morningcoffee1 t1_j9p14c2 wrote
Reply to comment by CrustalTrudger in What will be the environmental impact of de-orbiting 42,000 Starlink satellites every five years? (Explanation in post) by OvidPerl
No real answers, but some thoughts...
Metal in the atmosphere is normal of course, because a lot (most) meteors that are burning up in the atmosphere are metallic. From this newspaper article it is estimated that about a ton falls to Earth every day. Using another "source" this page from Smithsonian magazine estimates it to be about 50 tons.
Either way, we're talking about a significant increase. But would there be an effect, and what would is be?
Obviously, the amount of dust that is swept up from the Earth by wind is higher by several orders of magnitude, but won't reach that high an altitude.
Potentially more important though... the question is about metal in the atmosphere, but what percentage of said satellites are actually metal? OP makes the implication of 100%, obviously this will be way lower (10%?), but if true, what constitutes the other 90% and what are the implication of that? A nice piece of iron burning up in the atmosphere after all, is not the same as some Lithium Ion battery encased in plastics...
CrustalTrudger t1_j9p1yh9 wrote
As highlighted in most the papers I linked to (1) in comparing it to natural flux you have to consider not just the total mass but also the composition, i.e., for the natural flux of meteorites only about 5% are metal rich whereas most are silicates and (2) within the metal meteorite comparison to satellite comparison, we're talking primarily iron/nickel (for metallic meteorites) vs aluminum compounds (for satellites). The concentration and chemistry both matter for potential effects.
compounding t1_j9qkeu5 wrote
Composition does matter, but silicate minerals have tons of aluminum in them.
A quick check shows that most types of low-iron meteorites appear to still be very roughly 5-10% aluminum by mass.
VIRSINEPOLARIS t1_j9r9o3u wrote
>[...]silicate minerals have tons of aluminum in them.
That might be on Earth, because the lightness of aluminium drove its concentration in the crust.
> A quick check shows that most types of low-iron meteorites appear to still be very roughly 5-10% aluminum by mass.
According to https://periodictable.com/Properties/A/MeteoriteAbundance.html aluminium is ony 0.9 % of general meteorites mass.
zoicyte t1_j9q8opb wrote
here's a real answer:
don't be too worried about the 23 500-lb satellites that will also vaporize alongside the 44 tons of space rocks that already do the exact same thing.
tonyvila t1_j9qqkng wrote
Except your numbers are quite wrong. Each satellite weighs about 1200 kg, so each one is over a ton (~2600 lb). That's almost 60 tons, which is a 130% increase in pure mass, not to mention chemical composition.
fastspinecho t1_j9qx65q wrote
No, the first-generation satellites weigh only 250 kg.
SpaceX eventually plans to put second-generation satellites into orbit, which do weigh ~1200 kg. However, they will need fewer of them, because they are more powerful than the first-generation satellites. They are not currently capable of putting many of these into orbit, and only have permission to launch 7500 of them in the future.
Spacex ultimately plans for the first-generation satellites to constitute 75% of its fleet.
CMDR_Shazbot t1_j9rasrx wrote
Yep, also people aren't factoring in that the initial approval is best effort. Maybe they applied for 42k and claim they have a 5 year lifespan, but the reality is they want them to last longer and would be much happier doing it with fewer satellites. 5 years is under certain conditions and likely lowballed, if they don't need to do collision avoidance maneuvers could be longer, if there's a lull in space weather could be longer, if there's a lot of that could be shorter.
The gen 2s require starship, which is much MUCH larger than falcon, meaning fewer launches to expand the network and more users per satellite, more fuel per satellite which extends the lifespan, etc.
DaoFerret t1_j9sanh7 wrote
Starship also opens up orbital recovery/refueling as a possibility, both of which would also jiggle the equation around.
CMDR_Shazbot t1_j9sfwb3 wrote
Ya that would be insanely interesting to be able to go up and just...scoop whole sats for refurb and return. Calculating the conjunction, the entire landing leg with enough-but-not-too-much fuel with the added mass, and securing it in the vehicle to survive re-orbit wold be... challenging.
mdielmann t1_j9rbzj0 wrote
23 × 1.2 tonnes is 27.6 tonnes of debris. To convert to tons, multiply by 1.1, giving about 30.4 tons. (Remember, a tonne is 1000 kg, and a ton is 2000 lbs. Don't mix those numbers up.) So, it's more like a 65% increase daily, which may be no laughing matter, depending on what those compounds are. But first, make sure your facts are correct.
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