The Environmental Impact of Space Exploration
A single rocket launch emits 336 tonnes of CO₂, equal to a car driving around the world 70 times.
Exploring space may seem like an escape from Earth’s problems, but an average rocket launch brings new challenges to our planet. For example, NASA’s Solid Rocket Boosters burn 11,000 pounds of fuel per second. This is two million times more fuel than a regular car uses. These powerful boosters create 5.3 million pounds of force to push the rocket out of Earth’s gravity.
Rocket pollution involves more than just gas emissions; it also leads to problems like ozone depletion, ocean contamination, and space debris. However, let’s first focus on the issues caused by the release of hazardous gases.
Now, which rocket fuels produce which emissions? Let’s look at RP-1 (refined kerosene), hydrogen, methane, and solid rocket fuel. These cover most of the fuels used in rockets today and their environmental impact.
Let’s start with solid rocket boosters, which are known for being the dirtiest form of rocket propulsion. When burned, solid rocket boosters emit several pollutants. Aluminum Oxide contributes to particulate pollution. Soot (Black Carbon) absorbs sunlight and contributes to global warming. CO₂ (Carbon Dioxide) is a major greenhouse gas that drives climate change. Hydrogen Chloride leads to acid rain, which damages ecosystems and infrastructure. Nitrogen Oxides (NOx) cause smog and acid rain. Lastly, Hydrogen can contribute to atmospheric chemical reactions and long-term climate effects.
Let’s now consider the engines used in rockets such as the RS-25, which burns hydrogen combined with liquid oxygen (hydrolox).
Hydrogen is one of the cleanest burning fuels, producing primarily water vapor when burned with oxygen. However, there is a trace amount of Nitrogen oxide (NOx) produced, particularly when rockets are in the lower atmosphere (troposphere). NOx forms as a byproduct of the high-temperature combustion interacting with atmospheric nitrogen. This can contribute to smog and acid rain, which have harmful effects on both human health and the environment.
Next, let’s examine RP-1, a common propellant used in rockets. RP-1 is a highly refined form of jet fuel, essentially refined kerosene.
When burned with liquid oxygen (kerolox), RP-1 produces several pollutants: CO₂ (Carbon Dioxide), water vapor, NOx (Nitrogen Oxides), carbon soot, and carbon monoxide, which mostly converts to CO₂ but can still impact air quality; and sulfur compounds, which can contribute to acid rain.
Lastly, let’s discuss methane, or methalox when burned with liquid oxygen. When burned, it primarily produces CO₂ (Carbon Dioxide) and water vapor, along with a small amount of NOx (Nitrogen oxide).
Although rocket launches are relatively infrequent compared to other sources of pollution like airlines and cars, their emissions are still a concern. Currently, the trace amounts of gases from rocket launches may seem minor, but as the frequency of launches increases, their impact on the planet could become significant and potentially irreversible. Therefore, it is crucial to address these issues proactively. Before exploring solutions, let's first examine the problems of space debris and ocean contamination.
The rapid increase in rocket launches over the past few years has been alarming, with a sharp rise from 114 launches in 2020 to 146 in 2021, 186 in 2022, and an incredible 223 launches in 2023. Shockingly, 2024 has already seen 166 launches by September 10, with many more expected by year-end. This fast-growing space activity raises serious concerns about environmental damage, as the rising number of launches could lead to a major increase in atmospheric pollution and other harmful effects in the near future.
Over 60 years, more than 6,050 rocket launches have left around 56,450 tracked objects in orbit. Of these, about 28,160 remain in space, with roughly 4,000 still functioning as active satellites. This space debris, totaling over 9,300 tonnes, ranges from large discarded rocket stages to tiny paint chips. Most of it is in low Earth orbit (LEO) and some in geostationary orbit.
You might wonder, "What exactly is space debris?" Although we can't see this space junk with the naked eye, it's present in LEO, which is effectively a vast junkyard. There are millions of pieces of debris in this region, including fragments from spacecraft, tiny paint flakes, rocket parts, defunct satellites, and remnants from explosions in space.
Most space junk travels at incredibly high speeds, up to 18,000 miles per hour—nearly seven times faster than a bullet. This rapid movement and the sheer amount of debris pose significant risks to both current and future space missions. Even small pieces of debris can cause severe damage; for instance, space shuttle windows often needed replacement due to collisions with particles smaller than 1 mm.
Smaller pieces of debris can contribute to atmospheric depletion, while larger objects can collide with each other, creating even more debris. This cascading effect, known as the Kessler Syndrome or Kessler Effect, can significantly increase the amount of space debris and exacerbate the problem, posing ongoing risks to both space exploration and the environment.
Space debris also poses environmental risks to Earth. When space debris re-enters the atmosphere, it releases chemicals that can weaken the ozone layer, which protects our planet from harmful ultraviolet radiation. These chemicals can have long-term effects on both the environment and future space missions.
Most space debris falls into the ocean, primarily because oceans cover more of the Earth's surface than land. However, there is growing industry interest in reducing space debris to avoid congestion that could disrupt communications and future space exploration. This might involve deorbiting the International Space Station in 2028, with plans to drop it in the South Pacific.
The environmental impact of space debris on the ocean is not fully understood. While some argue that space junk might create habitats for marine life, the effects on local ecosystems, such as those in Baffin Bay or near Point Nemo, are still under-researched. The South Pacific Gyre, a similar region to Point Nemo, has revealed ancient microbial life, raising questions about the potential impact on such environments.
Certain spacecraft fuels, like hydrazine, are toxic, and while cryogenic fuels are less harmful, metals like beryllium are concerning. The risk of chemical spillage from re-entering debris, especially from controlled re-entries, poses a threat to marine environments. However, the primary concern remains the debris in orbit, which presents a more immediate risk.
To address space debris and rocket pollution, several key solutions are being considered. One crucial step is to eliminate solid rocket boosters, which release toxic compounds and deplete the ozone layer. Transitioning from these boosters to cleaner alternatives is essential for reducing environmental damage. Additionally, adopting more sustainable fuels like methane or hydrogen can make a significant difference. Hydrogen, produced through electrolysis, and methane, synthesized by capturing CO2 from the atmosphere, offer cleaner options compared to hypergolic and fossil fuel-based fuels like RP-1.
Another important measure is the use of closed-loop engines such as the RD-180, RS-25, RD-181, Raptor, and BE-4. These engines achieve more complete combustion and are more efficient, which helps to reduce pollution compared to traditional open-cycle engines. Promoting the reuse of rockets rather than discarding them after each launch is also critical. By reusing rockets, we can spread out the emissions from their manufacturing over multiple flights, which significantly lowers the overall CO2 emissions.
In addition to these measures, addressing space debris itself is essential. Preventing the creation of new debris and using advanced waste management techniques to collect existing debris is crucial. Methods currently being explored include guiding debris to burn up safely in Earth's atmosphere through controlled re-entry, using mechanical means such as nets, harpoons, or robotic arms to capture and remove debris, and employing powerful electromagnets to push debris into the atmosphere. Laser satellites can break down debris, and solar-powered nets can capture larger pieces.
Moreover, efforts to offset emissions, such as planting trees, and initiatives like Scotland’s space debris neutrality goals, underscore the importance of sustainability in space exploration. As technology advances, these solutions will help mitigate the environmental impact of space activities and ensure a cleaner future for both Earth and space.
As we explore the cosmos, it's crucial to balance our quest for knowledge with environmental responsibility. By adopting cleaner technologies and managing space debris, we can ensure that our advancements in space do not harm our planet. The future of space exploration depends on our commitment to sustainability both on Earth and beyond.