[JumpCrisscross]

> Soon, McDowell told us, there will be up to 5 satellite reentries per day

Starlink’s next-generation V3s, which will require Starship to launch, weigh in around 2 metric tonnes [1]. (They’re currently “around 260 and 310 kilograms” [2].)

“Every day, Earth is bombarded with more than 100 tons [91 metric tons] of dust and sand-sized particles” [3]. So we’re talking about a 2 to 10% increase in burn-up by mass. (Not accounting for energy, which natural burn-up has more of, or incomplete burn-up, which reduces the atmospheric effects of artificial mass.)

Broadly speaking, we don’t seem to be in a problematic place in respect of the atmosphere. Where improvement may be required is in moving from splashdown, where we sink space junk in the ocean, to targeted recovery.

[1] https://starlink-stories.cdn.prismic.io/starlink-stories/Z3Q...

[2] https://www.teslarati.com/spacex-elon-musk-next-gen-starlink...

[3] https://www.nasa.gov/solar-system/asteroids/asteroid-fast-fa...

[ogig]

I hear 10% increase on a global constant and that doesn't sound like peanuts. If we increase 10% each few years that might be a problem? I don't know anything about whatever field studies this but given that LEO constellations born yesterday even that 2% increase in stuff coming from the skyes sounds significant to me.

[JumpCrisscross]

Short answer is we're still theorizing. Models suggest we might see accumulation. But we might not, or it might not accumulate at relevant altitudes. (Current LEO satellites burn up before hitting the ozone layer.)

[SecretDreams]

The same could have been said about pollution from the industrial revolution compounding and hurting the atmosphere, but that never played out, right???

[shizcakes]

edit: okay I misunderstood what everyone meant

[lxgr]

> please recall that the mass of de-orbiting man-made satellites came from the earth in the first place.

Then again, so are CFCs, CO2, radioactive materials...

Just because some elements naturally occur on Earth doesn't mean we're completely insensitive to where they end up. (That said, I have no idea if atmospheric Aluminium is actually a problem or not.)

[VBprogrammer]

I was watching a video the other day which happened to mention that sodium lasers are used to create artificial stars, used for calibration of adaptive optics in ground based telescopes. This works because one particular layer of the upper atmosphere is rich in sodium due to impact with sodium rich debris.

Obviously it requires a more scientific analysis but it does seem to me that burning a lot of shit on the atmosphere might be problematic.

[organsnyder]

I don't see anyone worrying about planetary mass. I'd be more concerned about atmospheric effects.

[palata]

Is that what you say when you litter? "I don't see a problem with plastic in the ocean, it came from the Earth in the first place".

[dylan604]

Is that really what people are concerned about though?

[Y-bar]

Asking from a place of ignorance on my part, but does the chemical composition of the satellites versus asteroids/dust have any adverse effects?

[perihelions]

It's postulated that the high aluminum content of satellites (for perspective, Bennu samples are only 1% Al), as oxidized Al2O3 particles in the stratosphere, catalyze chemistry that destroys ozone. But that's far from a quantitatively meaningful problem, at the current scale.

This source[0] says satellite reentries are about about 12% of the space industry's contribution to ozone depletion (the big one is chlorine from solid rockets), which in turn is 0.1% of the entire anthropogenic contribution; i.e. satellite reentries are ~0.01% of the total.

https://www.space.com/spacex-starlink-reentry-pollution-dama...

[schiffern]

  >0.01% of anthropogenic ozone depletion

The sheer percentage increase in stratospheric AlO is still alarming.[0]

Satellite reentries in 2022 (ie mostly pre-megaconstellation) were already raising stratospheric AlO levels by 29.5% above normal levels (with satellites adding 'only' 17 t/year), but megaconstellations could raise that to ~480% above natural levels (360 t/year).

This isn't a rounding error, it's a non-trivial change in chemical composition across the entire globe, and effecting a complex and poorly-understood part of the climate system. What could go wrong?

What else can this effect (as usual, discovered belatedly) beyond ozone? Hopefully it's nothing! But I guess we're gonna find out...

[0] https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL10...

[perihelions]

That's still much less than the aluminum from solid rockets, which have been ongoing since the 1970's. Per your own link,

> "In situ measurements showed evidence of a 1,000% increase in stratospheric aluminum levels from 1976 to 1984 (Zolensky et al., 1989), which was associated with the emission of hundreds of tons of such particles from solid rocket motors (SRM) during atmospheric ascent (Brady et al., 1994)"

If you follow Brady et al. (1994)[0], you'll read that every Space Shuttle launch (Table 1) deposited 112 tons of Al2O3 into the stratosphere (>15 km).

[0] https://apps.dtic.mil/sti/pdfs/ADA289852.pdf

This isn't a new phenomenon at all; in fact the peak alumina pollution from in the past (112 tons per STS launch) exceeds the worst-case future estimates from academic research (360 tons per year from satellite reentries).

(/meta Coincidentally, I once linked that exact Brady paper on HN, three years ago[1]. Actually, long before the current social media fad for being concerned about satellites. At the time I wrote, and this has truly aged well, "No one ever gave a shit").

[1] https://news.ycombinator.com/item?id=34812863

[schiffern]

As I understand it, the concern is not just AlO but specifically nanoparticles with high reaction surface area and long lofting lifespans.

The importance of this distinction is acknowledged in Brady et al (1994):

  >The exact chemical nature, as well as size distribution (and total surface area) of particles formed in rocket exhaust in the stratosphere is currently unknown. Preliminary experiments at Aerospace by L. R. Martin indicate that plausible particle compositions give highly variable rates of direct ozone destruction.

The 17 t/year and 360 t/year figures are specifically for AlO nanoparticles (formed by hypersonic ablation), whereas Brady et al gives numbers for all AlO particles, regardless of size.

Nice username btw.

[JumpCrisscross]

> Satellite reentries in 2022 (mostly pre-megaconstellation) were already raising stratospheric AlO levels by 29.5% above normal levels

Those findings are simulated, not observed. Hence "potential."

> it's a non-trivial change in chemical composition over the entire globe, and effecting a complex and poorly-understood part of the climate system. What could go wrong?

Perhaps a lot. Perhaps not much. It's a good question to study. But if this is an issue, it's solvable--carbon composite satellite structures could use a boost in demand and funding.

[schiffern]

Interesting. Incidentally SpaceX is probably the most likely to preemptively adopt those measures.

Of all the megaconstellations, SpaceX has historically been the best at being a "good neighbor," with low orbits for debris and lots of engineering to reduce brightness.[0] But hype around SpaceX gives the real bad actors a pass, for example AST is much worse on brightness,[1] and OneWeb and Qianfan are much worse on debris risk.[2]

[0] https://www.youtube.com/watch?v=MNc5yCYth5E&t=1717s

[1] https://spacenews.com/astronomers-raise-interference-concern...

[2] https://spacenews.com/chinas-megaconstellation-launches-coul...

[tehjoker]

i still don’t understand why we need huge constellations of satellites at all

[HanClinto]

Because providing infrastructure to remote regions is incredibly difficult through other mechanisms. I don't believe it's hyperbole to say that -- for the goal of improving infrastructure access in some of the most remote and challenging places in the world -- Starlink in particular is one of the most successful pro-humanitarian engineering projects that I can think of in maybe the last 20 years.

Starlink is easily one of my favorite engineering projects. I don't believe anybody has done it cheaper, better, or at wider scale than Starlink has.

[Tuna-Fish]

Because it's a way to provide communications from space with acceptable total throughput and latency.

[svmt]

Bloomberg ran a piece about this in March: https://www.bloomberg.com/graphics/2025-space-orbit-satellit...

[SoftTalker]

The satellites are mostly metal and silicon I would guess, not too different from asteroids.

[cubefox]

I guess we can just read the article:

> The researchers found particles containing the rare elements niobium and hafnium. They also found a significant number of particles contained copper, lithium and aluminum at concentrations far exceeding the abundance found in space dust.

[bwestergard]

If someone has the time, I'd love to see the total amount of lead added to the atmosphere by burning up satellites compared to the amount from other anthropogenic sources.

[adastra22]

Rough napkin math would be negligible impact. The amount of lead in a satellite is very small, if not actually zero. The amount of lead added by burning coal is about 30 tonnes per day.

[everforward]

There is almost definitely a small, negligible amount of lead in the solder in them. Eg NASA requires a small (single digit I think) percentage of lead to prevent tin whiskering.

[JumpCrisscross]

> almost definitely a small, negligible amount of lead in the solder in them

Emphasis on negligible. Assuming 0.07 to 0.28 ppm lead [1] in meteoroids, space is dosing us with half to 2 kg a year [2].

[1] https://www.sciencedirect.com/science/article/abs/pii/001670...

[2] https://earthsky.org/space/tons-of-extraterrestrial-dust-fal...

[benjiro]

> (They’re currently “around 260 and 310 kilograms” [2].)

v1.5 is like 300kg, the v2.0 mini (ironic as its far from mini compared to its predecessors) are 800kg.

The V3's are the one's that need StarShip to deploy. But the current launch platform can take 21x v2.0 Mini's per launch vs the 60x v1.5's they did before.

Taking in account that the v2.0 Mini's are way more capably on a kg/capacity. And the tech keeps getting better. SpaceX does not really need Starship, that is more or less a bonus at this point.

[perihelions]

> "SpaceX does not really need Starship, that is more or less a bonus at this point."

Starship is the moat SpaceX needs to be developing today to stay ahead of where the Chinese competition will be in 5-10 years.

[skatingaway]

Moats are for direct competition. China is not a competitor to spacex because the US government is spacex’s largest subsidy/customer. Put another way: nasa won’t be using Chinese rockets. Unless they bribe trump. Which could happen.

[marcus_holmes]

NASA ended up using Russian rockets because the Space Shuttle program got politically awkward. There is definitely a world where they'd use Chinese rockets.

[JumpCrisscross]

> China is not a competitor to spacex because the US government is spacex’s largest subsidy/customer

SpaceX has loads of international launch and connectivity customers. China undercutting SpaceX would significantly compromise its prospects.

[wat10000]

A 2-10% increase seems like a hell of a lot.

Human CO2 emissions are well under 10% of natural CO2 emissions, and yet that additional amount has been enough to increase the atmospheric concentration of CO2 by over 50% and substantially alter the planetary climate.

CO2 in the atmosphere is at a vastly larger scale than mass falling in from space, so that doesn't mean this is a problem, but that percentage certainly seems to indicate that the question should be studied further.

[matthewdgreen]

See the first comment in this thread about aluminum oxide and the ozone layer. It’s not so much the amount, but what it is.

[cowpig]

Why is a 2-10% increase a small amount? What increase would be too much?

[nicce]

There is a limit how much satellites LEO/GEO can hold unless every satellite has perfect dodging system. Called as Kessler syndrome [1], and one estimate is around 70k satellites. So it is a race who can get the most satellites orbiting, because after a certain point, there is no "space" anymore, and anyone who tries to launch after that point, will be blamed for destroying the satellites of the others. Winner takes all.

[1]: https://en.wikipedia.org/wiki/Kessler_syndrome

[ricardobeat]

That’s one single estimate, and the problem is much more nuanced.

For example, Starlink satellites orbit so low, that even if every single one of them collides and becomes dust, it will all decay and burn up in a matter of months, a couple years at most. The debris cannot physically move to higher orbits to affect other “normal” satellites, though it might impair launches.

Conversely, collisions at much higher geosynchronous orbits can’t possibly create a dense debris field as the total area is immense, deorbit will take millions of years, and everything is usually moving at the same speed (the synchronous part).

[SiempreViernes]

The debris that ends up with equal or lower orbital energy than one of the satellites started with doesn't move up, that is true.

But all the bits the bits that end up with more energy than the orbit the satellites were on obviously do move up, and some bits will move up very substantially as we know from Mission Shakti debris: debris from that event at 300 km got apoapsis of up to ~2200 km.

[nicce]

> For example, Starlink satellites orbit so low, that even if every single one of them collides and becomes dust, it will all decay and burn up in a matter of months, a couple years at most.

That is way too long. The threshold we are speaking of cannot allow any fragments, because they start chain reaction and destroy more satellites. And there is always one which is on the highest level. What if that gets destroyed?

[JumpCrisscross]

> threshold we are speaking of cannot allow any fragments, because they start chain reaction and destroy more satellites

Kessler cascades are localised to specific orbits. In low-earth orbit, they're a problem for a few years.

They're going to be annoying. But not catastrophic.

> there is always one which is on the highest level

Highest level?

[nicce]

> Kessler cascades are localised to specific orbits. In low-earth orbit, they're a problem for a few years.

> They're going to be annoying. But not catastrophic.

I think there is a misunderstanding about the whole term. If it is not a big problem, then it does not meet the definition. So there must be some threshold where they aren't problem. What is that threshold? Because certainly there isn't space for infinite amount of objects. Primary question is that whether that threshold matters on practice. If it is 70k, then it is certainly a problem, but who knows the exact number yet.

> Highest level?

There is always the one which is classified orbiting on the highest level in LEO. Also that object can get destroyed; which means it will start deorbiting and with a chance to hit some other object below.

[JumpCrisscross]

> What is that threshold?

Way beyond anything we can currently achieve with current and planned launch capacity or radio technology.

> that object can get destroyed; which means it will start deorbiting and with a chance to hit some other object below

Got it, altitude.

Yes, in theory. In practice, the odds of that happening are vanishingly low. If it did happen, the volumes we're talking about are still so big that you'd struggle to come up with a way to cause a third collision even if we remove satellites' abilities to marginally change their orbits.

[Dylan16807]

> If it is not a big problem, then it does not meet the definition.

It's still a big problem to wipe out low orbit, but it's not a long lasting one.

> What is that threshold? Because certainly there isn't space for infinite amount of objects.

Even if you crash a billion objects together at 300km, they're all going to go away in a few years. There is no threshold for semi-permanently ruining low orbit.

[lxgr]

Why would there be a single numeric threshold?

You can pack many, many satellites into the same orbit without any danger, for example – as long as they move in the same direction. Let's make it 1000 for this thought experiment.

On the other hand, just two moving in opposite directions are obviously going to crash.

So is the number of "safe satellites in all of LEO" 1000 or 1?

[bryanlarsen]

No it's not. Kessler simulations show those chain reactions happening over multiple decades.

[nicce]

It purely depends of the density of objects. The whole definition of the Kessler syndrome is about the estimation when the density is too much to handle.

[zevon]

Maybe this is helpful: https://aerospaceamerica.aiaa.org/features/understanding-the...

[sidewndr46]

I don't know the specifics of starlink satellites but a rupture of any pressurized line has a chance of causing an unintended ascent. Thankfully in most cases the satellite is stabilized, so there is a good chance the satellite just gets a huge amount of rotational velocity added to it with no increase in altitude.

[nradov]

You seem to have a misunderstanding of basic orbital mechanics. That wouldn't cause an "ascent" like with an airplane or something. There will be a change in orbital parameters but a permanent change in orbital altitude isn't really possible in that scenario.

[Dylan16807]

Whatever you do to launch an object higher, it will return to its original altitude once per orbit. If you want to stay high you first have to boost up and then you have to boost again half an hour later, which will happen just about never with debris.

[lxgr]

You'd still have an eccentric orbit intersecting some "higher" ones periodically, no?

Certainly less dangerous than something "going the wrong way" in a given orbital shell, but not sure if it's completely negligible either.

[Dylan16807]

For the lucky few pieces that launch at just the right angle, they'll spend a few months or years intermittently intersecting higher orbits.

But almost all the debris will either stay close to the original orbit or burn up within hours.

[observationist]

It's a mass problem. Instead of imagining the gravity well as something moving away from earth out into the vacuum of space, think of it as a ball that needs to be rolled uphill - even if you give it a huge burst of energy, it's not going to go as far as you think from that one big push, and it's still going to roll back downhill. In order to make it out of the gravity well, you need a lot of focused, continuous energy over huge distances.

There are other factors, too - imagine you're trying to send a penny around the entire equator of the earth, and think of the largest possible explosion you could subject it to without vaporizing it. A stick of dynamite could launch a penny only around a half mile's distance around the equator, assuming ideal conditions, which is about .0025% of the circumference of the earth, which is 10% of the distance between the earth and the moon, and the moon is about 25% of the distance from which earth's gravity stops being a significant factor.

If you carefully deployed a large number of well timed series of dynamite sticks precisely located so that each blew up perfectly beneath the penny at its apex following each previous explosion - you'd need 150-300 sticks to get the penny out past the edge of the effective gravitational well, the point at which other factors in the solar system have the dominant influence - it'd effectively leave earth and start falling toward the sun. At any point closer to earth than that, it will slowly and inexorably return back to earth, reaching up to 25,000 mph before vaporizing itself in the atmosphere (if it fell from the outer edge). If you had no atmosphere, a clear shot, and the "ideal" penny cannon to launch it, you could hypothetically reach escape velocity with only a quarter stick of dynamite.

Incidental bursts of gas, or even outright exploding objects in space are not going to launch a bunch of stuff into much deeper orbit. There's a constant downward pull, and gas and dust creating drag and downward acceleration the closer in you get, and just vast, incomprehensible distances to travel under the influences of gravity. Getting things to go faster than 25,000mph, or reaching escape velocity, without vaporizing the thing you're trying to make go fast, requires as big a continuous explosion as you can make over as long a time period as possible.

I love that AI can whip up an xkcd style "What-If?" type scenario for these questions.

[peterfirefly]

Starlink's orbits are so low that everything deorbits automatically. The satellites need to actively work to stay up. That means no Kessler syndrome there.

How many you can fit depends on the available technology. It should eventually be a lot more than 70K just in those low orbits... and still leave plenty of space for rocket launches and returns to thread their way in between them.

[nicce]

> Starlink's orbits are so low that everything deorbits automatically.

It is enough if it goes one round around. They can make a cascading effect which can destroy tens of satellites at once, and few fragments are enough. And closer to earth you are, less space there is. They can't all orbit on exactly the same level. There is always one which is on slightly higher level.

[JumpCrisscross]

> closer to earth you are, less space there is

Humans are bad at intuiting exponents. There is roughly 200x more volume in LEO than there is between the ground and cruising altitude. Plane changes, moreover, take a lot of energy--you aren't going to get enough energy out of a collision to pollute nearby orbits.

[nicce]

> going to get enough energy out of a collision to pollute nearby orbits.

There is no infinite space. The problem is exactly defining the number objects when that "small" amount of energy is actually enough to cause problems.

[JumpCrisscross]

> There is no infinite space

Straw man.

> problem is exactly defining the number objects when that "small" amount of energy is actually enough to cause problems

The exercise, maybe. The problem? No. In LEO, which is where Starlink orbits, there is no known solution for causing a Kessler cascade that causes more than a few billion in damage. Space isn't infinite, but it's really big.

Again, a few hundred thousand planes land every day [1]. They operate in a volume less than 1% that of LEO. To approach the object densities where we start controlling an airspace, you'd need tens of millions of objects in LEO alone. We simply do not have--not have any roadmap to having--the sort of launch capacity required to keep 30 million objects in LEO at a time.

There are real problems with more Starlinks in space. Kessler cascades are not one of them.

[1] https://www.travelandleisure.com/airlines-airports/number-of...

[lxgr]

> They can't all orbit on exactly the same level.

Sure they can: Leading/trailing each other is quite common. Intersecting orbits are riskier, but also possible without inevitable collisions.

[dgs_sgd]

I’m just a layman, but why can’t they increase the orbital radius to solve this problem? Like, if the current “layer” is too full, have the new satellites orbit further out?

[JumpCrisscross]

> why can’t they increase the orbital radius to solve this problem?

Because there isn't a problem. LEO contains more than 200x the volume of commercial airspace.

We run out of spectrum and launch capacity well before Kessler cascades become a problem.

[4rt]

The reason starlink are so low in the first place is its cheaper to launch to that altitude, you need way less signal strength for devices to connect to them and the round-trip latency is vastly improved. They're intended to be essentially disposable, they're going for shorter lifetime and iterating on hardware improvements faster.

The further out you get, there's less atmospheric drag and each satellite is in view of the ground stations for longer but the cost of launch is higher and latency becomes a big issue. People expect 50ms latency for internet access not 500ms.

[01HNNWZ0MV43FF]

WP says Low Earth Orbit is popular because it's cheap to get stuff there, the latency is low (speed of light starts to matter when you're a couple Earth diameters up) and bandwidth to the ground is high (I assume it's harder to send a signal a longer distance, even through vacuum)

https://en.wikipedia.org/wiki/Low_Earth_orbit see "Use"

[tejtm]

Automatic EOL (end of life) deorbiting is a feature not a bug.

I will again note that if Saber Tooth tigers had put things in the orbits we have, it would still be our problem.

[parl_match]

very simple explanation but there's a few issues

radio bandwidth: higher frequencies travel a shorter distance and provide more bandwidth. so you get frequency contention and also you need your sats to be physically closer

latency: the further a sat is, the higher the latency. not an issue for text messages. a huge issue for phone calls and general internet tasks. the further you "push" your sat "back", the worst the user experience is

there's other issues too, like geostationary vs geosynchronous and coverage and exposure.

[nemomarx]

Low orbit is how star link is able to achieve their connections, isn't it? I think of they moved to normal telecom orbit the performance would be like normal satellite internet too

[peterfirefly]

They originally planned to be about 1100km up. They are currently about 550km up. Plenty of possible layers in between...

Another 500 km won't affect latency much. It'll be around 3 more ms per round trip.

[nemomarx]

That's not a bad latency addition, you're right. Good note

[michaelmior]

Not with a geostationary orbit. That must have a fixed radius. The problem is that satellites have to move to counteract the force of gravity to avoid falling out of orbit. But if they move too much or too little, then the satellite moves with respect to the earth and the orbit is no longer geostationary.

(Caveat: Not an expert by any means, just someone who had a similar question and did some reading, so my answer may well be incomplete or not fully correct.)

[zwily]

Starlink satellites aren't geostationary.

[michaelmior]

The parent comment wasn't specifically addressing Starlink.

[tejtm]

This has already been addressed as LEO is not geostationary but to point as to why. Consider the earths equator rotates at a particular velocity so there is a particular orbital radius where the two cancel and NO energy is needed to fall around the equator at the same rate the equator is moving. That is a geostationary orbit.

LEO maxes out ~ 1,200 miles radius, geostationary is at little over over 22,000 miles radius.

[01HNNWZ0MV43FF]

A land grab. That might explain the desire to put anything in space, even something useless like mirrors to reflect sunlight