Global electron content and thermosphere density shifts during Starlink launches show why space weather matters

The most dramatic Starlink failure occurred on February 3, 2022, when 38 out of 49 satellites from the S-36 launch re-entered Earth’s atmosphere within days. The cause was not a powerful storm but a relatively mild G1 – Minor geomagnetic storm. During this event, increased drag from the expanded thermosphere overwhelmed the satellites before they could raise their orbits.

A year later, on March 23, 2023, the S-77 mission launched into conditions shaped by a far stronger G3 – Strong storm. Despite this, all satellites survived and performed nominally. This striking contrast highlights that storm intensity alone does not dictate outcomes. What matters more is how atmospheric density is distributed across latitudes and altitudes at the time of deployment.

These two case studies form the centerpiece of the new research, demonstrating that even modest storms can devastate launches if conditions align unfavorably, while stronger storms can sometimes pass without incident. For satellite operators, the difference between failure and success can be measured not in storm category numbers but in subtle shifts of density and electron content.

How the solar cycle changes the upper atmosphere

The thermosphere and ionosphere respond strongly to solar activity. Between February 2022, when Solar Cycle 25 was in its rising phase, and April 2024, near its peak, both neutral density and electron content increased dramatically.

The study found that global electron content rose about two times, while thermospheric density increased more than three times over this period.

These multipliers result in significantly greater atmospheric drag at satellite altitudes. At heights of 300 to 500 km (185 to 310 miles), where many Starlink satellites initially orbit, drag increases can significantly shorten orbital lifetimes if not compensated quickly. This is especially critical during the first days after deployment, when spacecraft are still maneuvering to operational altitudes.

The solar cycle effect is not just a background influence but a risk multiplier. Launches that might succeed under quiet conditions can be pushed toward failure during solar maximum, even without strong geomagnetic storms. This means that mission planning in the coming years, as Solar Cycle 25 reaches its peak, must account for higher baseline densities in the upper atmosphere.

Why latitude decides satellite survival

The study emphasizes that the location of density enhancements is just as important as their global average. In the failed S-36 launch, the densest part of the thermosphere was concentrated near the equator. Since satellites in low Earth orbit spend much of their time crossing equatorial regions, drag effects were magnified, leaving them unable to climb to stable orbits.

In contrast, during the S-77 launch, increased density was mostly confined to northern high latitudes. The satellites passed through these regions only briefly, reducing the cumulative drag they experienced. This geographic difference largely explains why the weaker storm caused mass satellite losses while the stronger storm did not.

Such latitude-dependent effects arise from the way geomagnetic energy enters the atmosphere. Disturbances often begin in polar regions and spread unevenly, meaning satellites can encounter very different conditions depending on orbital geometry. For large constellations like Starlink, where dozens of satellites are deployed at once, this variability can determine the fate of an entire mission.

The role of electron content in orbital safety

Global electron content, a measure of ionospheric plasma density, also plays a critical role in launch outcomes. High GEC values increase drag through enhanced ion-neutral interactions and can disrupt radio communications between satellites and ground stations.

In the aftermath of the S-36 failure, GEC shifted from positive to negative anomalies, signaling rapid restructuring of the ionosphere. This abrupt change compounded the drag problem and created unstable conditions for satellite maneuvering. By comparison, during the S-77 launch, the ionosphere was dominated by a stable negative anomaly, which although affecting communications, reduced drag near the equator where the satellites spent most of their time.

The interaction between thermospheric density and GEC shows that single-parameter forecasts are insufficient. A comprehensive picture requires monitoring both the neutral and charged components of the upper atmosphere. Only then can operators anticipate whether conditions will amplify or mitigate drag risks.

Lessons for the era of mega-constellations

The findings have direct implications for the rapidly expanding satellite industry. Starlink already has more than 5 000 active satellites, and similar constellations are being planned by multiple operators. In such dense orbital environments, even small-scale failures could generate significant debris and financial losses.

The study recommends integrating real-time space weather monitoring into all phases of mission planning. This includes forecasting both thermospheric density and global electron content, mapping latitudinal variations, and adjusting deployment strategies accordingly.

Options may include delaying launches, selecting alternative altitudes, or modifying orbit-raising schedules to reduce vulnerability.

As Solar Cycle 25 approaches peak activity, the risks will grow. The February 2022 S-36 failure serves as a warning that even modest storms can destroy a launch when atmospheric conditions align unfavorably. Conversely, careful planning and robust monitoring can allow missions to succeed even under stronger geomagnetic disturbances.

References:

¹ Global Electron Content and Neutral Density of the Thermosphere during Starlink Satellite Launches in 2019–2023 – T. L. Gulyaeva – Cosmic Research – September 18, 2025 – https://doi.org/10.1134/S0010952524601221

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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