Physicists have discovered how a Falcon 9 launch changes the atmosphere

As the cost of launching a rocket into space drops, so does the number of rocket launches. In the past year, governments and companies around the world have succeeded fired 133 missiles into orbit, breaking a 45-year record.

but there is a problem. Breaking free from Earth’s gravity requires a rocket to release a massive amount of energy in a short amount of time. When a rocket leaves Earth, it Produces hot exhaust It changes the physics and chemistry of the atmosphere as it passes. at paper Published Tuesday in the journal fluid physicsTwo physicists simulated the launch of a SpaceX Falcon 9 rocket exploding into space.

They found several reasons for concern.

The carbon footprint is not the problem

Missiles are not responsible for placing this much importance Carbon dioxide in the atmosphere. A typical launch burns roughly the same amount of fuel as a one-day commercial flight but produces seven times as much carbon dioxide.₂ – between 200 and 300 tons – as a passenger aircraft. This is a lot more carbon than the average person does born in their lifebut it is a rounding error compared to 900 million tons of carbon dioxide^₂ The airline industry was tossing around annually before the pandemic.

But this is not the full story. “We don’t care about a missile’s carbon footprint. That’s irrelevant,” Researcher Martin Ross says. For him, it’s the particles in rocket exhaust – mainly alumina and carbon black – that really matter. These particles scatter and absorb sunlight. “They change the temperature and rotation of the stratosphere,” Ross says.

Unfortunately, scientists have only a poor understanding of the overall environmental impact of a missile launch. “The current level of data on missile emissions does not provide researchers with sufficient information to fully assess the impact of launches on the global environment,” Ross says.

The effect of high carbon emissions in the atmosphere is uncertain

The researchers behind the new study are working to highlight the problem more acutely by modeling the exhaust from the nine apertures of a Falcon 9 rocket as it launched into space. These simulations include data on the rocket and propellant (RP-1) with equations that describe how gases behave under different conditions. With some serious computing power, the researchers were able to predict the behavior of the exhaust after exiting the vents, at approximately 0.6 miles (1 km) in elevation.

The researchers analyzed the release by comparing the volume of exhaust released during one kilometer of travel uphill through a specific range of atmosphere (eg between 2 km and 2.99 km) with the characteristics of the atmosphere at that particular altitude. They had to adopt this somewhat confusing method because the physical and chemical composition of the atmosphere varies at different altitudes.

They found the amount of total exhaust to be “negligible” compared to the surrounding air, even at high altitudes. This is a surprise because the atmosphere is much less dense at higher altitudes. According to their calculations, the amount of exhaust emitted by a Falcon 9 as it travels between 70 kilometers and 70.99 kilometers (about 43 miles) is one-fourth the amount of mass contained in one cubic kilometer (about 0.25 miles)³) from the air at this altitude. (This conveys the blue line in the graph below).

what no It is negligible amount of carbon dioxide₂ Falcon 9 enters higher levels of the atmosphere as it passes (represented by the red dotted line in the figure above). Once its altitude exceeds 27 miles (43.5 km), the missile begins releasing more than one cubic kilometer of carbon dioxide.₂ For every kilometer climbed. By the time it reaches 43.5 miles (70 km), the Falcon 9 emits more than 25 times as much carbon dioxide.₂ It is found in cubic kilometers of air at this altitude.

And missile exhaust contains more carbon

It is more than carbon dioxide. “Perhaps the most important thing is that [amount of] Carbon monoxide (CO) and water (H2O) [in rocket exhaust] with a similar arrangement to carbon dioxide,” the authors write. This is a concern because there is hardly any carbon monoxide or water elevated in the atmosphere. Therefore, emissions of these vehicles at higher altitudes provide a more significant contribution/altitude to the trace amounts, if any, that are already present.”

The water vapor freezes instantly at this height, but the researchers have no idea where these ice crystals are. Carbon monoxide reacts with hydroxide (OH) to form more carbon dioxide₂. The researchers also discovered that dangerous exhaust emissions called thermal nitrogen oxides (NOx) can linger for a long time in hot rivers before spreading throughout the atmosphere, especially at lower altitudes.

The future is uncertain, but researchers and regulators are taking note

With just over 100 launches a year, some say pollution from missiles isn’t a problem. “One of the arguments people have used in the past is that we don’t really need to care about rockets or the space industry, or that the space industry is small, and always will be small,” Ross says.

did not agree. “I think the developments that we’ve been seeing in the last few years show that … space is entering a phase of very rapid growth like aviation that it had in the 1920s and 1930s.”

The authors behind the new study feel the same way. “We believe that the problem of atmospheric pollution from missile launches is vital and must be addressed appropriately because commercial spaceflight, in particular, is expected to increase in the future,” they wrote.

The problem of pollution from missiles is gradually becoming more and more obvious, and it is taken seriously in high places. Later this year, the World Meteorological Organization and the United Nations Environment Program will release a new report summarizing how rocket emissions are depleting the ozone layer. With any luck, this attention will cause atmospheric pollution to become a major factor in futuristic missile design.

Correction: An earlier version of this article incorrectly stated that the release released roughly the same amount of carbon dioxide₂ As a full day trip. In fact, a typical launch burns the same amount of fuel as a one-day flight, but produces nearly seven times more carbon dioxide.₂ emissions.