Defining the environmental impacts of satellite megaconstellation missions in a rapidly growing space sector

Emissions from the space industry are rapidly increasing due to surges in rocket launches and the amount of mass re-entering the Earth’s atmosphere. Satellite megaconstellations (SMCs) are a key contributor to this growth, representing a fifth of rocket launches and a quarter of object re-entries in 2020-2022. These activities release air pollutant emissions throughout the atmosphere, including in upper atmospheric layers where turnover rates are very slow. This results in extremely effective stratospheric ozone depletion and radiative forcing. Of the approximately 7500 satellites in low-Earth orbit (LEO), 75% belong to satellite megaconstellations, with 60,000 additional SMC satellites expected to be launched in the next decade. Despite this anticipated growth, the environmental impacts of SMC emissions lack characterization and are under regulated. Here we implement a recently published 3-D, global inventory of space industry emissions into a computational model to determine the impacts on stratospheric composition and radiative forcing from a decade of SMC missions. The inventory comprises emissions up to 80 km from all SMC and non-SMC rocket launches and spacecraft re-entries during the onset of the megaconstellation era (2020-2022). The emission species include gaseous nitrogen oxides (NO_x≡NO), water vapour (H₂O), carbon monoxide (CO), and chlorine species (Cl_y≡HCl+Cl₂+Cl), and particulate black carbon (BC) and alumina (Al₂O₃). We project the emissions to 2029 based on linear growth in SMC and non-SMC launch propellant consumption and re-entry mass. We use the GEOS-Chem 3-D model of atmospheric composition coupled to a radiative transfer model to simulate the response of atmospheric composition and radiative forcing to these emissions. We include a standard GEOS-Chem simulation of externally mixed aerosols and an updated simulation where BC and Al₂O₃ undergo prompt uptake to abundant stratospheric sulfate aerosols (SSA), as evidenced by observations from a recent aircraft campaign. We find a global stratospheric ozone loss of 0.03% (0.072 DU) from launch and re-entry emissions at the end of the decade. This is much smaller than stratospheric ozone loss attributable to surface sources (~2% in 2022). Depletion due mostly to Cl_y from solid rocket motors is concentrated in the northern midlatitude upper stratosphere. SMC missions are responsible for 13% of this ozone depletion, as solid fuel represents <1% of rocket fuel used by SMC missions from 2020-2022. Uptake of aerosol emissions to SSA results in nearly complete removal of wintertime stratospheric BC and Al₂O₃ concentrations and a summertime peak. This process greatly reduces the positive radiative forcing by stratospheric BC, resulting in stratospheric ozone depletion as the dominant forcing process and an overall negative forcing. Space industry emissions from all mission types result in radiative forcing of -3.38 mW m^-2 at the top of the atmosphere in summer 2029, with -0.59 mW m^-2 from SMC missions.  At the tropopause, there is a net negative radiative flux from all missions (-1.64 mW m^-2) and SMC missions (-0.35 mW m^-2). Current work includes conducting sensitivity simulations to quantify the impact of uncertainties in properties and chemical pathways of aerosol emissions on our results to inform future field and experimental studies.