our societal reliance on space-based services increases, ensuring the resilience of space infrastructure to solar storms will be critical. The lessons learned from the May 2024 event provide an opportunity to strengthen space traffic management processes and satellite operations to better weather future solar storms.

References

• https://en.wikipedia.org/wiki/May_2024_solar_storms
• https://www.swpc.noaa.gov/products/planetary-k-index
• https://arxiv.org/pdf/2406.08617
• https://www.esa.int/Space_Safety/Space_weather/The_May_2024_solar_storm_your_questions_answered
• https://www.discovermagazine.com/technology/satellite-collision-prediction-lost-during-recent-solar-storm
• https://www.mdpi.com/2674-0346/2/3/12