Rocket exhaust plume at 30 km s obtained by high-resolution computational fluid dynamics simulations

Rocket emissions can change the atmosphere’s composition, research finds

Image credit: Ioannis Kokkinankis, Dimitris Drikakis, University of Nicosia, Cyprus

Emissions created as a result of rocket launches result in heating and compositional changes in the atmosphere, according to a recently published study.

The space sector is on the rise, with companies like SpaceX, Blue Origin and Virgin Galactic making large investments in commercial spaceflights, and organisations like Nasa continuing to power missions to space. However, the impact of such launches on the Earth’s atmosphere is still poorly understood.

A team of researchers from the University of Nicosia in Cyprus set out to study the extent to which rockets' propulsion emissions can create significant heating and compositional changes in the atmosphere. To do so, the scientists investigated the heat and mass transfer and rapid mixing of the combustion byproducts for altitudes up to 67km into the atmosphere.

The findings of the study, published in Physics of Fluids, showed that rockets can have a significant impact on the Earth’s atmosphere.

"We show that pollution from rockets should not be underestimated, as frequent future rocket launches could have a significant cumulative effect on the Earth's climate," said co-author Ioannis Kokkinakis.

To come to this conclusion, the team modelled the exhaust gases and developed plume at several altitudes following a typical trajectory of a standard present-day rocket. They model the experiment as a prototypical example of a two-stage rocket to transport people and payloads into Earth's orbit and beyond.

"Improved understanding of rocket emissions requires modelling and simulation of fluid dynamics of rocket exhaust gases into the atmosphere," said Dimitris Drikakis, another co-author of the article.

The researchers found the production of thermal nitrogen oxides (NOx) can remain high up to altitudes with an ambient atmospheric pressure above or even slightly below 10km. At the same time, the emitted mass of carbon dioxide as the rocket climbs 1km in altitude in the mesosphere is equivalent to that contained in 26km³ of atmospheric air at the same altitude.

These emissions can impact the mesosphere and change its composition. While air currents will gradually transport and mix the exhaust CO2 throughout the atmosphere, eventually bringing the CO2 back down to its naturally occurring levels, the time scale over which this happens is not clear.

The research suggests that a certain number of rocket launches can lead to an accumulation of carbon dioxide and an acceleration of climate change.

In the worst-case scenario, sufficient NOx could be produced over the time it takes the rocket to reach an altitude of 10km to pollute over 2km³ of atmospheric air with a NOx concentration that would be at a level hazardous to human health.

“We believe that the problem of atmospheric pollution caused by rocket launches is vital,” said Drikakis. "We hope that commercial flight companies, such as SpaceX, Virgin Galactic, and the New Shepard, and their associated engine manufacturers, will consider these effects in future designs."

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