Rockets: Environmental Impact And Pollution Concerns

The topic of rockets and their impact on the environment has gained prominence, especially with the recent billionaire space race involving Richard Branson, Jeff Bezos, and Elon Musk. Rocket launches are an integral part of the modern world, but they do raise concerns about their polluting exhausts and climate change acceleration. While the number of rocket launches is relatively small compared to commercial aviation, the impact of rocket emissions on the atmosphere, temperatures, and the ozone layer is significant, especially at high altitudes. The pollution from rocket launches is influenced by the type of fuel used, with solid rocket boosters and hypergolic and fossil fuel-based fuels being particularly harmful. Some companies are experimenting with alternative fuels, such as bio-propane and liquified natural gas, to reduce their environmental impact. The manufacturing of rockets and the disposal of space debris also contribute to the overall environmental impact of the rocket industry.

Rocket fuel emissions

Rocket engines release combustion-driven propulsion, emitting pollutants such as black carbon or soot, nitrogen oxides, and other emissions. The fuel used by rockets can vary, with some common types including kerosene, hypergolic fuels, liquid hydrogen, solid fuels, and RP-1, a highly refined form of kerosene. The choice of fuel has an impact on the emissions produced, with some fuels being more environmentally friendly than others.

Some rocket fuels, such as UDMH (unsymmetrical dimethylhydrazine), have been dubbed "devil's venom" due to their highly carcinogenic nature and the ecological damage they can cause. Solid rocket boosters (SRBs) are also known to emit toxic compounds and deplete the ozone layer. Moving away from hypergolic and fossil fuel-based fuels is one step towards reducing emissions and their environmental impact.

Several companies are experimenting with more sustainable alternatives to traditional rocket fuels. For example, SpaceX's Starship uses methane-based fuel, which produces less soot residue and makes engine reuse easier. Blue Origin's BE-4 rocket runs on liquified natural gas, although this has been associated with methane emissions, a potent greenhouse gas. Orbex, a UK-based launch company, plans to use bio-propane, a renewable biofuel, for its Prime rocket, which is expected to result in significantly fewer emissions than an RP-1-fuelled launch.

The impact of rocket fuel emissions on the environment is a complex issue that requires further investigation. While rockets may not be the biggest polluters, the increasing demand for space-related services and the anticipated growth in rocket launches highlight the importance of addressing this issue. Additionally, the space sector remains unregulated by international treaties, making it challenging to assess the global impact of rocket fuel emissions on the atmosphere and climate.

Manufacturing pollution

The manufacturing of rockets is considered to be much worse for the environment than the rocket launch itself. However, the manufacturing of aluminium and steel is a whole different topic, and it is in no way exclusive to rockets. If we want to debate the impact that manufacturing has on our planet, that is a separate subject in itself.

The rocket industry could impact our climate even if it doesn't grow as big as other polluting industries. Rocket launches are an integral part of the 21st century and the global space industry is on the verge of a significant increase in the number of rockets launched into Earth's orbit. The global launch rate has already more than doubled in the past decade. With the increase in the number of launches, rocket engine emissions will also increase proportionately.

Rocket engine exhaust contains gases and particles that can affect Earth's climate and ozone layer. These emissions have historically been assumed to be insignificant due to the small size of the space industry. However, with the rapid growth of the space industry, the accumulation of rocket exhaust in the atmosphere will increase, and the impact on the planet is unknown. The unique nature of rocket combustion chemistry results in the emission of various gases and particles, depending on the type of rocket engine propellant used. The most common gaseous emissions are water vapour, carbon dioxide, and hydrochloric acid.

Some companies are experimenting with new types of fuel that may burn cleaner. For example, Orbex, a UK-based low-cost launch company, plans to launch its small rocket called Prime up to 12 times a year from Space Hub Sutherland in Scotland. The rocket will run on bio-propane, a renewable biofuel created as a waste product from biodiesel production. Similarly, Virgin Orbit has been experimenting with launching rockets from the air, with a rocket that runs on bio-propane. SpaceX's Starship burns liquid natural gas, which is almost pure methane, leaving less soot residue and making engine reuse easier.

Solid rocket boosters

The environmental concerns associated with solid rocket boosters primarily revolve around the emission of toxic compounds and their impact on the ozone layer. The combustion of solid fuel generates reactive chemicals, such as hydrochloric acid and aluminum oxide, which can spread into the surrounding environment, affecting soil and water quality and damaging vegetation. Additionally, the massive cloud generated during liftoff can contain these reactive chemicals, leading to ecological disasters, as seen with the use of UDMH fuel in Kazakhstan.

Furthermore, solid rocket boosters contribute to the depletion of the ozone layer. The release of soot and black carbon particles at high altitudes can affect how the atmosphere absorbs heat, leading to potential climate change. The unique combustion chemistry of rocket engines, including solid rocket boosters, results in a significantly higher emission of black carbon compared to modern jet engines.

However, it is important to note that the space industry is actively working on improving the environmental impact of rocket propulsion systems. Efforts are being made to move away from solid rocket boosters and towards more sustainable alternatives. Some companies are experimenting with cleaner-burning fuels, such as methane-based propellants, liquid natural gas, and bio-propane. Additionally, the use of rocket reusability and alternative launch methods, such as air-launch systems, can help reduce the environmental footprint of space missions.

Space junk

Several solutions have been proposed to address the problem of space junk, including the use of ground-based or satellite-based laser brooms to slow down or alter the course of debris, causing it to fall back to Earth or move into lower orbits where it will burn up upon re-entry. In 2019, the European Space Agency awarded a €120 million contract for the ClearSpace-1 mission, which aims to remove a 94 kg satellite from orbit using robotic arms.

While space junk does not currently pose a significant risk to our exploration efforts, it is important to address this issue through international cooperation and the development of innovative solutions to preserve the space environment for future space exploration missions.

Industry comparisons

The rocket industry has often been criticised for its negative impact on the environment. However, compared to other polluting industries, the rocket industry does not release a significant amount of carbon dioxide (CO2) into the air. The percentage of fossil fuels burned by the space industry is only about 1% of that burned by conventional aviation. The number of rocket flights is also currently very small: according to NASA, only 114 attempted orbital launches were made in 2020, compared to over 100,000 airplane flights per day.

That being said, the rocket industry still has a responsibility to reduce its environmental impact. The manufacturing of a rocket is much worse for the environment than the launch itself, but this is a separate issue that is not exclusive to rockets. The pollution caused by rocket emissions is also dependent on where they pollute. Most of the pollution from rocket launches is released higher up in the stratosphere and mesosphere, so the impact on ground-level air quality is lower. However, the alumina (Al2O3), chlorine (converted from hydrochloric acid, HCl), nitrogen oxides (NOx), hydroxyl (OH), and water vapour (H2O) in rocket launch plumes all contribute to ozone depletion through chemical reactions in the Earth’s stratosphere.

Several rocket start-ups are experimenting with sustainable alternatives to traditional fuel sources. For example, Orbex, a UK-based low-cost launch company, plans to launch its small rocket called Prime up to 12 times a year using bio-propane, a renewable biofuel created as a waste product from the production of biodiesel. Virgin Orbit has also been experimenting with launching rockets from the air, which could be an alternative to conventional launches. SpaceX’s Starship burns liquid natural gas, which is almost pure methane and leaves less soot residue, making it easier to reuse engines. However, it is not yet clear whether this fuel will reduce environmental impacts or cause different ones.

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