Rocket engine exhaust pollution spreads high into the Earth’s atmosphere

(ORDO NEWS) — Reusable space technology has led to an increase in lower cost space travel, as evidenced by commercial space flights from companies such as SpaceX and Virgin Galactic. However, the issue that rocket exhaust gases create significant heating and compositional changes in the atmosphere remains poorly understood.

In the journal Physics of Fluids, researchers at the University of Nicosia in Cyprus assessed the potential impact of a rocket launch on atmospheric pollution by studying heat and mass transfer and the rapid mixing of combustion by-products at altitudes up to 67 kilometers in the atmosphere.

“Improving the understanding of rocket emissions requires modeling and simulating the hydrodynamics of rocket exhaust gases into the atmosphere,” said study co-author Dimitris Drikakis.

The team simulated the exhaust gases and the evolving plume at several heights along a typical trajectory of a standard modern rocket. They did this as a prototype two-stage rocket to carry people and payloads to Earth orbit and beyond.

“We show that rocket pollution should not be underestimated, as frequent rocket launches in the future could have a significant cumulative effect on Earth’s climate,” said study co-author Ioannis Kokkinakis.

The researchers found that the production of thermal nitrogen oxides (NOx), a component of exhaust gases, can remain high up to altitudes with atmospheric pressure above or even slightly below the pressure at the outlet of the nozzles, that is, below an altitude of about 10 km.

At the same time, the mass of carbon dioxide emitted when a rocket rises to a height of 1 km in the mesosphere is equivalent to that contained in 26 cubic kilometers of atmospheric air at the same height.

They found that local and short-term atmospheric impacts in the mesosphere can be significant. While air currents will gradually carry and mix CO2 from exhaust gases throughout the atmosphere, eventually returning CO2 to natural levels, the time frame over which this will occur is unclear.

Scientists believe that there may still be a certain number of rocket launches above which mesospheric carbon dioxide can accumulate over time, thereby raising natural levels and affecting our climate.

Their results show that, in the worst case, in the time it takes a rocket to reach a height of 10 kilometers, enough NOx could be generated to pollute more than 2 cubic kilometers of atmospheric air with NOx concentrations that, according to the World Health Organization, are at levels dangerous for human health.

“We hope that commercial flight companies such as SpaceX, Virgin Galactic and New Shepard and their associated engine manufacturers take these effects into account in future developments,” Drikakis said.

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