The Future Chemistry and Climate Impacts of Large, Fully-Reusable Methane-Fueled Rockets

Rocket launches have clear local impacts on atmospheric composition, and the number of launches to

Low Earth Orbit (LEO) from space agencies and commercial space activities are projected to greatly

increase over the next few decades. The launch industry is moving toward a future dominated by

methane fuel and reusable first and second stages. Accordingly, a better understanding of the broader

impacts on stratospheric chemistry and climate under plausible frequency and technological scenarios

are essential to fully appreciate their potential effects. Depending on the level of expansion of space

exploration, the rate of launches is projected to significantly increase and is expected to include heavy

launch vehicles with recoverable stages.

Together with launch technology experts, we developed a discrete set of plausible future scenarios of

launch-related emissions from a range of feasible rocket technologies, including their frequency,

regional distribution, and vertical emission profiles, using realistic altitude-dependent simulations of

rocket combustion. Emission profiles include BC, NOx (rocket combustion and reentry heating), CO,

water vapor, with BC being by far the most important contributor on rocket fuel burning climate

impacts. Particular attention was given to the type of fuel that will likely dominate space launches in the

future, liquefied natural gas (LNG), which is also much cleaner in terms of BC emissions from the fuels

that dominate present-day launches.

Using the NASA GISS Earth system model ModelE, we performed future simulations (year 2050 following

SSP2-4.5) using realistic emissions for different launch vehicles and plausible number of launches per

year for a future that includes large satellite constellations and interplanetary exploration. We will

present a large number of simulations under plausible future climate backgrounds, with updated

emissions that correspond to future fuel types and a greatly increased launch rate per year. The goal is

to understand how chemistry and climate are impacted by not only the emissions themselves, but also

by the change in technology towards cleaner alternatives with less BC emissions, which is very absorbing

in the shortwave, resulting in warming of the atmosphere where it is abundant. Although the cleaner

LNG fuel emits much less BC than currently used kerosene, our simulations show that the significant

increase in launch rate still results in important impacts from BC emissions. We will focus on the

emissions of individual species, in particular BC, from the launch vehicle (ascent and stage two descent)

and their impact on atmospheric composition and climate, both individually but also together, to study

feedbacks involved with the non-linear chemistry; the role of the different background atmosphere

(present-day vs. future) in any climate effect; the climate impact of the less black carbon-emitting LNG

fuel compared to present-day fuels.