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Astronomer watches Starlink satellites sinking to build a 'planetary barometer'

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ortusdux · 1790364880 · focus · HN ↗
Link to article: <a href="https://www.spaceweather.com/starlink/starlink_drag_explainer.html" rel="nofollow">https://www.spaceweather.com/starlink/starlink_drag_explaine...
sandworm101 · 1790366324 · focus · HN ↗
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.
1. schiffern · 1790367242 · focus · HN ↗
  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.
  1. sandworm101 · 1790367714 · focus · HN ↗
    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.
    schiffern · 1790368730 · focus · HN ↗
    Based on losing "a few meters of altitude per day," if we assume 5m/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 goes above and beyond to expose TLE data for scientists and astronomers[1], so it's possible SpaceX may be open to collaborating on such a project.
    [0] <a href="https://www.pcb.com/sensors-for-test-measurement/accelerometers/high-sensitivity-icp" rel="nofollow">https://www.pcb.com/sensors-for-test-measurement/acceleromet...
2. crtified · 1790367535 · focus · HN ↗
  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 : <a href="https://www.spaceweather.com/starlink/starlink_drag_explainer.html" rel="nofollow">https://www.spaceweather.com/starlink/starlink_drag_explaine...
3. jjk166 · 1790373231 · focus · HN ↗
  > 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.
BlackRabbit1 · 1790367436 · focus · HN ↗
That's cool.
Reminds me that scientists can use GPS to track earthquakes indirectly as it interacts with the ionosphere: <a href="https://link.springer.com/article/10.1186/s40623-025-02211-y" rel="nofollow">https://link.springer.com/article/10.1186/s40623-025-02211-y
1. BlackRabbit1 · 1790406571 · focus · HN ↗
  Addendum: GNSS-R (R=Reflectrometry) is also established science.
  This way you can - for example - track water height of a river next to a station. You basically receive the direct GNSS signal and the reflected one. Then do magic math.
  It doesn't require super-cooled stuff and can be done with off-the-shelf-gear.
autoexec · 1790369609 · focus · HN ↗
> "The megaconstellation interferes with astronomy, pollutes the atmosphere with metallic re-entry debris, and has pushed Low Earth Orbit to the brink of the Kessler Syndrome... On the other hand, it makes a terrific barometer.”
I'm not sure we're coming out ahead on that one, but leave it to a guy who can detect things light-years away to be able to find a silver lining
pclowes · 1790369708 · focus · HN ↗
Any solid citations for "and has pushed Low Earth Orbit to the brink of the Kessler Syndrome."?
I would be honestly intrigued but wary of just the usual Elon bad/good so all things he does bad/good narratives.
If we are on the brink of Kessler Syndrome in LEO I would expect market pricing to reflect that.
1. smallerize · 1790370161 · focus · HN ↗
  <a href="https://arstechnica.com/space/2026/09/there-are-now-17000-satellites-in-orbit-and-growing-should-we-be-concerned/" rel="nofollow">https://arstechnica.com/space/2026/09/there-are-now-17000-sa...
  The report itself <a href="https://www.esa.int/Space_Safety/Space_Debris/ESA_Space_Environment_Report_2026" rel="nofollow">https://www.esa.int/Space_Safety/Space_Debris/ESA_Space_Envi...
  About pricing: <a href="https://www.satellitetoday.com/launch/2026/09/17/the-era-of-cheap-price-per-kilo-launch-is-over-launchers-say/" rel="nofollow">https://www.satellitetoday.com/launch/2026/09/17/the-era-of-...
  1. brandonagr2 · 1790370987 · focus · HN ↗
    If the report is predicting 100 years in the future, are we really "to the brink" now? Not to mention the decay time of these LEO is in months, hardly a kessler syndrome scenario.
    smallerize · 1790371583 · focus · HN ↗
    Yes. Look under "collisions causing collisions". Debris from previous collisions increases the risk of future collisions.
    drivingmenuts · 1790392091 · focus · HN ↗
    It probably doesn't matter. Global warming has proven that we are incapable of doing the necessary things to slow or stop the human-caused decaying of our planet. I'm starting to think we deserve what we're gonna get.
  2. schiffern · 1790422409 · focus · HN ↗
    The claim is "Starlink has pushed LEO to the brink of the Kessler Syndrome."
    This is an ESA collision rate prediction, but it has no demonstrated connection to Starlink. Are the underlying assumptions in the ESA paper representative of Starlink? Who knows! It certainly hasn't been shown here.
2. dzhiurgis · 1790372014 · focus · HN ↗
  Same. Somehow first 50% of mass to orbit was woke science and next 50% is fascist oppression.
3. ck2 · 1790372502 · focus · HN ↗
  almost positive Kessler LEO will be triggered by Russia taking out a cluster by the end of the decade
  * <a href="https://satellitemap.space" rel="nofollow">https://satellitemap.space
  * <a href="https://platform.leolabs.space/visualization" rel="nofollow">https://platform.leolabs.space/visualization
4. embedding-shape · 1790372715 · focus · HN ↗
  > If we are on the brink of Kessler Syndrome in LEO I would expect market pricing to reflect that.
  Wouldn't the market pricing only reflect this after that fact? Up until it happens and no one knows any better, business will continue as usual because otherwise numbers don't go up. Like any past financial crisis, things look fine until they don't.

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