Reducing the Environmental Impacts of Rocket Launch Emissions through Launch Parameter Variations

Increasing rocket launch rates in the last decade have prompted concerns over their environmental impacts. Launch vehicles are unique among anthropogenic pollution sources for directly emitting pollutants at all levels of the atmosphere. These high-altitude emissions have distinct – and poorly understood – consequences; emissions such as water vapor and black carbon aerosols have longer lifetimes in the stratosphere and thus a longer window for climate and ozone impacts. 

Accurately estimating launch emissions is an outstanding problem in launch vehicle research, complicated further by diverse combustion products which vary according to propellant type. We create unique emissions profiles for representative launches with equivalent payloads to LEO for three different propellants: RP1/LOx, CH4/LOx, and LH2/LOx. Using the GEOS-Chem High-Performance (GCHP) chemical transport model, we simulate an array of launch scenarios reflecting different choices of launch site, propellant, and launch season in a global three-dimensional atmosphere. 

We evaluate the impact of launch hemisphere by comparing launches at the same latitude in the Northern and Southern hemispheres, and show a greater ozone impact in southern-hemisphere launches. We simulate a range of launch sites across the northern hemisphere and show substantial variance in high-altitude ozone formation as a function of latitude. We show a several percent larger increase in stratospheric ozone for summer launches than in winter. Finally, we see net ozone column increase with RP1 and CH4 fuelled launches but net decrease with LH2, which we posit suggests black carbon is the dominant force in high-altitude ozone formation as a response to rocket launches. 

Using these results, we synthesize a variety of impact mitigation strategies for a given rocket launch and estimate the potential harm reduction across a variety of metrics: global ozone column changes, radiative forcing, surface air quality, and population exposure to fine particulate matter. These findings could be used to inform future developments in the launch industry, from selecting and researching fuel types for future launch vehicles, to choosing locations for future launch sites, and even optimal utilization rates for existing launch sites.