There Might Be A Limit on How Many Satellites We Can Launch

There are now well over 10,000 satellites in orbit around the Earth. And this is a huge number from what we had before. I recall when you could count in the couple of thousand and now here we are. And this number is accelerating. Not just what's happening with SpaceX and their Starlink constellation, but there are other constellations from other companies, other countries. China's putting out their constellations. It is not unreasonable to expect that there will be tens of thousands if not hundreds of thousands of satellites. And then when you put on top of that the potential for these data satellites which could be sent to space as well. SpaceX has asked to launch a million satellites. Like there's potential for a lot of satellites and there are a lot of concerns with that many satellites in space. You've got, of course, the possibilities of debris and collisions, and this could create additional risks and hazards for future missions that are going to be in that area. One of the real benefits of having satellites be at low orbit is that this is very self-cleaning. These things will burn up in the Earth's atmosphere relatively quickly and tidy themselves up. You don't get a lot of debris making it all the way down to the surface. you just get this stuff aerosolizing and disappearing. Well, uh, according to my guest today, uh, not exactly disappearing. There's the potential for harm to the atmosphere. My guest is Professor Laura Rall. She is at the department of atmospheric chemistry at the University of Canterbury and she and her colleagues are atmospheric modelers. So they are looking at the consequences, the chemistry of injections of large amounts of the kinds of particulate that come from satellites going into the upper atmosphere into the stratosphere and what implications this could have for say the ozone layer that at our current rates the atmosphere can clean this up. But at higher and higher levels, if we had maybe 10 times as many launches, then we will no longer be able to clean out this material from the atmosphere compared to what we have today. And so this is something to keep an eye on for the future. So if you want sort of like just another thing to be aware of about the implications of our growing space industry, uh enjoy this interview. Laura, people are, I guess, just starting to realize that there is a sort of a previously unknown form of pollution caused by rocket launches, and that is these things coming back down to Earth. So, can you explain sort of what happens to a rocket or satellite as it re-enters the Earth's atmosphere? Yeah. So, um because it's typically frowned on to leave defunct satellites up in orbit. They're typically um undergo atmospheric demise um where they enter the atmosphere at high speed and then they ablate or burn up. Um some sometimes they don't we know that they don't fully burn up and that's when we see space junk hitting the ground as has I believe has many examples of that been identified in Canada. Um but then there's if the burnup happens properly then there's a substantial fraction that forms tiny particles you know smaller than the width of a human hair and the very smallest of those will be we can hang around in the atmosphere for several years just because they're so small that they're not going to fall back to the ground anytime quickly. Um and so in terms of thinking about you know what are the climate pollution effects like we are seeing this already from uh the from the small number of satellites that are already in orbit 15,000 active satellites or so. Um, there's been rare earth metals found in aerosol samples measured in the stratosphere that could have only got there from spacecraft or space junk re-entry. So, we are seeing this, but it's set to get much larger is if we start putting more and more um mega constellations up in space. And um sort of connecting that back to like through a climate change lens, people like me get concerned about aerosol in the hanging around in the stratosphere or the upper atmosphere because of its interactions with the ozone layer. Um so we definitely don't want depletion of the ozone layer to happen because we need that to shield us from UVB radiation. And then also um the climate effect. So aerosol will absorb and scatter radiation. So there's this worry that if we get enough aerosol from ablating space junk um accumulating that we could start to see impacts on the Earth's surface climate, which I think is pretty wild that we're now talking about satellite constellations that could be

big enough to have those effects. — Yeah. I mean, you said there was around 15,000 satellites. Uh, I did a video, I remember maybe 12 years ago or so, where the number was 2,300, I think, — and here we are a little over 10 years later, and now the numbers are accelerating. Starlink Cologne is hoping to put in 30 to 40,000. Uh, but then but now you're seeing new calls for up to a million satellites. Like there's a lot of satellites. Um, so I want to understand sort of from an atmospheric perspective, you know, you're putting particles into a layer of the atmosphere that they just never naturally find their way in there. How, and you mentioned that they can stick around for, you know, months if not years. If you just like stopped if we just stopped injecting you know burning up satellites immediately what would happen? — Uh I guess it would take about 3 to 5 years for the particles that are already there to be washed or removed out of the atmosphere. So the um the circulation in the upper atmosphere will transport them naturally over towards the polar regions where they will then descend downwards and I guess end up washing out or being snowed out. — Right. So, so it is sort of a it's a flow in and a flow out that there's like a certain rate that depending on how much damage you're willing to do to your environment. There's a certain rate that these things can come down that beyond which sort of starts to exceed the carrying capacity of the stratosphere. — Yes, that's right. Um and because it's such a new issue, um it's really taken us by surprise. is, you know, you said about the number of satellites, like the numbers are just taking off exponentially and um and doing so much faster than the science can keep up with quite frankly. We keep making estimates which are then rapidly out of date. Um there's still a lot of gaps in our data and a lot of things we don't really understand, for example, um how much of a satellite will burn up into the very smallest particles that hang around. Um there's you we don't u yeah there's there's many gaps in our understanding and um which I think is why it's so concerning when I look at the numbers of you know requested satellites to go into orbit. — Yeah. I reported on a story ear maybe about a year ago or so and people were looking at this same idea that you're talking about and maybe this is even your research. I'm not sure. um that they were estimating that based on that I mentioned that kind of flow in flow out that where we're at today it's fine but it is moving in the wrong direction and we'll get to this place like if we launch 10 times as many rockets as we do today then we are definitely crossing over into it now it's just going to start accumulating and these downstream effects are going to keep happening. Yes, we did do a study on that looking at a t-fold increase in rocket launches would harm the ozone layer. — Yeah. Um, you know, so we've seen really good progress in the last couple of decades on healing the ozone layer with the bans on CFCs that were put in place in the 1980s and '90s. Um but because rockets put gases and particullet directly into the stratosphere where the ozone layer resides um and some of the fuels can cause ozone depletion then at large numbers we will start to see ozone losses. And this was a point that came up in the 1990s. there was this concern of, you know, are we going to see these many ozone holes being occurring as rockets um ascend into space. The modeling done back then showed that it wasn't really a cause for concern just because the number of launches were so small, but that's that has changed now. We we're seeing very many large Yeah. launches planned and the um the rockets are just getting bigger and bigger, so requiring more fuel to get them up and um Yeah. And this unfortunately runs counter to like right now Europe and other nations are you know as part of the ISSA and international collaborations they're working on this sort of zero space junk policy where you have to have a methodology for deorbiting your satellite or your boosters things that you're firing up into orbit so that they're not going to cause a Kesler syndrome down the road. some kind of runway debris field. But now it looks like the methods of deorbiting them is going to be a problem as well. So like what's the solution? — I don't know. Um I mean in the recent filing to the FCC, SpaceX talked about

using a con combination of um atmospheric re-entry and then placing them on a heliocentric orbit. So an orbit away from the Earth. Um that would al require a lot of fuel to get them out of the Earth's gravity. Well, so it remains to be seen if it's even possible. But also the emissions associated with carrying that extra fuel would cause more damage to the ozone layer. Um so until the engineers come up with a really clever solution, I think we have to be much more strategic about actually how many satellites we we're launching. you know, do we really need these mega satellite constellations and orbital data centers? Do — do we have a sense of the of like how much worse these fuels are going into the stratosphere than because I mean let's say that we launch a few hundred rockets a year across the entire planet. There are tens of thousands of airline launches every single day. I mean it is a drop in the bucket comparatively but we're looking at dam we're looking at gases being deposited in place that airliners just can't put them. Do we have a sense of of how much that sort of load is magnified? — So the calculations I've seen on terms of like greenhouse gas warming and the carbon dioxide emissions um the airline emission the airline industry still dominates that hands down just because there's so many flights happening. Um the problem with this the launches in the stratosphere is um the composition of some of the fuels. So like vehicles that use solid rocket motor fuel um emit a combination of chemicals and gases that basically what you get in the stratosphere is chlorine, reactive chlorine. And we know that chlorine is released from CFC's and directly attacks ozone. So, it just seems kind of crazy to me that we're allowed to we're not allowed to emit it in CFC's anymore, but we can put it in fuels and directly emit it into the stratosphere. But I also know that solid rocket motor fuel isn't really one that's um — it's not being used in the bigger vehicles under development. So, — yeah, they're all essentially going towards methane at this point. — Yeah. Yeah. So then we get water vapor and black carbon um which the water vapor I guess that should be fine. It it does have a greenhouse effect um in the stratosphere. Um the black carbon is concerning in large enough quantities because that is also damaging towards ozone. It also heats the stratosphere. Um, you know, we were chatting a bit about nuclear winter before we started this call. — We'll get to that in a second, but yeah. — Yeah. So, it's black carbon that we really worry about in terms of um from massive fires and in terms of being able to cause a massive like nuclear winter um effect. — Right. — Yeah. So I mean again it's this weird balance to me that you know we are like clearly the people have found a business model with using internet satellites to be able to communicate um that there is you always got all of these balances. I mean do you launch satellites or do you build millions and millions of cell towers? what is the carbon dioxide emissions from building millions of cell towers to be able to provide internet to various corners of the world compared to uh what is the loss of the night sky for astronomers, right? Like the pros and cons just go on forever. — Um and I wonder and then as you think about these like if you don't have low orbiting satellites then you're going to need to have high orbiting satellites — so they don't reenter the atmosphere. Uh but then if they do interact with each other, you get debris fields. The debris never clears up because it is also flooding flying high above the — um so I mean are you're interacting with governments with various stakeholders. What kind of response are you finding? It it's it seems at the moment that I'm not sure there's a lot of recognition that this just the scales of launches that and satellites that planned will lead to global impacts. Um and so we keep saying this is something that probably needs global regulation. It definitely needs discussion. It needs research. Um and it feels like there's a been yeah there's um those making those decisions as from my perspective at least have been a bit slow on the uptake but again things just move so quickly so the million satellite application I think took a lot of people by surprise. — Yeah. Well I mean hopefully

the idea is crazy and it never works. You know, it's almost like you have to be sort of nervous if the idea actually pans out, right? Because if you go and look on the internet right now, everybody is just thinks it's a hilarious idea that the, you know, the people who are pitching putting data centers in space don't understand thermodynamics. But I've done reporting that says actually, you know, the people who are doing this have do understand thermodynamics. They are engineers and have ideas for this. And so it it's funny to me that you sort of get these this balance where people are like that's ridiculous. The idea will never and but yet if it does work then we have these environmental consequences and there doesn't seem to be a middle path which is just like let's treat the planet — carefully and move forward in a way that we are certain is sustainable. — Yes. Absolutely. And I don't know if there's been in-house work done to look at environmental consequences, but um it it's really challenging for us on the outside when we don't know fully what the satellites are made up of. We you know we just don't have critical data to help us infer the effects. Um, and so I I think there needs to be a much closer cooperation between industry and scientists to sit down and figure this out together and let's make that research, you know, the data publicly available so that we can all reassure ourselves that either something is not going to be a problem or that it is and then we get a discussion going. — So when you say make that data public, what are you looking for? Are you looking for the composition of the satellites themselves or are you looking for the observations? — Uh what sort of metal alloys are in them for example? How much you know we assume a reasonable proportion of them is aluminium and so that we think it'll burn up and form aluminina particles. So aluminium oxide um in the atmosphere. But uh there's a lot of guesswork that goes into that and then trying to figure out what the chemistry is going to be. So, so you don't feel confident that you have a complete enough picture even of what these satellites are made out of? That feels I mean it feels to me like there are enough people in the aerospace industry that could give you that breakdown. Is that not available? — It's um not available as I've seen for this for the new planned um SpaceX and um Yeah. Yeah. But for some of the older ones like the existing satellites and the existing kinds of telecommunication satellites and stuff, you know, the the materials that go into them. — Um so my colleagues who work on this have said that they they've struggled to find the exact data that they would need to infer what the burnup is um products are. So um I mean someone will know and but yeah again a sort of I know the atmospheric scientists are struggling to get the relevant information to put into models. Um so perhaps there needs to be some more cross field you know um discussion happening — and then what about those that observations of the upper atmospheric layers right this you know do we feel confident that we are observing that or is this just the calculations like we know when a satellite burns up and if it's made of these components then this is the particle load that's being injected into the atmosphere and then you can make the calculations from there. Are is there any like direct observations of these particles in the atmosphere? — No is the short answer. I think there are some missions planned subject to various work programs being approved to go ahead. Um it is unfortunately very difficult to do insitue sampling at these very high altitudes. So a lot of inferences have to be made. And then this is where things get really complicated with the chemistry that we don't really have a good handle on because we we're not atmospheric scientists aren't really concerned with the natural chemistry involving like natural aluminina sources because it's typically really small when you know the stuff coming in from meteorites. So we don't usually include this in our chemistry climate models. Um but yeah, I mean I've seen studies that make quite different like make assumptions about what we think could be occurring and even um just the particular type of clusters that form can lead to very significant effects on the on on the downstream changes that occur. So um I would say it's really an area that needs much further study so that we understand the burnup processes you know what altitudes are they coming in at um what's what is the size distribution of particles being formed what's the chemistry happening

and then you know that information can then be fed into climate models to make predictions about yeah the downstream impacts — and how would you want to gather that like I guess I can imagine. Ironically, satellites are able to monitor that from above. Uh, stratospheric balloons, you know, monitoring it in situ. Uh, as well as like observations from the ground during, you know, trying to sort of detect the chemicals, you know, the spectra of this of the chemicals in the atmosphere. — Um, so you're talking to a modeler here. So, um, right. There will be ways and means to do it. Um I think in all of those options that you said are possible. Um possibly groundbased is potentially a bit tricky with the altitudes that we're talking about. Um yeah likewise with you know there's there've been a few aircraft campaigns in the stratosphere. it is a bit harder to fly much higher than that unfortunately and we would need quite high altitude um observations say around 60 km or so it's just a very tricky area of the atmosphere to sample — but the I guess so then as a modeler the heart of your argument is that we know roughly this amount of these chemicals are being injected into the stratosphere we know the chemistry and we can sort of calculate how much of the ozone layer is depleted based on those chemicals. And we've learned a ton from the CFC's and what they did to the ozone layer from the 80s onward. — Yeah, pretty much. If you're looking at a really large forcing of satellites coming into the atmosphere each year, then the numbers um we might know precisely what they're going to do. We just know that it's going to be enough, you know, submicron satellite particles that it will for sure do something, — right? the but you mentioned, you know, the micromediates. I mean, there's 100 tons of micromedorates and various debris hitting the Earth's atmosphere every day, right? Um, but whatever 15% of those are metal, the rest of it is rock. Um, those metals, it's how much of them are actually vaporizing, surviving and raining down. You know, we have metal meteorites on our roofs that we can go and collect. So, I wonder how that compares because this is a process been going on forever. It hasn't affected the ozone layer. — Uh, yeah. Um, that's it's a pretty it it's it's a pretty small compared to the levels that we would start to see if the planned satellite constellations go ahead. Um, so it's yeah, as you say, it's been going on forever. There is some chemistry that happens a little bit above where the bulk of the ozone layer sits involving the metals and that come in from those meteorites. Um but not in quantities large enough obviously that we because we don't see massive ozone depletion from micromedorites. Um but now that the flux of anthropogenic um aluminina coming into the atmosphere, so from human sources is uh I think it was a paper came out earlier this year, it's like it now exceeds the natural influx. — Wow. — That's kind of amazing when like I said 100 tons a day and yet we are now producing we are injecting more aluminum into the stratosphere than the universe — Yeah. Yeah. It is. It's incredible and it's happened so quickly. — Yeah. And we're just at the beginning of this. I mean, again, uh a mere few hundred launches a year. Imagine when we get to 700, a thousand. That's then the numbers start to really add up. — Yeah, it is concerning, — right? Yeah. Yeah. It's like another one of these situations where it's just like a little planning would be great, please. Yeah. Um so I'd like to shift gears then and talk about your work on possible nuclear wars. Um how what does that do to our atmosphere? — Well, let's we will hopefully never — Yeah, let's never find out. Um yeah so the concern um from an atmospheric chemistry or particularly the upper atmosphere so the stratosphere is uh that the in smoke from massive fires gets entrained into the stratosphere um and where it then gets spread around the world by just the natural stratospheric circulation. We call that the Brewer Dobson circulation. Um, we would assume that a lot of that would be black carbon aerosol. So, say soot

particles and soot's very good at absorbing sunlight. So, that means that basically you get this layer of soot blanketing the earth. It's blocking sunlight and leading to global cooling at the surface. So, um yeah, and that that is the nuclear winter hypothesis. So, as a result, it becomes too cold to grow crops. your shipping lanes freeze over, supply chains shut down, um mass starvation occurs. Uh it's a horrifying prospect. — Do we have a sense of like from my understanding it doesn't take a lot to start that to start that cycle? — Indeed. So there's a lot of literature looking at um a like a hypothetical regional so-called regional nuclear war between India and Pakistan where they assume that around 5 teroggrams of soot gets entrained into the lower atmosphere. Um so there's many papers published on this that have come out over the last uh 20 odd years. Um, so that's and that's equivalent to around I believe around about 100 Hiroshima sized bombs going off. Um, — which is one what 150th the world stockpiles like. — Yeah, there's Yeah, it's um fairly small I believe relative to the Yeah. So there are also much larger scenarios that are modeled um that assume around like 95% of the stockpile getting used which lead to much more drastic effects. But it is concerning that even like a moderate nuclear war could lead to nuclear winter which is shown in these papers. Um so for so 5 teroggrams of black carbon getting into the stratosphere. So that's 5 billion kilograms. Um uh yeah and then then recent studies have started to look at well that's only the black carbon but actually modern cities contain a lot of like novel materials involving plastics. Plastics have um hogens in them so chlorine and bromine. So there was a really interesting study that came out just at the end of last year where they looked at the possible hogen release from a lot of plastic incineration and showing that leads to ozone holes over the Arctic. So um yeah that I mean the stratosphere is such a fragile environment and we need to be so careful about what we place in there because it it doesn't get removed quickly. It is long lived over several years and it does have global climatic consequences. — Now I live in Canada and we've had some really bad forest fires for the last couple of years. A lot — and it just felt like the whole country was burning for a while there. — It's awful. — Yeah. Um what how does that compare? I can sort of I can imagine tons and tons of gigantic fires across Canada raging for weeks pumping huge plumes of smoke into the atmosphere. There had to have been consequences. Is it the same kind of like black carbon? — Yeah, it would be a mixture of black carbon and also organic carbon. Um and uh I could look up for you the numbers. — No. of but I don't have them into my head. Sorry. — I mean we didn't have a nuclear winter or I don't know a fire a forest fire winter so it wasn't that much would — be relatively small. Same with the Australian bush fires that we saw um devastating fires down here in 2019 2020 um in my part of the world. — Uh yeah huge amounts of smoke going in the stratosphere which did lead to regional ozone losses in the year that followed. Um but not on not on the scale that is simulated in the nuclear war studies. — Mhm. Yeah. Right. So war bad. — I think that's — Yeah. Yeah. Let's not do that. Yeah. — Um so a question I always ask my guests, what are you obsessed with right now? — Oh gosh. Um, I am I'm really interested in how the rocket launch industry and satellite pollution could affect the upper atmosphere. I think it's going to be a fascinating new era for the science scientists to work on the stratosphere. Um, I'm also really interested in microplastics in the atmosphere because we've started finding them uh over the last decade and in like just about everywhere we look. So, I'm really interested in where we find them and how they're transported around the atmosphere and if they have any implications for um climate change as a novel source of aerosol. — H do we have a sense of the I don't know the what effect you know is microplastics a greenhouse gas? not a

greenhouse gas, but as a source of aerosol, they they have that ability to absorb and scatter light, right? The same as black carbon aerosol, the same as um the submicron aluminina from ablating satellites. So, yeah, my group actually published a paper about 5 years ago showing that they could have a very minor climate forcing. So, but we've recently been updating our estimates with um better data that's emerged based on the different colors of plastics that we find and where we find them. Uh so that that is that research is currently out for review. So I can't comment on that too much, but um yeah. And then there's other people in my research community are concerned about well some types of aerosol can form clouds. So could microplastics also form clouds? And so there's just a lot of really interesting questions to unpick there because microplastics are also one of those things that like satellites that they're not going to go away anytime soon. — Yeah. I mean I know that like for example we had the shipping that was happening and they changed the fuels that the ships were using was it so they were putting out less was it sulfur dioxide? I forget exactly what it was but — and that in fact it turns out that those had been suppressing temperature rises in the ocean where the shipping lanes were. And then once that was resolved, then suddenly the temperature bounces back. And so you as I guess as you look at this stuff and you sort of see some of it is going to raise temperatures, others are going to suppress temperatures, some things are going to do things to the ozone layer at upper levels, other things. And it it feels like almost like unintentional geoengineering at this point where we're just running these random experiments without any care. — Yeah. We're great as a species at just inventing new things and using them and then finding out years or decades later that actually they were releasing part particles or chemicals into the environment which tend to matter. Um, so I feel like the environmental scientists are always playing catchup on trying to figure out what's in our environment and what is it doing. — And even in this what we talked about for most of this episode, right, that you we're in this kind of nent stage of understanding particulates are being injected by re-entering uh satellites. That is brand new and — we don't know — the consequences. And yeah, and you know, you have to tell your environmental colleagues, uh, surprise, here's something new to think about. — Yeah. And I think the really concerning thing is that the effects could be really big. You know, we don't know what's techn technologically possible in terms of putting them all up there, but they could be really big. And yet there's no kind of like global regulation or conversation about um because the stratosphere just sort of although the area at which these launches happen and the satellites reenter it falls outside any legislation. So it's um you know there's the Montreal protocol for protecting the ozone layer but that doesn't include anything related to rocket launches or satellite pollution in its current form. Um the environmental impact statements that the launch operators are required to look at, you know, to do with things like your local air pollution, um any impact on national parks, you know, if you're operating in those or or those sorts of statements. So very much focused on the local effects. And then um there's just sort of this regulatory gap where everyone goes, well, it's kind of not my problem to care about what happens in the stratosphere, but actually we should all care because it affects all of us. — Yeah. I mean, it is just once again this kind of shared space — that we have to be able to navigate. And in many other places, we have so much experience with this now. We have shipping lanes for boats. We have lanes that air travel takes. And we probably need that same kind of world agreement on, you know, we're deriving incredible value from satellite constellations, just from satellites, earth observation, communication, weather forecasting, all of that. What's the best way to organize these and let's work together to follow that plan as opposed to absolutely — every everyone for themselves, which is where we're at right now. And we know how that works out in the end. — Yeah. I 100% agree with you that we do need to be having a global discussion about this. — Yeah. Interesting. Well, thank you so much for your time and good luck with your research. Good luck getting that uh that balloon mission and that satellite that will help you observe satellites. — It's been great chatting to you today. — Thanks a lot. I hope you enjoyed this interview. Now I'm going to give you some final thoughts, but first I'd like to thank our patrons. Thanks to Abe Kingston, Andrea Padretti, Barely Griffin, Brian Bod, Carwin, Chuck Hawkins, Commander Block, Cooperelli, Darkfinger, David Gilton, and David Mats, Evanpro, Greg Phy, James Clark

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