CrustalTrudger t1_j9otg0d wrote
It's a good question, but one that does not seem like it's answered yet (though it is theoretically addressable with global climate models, etc). There are a variety of papers in the last few years highlighting that both emissions from increasingly frequent rocket launches and material (like aluminum and other metals) added to the atmosphere via satellite deorbiting could have substantial impacts on a variety of things, but almost all of these are really calls for more attention and research as opposed to answers to the question itself (e.g., Ross & Toohey, 2019, Hobbs et al., 2020, Boley & Byers, 2021, Schulz & Glassmeier, 2021, Adilov et al., 2022, Ross & Jones, 2022, Shutler et al., 2022, Lawrence et al., 2022). There is at least one paper directly trying to answer this with modelling for the emissions from increasingly frequent rocket launches (e.g., Maloney et al., 2022), but I at least could not find a paper actually demonstrating what the impact of addition of significant amounts of metal to the upper atmosphere would be (beyond the generalizations in the previously linked papers that suggest it would likely do something). The closest is really the Hobbs et al., 2020, but sadly this is an abstract for a conference presentation and I couldn't find a follow up (might still be in the works, lag time between stuff presented at conferences and eventual publication can definitely be several years). It does seem like there is a fair bit of interest in this within pockets of the scientific community (as illustrated by all the "we should pay attention to this" papers cited above), so I wouldn't be surprised if there are studies in the works on this, but at least for me it's far enough outside my area that I don't know that for sure (maybe others more in this space can provide some details).
kittenTakeover t1_j9owor1 wrote
This really sounds like one of those "what goes up must come down" moments. Presumably it would be through precipitation, which means it would end up in our water. The effect of this would depend on the metal concentration when spread out. Is there anything that would prevent this and keep the metal afloat? Seems like this should be a pretty simple chemistry question, but I guess I'm not an expert.
mfb- t1_j9p2k1z wrote
A really rough estimate: We have ~500,000 km^3 of global precipitation per year (1 meter averaged over the surface). If we put all of the 10,000 tonnes of aluminium into that, ignoring chemistry or what happens afterwards, we get an average of 20 ng/liter. For scale, the US EPA recommends no more than 0.05-0.20 mg/liter or 50,000 to 200,000 ng/liter for drinking water.
jedadkins t1_j9rqjvz wrote
Yea this really seems like a problem of scale, ~2.5m tonnes of aluminum needed to reach the lower bound is an insane amount. Maybe once we start actually commercializing space it could be an issue but by then we should have a better option then just crashing stuff to get it out of orbit
killercurvesahead t1_j9qauk6 wrote
At that rate whoever’s selling rocketship tickets and plots of land in their own Mars colony is gonna make bank.
Waitaminnit…
Imperator-Solis t1_j9r8n08 wrote
You might have misread, at that rate it won't reach limits for 2500 years
EBtwopoint3 t1_j9s3fam wrote
Not 2500 years, until the rate of satellite re-entry becomes 2500 times higher. That is a per year figure, not one that adds up.
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CrustalTrudger t1_j9oybjw wrote
The variables at play are (1) the mass of material added, (2) the level of the atmosphere to which the material is added, (3) the specific chemistry of the material added, and (4) the potential effects (e.g., change in albedo, etc) of those materials as a function of time and concentration. The type and magnitude of effect will scale with the mass and whatever the particular material does, but points 2 and 3 are also important as they control the residence time (i.e., the duration). We could consider something like sulfate aerosols that are injected into the atmosphere during things like large impacts or large volcanic eruptions. Residence time for these depend a lot on the level of the atmosphere the particles are in, e.g., Junium et al., 2022 consider residence times for sulfate related to the Chicxulub impact and highlight that particles injected into the troposphere might last a few days to weeks, whereas those in the stratosphere would linger for months to years. The specific chemistry also matters though, so behavior of one type of particle is not representative for all, i.e., if the particle in question readily reacts with something, the residence time might change. All of this is to highlight the uncertainty, i.e., without dedicated experiments we don't know exactly what the effect will be and it's not necessarily safe to just assume that it will be negligible.
morningcoffee1 t1_j9p14c2 wrote
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.
ARobotKneltInTheLane t1_j9przct wrote
Isn't it funny that "stop that till we know exactly how much harm it does" is never really pursued as a policy option
More research is needed! the scientists cry as the entrepreneurs do whatever they like
And of course when what they are doing is proven deadly & regulated out of feasibility, they will have new unproven methods to turn to
cyberentomology t1_j9s63wb wrote
Because there will never be enough research to satisfy someone who doesn’t understand that you can’t prove a negative.
ARobotKneltInTheLane t1_j9sj8ks wrote
I don't follow perfectly. Are you saying entrepreneurs don't have time to wait to find out that today's cockamamie scheme for turning $1 into $2 does "no harm"?
Alblaka t1_j9sueww wrote
Seems more like they're implying that entrepreneurs will not accept anything that isn't straight up proving a negative. Which is logically impossible. Thus whatever "this is possibly bad" scientists come up with, will end up dismissed because it's not "This is 100% certainty bad".
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ARobotKneltInTheLane t1_j9swb06 wrote
Ah I see! I felt confusion cos for sure we have pretty conclusive evidence of the deep harm of many industrial processes but what you're saying makes sense
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