Since the dawn of the space age, rockets have blazed new trails to the great expanse beyond our planet. But as the number of rocket launches steadily ticks upward each year—a trend linked in part to the maturation of the commercial space sector—scientists are starting to express concerns about the hazardous gasses that these vehicles spew into Earth’s skies.
Now, Ioannis Kokkinakis and Dimitris Drikakis, a pair of scientists at the University of Nicosia in Cyprus, have quantified, in unprecedented detail, the potential health risks and climate impacts of pollution from rocket exhaust. By merging real rocket launch data with sophisticated simulations, the researchers concluded that “pollution from rockets should not be underestimated as frequent future rocket launches could have a significant cumulative effect on climate,” and may also become “hazardous to human health,” according to a study published on Tuesday in the journal Physics of Fluids.
“It is the first high-resolution and high-order computational modeling computational fluid dynamics study regarding exhaust gasses impact on the atmosphere,” said Drikakis, referring to the new research, in an email. “The topic will attract more interest in the future as more frequent rocket flights take place.”
Rocket launches make for dramatic spectacles precisely because of the mesmerizing trail of combustible exhaust that powers their ascents into space. For decades, the atmospheric pollution produced by these gassy emissions has been regarded as functionally negligible because launches were relatively rare. As a result, Drikakis and Kokkinakis note that research into the polluting effects of space travel is “limited” and “still in its infancy,” in the study.
However, companies such as SpaceX, Virgin Galactic, and Blue Origin are fueling a commercial spaceflight boom that will significantly increase atmospheric pollution from rockets. At the turn of the 21st century, only a few dozen trips to orbit took place each year, but orbital launches are likely to number in the hundreds every year this decade.
To anticipate the potential climate and health impacts of this trend, Drikakis and Kokkinakis studied detailed telemetry data of SpaceX’s Falcon 9 rocket during an orbital launch of a mission called Thaicom-8 in 2016. The researchers note that this “prototypical example” was selected due to helpful webcam footage showing exhaust gasses throughout the launch, rather than to single out SpaceX, according to the study.
The pair used the launch to produce high-quality simulations of rocket pollution during the vehicle’s ascent through the atmosphere. One of the most surprising findings, according to Drikakis, was that at an altitude of one kilometer above Earth’s surface, which is in an atmospheric layer called the mesosphere, the rocket’s emissions of carbon dioxide (a greenhouse gas) are equivalent in mass to the carbon dioxide contained in a full 26 cubic kilometers of air at that same altitude, which the researchers called “a significant value” in the study.
They added that carbon monoxide and water vapor expelled from the rocket in the mesosphere are comparable to the carbon dioxide emissions, which may alter the local composition of that layer in ways that are poorly understood. This mesospheric rocket pollution may have long-term effects on the climate in the coming decades.
“We need to understand further the pollution in the mesosphere, particularly the turbulent diffusion of pollutants,” Drikakis said. “At present there is no significant concern due to the small number of launches. However, as the launches increase, pollution will further increase.”
The team’s models also emphasized the potential risks of rocket pollution across higher altitudes of up to 10 kilometers, or six miles, above Earth’s surface. As rockets ascend to these heights, they introduce hazardous chemicals known as thermal nitrogen oxides (NOx) into the sky.
The study suggests that as much as two cubic kilometers of atmospheric air may be affected by NOx pollution during these early stages of an orbital launch, a level that is considered hazardous to human health by the World Health Organization because “it is associated with exaggerated/prolonged response to allergen challenges in asthmatics/atopics,” according to the study. In addition, at even higher altitudes in the stratosphere, rocket launches could deplete ozone gas, which protects life on Earth from harmful radiation.
“The atmospheric pollution from exhaust gasses is undesirable,” Drikakis said. “We do not know yet the threshold that pollution from rockets may start having significant adverse effects on the atmosphere or the climate, and in turn, on human health. However, the findings of our study suggest that further research into the topic is needed.”
Drikakis added that some of the emerging problems that stem from rocket pollution might be mitigated by comparing the climate and health impacts of different propellants or vehicle designs. For instance, non-toxic “green” fuels are currently in development at federal organizations, including NASA and the European Space Agency, while the private company Orbex aims to produce an environmentally friendly rocket biofuel.
To that end, Drikakis and Kokkinakis look forward to more concerted attention to this topic as humans expand our presence in space with new missions to Earth’s orbit, the Moon, Mars, and other outer space locations.
“We plan to perform further studies on the particles emitted into the atmosphere, the turbulent diffusion mechanisms, and the effects on ozone,” Drikakis concluded.
“The entire New Shepard system has been designed for operational reusability and minimal maintenance between flights from day one to decrease the cost of access to space and reduce waste,” a Blue Origin spokesperson said. “Nearly 99% of New Shepard’s dry mass is reused, including the booster, capsule, ring fin, engine, landing gear, and parachutes. New Shepard’s BE-3PM engine is fueled by highly efficient and clean liquid oxygen and hydrogen. During flight, the only byproduct of New Shepard’s engine combustion is water vapor with no carbon emissions.”
Update: This article has been updated to include comments from Blue Origin.