Speaker
Description
In just three years since 2019, satellite megaconstellations have grown to comprise 69% of the reported 8763 satellites in orbit, with an additional 530,000 megaconstellation satellites proposed. These megaconstellations have driven surges in rocket launches and re-entry destruction of spent satellites, contributing to large increases in anthropogenic emissions throughout all atmospheric layers. Despite the increased emissions, the potential environmental impacts of satellite megaconstellations remain uncharacterized and unregulated. Here we calculate 3D, hourly-resolved emissions of the dominant pollutants from megaconstellation and non-megaconstellation rocket launches and re-entries starting with 2020 to determine the impact of satellite megaconstellations on climate and stratospheric ozone. The pollutants include black carbon particles, nitrogen oxides (NO$_\text{x}$), water vapour, carbon monoxide, alumina particles (Al$_\text{2}$O$_\text{3}$) and chlorine species from rocket launches and NO$_\text{x}$ and Al$_\text{2}$O$_\text{3}$ from re-entries. Online repositories are used to compile information on all objects re-entering Earth’s atmosphere from above 50 km in 2020-2022, including spacecraft, rocket stages, fairings, and components from orbital and suborbital launches. The object class (core or upper stages, payload) and object reusability are used to define the chemical composition and mass ablation profile of each re-entering object. Where geolocation data is not available, geographic coordinates are randomly assigned with latitude bounded by the orbital inclination. The anthropogenic mass influx of Al$_\text{2}$O$_\text{3}$ from object re-entry in 2020 is calculated to be 0.62 Gg (1 Gg = 1000 tonnes), which is more than twice both the estimated anthropogenic and natural meteoritic injections in 2019. Over 85% of megaconstellation satellites decay within 2 years, and as a result megaconstellation re-entries have already grown to contribute 10% of the anthropogenic Al$_\text{2}$O$_\text{3}$ object re-entry emissions in 2020. The 2021-2022 megaconstellation contribution will be determined and is expected to dramatically increase as the large number of recently launched megaconstellation satellites re-enter the atmosphere. In addition, spacecraft and rocket re-entries led to a calculated mass influx of 2.70 Gg of NO$_\text{x}$ in 2020. This is an increase of 42% since 2019, with megaconstellation missions accounting for 9% of these NO$_\text{x}$ emissions. The megaconstellation emission inventories will be implemented into the 3D GEOS-Chem atmospheric chemistry transport model to simulate the impacts of megaconstellations on the ozone layer and climate. Large uncertainties remain in the size distribution, mass, and optical properties of Al$_\text{2}$O$_\text{3}$ released during object ablation, and the mass of Al$_\text{2}$O$_\text{3}$ and NO$_\text{x}$ released during controlled re-entry of reusable rocket stages and capsules. Further research in these areas would increase the accuracy of the simulation, helping to inform future megaconstellation regulation.
