Satellite megaconstellations are usually discussed in terms of light pollution and orbital debris, but astronomer Tony Phillips has found a scientific use for them. By mining the US Space Force's public two-line element sets (TLEs), he turns thousands of commercial spacecraft into a distributed sensor for Earth's upper atmosphere.
Each TLE contains a drag coefficient called B*. The standard orbit model assumes a fixed atmosphere, so when the real atmosphere expands and slows satellites more than expected, B* must be adjusted to keep the fit. Phillips collects these values for about 2,100 satellites across four fleets and uses them to track how the thermosphere swells and contracts.
His early results show the sink rate follows the sun's 10.7 cm radio flux with a two-day lag, while geomagnetic storms produce sharper spikes. Other researchers have used Starlink data for similar work, especially after the 2022 storm that destroyed 40 satellites. What is new, Phillips says, is a running public daily index cross-checked by three independent constellations.