Now, every few days, a giant rocket explodes a fiery trail in the atmosphere, lifting satellites into orbit, performing space missions or other missions. Since 2017, the number of launches and the size of cargo loads has increased dramatically, with each launching larger rockets carrying larger numbers of satellites and other objects. In 2016, a total of 221 objects entered space. In 2023, this number is 2,644. There are about 10,000 satellites in low-Earth orbit now, and thousands of satellites are still out of service. About 6,000 people belong only to SpaceX Company, and its owner Elon Musk vowed to increase the companies to 40,000. Most importantly, there are more than 130 million “space garbage” floating around, which is the spawning of larger crafts.
The launch has local effects, including huge temporary pollution clouds in fuel combustion, and short-lived rocket phases caused by sheet metal, insulation and other debris. And, of course, things to rise must fall – everything sent into orbit will eventually fall back to Earth, and with the increase in launches, re-form the failed or retired spacecraft. Most people burn in the atmosphere, but not always completely. Just last year, a considerable metal part landed near woods in rural North Carolina, on roofs of Florida houses, a farm in Saskatchewan and a small village in Kenya.
Kostas Tsigaridis is an atmospheric scientist at the Climate Systems Research Center of Columbia Climate School and its NASA Space Research Institute affiliated with NASA. He doesn’t have to worry about the brief local pollution in the lower atmosphere, nor about the fall of complete debris. However, he was concerned about the by-product of the rocket’s combustion through the high atmosphere and the by-product of burning debris. Both may change the chemistry, temperature and circulation of the upper atmosphere, having a possible impact on the planetary climate.
He and his colleagues are trying to understand the potential of this impact. The preliminary model assumptions they used to make estimates could be 1,000 or even 10,000 releases per year by 2050. We talked to Tsigaridis about this relatively new field of research.
Why do you want to investigate the possible impact of the Rockets?
Rocket launches and satellite reentry increased at unprecedented speeds. Given the lack of any provision on their number, we hope that they will start to become a distinct pollutant in the near future. More importantly, they include unique anthropogenic sources of short-lived chemicals in the upper atmosphere. Given the rapid expansion of activities, we should not wait for what happened and then conduct research. It’s better to try to figure this out from now on.
Most rockets are used for fuel, what are the typical by-products?
Kerosene is the most popular kerosene, and is also a solid fuel, rich in carbon and produces black carbon as a by-product like a car. The hydrogen used by Blue Origin does not contain carbon and is primarily water as a by-product, but has less lifting capacity per fuel mass compared to carbon-based fuels. Liquefied natural gas (LNG) is mainly methane and is expected to dominate in the future. LNG is still based on carbon, but the combustion efficiency is much higher than kerosene, and the combustion efficiency of black carbon is much less.
Black carbon is important because it has a long life span in the upper atmosphere. Near the surface, it will soon rain due to precipitation, but in the absence of clouds or high surfaces, including in the stratosphere, only gravity and atmospheric circulation can eventually be removed. Both of these are very slow processes. Therefore, it accumulates impacts on chemistry and climate. The fuel from clean liquid liquefied natural gas does reduce the amount of black carbon per launch, but given the number of launches released in the future, we are still talking about the large amounts of injection into the upper atmosphere.
Is there any obvious impact? What will happen in the future?
Let me first explain why we care about the stratosphere starting from the altitude of the aircraft. This is where the ozone layer is located, which protects life on the planet from harmful solar radiation. It is sandwiched between the troposphere, part of the atmosphere where we live, and the middle layer above. The troposphere is very humid, so we have clouds, rain, humidity, etc. Due to the extremely high temperature, the stratosphere is very dry. The coldest part between the troposphere and the stratosphere is called the troposphere top, which prevents water from entering the stratosphere. There are more functions that make the stratosphere unique, but water and ozone are important here. And, as I have already said, the new component introduced by the Rockets is Black Carbon.
As the name suggests, black carbon is black, so it absorbs solar radiation. This heats up the surroundings. This is a very familiar effect. What we have recently discovered is that heating the troposphere from the black carbon heats the stratosphere, thus allowing water to “leak” into the stratosphere. This changes chemistry and destroys stratospheric ozone. Ozone erosion does not appear to have a large impact on the global scale, but the ongoing analysis means enhanced polar ozone destruction will occur. In addition, normal atmospheric circulation will cause most of the black carbon to land near polar regions, which can land on snow and ice and accelerate melting by reducing the reflectivity of these surfaces. This is an effect that has not been studied yet, but we have plans to conduct in-depth research as soon as possible.
How do fragments that re-enter the atmosphere produce and what are the consequences?
Space Fragments are a completely different story. In the middle layer, no black carbon is involved, combustion (more precisely ablation) occurs at higher conditions. The ablation temperature is high enough that they break down molecular nitrogen, the richest chemical in our atmosphere. This then forms nitrogen oxides, which affects the middle layer chemistry. Moreover, the satellites we send to orbit contain a lot of aluminum in their structure. This will oxidize to alumina, which then forms very small particles that reflect sunlight and affect chemistry. In principle, they are similar but not exactly the same as gases in major volcanic eruptions, which we know reflects sunlight and cools the earth. These particles, along with a variety of other satellite-filled metals, are detected on the way from Mesosphere to the surface in the stratosphere. Their role has not been accurately quantified.
What’s your next step?
In determining the role of black carbon in stratospheric water, we are preparing to study debris reentry in nitrogen oxides and alumina. We are also studying regional effects, not global effects, as our preliminary analysis shows that polar atmospheres will be disproportionately affected.
