In situ observations of a kerosene-fueled rocket plume sampled during SABRE 2023

Rocket launches and space debris from reentries are the only direct anthropogenic emission sources above ~20 km in the atmosphere. Space launch activities, and consequently these emissions, are expected to grow by an order of magnitude in just the next decade. Modeling the impact of rocket emissions on the stratosphere requires accurate specification of exhaust composition profiles that depend on rocket propellant types (fuels) and operational and design parameters. Global models predict that black carbon (BC) is the most significant radiative forcing component in both kerosene (RP-1) and liquefied natural gas (LNG, methane) fueled rocket exhaust, although these emissions have never been measured from a rocket in flight. Validation of rocket combustion models, in turn, requires comprehensive in situ composition data from rocket plumes at stratospheric altitudes where near-field hot plume chemistry is expected to weaken.

In February 2023, the NOAA SABRE mission, using a NASA WB-57F aircraft, obtained in situ plume composition data (H₂O, SO₂, NO, NO₂, NO_y, HONO, CO, CO₂, BC, particle concentration) just above the tropopause from a kerosene-fueled rocket launched from Cape Canaveral, FL. The nighttime plume (not visible to the aircrew) was intercepted twice using a predetermined search pattern flown by the WB-57F. Measured ratios of emissions constituents reveal potentially surprising clues about near-field exhaust chemistry and kerosene engine BC emission in the lowermost stratosphere. The plume data acquired here, while limited, demonstrate the utility of such measurements toward resolving key questions about rocket emissions, and the SABRE 2023 flight experience suggests ways to improve plume sampling (e.g., need for plume direction finding capability) for future stratospheric rocket emission studies.