Dr. Tony Phillips, astronomer and operator of spaceweather.com, has developed a method to use commercial satellite megaconstellations as a barometer to measure Earth’s atmospheric density in real time. By analyzing public tracking data for thousands of spacecraft, researchers can now monitor how the upper atmosphere expands and contracts in response to solar radiation and geomagnetic storms without launching dedicated scientific instruments.
Tracking Atmospheric Expansion Through Orbital Decay
Earth’s thermosphere swells when heated by solar ultraviolet radiation and geomagnetic activity. As the atmosphere expands outward, it increases aerodynamic drag on objects in Low Earth Orbit, causing satellites to lose altitude more rapidly. While commercial megaconstellations like SpaceX’s Starlink introduce well-documented challenges for ground-based astronomy and orbital congestion, their orbital adjustments provide a continuous record of these atmospheric shifts.
The US Space Force tracks artificial satellites and publishes orbital data known as Two-Line Elements, or TLEs. According to Phillips, each TLE contains a specific drag term designated as B*, or B-star. Standard orbit models assume a fixed atmosphere, meaning that when the upper atmosphere swells, a satellite slows down beyond model projections. To compensate, the fitted B* value increases to match actual tracking observations, effectively capturing shifting air densities.
Multi-Constellation Monitoring of Space Weather
Phillips collects and analyzes TLE data across multiple commercial networks, encompassing approximately 1,000 Starlink satellites, 107 Planet Labs SuperDoves, 391 Amazon Kuiper spacecraft, and 651 Eutelsat OneWeb satellites. Although these constellations operate at varying orbital altitudes, they consistently register identical solar events.
Solar ultraviolet heating of the thermosphere corresponds with a measurable two-day lag in satellite sink rates, indicating the duration required for the upper atmosphere to respond to solar output changes measured via 10.7 cm radio flux. Meanwhile, major geomagnetic storms trigger immediate atmospheric expansion, producing sharp, sudden spikes in orbital sink rates across the monitored fleets.
A Public Daily Index for Space Weather Research
While severe space weather events—such as the 2022 geomagnetic storm that forced 40 Starlink satellites out of orbit—have previously demonstrated the vulnerability of low-altitude spacecraft to atmospheric drag, the new methodology establishes a running, public daily index. By cross-referencing three independent satellite constellations using public tracking feeds, researchers gain a reliable atmospheric dataset derived entirely from existing orbital infrastructure.
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