Rockets' Air Pollution Impact: Understanding The Environmental Cost

As economic activity in space increases, scientists are re-examining the impact of rockets on Earth's atmosphere. Rocket launches are known to release pollutants into the stratosphere and mesosphere, which can have a significant climate impact due to their persistence in those layers. The exact extent of harm caused by rocket launches and re-entering space debris is unknown, but research suggests that it could be significant. The production of rocket fuel and the electricity usage required for launches also contribute to overall pollution levels.

Rocket fuel production

The production of rocket fuel has a significant impact on the environment, with potential ecological disaster resulting from the use of certain fuels. UDMH (unsymmetrical dimethylhydrazine), a highly carcinogenic fuel, was used by many rockets that blasted off from the Baikonur launch site in Kazakhstan, resulting in a large zone of pollution due to the toxic fuel seeping into the soil. This fuel, dubbed "devil's venom" by scientists, is blamed for turning a large area of the Kazakh Steppe into an ecological disaster zone.

The choice of rocket fuel can have a significant impact on the amount of pollution produced. RP-1, a highly refined form of kerosene, is one of the most popular rocket fuels due to its low cost, stability at room temperature, and low explosivity. However, RP-1 fuelled rockets produce soot and carbon dioxide, a greenhouse gas contributing to climate change. To reduce emissions, some companies are experimenting with sustainable alternatives to RP-1, such as bio-propane, a renewable biofuel created as a waste product from biodiesel production. Orbex's rocket, which runs on bio-propane, is estimated to produce around 90% fewer emissions than an RP-1-fuelled rocket, with reduced soot production.

Methane-based rocket propellant is another alternative fuel that may help reduce pollution. Methane burns more cleanly than RP-1 and provides higher energy. It has a high propulsion efficiency, resulting in minimal residues. However, there are concerns about methane as a potent greenhouse gas. SpaceX's Starship, which uses liquid natural gas, a form of methane, produces less soot and facilitates engine reusability. Blue Origin's BE-4 rocket also utilizes liquified natural gas but has been associated with methane emissions, as reported by Carbon Mapper near their Texas facilities in 2023.

Liquid oxygen and liquid hydrogen are used as the main fuels for the Ariane 6 rocket. NASA will employ longer versions of these polluting boosters for its Artemis moon missions. Hybrid rocket engines, such as those used by Virgin Galactic's SpaceShipTwo, burn solid fuel with a liquid or gaseous oxidizer. These engines are relatively safe and simple to operate but tend to generate significant amounts of soot. The burning process in these engines creates favourable conditions for soot generation, similar to that of a candle.

While the space industry's contribution to fossil fuel burning is relatively small, about 1% compared to conventional aviation, the impact of rocket emissions on the atmosphere cannot be overlooked. Rocket emissions deliver gases and particles directly into the middle and upper atmosphere, including the stratosphere and mesosphere. The pollutants released in these upper layers can persist for longer periods, affecting ozone depletion and climate change. As the space industry expands, with an estimated market value of $2.58 billion in 2031 and projected annual growth of 17.15% over the next decade, the cumulative effect of rocket launches on the atmosphere will become increasingly significant.

Rocket exhaust

The extent of the pollution caused by rocket exhaust is not yet fully understood, and it is a topic that requires further research. However, it is known that the soot or black carbon particles from rocket exhaust accumulate in the upper stratosphere, where they absorb sunlight, leading to an increase in temperature. This, in turn, affects chemical reaction rates and is likely to contribute to ozone depletion. The issue of rocket emissions is expected to be addressed in the United Nations 2018 Quadrennial Global Ozone Assessment, which will investigate the substances responsible for ozone depletion.

The type of propellant used in rockets determines the specific pollutants emitted. For example, SpaceX's Falcon 9, which burns fossil-based rocket fuel RP1 and liquid oxygen, produces exhaust containing carbon dioxide, water vapour, soot, nitrous oxides, and sulfur. In contrast, Blue Origin's next-generation rockets, Starship and New Glenn, will use methane-based fuel, resulting in emissions of carbon dioxide, water vapour, and trace amounts of nitrous oxides.

The production of rocket fuel can also contribute to pollution. For instance, liquid hydrogen is typically made from natural gas, which releases carbon dioxide during production. Similarly, liquifying oxygen requires significant electrical power, which may be generated by fossil fuels, further contributing to carbon dioxide emissions.

While the direct impact of rocket exhaust on ground-level air quality may be relatively low, the increasing frequency of rocket launches and the potential for future growth in the space tourism industry highlight the need to address this issue.

Climate impact

The climate impact of rocket launches is a growing concern, especially as the rate of rocket launches is expected to increase significantly in the coming years. While rocket launches are not as frequent as aircraft flights, the pollutants from rockets are released at much higher altitudes, from the Earth's surface up to the mesosphere (approximately 50-85 km), and can persist in the atmosphere for 2-3 years. This includes emissions of carbon dioxide (CO2), water, black carbon, and alumina particles, which can have a significant impact on the climate.

CO2 emissions from rocket launches are considerable, with a typical long-haul plane flight producing 1-3 tonnes of CO2 per passenger, while rocket launches generate 50-75 tonnes of CO2 per passenger. However, it is important to note that the number of rocket flights is currently much lower than that of airplane flights. According to NASA, there were only 114 attempted orbital launches in 2020, compared to over 100,000 airplane flights per day.

Rocket soot, or black carbon, is of particular concern as it accumulates in the upper stratosphere, absorbing sunlight and leading to potential ozone loss. A recent study found that soot from rockets has up to 500 times the climate impact of soot from airplanes. While the space industry currently accounts for only about 3% of warming from black carbon, the expected growth of space tourism could increase this share to 6%.

In addition to the direct emissions from rocket launches, there is also the issue of space debris, including derelict satellites, rocket stages, and other space junk, falling back to Earth and burning up in the atmosphere. This process can release various particles that can have unknown and potentially significant effects on atmospheric chemistry. The increasing rate of rocket launches and the growing number of satellites in orbit are raising concerns about the potential environmental impact of this space debris.

While the exact implications of rocket emissions on the climate are still unclear and require further study, there is a growing sense of urgency as the space industry continues to expand. Some researchers and advocacy groups are calling for preventive measures and interventions, such as regulations on satellite launches, to address this novel environmental threat.

Air quality impact

The air quality impact of rocket launches is a complex issue that is currently under scrutiny by scientists and researchers. While it is challenging to determine the precise effects on air quality, several factors and potential consequences are worth considering.

Firstly, it is important to recognize that rocket launches release emissions into the atmosphere, just like any form of combustion-driven propulsion. These emissions include gases and particles such as alumina (Al2O3), chlorine (converted from hydrochloric acid, HCl), nitrogen oxides (NOx), hydroxyl (OH), water vapour (H2O), and carbon dioxide (CO2). The interaction between these emissions and the Earth's atmosphere can lead to ozone depletion and other chemical reactions that impact air quality.

Secondly, the altitude at which rocket emissions are released plays a crucial role in their impact on air quality. Most rocket emissions are released into the stratosphere and mesosphere, which are located at higher altitudes than aircraft emissions. As a result, these pollutants can persist in the atmosphere for an extended period, ranging from two to three years. The duration of their presence in the atmosphere can have cumulative effects on air quality over time, especially with the expected increase in rocket launches.

Additionally, the production of rocket fuel and the operation of the space industry as a whole contribute to air pollution. For instance, the extraction, liquification, and transportation of hydrogen fuel can result in carbon dioxide emissions, particularly if fossil fuels are used in these processes. Moreover, the burning of conventional aviation fuel, UDMH (unsymmetrical dimethylhydrazine), by rockets has been dubbed "devil's venom" due to its highly carcinogenic nature and long-lasting ecological impact.

While the number of rocket launches currently represents a small fraction of aircraft flights, the potential for the space tourism industry to grow significantly cannot be overlooked. This anticipated increase in rocket launches, coupled with the lack of regulations surrounding air pollution from rockets and reentering satellites, underscores the urgency to address this issue. As Sebastian Eastham, an aerospace sustainability researcher at Imperial College London, stated, "If we don't take any action now or in the next five years, it might be too late."

Space debris

The impact of rocket launches on Earth's atmosphere is an area of growing concern, particularly with the expected increase in rocket launches and the burgeoning space tourism industry. While most of the pollution from rocket launches is released into the stratosphere and mesosphere, it is important to understand the potential risks to the Earth's atmosphere posed by rocket emissions.

The accumulation of rocket soot in the upper stratosphere is another concern. Soot particles absorb sunlight, leading to heating of the upper stratosphere and altering chemical reaction rates, which is likely to result in ozone loss. The impact of this soot is estimated to be about 500 times greater than that of surface and aircraft sources of soot.

The issue of space debris is further exacerbated by the increasing number of satellites being launched into space. Satellite mega-constellations have been identified as a significant risk to climate and the environment, and there are calls for tighter global regulations to ensure space sustainability. The current regulatory regime has been described as inadequate, with no meaningful penalties to deter rule-breaking. To address this issue, countries with the largest footprint in space should come together to agree on basic standards and limits on the number of satellites in a given orbital shell.

In summary, space debris is a pressing issue that requires immediate attention. The potential risks to the Earth's atmosphere and the sustainability of space exploration are significant, and the impact of rocket launches and space debris on stratospheric ozone and global climate needs to be thoroughly assessed and addressed through international cooperation and regulation.

Frequently asked questions