Bronte Wells
Rocket launches are an integral part of the 21st century, but they also contribute to air pollution and climate change. The propellants used by rockets determine the kind of pollutants emitted during launch. For instance, SpaceX's Falcon 9 rocket uses a fuel mixture of liquid oxygen and kerosene, which creates black soot that is injected directly into the stratosphere and remains there for up to five years, contributing to climate change and ozone depletion. While the space industry's fossil fuel usage is only about 1% of that burned by conventional aviation, the growing number of rocket launches could lead to a substantial increase in pollution. Additionally, space junk from disused satellites and other objects poses a risk to the environment. As economic activity in space surges, scientists are reexamining the impact of rocket launches on Earth's atmosphere, with an emphasis on understanding the chemical kinetics and reactivity of particles produced during re-entry.
| Characteristics | Values |
|---|---|
| Percentage of fossil fuels burned by the space industry compared to conventional aviation | 1% |
| Number of commercial rocket launches per year | 140 |
| Number of SpaceX Falcon 9 launches in 2022 | 61 |
| CO2 emitted by a typical long-haul plane flight per passenger | 1-3 tonnes |
| CO2 emitted by a rocket per passenger | 100 times more than an airline passenger |
| CO2 emitted by a SpaceX Falcon 9 rocket in the first stage | 116 tons |
| Pollutants in rocket launch plumes | Alumina (Al2O3), chlorine, nitrogen oxides (NOx), hydroxyl (OH), and water vapour (H2O) |
| Effects of pollutants in rocket launch plumes | Ozone depletion, increased cloud formation, radiative forcing, exposure to harmful UV radiation |
| Fuels used by rockets | Kerosene, methane, liquid oxygen, liquid hydrogen, UDMH (unsymmetrical dimethylhydrazine) |
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What You'll Learn
Rocket fuel and propellant types
Rocket Propellant-1 (RP-1)
RP-1 is a highly refined form of kerosene, similar to jet fuel. It is widely used, powering iconic rockets such as the Saturn, Delta, Atlas, Soyuz, SpaceX's Falcon 9, and Virgin Orbit's horizontally launched rocket. When burnt, RP-1 produces carbon dioxide (CO2), water vapour, nitrogen oxides (NOx), carbon soot, carbon monoxide, and sulfur compounds. While the exhaust from RP-1 is polluting, it is comparable to the emissions from a typical internal combustion car, albeit released in larger quantities at once.
Solid Rocket Boosters
Solid rocket boosters are composed of ammonium perchlorate, the salt of perchloric acid and ammonia, along with aluminium or magnesium powders. These boosters emit pollutants such as aluminium oxide, soot or black carbon, CO2, hydrogen chloride, nitrogen oxides, hydrogen, and trace gases. Solid rocket boosters are considered a source of pollution, especially during the launch and re-entry of rockets.
Liquid Oxygen and Liquid Hydrogen
Liquid oxygen, often combined with liquid hydrogen, is used in rockets like the Ariane 6. This combination is also known as hydrolox. NASA's upcoming Artemis moon missions will utilise longer versions of these polluting boosters. Liquid oxygen was also used in the first stage of the Saturn V rocket.
Unsymmetrical Dimethylhydrazine (UDMH)
UDMH, also known as "Devil's Venom," is a highly carcinogenic propellant that does not require ignition and can be stored at room temperature. It was used at the Baikonur Cosmodrome in Kazakhstan, turning a large area of the Kazakh steppe into an ecological disaster zone due to its toxic nature.
Methane
Methane is another rocket fuel that has been gaining attention. SpaceX's Starship is planned to run entirely on methane. However, the interactions between methane-fuelled rocket engines and the Earth's atmosphere are not yet fully understood, and more research is needed to assess the environmental impact of this fuel type.
Hydrogen
Hydrogen is considered one of the cleanest-burning fuels and is used in rockets like the Delta IV, Ariane V's core engine, and the Centaur upper stage.
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Climate change impact
The impact of rocket launches on the climate is a complex and nuanced issue. While rocket launches are relatively infrequent compared to other forms of transportation, their emissions contribute to the pollution in the Earth's atmosphere. The pollution from rocket launches is released primarily into the stratosphere and mesosphere, which are located between 12 km and 85 km above the Earth's surface. This pollution can persist in these layers for at least 2-3 years and has been found to have a climate impact, with the potential to accelerate climate change.
Rocket launches emit various gases and particles that contribute to ozone depletion and climate change. These emissions include black carbon or soot, alumina (Al2O3), chlorine, nitrogen oxides (NOx), hydroxyl (OH), and water vapour (H2O). The alumina, chlorine, and nitrogen oxides are particularly harmful as they deplete the ozone layer, which protects the Earth from harmful UV radiation. The water vapour leads to increased cloud formation in the stratosphere and mesosphere, which can reflect solar flux back into space. Additionally, the black carbon and alumina can absorb solar flux, resulting in a cooling effect.
The impact of rocket launches on the climate is expected to increase in the coming decades due to the growing demand for services like satellite internet and space tourism. The increase in the number of rocket launches, as well as the size of the rockets, will result in a higher volume of emissions. For example, SpaceX's anticipated Starship spacecraft is expected to be a significant contributor to pollution, with its 33 engines burning a mixture of methane and kerosene, which produce black soot that contributes to climate change and ozone depletion.
The space industry, including companies like NASA, SpaceX, and Blue Origin, has been criticized for the environmental impact of their rocket launches, especially considering their involvement in sustainable energy initiatives. While some companies are attempting to reduce their environmental impact, such as Blue Origin's New Shepard rocket, which burns liquid oxygen and liquid hydrogen, producing only water vapour as exhaust, the overall trend is towards increased pollution from the space industry.
It is important to note that the impact of rocket launches on the climate is not limited to their emissions. "Space junk", or the accumulation of disused satellites and other objects in Earth's orbit, is also a growing concern. The re-entry of space debris into the Earth's atmosphere generates "re-entry smoke particles" (RSPs) of unknown composition and reactivity, which can have unknown effects on the atmosphere and climate.
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Space junk and debris
Since the 1950s, when the space age began, humans have launched thousands of rockets and satellites into orbit. Many of these are still in orbit, and the risk of collision increases with each new launch. This debris, known as space junk or space debris, includes defunct satellites, derelict spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris from the breakup of rocket bodies and spacecraft. Some objects in lower orbits will re-enter the Earth's atmosphere and burn up, but those at higher altitudes can circle the Earth for hundreds or thousands of years.
Space junk poses a significant risk to active satellites and spacecraft. Several countries, including the USA, China, and India, have conducted anti-satellite tests, deliberately blowing up their satellites and creating thousands of new pieces of dangerous debris. This has triggered concerns that countries may target LEO satellites to create debris clouds and impede precision attacks. The deliberate destruction of the Chinese Fengyun-1C spacecraft in 2007 and the accidental collision of an American and Russian spacecraft in 2009 increased the large orbital debris population in LEO by approximately 70%.
The vulnerability of satellites to debris has led to the performance of hundreds of collision avoidance manoeuvres each year, including by the International Space Station (ISS). While collisions are rare, a Chinese satellite broke up in March 2021 after a collision. The biggest danger posed by space junk is to other satellites in orbit, and some experts worry that the increasing amount of space debris could render Earth orbit unusable. This scenario, known as the Kessler Syndrome, was popularised in the movie "Gravity."
Several companies are developing methods to address the issue of space junk. In 2012, the Swiss Space Center announced the Clean Space One project, a nanosatellite demonstration project to match orbit with a defunct nanosatellite and de-orbit it. In 2019, the European Space Agency awarded a €120 million contract to ClearSpace-1, slated to launch in 2026, to remove a 94 kg satellite from orbit. NASA's Orbital Debris Program, which began in 1979, also focuses on creating less orbital debris and designing equipment to track and remove existing debris.
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Ozone layer depletion
The ozone layer, located in the stratosphere, protects life on Earth from harmful ultraviolet (UV) rays from the sun. In the 1980s, scientists discovered that man-made chemicals were damaging this vital protective layer. The worst offenders were compounds called chlorofluorocarbons (CFCs), which were found in aerosols like hairspray and cooling devices.
Due to coordinated global action and legislation, the ozone layer is now on track to heal this century. However, an increase in rocket launches could threaten this progress. Rocket launches emit gases and particulates that damage the ozone layer, including reactive chlorine, black carbon, and nitrogen oxides. Researchers at the University of Canterbury, New Zealand, have warned that rockets 'punching' through the stratosphere could contribute to ozone depletion and potentially reopen the hole in the ozone layer.
A study by scientists from the U.S. National Oceanic and Atmospheric Administration (NOAA) and The Aerospace Corporation examined the impact of increased future emissions of black carbon from rockets burning kerosene fuel. The study found that a projected increase in rocket launches for space tourism, moon landings, and missions to Mars could damage the protective ozone layer. Kerosene-burning rocket engines emit exhaust containing black carbon or soot directly into the stratosphere, which can lead to warming in those atmospheric layers and the degradation of the ozone layer.
Another study by NOAA and The Aerospace Corporation, led by Christopher Maloney, simulated the impact of approximately 10,000 metric tons of soot pollution injected into the stratosphere over the Northern Hemisphere every year for 50 years. The research found that all locations north of 30 degrees North experienced at least some reduced ozone throughout the year, with a maximum reduction of 4% at the North Pole in June. Maloney warned that projected increases in rocket launches could expose people in the Northern Hemisphere to increased harmful UV radiation.
While some argue that the amount of pollution generated by space missions is negligible compared to other sources, such as the aviation industry, the potential impact of rocket launches on the ozone layer is a cause for concern. Further research is needed to understand better the relative impacts of different rocket types on the ozone layer and climate.
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Comparisons to other industries
While the rocket industry has long been a symbol of human innovation and exploration, its environmental impact is increasingly coming under scrutiny. As the commercial space sector expands, emissions from rocket launches are projected to increase by 20-30% over the next decade. This growth reflects a surge in satellite deployment, space tourism, and exploration missions.
However, even with this anticipated rise in launches and emissions, the overall environmental footprint of the space industry is expected to remain minimal when compared to other high-emission sectors. For instance, the coal-fired power plant sector provides a stark contrast to the emissions of spaceflight. A single coal-fired power plant can emit more carbon dioxide (CO2) in just one day than all global rocket launches combined in an entire year. Beyond CO2, coal plants also release large quantities of sulfur dioxide, nitrogen oxides, and particulate matter, causing far-reaching damage to air quality and human health.
The aviation industry is another major polluter, with aviation alone accounting for 2.5% of global annual CO2 emissions. In comparison, rockets contributed approximately 0.1% of global CO2 emissions in 2022, a figure that is almost negligible in contrast to other major industries. Furthermore, the shipping industry produces an astronomical 940 million metric tons of CO2 each year, nearly 1,000 times the combined emissions of all rocket launches worldwide.
The disproportionate impact of rocket emissions on the stratosphere and upper atmosphere has also been highlighted. Approximately two-thirds of rocket propellant exhaust is released into the stratosphere (12 km-50 km) and mesosphere (50 km-85 km), where it can persist for at least 2-3 years. This is significant due to the climate impact of rocket emissions trapped in those layers, which include alumina, chlorine, nitrogen oxides, hydroxyl, and water vapour. These pollutants contribute to ozone depletion through chemical reactions in the Earth's stratosphere.
While the rocket industry's environmental impact is relatively small compared to other major industries, the increasing launch rates and unique effects on the upper atmosphere highlight the need for sustainable advancements in rocket design and fuel composition.
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Frequently asked questions
Rocket launches emit gases and particles that are released into the stratosphere and mesosphere, which can persist for at least 2-3 years. The pollution caused by rocket launches is expected to reach 10 gigagrams a year in a couple of decades, along with a temperature rise in parts of the stratosphere of up to 1.5 degrees Celsius, and a thinning of the ozone layer.
The main types of pollutants emitted by rockets include alumina (Al2O3), chlorine (converted from hydrochloric acid, HCl), nitrogen oxides (NOx), hydroxyl (OH), water vapour (H2O), and black carbon (BC).
Rocket launches are relatively infrequent compared to aviation, so their overall impact on the climate is much smaller. However, a single passenger aboard a rocket is responsible for 100 times more pollution than an airline passenger.
Space tourism will come at a significant environmental cost as rockets require huge amounts of propellants, which contribute to air pollution during the launch process.
The United States' Federal Aviation Administration (FAA) has conducted environmental assessments on the potential impact of rocket launches, specifically examining air quality under National Ambient Air Quality Standards (NAAQS).
