Chatbots vs. Ozone

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Back in February I posted The Kessler Syndrome, which also included a brief section mentioning the impacts of the proposed megaconstellations on the environment, specifically global warming from CO2 and black carbon, and depletion of the ozone layer. Three months earlier Anton Petrov had examined the last of these in Risk of Ozone Layer Destruction from Internet Satellite Swarms and Rocket Fuel. He has now followed up with SpaceX Is Conducting a Giant Chemical Experiment on Our Atmosphere Without Realizing. Below the fold I survey the papers Petrov cited and a few others.
The papers involved are, in date order, as follows together with extracts from their abstracts:

Impact of Rocket Launch and Space Debris Air Pollutant Emissions on Stratospheric Ozone and Global Climate by Robert Ryan et al (9^th June 2022):

Rockets, unlike other anthropogenic pollution sources, emit gaseous and solid chemicals directly into the upper atmosphere. We compile inventories of these chemicals from rocket launches in 2019 and projections of future growth and speculative space tourism activity. We incorporate these in a 3D atmospheric chemistry model to simulate the impact on climate and the protective stratospheric ozone layer. We find that loss of ozone due to current rockets is small, but that routine space tourism launches may undermine progress made by the Montreal Protocol in reversing ozone depletion in the Arctic springtime upper stratosphere. The BC (or soot) particles from rockets are also of great concern, as these are almost five hundred times more efficient at warming the atmosphere than all other sources of soot combined.

Note that even four years ago it was already clear that the space industry was both depleting ozone and aggravating global warming. But this was before the scale of the proposed mega constellations was evident.

Metals from spacecraft reentry in stratospheric aerosol particles by Daniel Murphy et al (7^th September 2023):

So far, models of spacecraft reentry have focused on understanding the hazard presented by objects that survive to the surface rather than on the fate of the metals that vaporize. Here, we show that metals that vaporized during spacecraft reentries can be clearly measured in stratospheric sulfuric acid particles. Over 20 elements from reentry were detected and were present in ratios consistent with alloys used in spacecraft. The mass of lithium, aluminum, copper, and lead from the reentry of spacecraft was found to exceed the cosmic dust influx of those metals. About 10% of stratospheric sulfuric acid particles larger than 120 nm in diameter contain aluminum and other elements from spacecraft reentry. Planned increases in the number of low earth orbit satellites within the next few decades could cause up to half of stratospheric sulfuric acid particles to contain metals from reentry.

Much of the reentry burn happens above the stratosphere, and it takes time for the aluminum nanoparticles to drift down to the levels where they were collected. So the 10% number represents pollution from an earlier period with fewer reentries that the 2020s. Murphy notes that:

Most of the meteoric mass is deposited at altitudes between 75 and 110 km by a very large number of sub-millimeter meteoroids. Reentering spacecraft, which are larger and moving more slowly, ablate between 40 and 70 km over a ~300 km long footprint

His samples were collected at 19km altitude.

Potential Ozone Depletion From Satellite Demise During Atmospheric Reentry in the Era of Mega-Constellations by José P. Ferreira et al (11^th June 2024):

This paper investigates the oxidation process of the satellite's aluminum content during atmospheric reentry utilizing atomic-scale molecular dynamics simulations. We find that the population of reentering satellites in 2022 caused a 29.5% increase of aluminum in the atmosphere above the natural level, resulting in around 17 metric tons of aluminum oxides injected into the mesosphere. The byproducts generated by the reentry of satellites in a future scenario where mega-constellations come to fruition can reach over 360 metric tons per year. As aluminum oxide nanoparticles may remain in the atmosphere for decades, they can cause significant ozone depletion.

Ferreira et al confirm the potentially long delay between reentry and the nanoparticles reaching the ozone layer and depleting it:

we find that these reentry byproducts may take up to 30 years to settle from the top of the mesosphere into the stratospheric ozone layer. Upon reaching an altitude of about 40 km, aluminum oxides catalyze chlorine activation which promotes ozone depletion. This suggests that concentrations of aluminum oxide compounds may start increasing in the mesosphere well before reaching the stratospheric ozone layer. This would introduce a noticeable delay between the beginning of the injection process when orbiting bodies are decommissioned and the eventual ozone-depletion consequences in the stratosphere.

Investigating the Potential Atmospheric Accumulation and Radiative Impact of the Coming Increase in Satellite Reentry Frequency by Christopher Maloney et al (21^st March 2025):

A lack of observations and validated models of reentry demise limits our ability to simulate the complex aerosols associated with reentry, which makes estimating the climate impacts difficult. Aluminum is a primary satellite component and will likely be emitted during reentry vaporization in the form of alumina. Unmodified alumina is a useful approximation for metallic reentry aerosol. In this study, we simulate a potential yearly emission of 10,000 metric tons of alumina from reentering space debris. We investigate how the location of atmospheric accumulation, aerosol size distribution, and radiative properties of reentry alumina impacts the middle atmosphere. We find that 20,000–40,000 metric tons of alumina accumulates at high latitudes between 10 and 30 km in both hemispheres. Small changes in mesospheric heating rates lead to 1.5-K temperature anomalies in the middle atmosphere at high latitudes. These temperature anomalies are accompanied by changes in wind speed in the polar vortex.

So there are thermal effects on the climate as well as the effects on the ozone layer.

Near-future rocket launches could slow ozone recovery by Laura Revell et al (9^th June 2025):

To understand if significant ozone losses could occur as the launch industry grows, we examine two scenarios. Our ‘ambitious’ scenario (2040 launches/year) yields a −0.29% depletion in annual-mean, near-global total column ozone in 2030. Antarctic springtime ozone decreases by 3.9%. Our ‘conservative’ scenario (884 launches/year) yields −0.17% annual, near-global depletion; current licensing rates suggest this scenario may be exceeded before 2030. Ozone losses are driven by the chlorine produced from solid rocket motor propellant, and black carbon which is emitted from most propellants. The ozone layer is slowly healing from the effects of CFCs, yet global-mean ozone abundances are still 2% lower than measured prior to the onset of CFC-induced ozone depletion. Our results demonstrate that ongoing and frequent rocket launches could delay ozone recovery. Action is needed now to ensure that future growth of the launch industry and ozone protection are mutually sustainable.

Note that this paper addresses only the ozone depletion from launches, not from reentry. But their 'ambitious' scenario of 5.6 launches/day is far short of Musk's ambitions, let alone the other planned megaconstellations. My understanding is that the 2040 launches/year in their scenario are of Falcon 9 class vehicles but "only 4.4% of launches are using vehicles designed for re-entry", which is implausible. But the mega-constellations can't be built or maintained with Falcon 9s.

Will Lockett is, as one should be, skeptical of Musk's claims. In Musk’s Orbital Data Centre Idea Is Getting More Stupid By The Day he analyzes the claimed "million satellite data center" assuming it is built, as Musk claims, with Starship but over 15 years, a longer timescale than Musk's:

To achieve that, they would need to launch 120,000 satellites per year. Over the 15 years, they would launch 1.8 million satellites, but 800,000 of them would fail (as part of our 9% failure rate), leaving a total operational fleet of one million satellites. This equates to 3,158 Starship launches per year, or nearly nine launches per day. For some context, the current launch rate for Starship is just five per year.
...
In order to keep a million satellites in the constellation, it needs to be maintained. So, each year, SpaceX would have to launch 90,000 AI Sat Minis to replace the roughly 9% of the constellation that failed. That equates to 2,368 Starship launches per year, or 6.4 per day.

That's 9 launches/day for 15 years then 6.4 launches/day indefinitely of a much rocket that is vastly bigger than Falcon 9 and is completely re-usable.

Of course, these claims are ridiculous - neither logistically nor economically feasible. But assuming Starship or a competitor such as Blue Origin does manage to create a reliable, reusable, 100 ton to LEO launch vehicle, there will be a lot more mass in LEO and a lot more of it reentering.

Measurement of a lithium plume from the uncontrolled re-entry of a Falcon 9 rocket by Robin Wing et al (19^th February 2026):

A 10-fold enhancement of lithium atoms was detected at 96 km altitude by a resonance lidar at Kühlungsborn, Germany, approximately 20 hours after the uncontrolled re-entry of a Falcon 9 upper stage. The upper-atmospheric extension of the ICON general circulation model, nudged to ECMWF, was used to calculate winds. Backwards trajectories, including wind variability as measured by radar, traced air masses to the Falcon 9 re-entry path at 100 km altitude, west of Ireland. This study presents the first measurement of upper-atmospheric pollution resulting from space debris re-entry and the first observational evidence that the ablation of space debris can be detected by ground-based lidar. The analysis of geomagnetic conditions, atmospheric dynamics, and ionospheric measurements supports the claim that the enhancement was not of natural origin. Our findings demonstrate that identifying pollutants and tracing them to their sources is achievable, with significant implications for monitoring and mitigating space emissions in the atmosphere.

The effect of lithium and other spacecraft ingredients on the ozone layer doesn't appear to have been studied compared to aluminum. To be fair, there will be a lot more aluminum.

Radiative Forcing and Ozone Depletion of a Decade of Satellite Megaconstellation Missions by Connor Barker et al (14^th May 2026):

We use a global inventory of launch and re-entry emissions covering the onset of the megaconstellation era (2020–2022), and project these to 2029 based on 2020–2022 growth rates. We implement this inventory into a 3D atmospheric chemistry model to determine the impacts of megaconstellations on the ozone layer and climate. We find that global stratospheric ozone depletion from all mission types is relatively small compared to surface sources and megaconstellation missions only account for about one-tenth of this depletion. This is because rockets launching megaconstellations almost all use kerosene, a large source of black carbon or soot particles, but not of chemicals such as chlorine that directly destroy ozone. Soot from rockets absorbs sunlight, warming the upper layers of the atmosphere and decreasing the amount of sunlight reaching Earth's lower atmosphere, causing it to cool. Megaconstellation missions are responsible for about half of this climate effect. In this regard, rockets launching megaconstellations and other missions are like small-scale stratospheric aerosol injection experiments without forethought for potential unintended consequences.

Again, this paper addresses only atmospheric impacts from launches, not from reentries. And, the launch rate for 2020-2022 is far less, and uses much smaller rockets, than the proposed "million satellite data center" and its competitors.