What will be the environmental impact of de-orbiting 42,000 Starlink satellites every five years? (Explanation in post)

Submitted by OvidPerl t3_119wv28 in askscience

Inspired by a Mastodon thread by Astronomy Professor Sam Lawler.

Elon Musk plans 42,000 Starlink satellites. With an operational lifespan of five years, after which they're de-orbited. We will have an average of 23 (42,000/(365*5)) satellites entering the Earth's atmosphere every day.

At 1,250 kg each (for the Starlink 2.0 satellites), that's 29 tons of satellites entering our atmosphere every day, much of that being aluminum. In other words, that will be almost 10,000 tons of aluminum effectively being aerosolized in our upper atmosphere every year.

Have there been any environmental impact studies of this?

Side note: For those who point out that we have two to three times more meteorites (by mass) entering our atmosphere than Starlink satellites, the meteorites are mostly silicates.

Also, unlike geoengineering techniques to inject aerosols into our atmosphere to combat global warming, we will have no effective way of shutting off the rain of Starlink satellites. Even if launches are stopped immediately, that's five years worth of satellites coming down. And without a "smoking gun" demonstrating the damages, SpaceX will likely continue launching those satellites to protect their revenue.

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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).

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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.

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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.

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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

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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…

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Imperator-Solis t1_j9r8n08 wrote

You might have misread, at that rate it won't reach limits for 2500 years

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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.

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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...

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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.

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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.

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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.

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zoicyte t1_j9q8opb wrote

here's a real answer:

Scientists estimate that about 48.5 tons (44 tonnes or 44,000 kilograms) of meteoritic material falls on the Earth each day.

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.

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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.

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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.

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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.

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DaoFerret t1_j9sanh7 wrote

Starship also opens up orbital recovery/refueling as a possibility, both of which would also jiggle the equation around.

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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.

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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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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

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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.

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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"?

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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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[deleted] t1_j9plffv wrote

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bladeelover429 t1_j9rlkmr wrote

Well, from purely a chemistry standpoint, aluminum metal burning up in the atmosphere would mostly create aluminum trioxide. The EPA doesn't consider it to be a dangerous substance, and I can't come up with other reactions with Atmospheric gasses that would form anything significant.

Now from a climate standpoint- large amounts very tiny particles do have a measurable effect on global warming. If we're burning up a mass of aluminum on the same order as all of the meteorites that enter the atmosphere, then the effect is probably negligible, however. But I only say this because I haven't yet seen any climate models that consider particles added by meteorites. This could mean that it's either too difficult to model or its just not important enough. Climate change is notoriously difficult to model, unfortunately.

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CoffeeFox t1_j9seco7 wrote

>Now from a climate standpoint- large amounts very tiny particles do have a measurable effect on global warming. If we're burning up a mass of aluminum on the same order as all of the meteorites that enter the atmosphere, then the effect is probably negligible, however.

That's a good point to add to the discussion. Micrometeorites are believed to enter the Earth's atmosphere at a rate of many tons per year. One study estimates roughly 10^6 kilograms yearly

So the Earth has already long had massive amounts of metallic elements entering the atmosphere and vaporizing.

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bladeelover429 t1_j9t16nf wrote

Also, another thing that can be done to get an idea of how problematic the materials the satellite is made of might be depends on this pretty convenient chart of common spacecraft metals and their thermal conductivity: https://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html

If an object starts in space and you assume it's at an ambient temp of 2.7K, you can test different values of the distance travelled through the atmosphere, m. Then you have the amount of energy absorbed per degree, so factor in the energy absorption rate of the metal, and you have how long it takes for it to aerosolize. In this case, if the particles added by the object do end up being problematic to the climate, we would want to make sure that they're being aerosolized as close to the surface of the earth as possible.

So best case scenario, it exits the atmosphere before the amount of light being blocked can do any harm. (Ref. https://www.nesdis.noaa.gov/news/the-dirt-atmospheric-dust)

Worst case scenario, it subtracts a few years from the time left we have to solve this problem before getting sent into an ice age.

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fastspinecho t1_j9q9gwm wrote

They aren't planning to use 42,000 Starlink 2 satellites.

The current plan is to deploy 10K to 30K satellites. They don't think they will actually need 40K.

Furthermore, the majority of their satellites are first generation, which weigh only 250 kg. They are only authorized to launch 7000 Starlink 2s. Starlink 2 satellites are more capable, so every Starlink 2 they launch will reduce the total number needed.

SpaceX launches 10 or so Falcon 9s a month. Each one can carry 60 of the smaller satellites, but only a handful of the Starlink 2. I don't think it's feasible for them to launch an average of 23 Starlink 2 satellites a day, even after switching to their bigger Starship rocket. And what comes down must go up.

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cagandrax t1_j9qr62c wrote

SpaceX had 61 total launches in 2022, 34 of which were for Starlink. Your numbers are a little off

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[deleted] t1_j9por86 wrote

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[deleted] t1_j9q6ib0 wrote

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[deleted] t1_j9ptlj5 wrote

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[deleted] t1_j9rxh84 wrote

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bigsoftee84 t1_j9sc6as wrote

Coal plants burn aluminum?

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Alphageds24 t1_j9sk9bq wrote

Context of global warming severity, aluminum particles are probably minor compared to a coal plant pumping CO2 or even methane from the north.

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bigsoftee84 t1_j9skm2v wrote

There are more impacts on the environment than just climate change. Burning off tons of metal to be washed down into our water sources is probably something that should be discussed and not waved away because coal plants contribute to another problem.

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Alphageds24 t1_j9smj5v wrote

Earth can't spread its resources to correct every little thing, we need to focus on bigger items. Aluminum oxide in our water is probably minor compared to the acidification of the oceans, also plastic pollution, mercury, etc.

Yes it might contribute but it's minor and so I'd say forget about trying to solve it, fixing it wouldn't change the course in any major way.

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bigsoftee84 t1_j9sn2vu wrote

This opinion shows little concern for the environment or the future impacts on the environment from new technologies. You want to ignore potential issues because there are already issues. Compounding the problem will never fix it, and adding more trash burning isn't a fix. Prevention of future pollution should be as important as stopping current pollution, otherwise what is the point?

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calvin4224 t1_j9stugf wrote

Heavy metals in the water may be really bad for animals, e.g. the European oysters which are nearly extinct in the copper-rich (tiny particles) north Sea. We should care about everything we do to our planet. You don't have to care about everything yourself of course. But don't dismiss it as unimportant just because you don't have the energy to care.

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[deleted] t1_j9sziq4 wrote

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veerKg_CSS_Geologist t1_j9t2o22 wrote

That doesn’t answer the question of what impact if any all the satellites will have.

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Unlikely_Plankton_11 t1_j9t6tug wrote

It’s a relevant point to make, because we still have barely started to fix the actual massive problems and people are already bored and looking for distractions in the noise.

Of the two things, coal plants are so hilariously worse and larger in scale that satellites may as well not exist at all for all the difference it makes. When you have people going “yeah yeah coal whatever, let’s look into these satellites though!” it takes up mind space, airtime, political capital, and manpower that could be used on far more impactful things.

And in this case it sure seems like the motive is “ugh corporations,” not genuine concern for the environment.

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Alphageds24 t1_j9tidor wrote

Exactly my point, and ya totally feels like it's "ugh corporations", and targeting just starlink seems like it's an Elon attack and not at all looking at the satellite junk from many companies and governments.

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DreamOfTheEndlessSky t1_j9slomg wrote

Coal plants burn what you throw in them, and coal isn't pure. That's how you get things like radioactive coal ash.

The questions to ask next would be along the lines of:

  • what metallic contents are found in typical fuel coal?
  • how much of that gets into fly ash?
  • how different are near-surface metallic emissions and stratospheric metallic emissions?

But I don't have data for those.

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bigsoftee84 t1_j9smj01 wrote

Ok, but again, that issue doesn't negate the possible environmental impacts of burning off tons of metal in the atmosphere by a different industry. Does SpaceX get a pass because coal companies are bad? We should be limiting this type of waste and pollution, not trying to wave it away because a different industry is worse.

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DreamOfTheEndlessSky t1_j9sn69m wrote

That's not how I read the above comment at all.

I saw it saying something more like "if the satellites create a problem, you could offset that by a small reduction in an existing terrible industry". But, as I pointed out, I don't have sufficient information to connect them as substitutable effects.

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bigsoftee84 t1_j9sny23 wrote

Do you remember carbon credits? Incentives to try to encourage carbon reduction? When you offset pollution with another form of pollution, you haven't reduced pollution, just moved the source. We shouldn't ignore one source of pollution for another because we support one industry over the other. We should be reducing all pollution as much as possible, not adding new sources and types of pollution.

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DreamOfTheEndlessSky t1_j9ssz87 wrote

That would be a terrible rule. If you can't "add new sources and types of pollution", as you say, you've just eliminated perfectly reasonable ways to significantly reduce the sum: you couldn't use wind power, because it adds a "new source and type of pollution" in the form of broken turbine blades. Your rule, as stated, wouldn't let us consider the drastic improvement it makes in the form of reduced coal/natgas combustion. You would effectively mandate BAU.

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veerKg_CSS_Geologist t1_j9t2udy wrote

Wind power is net negative in pollution. It’s not replacing one source with another equal source aka carbon credits.

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DreamOfTheEndlessSky t1_j9t3qs1 wrote

Their rule doesn't allow "net negative". They went with "no new positive, no matter how much it helps elsewhere". Any new type of pollution would be prohibited, so the (agreed) significant improvement of switching coal to wind power generation would be disallowed ... showing that it's a bad rule to choose.

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bigsoftee84 t1_j9sx4kw wrote

You're missing the point. Yes, those materials may be naturally occurring in the earth's crust, but so is carbon. We don't know the effects of this, and it should be studied way before we just allow them to dump tons of new pollution into the atmosphere. The current method is also exceptionally wasteful, I don't understand the waving away of people's concerns. These issues need to be addressed now, not when they become disasters.

When that satellite burns up, those resources are just wasted. We need a real plan to deal with space junk. Burning our waste is part of what put us in this mess. It needs to stop being the default solution. Is the internet so vital that we should continue the practices that put us in the environmental mess we find ourselves in currently?

Fossil fuel consumption is absolutely an issue that needs to be addressed, I am saying we need to be watchful of new waste and wasteful practices. I don't want my grandchildren asking me why we let them poison the sky.

I wish I knew how to properly express my concerns. I live in a state whose fish are poisoned with mercury from the logging industry. There are areas where landfills poisoned the ground. Whole towns smell like rotten eggs because the mills have poisoned the air and water. Everyone let it happen because other issues seemed more pressing. Now the mills are dead or dying, the landfills are leaking, and those responsible are long gone or already rich enough to not care. We are losing trees to invasive species and diseases because folks and companies have more pressing issues.

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veerKg_CSS_Geologist t1_j9t2rv1 wrote

Why not both?

Otherwise all you’ve done is stand still (say the pollution reduced by shutting down a single coal plant is negated by the pollution from all the satellites).

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Minionmemesaregood t1_j9sxa3p wrote

Do satellites really have that much of an impact where they could potentially cool down the earth?

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Alphageds24 t1_j9thcra wrote

MIT did a study Study: Reflecting sunlight to cool the planet will cause other global changes

But it talks about aerosols in the air. So maybe burning them up the aluminum particles would be reflective aerosols?

A satellite reflecting sun back into space is probably very small amount of change, but with 30k maybe it adds up, I don't know.

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Monkfich t1_j9swy5k wrote

I’ve seen estimates of an average of 100 tonnes per day of meteorites and space dust entering earth’s atmosphere every day, and if we add on avg ca 28 tonnes more per day for the satellites, it doesn’t significantly change mass.

Like the other commenters though, a range of other factors needs to be considered.

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PastGround7893 t1_j9tgrnh wrote

I don’t know much about metallic particle interaction, but I think it would be important to understand how aluminum interacts with Chlorine and copper piping/pvc piping because that’s where it will inevitably end up, making sure we understand how that affects the life span of copper piping particularly so we understand how much we affect our plans for infrastructure. It will undoubtedly shorten the life span of water infrastructure after enough enters water sources that are used for supplying homes/businesses with water. Not to mention the upkeep on the water plants before it enters main lines that will of course take more of a beating.

I don’t know the answers to that, let alone what kind of effects this has on an ecosystem, but I do know adding 28% to anything does indeed significantly change it.

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j4ckbauer t1_j9sxaw5 wrote

> we will have no effective way of shutting off the rain of Starlink satellites

To this point, if we wanted to stop the 'starlink rain': The satellites have small ion engines that are used to enter and maintain the correct low earth orbit. Depending on available fuel, it may be possible to raise them into a significantly higher orbit. (This might end their usefulness as Starlink). At a high enough orbit, objects take decades or longer to return.

Maybe someone knows the typical delta-V these things have and how much is needed to raise an object to a typical 'graveyard orbit'.

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MorRobots t1_j9shia0 wrote

How much silicate dust and aluminum oxide do you think the worlds volcanos spews into the upper atmosphere every year? Now ask yourself, if that number is larger or smaller than 29 tons a day and by how many orders of magnitude. I have a feeling you will find the the environmental impact will be ever slightly higher then a butterfly flapping it's wings in china in an effort to cause a hurricane in the Atlantic.

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politeeks t1_j9tdwn5 wrote

In the context of global warming, it is an absolutely irrelevant amount of "environment impact". Especially given the usefulness of global Internet coverage, I don't think this is something we should be bitter about.

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[deleted] t1_j9p2a7v wrote

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NotAnotherNekopan t1_j9pl5rl wrote

No sources...

Also, there's considerations here to be made about what is going up. It's not just generic particulate matter, but more exotic materials in the upper atmosphere. There's simply no precedence for what that might do.

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15_Redstones t1_j9sutzh wrote

Exotic?

The structure of the satellite is mostly aluminum, and the solar panels are mostly silicon. Burning them in reentry forms compounds with oxygen.

Those are the three most common elements on the planet. Aluminum-Silicon-Oxygen compounds make up more than 60% of the Earth's crust. Add water and you basically have common clay.

There isn't a single combination of elements that's less exotic.

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