Comment by sandworm101
3 hours ago
The author seems to treat the atmosphere as a, well, sphere. It isnt. It is not of equal depth at all areas. As starlink (and every other sat) only travels in part of the atmosphere each day they cannot measure the entire atmosphere. So you measure a thousand starlinks to get an average. Ok, but a significant bulge on one side of the planet will slow all sats, giving the false impression of a homegenous trend. So you have to track very specific sats in very specific survey orbits... but also update that list as the orbital shell rotates around the earth. It is a very complex problem.
Unfortunately the data doesn't have the required time or space resolution. The drag term is averaged over many orbits, and you can't even use perigee/apogee drift to localize it since the atmosphere rotates so it gets averaged over all longitudes.
You can do some rudimentary localization by latitude, however, by comparing satellites in different inclinations. You also get data by altitude, of course.
What you want is realtime accelerometer records from satellites in flight, exposing their drag factors over specific parts of the planet. The only tricky variable would be their orientation, but that is certainly recorded too.
Something like this: https://en.wikipedia.org/wiki/GOCE
Based on losing "a few meters of altitude per day," if we assume 5 meter/day at 500 km that's 3 nano-gee. Sensitive piezoresistive accelerometers seem to run in the single digit micro-gee range.[0]
Easier to look at the altitude loss and infer the acceleration indirectly. With access to the raw higher time-resolution altitude data, mapping should be possible.
SpaceX has in the past gone above and beyond to expose TLE data for scientists and astronomers[1], so it's possible that people inside SpaceX would be open to collaborating on such a project.
[0] https://www.pcb.com/sensors-for-test-measurement/acceleromet...
[1] https://youtu.be/MNc5yCYth5E?t=1719
I suspect the author understands the concept of a spheroid, though they don't mention the term as such.
There is a fair bit of statistical rigour described in the original article at : https://www.spaceweather.com/starlink/starlink_drag_explaine...
> Ok, but a significant bulge on one side of the planet will slow all sats, giving the false impression of a homegenous trend.
A bulge would not homogenously slow all satellites, each one would be slowed by a different amount depending on its particular path through the bulge. Those that pass through more of the bulge will be slowed to a greater extent than those passing briefly through. Satellites in different orbits tell you where the bulge is, satellites in the same orbit tell you how the bulge is moving.