Researchers at Kyoto University have transformed approximately 1,200 Starlink satellites into a giant atmospheric scanner, applying medical imaging tomography to map Earth’s thermosphere. By tracking orbital drag and altitude decay at roughly 482 kilometers, scientists produced the first two-dimensional latitude-longitude snapshot of this notoriously difficult-to-observe neutral gas layer.
Bridging Space Science and Orbital Engineering
Low Earth orbit is getting crowded. Thousands of operational spacecraft and discarded pieces of space debris constantly carve paths through the thermosphere—a region stretching from about 100 to 1,000 kilometers above the planet’s surface. Here, traces of the upper atmosphere create aerodynamic drag that gradually slows down spacecraft and alters their trajectories.
Accurately calculating this atmospheric density is vital for collision avoidance. Yet, observing the thermosphere has historically been an uphill battle for researchers. While the ionosphere accounts for less than one percent of the upper atmosphere and relies on ionized gas that conveniently bends radio waves, the thermosphere is made up of over 99 percent electrically neutral gas. Radio waves pass right through it, blinding traditional remote sensing tools.
To crack this observation barrier, a team at Kyoto University realized they needed a systemic shift. “This is a multidisciplinary study between space science and space engineering,” notes corresponding author Mamoru Yamamoto, emphasizing the necessity of dialogue across historically siloed academic fields.
Tomography Meets Low Earth Orbit
Instead of launching costly, dedicated atmospheric probes, the team looked at the massive mega-constellation already screaming through the skies. They tapped into publicly available orbital data from Starlink satellites operating at an altitude of 482 kilometers.
The researchers applied tomography—a mathematical reconstruction technique typically reserved for medical CT scans—to the atmospheric drag experienced by the satellites. As air density fluctuates, it causes microscopic, continuous decay in a satellite’s orbit. By aggregating these orbital shifts across roughly 1,200 spacecraft, the team estimated thermospheric density profiles with unprecedented spatial distribution.
This achievement builds directly on earlier work. Previously, the same Kyoto University team utilized general orbital telemetry known as Two-Line Element (TLE) data to track how thermospheric density changed over time and altitude. The new analysis adds a crucial horizontal dimension, charting how density varies across distinct latitudes and longitudes to reveal the complex geographic structure of the upper atmosphere.
To validate their novel tomographic maps, the researchers cross-referenced their findings with observational data from the European Space Agency’s SWARM satellites, which measure atmospheric density variations directly along their orbital paths. The comparison showed strong consistency, confirming that commercial broadband constellations can double as high-resolution scientific instruments.
Securing Crowded Orbits Against Space Weather
The implications of turning commercial telecommunications hardware into atmospheric sensors stretch far beyond academic curiosity. As the commercial space race accelerates, managing traffic in low Earth orbit becomes a high-stakes operational challenge.
Better density models directly improve predictions of satellite motion. With more accurate, geographically detailed data on thermospheric drag, operators can run sharper conjunction assessments, significantly cutting down the risk of catastrophic collisions between active payloads and orbital debris. Furthermore, this technique lays the groundwork for near-real-time atmospheric density monitoring around individual satellites.
Such rapid-fire data feeds could dramatically upgrade modern space weather forecasting. As solar flares and geomagnetic storms heat up the thermosphere—expanding it outward and instantly spiking atmospheric drag—having a live, distributed sensor network in the sky could keep next-generation satellite operations safe and dependable.
