Rocket Ships: Polluters Or Green Commuters?

As companies like SpaceX, Blue Origin, and Virgin Galactic launch more rockets than ever, the environmental impact and carbon emissions are becoming a growing concern. Rocket launches can have a large carbon footprint due to the burning of solid rocket fuels, and the production of hydrogen fuel can cause significant carbon emissions. Rockets require large amounts of propellants to exit the atmosphere, and the composition of these propellants determines the kind of air pollutants emitted during the launch process. While the overall impact of rocket launches on our climate remains much smaller than aviation's, the growing space tourism industry will come at a significant environmental cost.

Rocket fuel production and emission indexes

Rocket fuel production and its emission indexes have been a topic of discussion and concern for environmentalists and space enthusiasts alike. The production of rocket fuel, especially hydrogen, can cause significant carbon emissions. The burning of solid rocket fuels also contributes to a hefty carbon footprint. However, many rockets use liquid hydrogen fuel, which produces 'clean' water vapour exhaust. Rocket engines release trace gases into the upper atmosphere, contributing to ozone depletion and releasing particles of soot.

The specific type of rocket fuel used determines the emissions produced. Solid rocket boosters, for example, are considered the dirtiest form of rocket propulsion, producing over 85% of the thrust of the rocket at takeoff. On the other hand, methane-based fuels, when produced using renewable energy sources, can become mostly carbon-neutral.

Several startups are experimenting with sustainable alternatives to traditional rocket fuels. For instance, Orbex, a UK-based company, is developing a 3D-printed micro-launcher called Prime, which runs on biopropane and is expected to produce 86% less emissions than similar-sized RP-1 fuelled rockets.

While the overall impact of rocket launches on the climate remains relatively small compared to other industries, the anticipated surge in rocket launches in the coming years will likely lead to a significant increase in rocket engine emissions. This has raised concerns about the potential climate impacts of these emissions, especially when compared to other sources of climate change.

Additionally, the manufacturing of rockets and the fuel released during testing, fueling, and landing operations contribute to the overall pollution caused by rocket fuel production and use.

Solid rocket boosters and their environmental impact

Solid rocket boosters are considered the dirtiest form of rocket propulsion. They produce over 85% of the thrust of the rocket at takeoff. They emit nasty toxic compounds and are very bad for the environment. The Space Shuttle and its bigger wingless brother, the SLS, mainly produce CO2, a lot of water vapour, a little soot, NOx, and a lot of chlorine and alumina because of those massive solid rocket boosters.

Solid rocket boosters are used to help rockets overcome the initial pull of Earth's gravity. They are usually found on the first stage of rockets where high thrust is crucial. The most famous solid rocket boosters were the two giant white boosters on the sides of the Space Shuttle. There are also two massive solid rocket boosters on ESA's Ariane 5.

Hybrid rocket engines, which burn solid fuel with a liquid or gaseous oxidizer, produce a lot of soot. These engines work like a candle, and their burning process creates conditions that are favourable for soot generation. Soot particles, or black carbon, can affect how the atmosphere absorbs heat.

While research is limited, and experts caution that not enough data has been gathered to precisely assess the impacts of various types of rocket propellants and rocket engines on the environment, some fuels have been found to have disastrous consequences. Unsymmetrical Dimethylhydrazine, dubbed "Devil's venom" by Soviet scientists, is responsible for turning a vast area of a Kazakh steppe into an ecological disaster zone.

In the grand scheme of emissions, rockets are a tiny drop. However, that does not mean that the aerospace industry should not strive to make improvements.

Carbon emissions and carbon capture

Carbon emissions from rocket launches are a cause for concern, particularly due to the burning of solid rocket fuels. The production of hydrogen fuel, which is considered 'clean' as it produces water vapour exhaust, can also lead to significant carbon emissions. Rocket engines release trace gases and soot into the upper atmosphere, which contribute to ozone depletion.

The impact of rocket launches on the environment is a complex issue. While rocket launches are relatively infrequent, and their overall impact on the climate is smaller than that of the aviation industry, the type of fuel used and the efficiency of the propulsion unit are important factors in determining the level of emissions produced. For example, smaller rockets, such as Blue Origin's Blue Shepard, can be powered by clean liquid oxygen and liquid hydrogen, which is considered environmentally friendly.

On the other hand, solid rocket boosters, commonly used during the first stage of a rocket launch when high thrust is required, are considered the dirtiest form of rocket propulsion. These boosters have been known to produce over 85% of the thrust of a rocket at take-off and leave a trail of material, including gases and particulate matter, in the stratosphere. This includes black carbon, or soot, which has a detrimental effect on the ozone layer and contributes to warming and disrupting stratospheric material flow patterns.

To address the issue of carbon emissions, some companies are experimenting with sustainable alternatives to traditional rocket fuels. For example, Skyrora, a UK rocket startup, is testing an alternative to RP-1 called Ecosene, made from non-recyclable plastics, which is claimed to produce up to 40% less carbon emissions. bluShift Aerospace is also working on a solid biofuel made from agricultural waste. Additionally, the production of zero-carbon rocket fuel is a possibility, with some suggesting that carbon-capture initiatives could be used to obtain the carbon monoxide required for the Fischer-Tropsch process of making kerosene.

While rocket launches do contribute to carbon emissions and pollution, it is important to note that they are not a significant contributor when compared to other industries. The focus on reducing carbon emissions should be on larger offenders, such as the aviation and automotive industries, where greater reductions can be made with existing technology.

Space junk and its effect on the environment

Space junk, also known as space debris, is any piece of machinery or object left by humans in space that no longer serves a useful function. This includes big objects such as dead satellites that have failed or been left in orbit, as well as smaller things like bits of debris or paint flecks that have fallen off a rocket. There are about 2,000 active satellites orbiting the Earth, with 3,000 dead ones also in orbit, and around 34,000 pieces of space junk bigger than 10 centimetres.

Space junk has a negative impact on the environment as it can release chemicals into the atmosphere, contributing to the depletion of the ozone layer. It can also prevent successful future launches, meaning fuel meant to take an aircraft into space could pollute the atmosphere. The accumulation of space junk also increases the risk of collisions, which can create thousands of new pieces of debris. This could result in a chain reaction, as predicted by NASA scientist Donald Kessler in 1978, where more and more collisions occur, creating new space junk and rendering Earth's orbit unusable.

Space junk in low Earth orbit will gradually lose altitude and burn up in the Earth's atmosphere. However, larger debris can impact Earth and have detrimental effects on the environment. For example, debris from Russian Proton rockets launched from Kazakhstan has littered the Altai region of eastern Siberia with toxic fuel residue, unsymmetrical dimethylhydrazine (UDMH), which is harmful to plants and animals and carcinogenic.

There are several proposed methods for removing space junk, including using giant fish nets, lasers, robots with giant claws, magnets, and harpoons. However, these methods are only suitable for larger pieces of debris, and there is currently no universally recognised solution to the problem. To prevent the accumulation of space junk, some economists have proposed attaching an annual fee to each satellite put into orbit, which would increase by 14% per year.

The environmental cost of space tourism

The environmental costs of space tourism are numerous. The powerful engines that power space flights burn rubber and fossil fuels, generating a lot of soot—a type of highly toxic carbon. This can have a severe impact on the atmosphere. A space tourism flight, which lasts on average about an hour and a half, generates as much pollution as a 10-hour transatlantic flight and has the same carbon footprint as 278 people combined.

The soot released by increased traffic would raise temperatures in the stratosphere, deplete the ozone, and have a warming effect almost 500 times more intense than similar emissions from aircraft or surface sources. This black carbon would also disrupt atmospheric circulation by slowing the movement of air from the tropics to the upper atmosphere, leading to further depletion of the ozone layer.

Rockets release a large amount of water vapour into the atmosphere, and this occurs at much higher altitudes than with aeroplanes. While water sounds harmless, at high altitudes, it has a potent warming effect. The high temperatures generated during launch and re-entry transform the nitrogen in the air into nitrogen oxides, which are potent greenhouse gases.

Another environmental cost of space tourism is space junk. Currently, there are about 34,000 pieces of space junk larger than 10 centimetres and 128 million pieces larger than 1 millimetre in space. If space tourism takes off, these numbers will increase.

While the amount of fuel burned by the space industry is less than 1%, and space tourism is still a small part of the overall tourism industry, it is predicted to grow exponentially. This will inevitably lead to an increase in the sector's climate footprint, with far-reaching environmental consequences.

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