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Almost 4 #StarLink satellites fall back to Earth every day and they rain out aluminum oxide into the stratosphere which destroys the ozone layer. These satellites are more and more problematic with every article I read. Edit: corrected microsatellites to satellites per @sundogplanets 's correction that these are larger satellites than microsatellites.
Except ... when this claim (not about the satellites re-entering, just the amount of damage they cause to the atmosphere) started circulating some months back, I read an article (somewhere...) that analyzed the amount and type of matter it would distribute, and it pales in comparison to the amount the earth receives in "space dust" and micrometeroids every day.
Best figure I know of for the mass of "normal" space matter hitting our planet is 5,200 tonnes / year:
https://www.scientificamerican.com/article/antarctic-study-shows-how-much-space-dust-hits-earth-every-year/
The current Starlink satellites are "gen2 mini", and are 740 kg. So you would need to de-orbit more than 7,000 of them every year - not 4 per day - to even match the natural space dust falling on earth. Except it's even worse (for the argument) than that, because 740kg is their launch mass, including all their maneuvering fuel/gasses, which by definition are gone before the satellites are deorbited. I don't have an exact figure for how much mass the fuel accounts for, but it wouldn't surprise me if it was more than 25% of the mass of the spacecraft at launch.
The residue left in the atmosphere doesn't seem to be a very big deal.
#science #mass #satellite #deorbit #RunTheNumbers #calculation
edit: typo
@cazabon That is probably a bit oversimplified, but I appreciate the context of mass. Not all mass is equal. The space dust you speak of likely has a chondritic composition, rich in iron and silicates and similar to the primordial composition of the universe. Beryllium and lighter elements are probably nit significant portions of that mass of space dust because they are more volatile.
The satellites, on the other hand, represent a concentration of elements which are useful for communications and light enough for launch. The bulk composition of all those satellites is likely quite different, and enriched in rare Earth elements and volatiles like beryllium.
So the danger, then, is not the mass. It is the composition, or the mass of the harmful elements. In this case, the articles linked point out the harmful effects of these elements on the ozone layer, which protects life on Earth from UV radiation. Space dust doesn't have that negative effect.
I'm not so sure. The space dust we get isn't all one type of meteorite; it's essentially all the different types that are out there, so the composition as a whole tends towards the composition of the solid parts of the solar system. For example, it's easy to find metallic micrometeorites in your rain gutters, and they're not all just iron. Copper, aluminum, etc, etc.
I don't know exactly how much beryllium a Starlink satellite contains. I didn't think it was pure anyways - it would be as part of a beryllium-copper alloy? So the amount of beryllium entering our atmosphere from satellites may or may not equal the amount in space dust. I haven't found a study on this, everything I see said on this subject online seems to be speculation. Speculation is not a great basis for evaluating danger.
@cazabon Chondritic composition is not only iron. It is the base composition of the universe since formation, as analyzed in chondritic meteorites. The composition of the chondrite is well known and serves as a basis for evaluating other younger meteorites, like Martian meteorites from impact on the Red Planet. Beryllium is present in the chondritic composition, but at exceedingly low amounts.
Rest assured that, in the same mass of space dust and Musk satellite, the satellite has more beryllium and likely more aluminum. We cannot make satellites out of bulk Earth or chondritic composition; that is the whole point of mining.
These reports are based on two peer-reviewed scientific studies, one in Proceedings of the National Academy of Science, and the other in Geophysical Research Letters. The first study uses the number 10% aluminum, which is much more enriched than the chondritic composition. The studies don't mention beryllium; that was brought up as a concern by someone responding to my original post. The mass and the altitude interplay to directly inject more of this aluminum oxide to the stratosphere directly, whereas lighter dust particles generally do not burn up or melt, and they make it to the surface of the Earth. In the second link, the authors calculate a 29.5% increase in aluminum over natural levels, which would include space dust.
I hope that helps allay your concerns about speculation.
Sources:
https://www.pnas.org/doi/10.1073/pnas.2313374120
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL109280
The natural amount of "space stuff precipitation" does not destroy the ozone layer [anymore].
Add more, and the story changes.
And with an orbital life of 5 years for the target of 40k simultaneous satellites, Starlink would be trashing 8k sats per year. This would more than double the natural amount - if those 7k that Cazabon mentioned are correct.
Today, those 120 sats burning up in January alone, got shot up there in 2019.
Wait till 2023 rains down.
Or don't. Wait, I mean. Don't wait. But instead regulate Starlink out of business immediately.