Satellite Drag: We’ve Turned Starlink right into a Planetary Barometer

How the SATELLITE DRAG quantity on our house web page is made, and what it is telling us. Sept. 2026.

Starlink has many downsides. The megaconstellation interferes with astronomy, pollutes the environment with metallic re-entry particles, and has pushed Low Earth Orbit to the brink of the Kessler Syndrome.

On the opposite hand, it makes a terrific barometer.

Earth is completely surrounded by Starlink satellites. More than 11,000 of them are circling our planet proper now. Without exception, all of them skim the outermost layers of our environment, and they also expertise aerodynamic drag. Drag pulls them down, and so they must battle again with thrusters. This makes them advert hoc detectors of air strain. Every day, we learn these detectors and boil the outcome down to 1 quantity: the sink price.

What the quantity means

The sink price is the reply to a easy query. If a typical Starlink at 480 km switched off its thrusters right now, what number of meters of altitude would it not lose in a day? A price of, say, 30 m/day means it might sink 30 meters. Why 480 km? Because that is the place most Starlinks are.

The quantity adjustments daily in response to photo voltaic exercise. In 2026 it has ranged from 19.7 m/day on Aug. tenth, the quietest air of the yr, to 127.6 m/day on Jan. twentieth, throughout the yr’s greatest geomagnetic storm. That’s an element of six. The satellites did not change; the air did.

Here’s a technique to really feel the numbers. At 40 m/day, a useless satellite tv for pc at 480 km would take roughly 4 years to fall out of orbit. At the January storm price it might come down in a little bit over one yr. These are paces, not forecasts, as a result of the air by no means stays the identical for a yr. But they present why house climate issues to anybody who owns a satellite tv for pc.

2026 to this point

The yr opened with a bang. On Jan. 19-21 a G4 geomagnetic storm (Kp 9-, Ap 144 on the twentieth) heated the thermosphere and the sink price jumped to 127.6 m/day, about 5 instances the quiet-day flooring. It took two weeks for the air to calm down. Smaller storms in March (G3 on the twenty second), April, May, June and July (G3 on the 4th) every produced a pointy spike. Storms weaker than about Ap 45 are buried within the background.

Then got here summer season. As Solar Cycle 25 continued its decline, the air thinned to the yr’s minimal on Aug. tenth. Starlinks have been sinking solely 19.7 meters a day.

Look carefully on the orange bands. Each one marks a stretch of days when the Starlink fleet’s median altitude sagged by greater than 8 m/day or rebounded by greater than 10 m/day. That’s SpaceX combating again. There have been eight such episodes in 2026, and each one among them sits on or simply after a spike in Ap. We did not feed the storm calendar into the software program. The maneuvers discovered it on their very own.

How we do it

Monitoring is simple, as a result of another person does the onerous half. Using radar, the US Space Force’s 18th Space Defense Squadron tracks each object in orbit and, two or 3 times a day, publishes contemporary orbital components (also called “TLEs”) for each. They are distributed by way of Space-Track and CelesTrak.

Buried in every TLE is a drag time period, known as B* (“B-star”). Here’s the trick: the orbit mannequin that reads a TLE assumes a hard and fast environment. When the actual environment swells, the satellite tv for pc slows down greater than the mannequin expects, and the fitted B* has to develop to maintain the orbit matching the monitoring. B* is the place the air density finally ends up.

Any one satellite tv for pc’s B* is noisy. The matches are blurred over one to a few days, and station-keeping burns corrupt them. So we by no means belief a single satellite tv for pc. We comply with a hard and fast pattern of 1,000 Starlinks launched earlier than 2026, and for each we examine right now’s B* to that satellite tv for pc’s personal quiet-air flooring. Then we take the median throughout the entire cohort. The median of a whole lot of satellites is the instrument. The noise of any one among them falls away.

That offers a ratio: what number of instances denser the air is right now than on a quiet day. One calibration fixed turns it into meters per day, and the Planet Labs Doves provided it. In a quiet week of May 2026 their measured fall, scaled to 480 km, fastened the worth at 35.7 m/day per unit of the index. Then got here the verify. During the January storm week, the Doves’ precise decay rose 2.74-fold and the Starlink index rose 2.71-fold. Two impartial strategies agreed to 1 %.

Every morning we fetch the latest TLEs, compute the day’s worth, and publish it within the SATELLITE DRAG field on the house web page. TLEs are sometimes a day previous, so the quantity describes yesterday’s air.

The three checks

Starlinks aren’t the one ones we’re monitoring. We monitor three different impartial constellations: Planet Labs’ TremendousDoves (107), Amazon’s Kuiper satellites (391), and Eutelsat’s OneWeb satellites (651). Each one solutions a special query.

The TremendousDoves, orbiting at 400-500 km, don’t have any thrusters in any respect. They can’t battle the environment, so that they actually do sink. Their measured descent is our floor reality. In 2026 a typical Dove has been shedding about 62 meters a day; between Jan. 1st and late August, the median Dove fell 15.5 km. They are exquisitely delicate.

Amazon’s Kuiper satellites, at about 630 km, belong to a special firm. Their maneuvers don’t have anything to do with SpaceX’s. Anything the 2 fleets do in unison is the environment, and so they do quite a bit in unison: day after day, Kuiper and Starlink agree with a correlation of 0.94.

OneWeb orbits at 1,200 km, the place the air is so skinny that daylight strain issues greater than drag. They are our null management, flat all yr. Yet even OneWeb twitched throughout the January storm, rising 1.3-fold. The exosphere felt it too.

The environment breathes

Using this new information stream, we are able to watch the environment breathe. The envelope of air round our planet expands and contracts in response to photo voltaic exercise. Solar ultraviolet heats the thermosphere, and the sink price tracks the solar’s 10.7 cm radio flux with a two-day lag: the higher environment takes about two days to reply a change within the solar. Big geomagnetic storms puff up the environment sooner than that and trigger sharp spikes within the sink price.

Because our satellites fly at six completely different heights, we are able to watch the puff occur layer by layer. For the January storm, right here is how a lot the drag rose at every altitude (storm days in comparison with the 5 quiet days earlier than):

The response climbs with altitude to about 550 km, then turns over and is almost passed by 1,200 km. Heated oxygen expands upward till it thins out into the exosphere. Textbooks predict the climb. The turnover is the form of factor you solely see with sensors at six heights.

Why it issues

The density of the thermosphere is the most important uncertainty in orbit prediction and collision avoidance. The customary environment fashions err by 20-30% on odd days and by way more throughout storms. A measured every day quantity can calibrate them, daily.

Research teams have used Starlink orbits earlier than, most famously to dissect the February 2022 storm that killed 38 newly launched Starlinks at their 210 km insertion altitude. What’s new here’s a operating, public, every day index with three impartial constellations checking the reply. It’s the form of factor no one publishes every day. Now anyone does.

No instrument was launched for this. The swarm itself is the sensor, learn from public monitoring information.

Caveats

The index is relative. It measures air density as a a number of of every satellite tv for pc’s quiet flooring, transformed to meters per day with one calibration fixed. Absolute density nonetheless wants a mannequin.

TLE matches blur over one to a few days, so sharp occasions lag and smear a little bit.

SpaceX turns its satellites edge-on throughout storms to chop drag. Storm peaks learn from Starlink are subsequently decrease bounds. The Doves, which can’t duck, are the verify.

The measured report started Jan. 1, 2026. Scaling by photo voltaic flux, we estimate that solar-minimum air would give roughly 13 m/day, and quiet days on the 2024 photo voltaic most roughly 150. Those are estimates, not measurements.

Data

Daily collection for 2026: drag_sink_2026.csv (date, meters per day). Full-size chart: effective_sink_2026.png.