Rocketship Pollution: How Bad Is It?

Rocket launches are an integral part of the 21st century, but they also contribute to air pollution. The extent of the impact of rocket launches and re-entering space debris on Earth's atmosphere is not yet fully understood, but scientists are actively studying the issue. Rocket engines emit pollutants such as black carbon, nitrogen oxides, alumina particles, chlorine, hydrochloric acid, and water vapour, which are released at high altitudes, from the surface of the Earth up to 80 km. The rate of rocket launches is increasing, with a record of 180 launches in 2022, and the growth of the space tourism industry is expected to further increase launch rates. While the amount of pollution produced by rocket launches is small compared to other industries, the pollutants released at high altitudes can persist for years and have climate impacts, contributing to ozone depletion and global warming.

Rocket fuel and propellants

Rocket propellant is the chemical mixture burned to produce thrust in rockets. It consists of a fuel and an oxidizer. The fuel burns when combined with oxygen, producing gas for propulsion. An oxidizer is an agent that releases oxygen to combine with the fuel. The ratio of oxidizer to fuel is called the mixture ratio.

Propellants are classified according to their state: liquid, solid, or hybrid. Liquid propellants can be further classified into petroleum, cryogens, and hypergols. Petroleum fuels are refined from crude oil and are a mixture of complex hydrocarbons, i.e., organic compounds containing only carbon and hydrogen. The petroleum used as rocket fuel is a type of highly refined kerosene, called RP-1 in the United States. Kerosene delivers a specific impulse considerably less than cryogenic fuels but is generally better than hypergolic propellants. Cryogenic propellants are liquefied gases stored at very low temperatures, most frequently liquid hydrogen as the fuel and liquid oxygen as the oxidizer.

Solid propellants come in two main types: composites and single-, double-, or triple-base propellants. Composites are composed mostly of a mixture of solid oxidizers and energetic fuel compounds. Plasticizers, stabilizers, and/or burn rate modifiers can also be added. Solid rockets are a good choice when large amounts of thrust are needed, and cost is an issue. They are also easier to store and handle than liquid propellant rockets. However, they have lower specific impulses than liquid fuel rockets, meaning their overall performance is less than that of liquid stages.

Hybrid rockets use a combination of solid and liquid or gaseous propellants. An example of a hybrid rocket is the Blue Origin BE-4 rocket, which runs on liquified natural gas. While methane-fuelled rockets produce less soot than kerosene-fuelled ones, they still release some soot and methane, a potent greenhouse gas.

The pollution caused by rocket emissions is a growing concern as launch rates have more than tripled in recent decades. Rocket soot accumulates in the upper stratosphere, where the particles absorb sunlight, heating the stratosphere and likely leading to ozone loss. While rocket soot only accounted for about 0.01% of all soot from traditional sources in 2019, it contributed an estimated 3% of global warming caused by soot emissions. Some scientists are also worried that the carbon particles from rocket emissions can absorb heat and act as a form of geo-engineering.

Rocket launches and pollution

Rocket launches have become a growing source of pollution as the rate of launches has tripled in recent decades, with a record-setting 180 launches to orbit in 2022. The pollution caused by rocket emissions is a complex issue that is challenging to measure and compare to other sources of pollution. However, it is clear that rocket launches release pollutants directly into the middle and upper atmosphere, from the surface of the Earth up to the mesosphere. This includes pollutants such as water vapour, nitrogen oxides, black carbon, alumina particles, and gaseous chlorine, among others. The accumulation of rocket soot in the upper stratosphere can absorb sunlight, leading to potential ozone loss and contributing to global warming.

The impact of rocket emissions on the atmosphere, temperatures, and the ozone layer is a growing concern, with at least three scientific research papers published on the topic in 2022. Scientists are particularly interested in the potential for these carbon particles to act as a form of geo-engineering by absorbing heat. While the percentage of fossil fuels burned by the space industry is relatively low compared to other industries, the increase in launch rates and the unique nature of rocket emissions means that rocket launches are a significant contributor to pollution above 20 km altitude.

The type of fuel used in rockets can also impact the level of pollution emitted. For example, methane-fuelled rockets produce less soot than kerosene-fuelled ones, but they still release some soot and methane, a potent greenhouse gas. The fuel UDMH, used by many rockets, is also a concern as it releases a lot of energy. The composition of rocket propellants, which are required in huge amounts, determines the specific pollutants emitted during launch.

In addition to the emissions produced during launch, rocket launches also contribute to pollution through the vaporization of discarded space hardware and the re-entry of reusable components and space debris. This has led to concerns about the potential impact on the environment and the need for more detailed examinations of the effects of rocket launches on the Earth's atmosphere. While the benefits of the space industry are significant, addressing the pollution caused by rocket launches is crucial to ensuring a sustainable future for spaceflight and space exploration.

Space junk and pollution

Since the 1950s, humans have launched thousands of rockets and sent even more satellites into orbit. Many are still there, and we face an ever-increasing risk of collision as we launch more. As of August 2021, the European Space Agency (ESA) reports that approximately 29,210 pieces of space junk are tracked regularly by Space Surveillance Networks. There are also about 3,000 dead satellites and 34,000 pieces of space junk bigger than 10 centimetres in size. Millions of smaller pieces could nonetheless prove disastrous if they hit something else.

Space junk, also known as space debris, is any piece of machinery or debris left by humans in space. It can refer to big objects such as dead satellites that have failed or been left in orbit at the end of their mission. It can also refer to smaller things, like bits of debris or paint flecks that have fallen off a rocket or a functioning space station. Some human-made junk has even been left on the Moon.

Space junk is a direct result of human activity, as it was never left behind before humans started developing the technology and interest in space exploration. It can also refer to the debris or various materials that fall behind from a rocket when it takes off or ultimately fails to return to home base.

The accumulation of space junk poses a particularly catastrophic threat to humankind’s future in space exploration, due to the increased risk of collision with and damage to functioning satellites. It could also have detrimental effects on Earth’s environment. Objects left behind in space release various chemicals into the atmosphere and ultimately contribute to the depletion of the ozone layer.

Some measures that could be taken to mitigate the current space junk predicament include improving the monitoring and mitigation strategies used to manoeuvre satellites and implementing a fee for each satellite put into orbit to discourage the unnecessary accumulation of space junk.

Climate change and global warming

Climate change is a pressing issue that encompasses global warming and refers to a wide range of changes occurring on our planet. These changes include rising sea levels, shrinking mountain glaciers, accelerating ice melt in Greenland, Antarctica, and the Arctic, and shifts in plant blooming times. The primary cause of climate change is the emission of greenhouse gases, mainly carbon dioxide and methane, which trap heat in the Earth's atmosphere. Human activities, such as burning fossil fuels for energy, transportation, and industrial processes, are the primary contributors to these emissions. Deforestation and agricultural practices also play a role in releasing carbon dioxide into the atmosphere.

Global warming is the long-term warming of the planet, which has been well-documented since the early 20th century, especially since the late 1970s. Since the Industrial Revolution, the global annual temperature has increased by more than 1 degree Celsius, with the rate of increase accelerating in recent decades. The consequences of global warming are far-reaching and impact various aspects of our lives, including our health, economy, food supply, and ways of life.

To address climate change and global warming, a multifaceted approach is necessary. Cutting emissions is crucial, and this can be achieved by transitioning from fossil fuels to renewable energy sources like solar and wind power. Additionally, adapting to climate impacts and financing required adjustments are essential. Global frameworks such as the Paris Agreement aim to limit global warming to 1.5 degrees Celsius, recognizing that immediate and significant reductions in emissions are necessary to avoid the most devastating effects of climate change.

Rocket launches have also been identified as a source of pollution, contributing to the complex dynamics of climate change. While rocket soot may seem insignificant compared to traditional sources, it still plays a role in global warming. The impact of rocket emissions on the atmosphere, temperatures, and the ozone layer is an emerging area of research, with scientists expressing concern about the potential for carbon particles to act as a form of geo-engineering, absorbing heat and leading to ozone loss. As launch rates continue to increase, understanding and mitigating the environmental impacts of rocket pollution become increasingly crucial.

Ozone layer depletion

The ozone layer is a vital shield in the Earth's atmosphere, absorbing over 90% of harmful ultraviolet radiation that would otherwise harm humans and ecosystems. Ozone layer depletion is a significant concern, and while the use of ozone-depleting chemicals like chlorofluorocarbons (CFCs) has been banned since 1987, other sources of ozone depletion continue to emerge.

Rocket launches are one such source, delivering gases and particles directly into the middle and upper atmosphere. The impact of rocket emissions on the ozone layer is an area of active research, with at least three scientific papers published in 2022 exploring this topic. The extent of ozone layer depletion caused by rocket launches is uncertain, with estimates ranging from a negligible amount to a few hundredths of 1% annually. However, as the space industry expands and the number of rocket launches increases, the impact on the ozone layer is expected to become more significant.

Rocket launches introduce a variety of chemicals and pollutants into the atmosphere, including soot, methane, and nitrogen oxides. These emissions can remain in the upper atmosphere for extended periods, affecting chemical reaction rates and contributing to global warming and ozone depletion. The accumulation of rocket soot in the upper stratosphere, for example, can absorb sunlight and heat the surrounding area, altering chemical reactions and likely leading to ozone loss.

To address this issue, researchers have suggested more stringent regulations for the rocket launch market to prevent significant damage to the Earth's stratospheric ozone layer in the future. Martin Ross, a lead author on the topic, emphasizes the need for a robust understanding of how rockets affect the ozone layer to guide possible regulation of commercial and government rocket launches. The upcoming United Nations 2018 Quadrennial Global Ozone Assessment will include a substantial section on rocket emissions, marking a significant step in addressing this issue.

Frequently asked questions