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...
>0.01% of anthropogenic ozone depletion
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...
> "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").
The importance of this distinction is even 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.
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.
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...
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.
Better than gates' effort to eradicate malaria?
Sorry to be snarky, but to me Starlink is something rich people in rural England have, because it's slightly easier than paying OpenReach to connect them to proper network. And it's hard to imagine anyone else being their clients, at the prices that they charge.
That claim does not exclude Gate’s projects or any other as being superior. You’re looking for conflict that isn’t there.
Starlink is used all over the world, by regional governments, NGOs and companies where it’s too expensive for individuals.
You might well find that rich English people are subsidizing the project for poorer people elsewhere.
Not to diminish Gates’ malaria efforts, but remote villages having access to information about malaria and prevention methods could be helpful. Along with techniques for filtering water, etc. Access to telehealth.
Yeah, so our perspectives may differ a bit. My personal focus has primarily been with Africa, where Starlink is truly transformative. Demand for Starlink may be underwhelming in developed countries (such as your "rural England" example), while in underdeveloped countries, the demand regularly outstrips the supply [0]. I love that it's affordable enough for my African colleagues to use. In the last couple of weeks, I've had more than one full-motion screen-sharing video call to northern Nigeria (I.E., not the capital city) to do collaborative engineering. Even just a handful of years ago, this would not have been possible before Starlink was available.
I'm not casting any shade on malaria eradication -- that is awesome as well. I can love both things, but the subject here is Starlink, and I want to underscore how truly impressive and effective Starlink has been for advancing infrastructure in a quantum leap.
Improving African infrastructure has been an extremely difficult problem for a very long time (for a quagmire of reasons -- regulatory, power, cost, distribution, etc etc etc). I think most people in the developed world simply don't understand how challenging it is to live day-to-day without solid and reliable infrastructure, or how effective Starlink has been in improving that. Very few other projects have been THIS successful at THIS scale. I think more people should be aware of the good that it does.
It has been a disruptive technology in so many of the best ways.
https://www.reuters.com/investigations/musk-ordered-shutdown...
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...
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.
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).
Certainly less dangerous than something "going the wrong way" in a given orbital shell, but not sure if it's completely negligible either.
But almost all the debris will either stay close to the original orbit or burn up within hours.
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.
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?
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?
> 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.
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.
How are you so sure, when scientist have been debating this for decades?
> Got it, altitude.
Quibbling isn't an argument.
They have been. That's what I'm basing my arguments on.
You've been mentioning a ca. 70,000-bird limit. I think that comes from Bongers & Torres [1]. Their paper runs LEGEND (LEO-to-GEO Environment Debris Model). It does not distinguish between LEO and GEO. That's material because the natural decay period for an object in LEO is on the order of months to years, for LEO, to decades to centuries, for GEO.
Kessler in GEO? Real problem. If you wanted to be a space terrorist, you could probably engineer a cascade today that would make large sections of GEO unusuable for decades if not centuries. The point is that isn't possible for LEO, where you may make a mess in a few orbits for a few years at best.
> Quibbling isn't an argument
Sorry, wasn't quibbling. I genuinely couldn't tell what you meant by "highest level." (I was picturing a food chain, where big clouds of debris "eat" smaller satellites in their way.)
[1] https://www.sciencedirect.com/science/article/pii/S092180092...
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?
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.
You're not wiping out LEO, but a particular LEO.
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.
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.
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.
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.
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.
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...
Space isn't infinite in the same way that 64 bit integers aren't infinite. Both are infinite for typical usecases.
Sure they can: Leading/trailing each other is quite common. Intersecting orbits are riskier, but also possible without inevitable collisions.
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.
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.
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.
Another 500 km won't affect latency much. It'll be around 3 more ms per round trip.
(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.)
LEO maxes out ~ 1,200 miles radius, geostationary is at little over over 22,000 miles radius.
I will again note that if Saber Tooth tigers had put things in the orbits we have, it would still be our problem.
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.)
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.
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.
Starship is the moat SpaceX needs to be developing today to stay ahead of where the Chinese competition will be in 5-10 years.
SpaceX has loads of international launch and connectivity customers. China undercutting SpaceX would significantly compromise its prospects.
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...