Resource extraction on Earth

In 1964, Soviet astronomer Nikolai Kardashev proposed a novel scale for quantifying a civilization’s level of technological advancement based on the amount of energy it is able to harness. In a paper he titled "Transmission of Information by Extraterrestrial Civilizations", he classified civilizations into three types based on the postulate of exponential progression:

“A type I civilization is able to access all of the energy available on its planet and store it for consumption; a type II civilization is able to directly consume the energy of a star; and, finally, a type III civilization is able to harness all of the energy emitted by its galaxy.”

Kardashev was presenting his paper at the Byurakan conference, a scientific meeting of the Soviet radio astronomy space listening program—effectively the Soviet equivalent of America’s search for extraterrestrial intelligence (SETI). While only a theoretical exercise, the Kardashev scale sparked the imagination of science fiction writers and scientists alike, leading the former to imagine exotic alien techniques for resource extraction and the latter to search for signatures of their existence.

For example, one such proposed alien technique is the Dyson sphere, an artificial structure built around a star in order to capture some or all of its energy. First imagined by science fiction author Olaf Stapledon in 1937 and formalized scientifically by the physicist Freeman Dyson in 1960, such a structure would imply the existence of a type II Kardashev civilization. Astronomers have already begun searching for Dyson spheres by using telescopes to look for the telltale infrared glow that they would emit.

Yet, despite our ability to imagine such grand scales of resource extraction, humans do not even rank as Type I on the Kardashev scale. Indeed, humans have (quite literally) only scratched Earth’s surface, extracting resources almost exclusively from the upper portion of our planet’s crust. With an average thickness of 40 km, Earth’s crust accounts for a mere 1% of the planet’s mass. By this measure, humanity is perhaps better categorized as a Type 0 civilization—and a very early one at that.

Nonetheless, the relatively small scale of resource extraction on Earth hasn’t stopped humans from exhausting several types of resources and repeatedly fighting wars over others. More worrying yet, the existing scale of resource extraction and energy usage by humans on Earth is already causing disastrous changes to the planet’s climate.1 It is only natural then that humans have begun to look to the effectively infinite expanse of space for new and inexhaustible sources of energy and materials.

The proponents of space resource extraction and utilization are varied in their backgrounds and motivations. For some, space resources hold the key to alleviating competition over Earth’s limited resources and mitigating climate change by reducing humanity’s dependence on Earth-bound resources. For other, more capitalist-minded proponents, space resources hold the promise of infinite growth and inexhaustible wealth, a position often based on fantastical valuations ranging from billions to quintillions2 of dollars for a single asteroid. Finally, looking beyond Earth altogether, many proponents herald space resources as humanity’s key to accessing the solar system and beyond.

Space resources

The solar system contains an effectively inexhaustible reserve of natural resources. From solar energy in Earth's orbit to helium-3 in the atmosphere of Neptune, not all of these resources are equally accessible or economically feasible. Therefore, in what follows, we will discuss the subset of space resources that are likely to be accessible in the near future (i.e., the next several decades). These resources are: space-based solar power (SBSP), water and helium-3 (He-3) on the lunar surface, and volatiles and metals from asteroids and comets near Earth.

Space-based solar power

The concept of SBSP first appeared in a 1941 novel by the renowned science fiction writer Isaac Asimov. In the novel, a space station harvests energy from the Sun via a solar array and sends the energy to various planets using microwave beams. SBSP as a sustainable energy source for Earth was first formalized in 1968 by Peter Glaser in a Science article, wherein he described transmitting energy collected by space-based solar arrays to Earth using microwaves from a one square kilometer antenna in space to a much larger rectenna on the ground.

While solar panels are already widespread on Earth’s surface, placing solar panels in space offers significant benefits. Namely, the amount of sunlight that reaches the solar panels is much higher in space than on the ground due to the lack of absorption by Earth’s atmosphere. Moreover, the efficiency of the solar panels does not depend on local weather patterns (e.g., the presence of clouds) and there are certain sun-synchronous orbits that are always illuminated by sunlight (i.e., the satellite is never in Earth’s shadow).

ESA has already begun a preparatory initiative around SBSP called SOLARIS, the goal of which is to guide decision making in Europe within the context of SBSP. In support of the SOLARIS initiative, ESA commissioned two independent cost vs. benefit studies of SBSP in early 2022. The results of these analyses were promising, concluding that:

“SBSP could provide competitively-priced electricity to European homes and businesses by 2040, displacing fossil-fuel sources of power and complementing existing renewables such as solar [photovoltaic] and wind, reducing the need for large-scale storage solutions… When deployed at scale, SBSP would provide substantial environmental, economic, and strategic benefits for Europe, including energy security.”

Movie credit: European Space Agency

Currently, the SBSP concept remains economically infeasible due to the large amount of material required to construct the solar arrays and the high launch costs to orbit. However, the cost per kilogram of launching material into orbit has decreased significantly in recent years and is expected to drop to approximately $100 per kilogram once SpaceX’s Starship becomes fully operational. It may also be possible in the near future to construct the solar arrays using material mined primarily from near-Earth asteroids, thereby avoiding the need to launch the material from Earth. This approach is possible because of the fact that many near-Earth asteroids require significantly less delta-v (i.e., energy) to reach than it takes to launch from Earth’s surface. It would, however, require a robust in-space manufacturing sector to convert the raw asteroidal materials to useable alloys.

There are still many unresolved concerns around SBSP, especially with regard to the risks posed by persistent and powerful microwave beams passing through the Earth’s atmosphere. Many critics have pointed out the danger such beams pose to aircraft and migrating birds. While the flight paths of the former can safely be directed around the beams, birds are notoriously less amenable to NOTAMs (Notices to Air Missions).3 Similarly, some critics are concerned that SBSP could be easily weaponized by redirecting the beams at terrestrial targets—effectively turning the solar arrays into giant death rays—or using them to melt the ice caps à la James Bond villain.

From a technical standpoint, the future of SBSP is bright. Its success, however, is more likely to be constrained by social and political considerations.

Lunar Resources

As Earth’s nearest celestial neighbor, the Moon is an energetically-favorable location to exploit for its resources.4 Averaging a mere 384,400 km from Earth, any resources extracted from the Moon could be returned to Earth within a matter of days and at a relatively low cost. Alternatively, lunar resources could be used in-situ—to sustain a lunar base, for example—or used to provision spacecraft headed deeper into space.

Unfortunately, as suggested by its drab, airless surface, the Moon isn’t exactly a cornucopia of useful resources. Its surface is primarily anorthosite in the highlands and basalt in the mare—neither of which is particular interesting as an ore given their high abundances on Earth. Nonetheless, 60 years of extensive exploration, including six crewed landings, have allowed scientists to identify a number of potentially useful resources that might be extracted from the lunar surface.

Foremost among these lunar resources is water ice, located in permanently-shadowed craters near the lunar poles. Far less abundant, but still potentially useful, is helium-3 embedded in the lunar regolith, deposited by billions of years of solar wind. Another potentially useful resource present in the lunar regolith is titanium dioxide (TiO2), also called rutile, which could be used to manufacture heat shields for aerobraking and reentry on other celestial bodies.

Lunar water (H2O)

Relative to Earth, the Moon is exceptionally dry. That doesn’t mean, however, that it’s entirely devoid of water. Indeed, in 2009, NASA’s Moon Mineralogy Mapper (M3) spectrometer located onboard the Indian Space Research Organization’s (ISRO) Chandrayaan-1 lunar orbiter detected water ice on the surface of the Moon (Figure 2). In 2018, after extensive research, NASA finally confirmed the presence of water ice at the lunar poles on the basis of the M3 results.

The origin of the Moon’s water is still debated, but the prevailing scientific theory is that the water was delivered by impacts of water-bearing comets, asteroids, and meteoroids over billions of years. Other scientists have suggested that it may have also been produced in-situ by hydrogen ions (i.e., protons) of the solar wind impacting oxygen-bearing minerals. In any case, it is likely that both of these delivery mechanisms have contributed to the Moon’s water content since its formation.

There are two difficulties associated with accessing the water deposits at the lunar poles. The first problem is reaching the lunar poles in the first place; the fuel required for a spacecraft to land (and return) from the Moon’s poles is significantly higher than that required to reach the equatorial regions. The second problem is the low angle of the Sun on the horizon at the lunar poles; the solar power available to power the extraction and processing equipment—as well as any life support or other systems—is significantly less than at the lunar equator. Thus, any mission to extract and return (or utilize in-situ) the lunar polar water will have to contend with these constraints.

Surprisingly, water ice deposits at the lunar poles are not the only reservoir of water on the Moon’s surface. In 1976, the Soviet’s robotic Luna 24 probe landed on the lunar surface at Mare Crisium and took several samples at depths ranging between 100-200 centimeters. These samples were returned to Earth where, in 1978, laboratory analysis showed that the samples contained 0.1% water by mass. This water is locked in the lunar regolith, meaning that it would first have to be separated from these minerals before it could be used. While not as accessible as water ice, this water may be a valuable (but minor) byproduct of helium-3 mining, which we discuss next.

Lunar helium-3

In the late 1990s, NASA’s Lunar Prospector mission discovered evidence of small amounts of helium-3 on the lunar surface, leading to speculation that it could be mined as a potential fuel for nuclear fusion.

The source of this helium-3 is surprising. Over billions of years, the solar wind has enriched the lunar regolith with isotopes of helium. With two protons and only one neutron, helium-3 is a light isotope of helium that is stable (meaning that it doesn’t spontaneously decay over time). It is considered to be extremely valuable due to its extreme scarcity on Earth and its potential use as fuel in aneutronic fusion reactors.5

More recently, the Chinese lunar orbiter Chang-E 1 (嫦娥一号) measured the helium-3 abundance in the lunar regolith, identifying deposits with more than 50 parts per billion (ppb) per square meter. Most of these deposits are located near the equator on the lunar nearside (see Figure 4) and thus relatively easy to reach with spacecraft.

However, the extremely low concentration of helium-3 in the lunar regolith raises questions about the economic feasibility of mining lunar helium-3. Indeed, in order to extract 1 gram of helium-3 from the lunar surface, we would have to mine and process 150 tons of regolith. Not only does this present serious technical difficulties, but it also risks permanently altering the surface of the Moon—likely to the extent that the scars would be visible with the naked eye from Earth.

Indeed, the characteristic light gray color of the lunar regolith is the result of more than four billion of years exposure to sunlight and the solar wind. However, this light gray color only extends a few centimeters below the surface and the regolith below this depth evinces a much darker color. Mining the regolith at depth while leaving the top few centimeters undisturbed is not an option, because the top few centimeters is exactly where the helium-3 has been deposited by the solar wind and, consequently, that is where the concentrations are highest. Thus, any feasible method of extraction would overturn large swaths of the lunar surface, exposing the darker regolith and changing the characteristic color of the Moon forever.6

Given that many of Earth’s cultures and religions hold the Moon to be sacred, not to mention the billions of people that enjoy the Moon simply for aesthetic reasons, lunar helium-3 mining is extremely controversial. Indeed, there are proposals to designate the Moon as the first extraterrestrial “national park” to protect it from mining and tourism and thereby preserve it for future generations.

Note that such preservation frameworks may allow for helium-3 extraction on the far side of the Moon, which is always out of sight of Earth because the Moon is tidally locked to Earth. However, given the low concentrations of helium-3 on the lunar farside and the increased mission complexity of missions to that part of the Moon, such frameworks might be tantamount to banning lunar helium-3 mining altogether.

Titanium Dioxide (TiO2)

One major byproduct of regolith processing is titanium dioxide, also known as “rutile”. Research has demonstrated that loose rutile grains can be welded into very strong material for heat shields. This implies that practical heat shields could be manufactured in reusable molds on the Moon and subsequently used for aerobraking maneuvers on ships traveling to celestial bodies with sufficiently dense atmospheres (e.g., Earth). While lunar TiO2 would likely not be profitable to produce on its own, it could be a useful byproduct of the processes used to extract helium-3 or oxygen from the lunar regolith.

Lunar base

If, as we just saw, the mining of lunar resources is not as efficient or as feasible as expected, then why is everyone talking about going back to the Moon before going to Mars? The answer lies in the energy needed to reach Mars from Earth’s surface, as opposed to launching from the lunar surface. Earth’s attraction is several orders of magnitude stronger than that of the Moon, so departing from the Earth's surface requires a lot more energy. One proposed idea is, therefore, to set up a base on the lunar surface or in lunar orbit (in what is called the Lunar Gateway). From these locations, the spacecraft used to transit to Mars can assembled and launched at much lower cost, thereby enabling the possibility to bring much higher masses.

Asteroids & Comets

Scourge of the dinosaurs7 and harbingers of bad omens8, asteroids and comets, respectively, tend to have a bad reputation. This reputation is changing, however, thanks to humanity’s newfound interest in asteroid (and comet) mining. While science fiction authors have been writing about asteroid mining for the better part of a century, only the recent commercialization of space has moved asteroid mining from the realm of science fiction into the realm of near-term possibility.

Small and unremarkable compared to the planets, asteroids expertly evaded detection until 1801. Similarly, comets went largely unnoticed outside of the rare events during which they passed near the Earth while exhibiting a noticeable tail. As a result, it took the astronomy community time to discover these minor objects at scale, study them, and understand their location and distribution in the solar system.

Now, thanks to widespread surveys with modern telescopes, we know that three major reservoirs of asteroids and comets exist in the solar system: the asteroid belt between the orbits of Mars and Jupiter, the Kuiper Belt beyond Neptune out to about 55 AU, and the Oort Cloud extending from roughly 2,000 to 200,000 AU. In addition to these major reservoirs, many asteroids have been discovered in the region of Earth’s orbit. This population of objects is known as the near-Earth objects (NEOs).

Interestingly, many of the near-Earth asteroids are easier to reach and return from than the Moon9 (in that it takes less energy). This is largely due to their small size, which means that they have negligible gravity wells from which spacecraft need to expend energy to escape. In order to land (successfully) on the Moon, a spacecraft in lunar orbit has to reduce its velocity by roughly 2 km/s, expending a large amount of fuel in the process. Subsequently, the spacecraft has to climb out of the gravity well of the Moon and into lunar orbit by increasing its speed by 2 km/s—this time with whatever additional resources it’s carrying. In contrast, an astronaut standing on the surface of a typical asteroid could almost jump out of the gravity well.

As the building blocks of planets (and moons), asteroids contain many of the same resources that are found on Earth. Surprisingly, Earth is seemingly poor in many of the heavy elements that are readily found in asteroids. However, this is only because these elements sank to the core of the planet early in Earth’s history and, therefore, are no longer found at high concentrations in the crust. The heavy elements that are found today in the crust were likely delivered by asteroids long after the formation of the Earth. In any case, any material located in or near Earth’s core is not accessible to humans and asteroids are thus an attractive source of these resources.

Asteroidal and cometary water (H2O)

Water is so abundant here on Earth that it doesn’t seem like it would be a profitable resource to extract in space. However, its ubiquitous use combined with the high cost of launching water into orbit around Earth make it one of the most potentially profitable resources in space. Indeed, the historical price of bringing water to low Earth orbit is around $10 million per ton—$20 million if you need it in high Earth. While this cost is coming down with the decreasing trend in launch-to-orbit prices, it will likely remain a lucrative resource to sell in space.

In space, water can be used for a wide range of applications. As H2O, it can be used for life support, most notably as drinking water and effective radiation shielding. Broken down into its constituent parts—hydrogen and oxygen—it can be used as breathable air (O2) or as rocket fuel (liquefied hydrogen and oxygen).

Perhaps the most easily accessible and economically feasible sources of water in space are near-Earth asteroids and comets. With 20,000 NEOs currently cataloged, there are many candidates that could be reached with current technology. Amazingly, a typical near-Earth asteroid of just 9 meters across could potentially yield $1 billion in water. Given that nearly all of the 20,000 known near-Earth asteroids are larger than this, there is a lot of water in Earth’s local neighborhood.

Platinum Group Metals (PGMs)

The platinum-group metals include ruthenium, rhodium, palladium, osmium, iridium, and platinum. On Earth, these metals are extremely valuable for their resistance to wear, ductility, electrical properties, and use as catalysts. Notably, PGMs are used in anti-cancer drugs, electronics, and as catalytic converters for automobiles, which reduces harmful pollutants in their exhaust. PGMs are likely to play an equally important role in future in-space manufacturing.

In asteroids, PGMs are found at concentrations much higher than that of Earth’s crust. This is because most asteroids never underwent melting and differentiation and therefore these elements did not sink to the center of these bodies like on Earth. However, unlike asteroidal water, even the most precious metal-rich metallic asteroid contains only about 30 grams of precious metals per ton. Thus, in order to realize at least $1 billion in value (a common benchmark in asteroid mining for economic feasibility), an asteroid of 200 meters across would be required. Surveys and studies suggest that there are only about 10 such asteroids that are accessible from Earth.

Asteroid mining, science, and planetary defense

Proponents of asteroid mining are quick to promise an inexhaustible supply of resources and infinite wealth, quoting scarcely believable valuations of several quintillion dollars for a single asteroid—never mind that such a number exceeds the global GDP of Earth by several orders of magnitude.10 At the same time, resources sourced from asteroids and comets are put forward as a solution to resource scarcity on Earth and a solution to the climate crises, as well as the key to humanity’s expansion into the solar system and beyond.

Whatever the true value of the asteroids and comets might be, there are tangible benefits to mining at least some of these bodies. For example, an early target for asteroid miners might be the subset of Earth-crossing asteroids that pose an impact risk to Earth. By identifying and incentivizing these asteroids for mining, terrestrial governments could remove an existential threat to humanity while simultaneously supporting the asteroid mining sector.

Similarly, asteroid mining companies could work with (rather than against) scientists by offering to carry out a range of scientific measurements on each asteroid or comet before they begin mining it, as well as return samples for study. In any case, it would be to the asteroid mining companies’ benefit to conduct many of these measurements before extraction in order to better understand and optimize their mining operations. The subsequent scientific analysis of this data could greatly improve the efficiency of asteroid mining operations. To scientists’ benefit, this would greatly expand the number of asteroids and comets they could study, especially given that the current funding for such missions is extremely small and unlikely to rise. The additional funding from governments and scientific institutions in return for scientific data would help fund the asteroid mining companies’ operations.

Whom do space resources benefit?

When discussing space resources, it is often taken for granted that the extraction of these resources will benefit “humanity”. While this is a grand sentiment, it is equally naive. Indeed, a short review of human history will show that such endeavors rarely end up benefiting humanity at large. Rather, resource extraction tends to benefit, at best, a nation state while enriching a small handful of privileged individuals.

Given the staggering scale of space resources, their exploitation risks super-charging wealth inequality on Earth (which is already a significant problem) and destroying the economies of developing nations that rely on terrestrial resource extraction. Thus, while we are quick to ask whether we can extract space resources, the question should perhaps be should we extract space resources? If the answer to this question is yes, then how do we go about it in a way that truly benefits humanity at large?

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Bibliography

• DeMeo & Carry (2014), Solar System evolution from compositional mapping of the asteroid belt, Nature

• Glaser (1968), Power from the Sun: Its Future, Science

• Kardashev (1964), Transmission of Information by Extraterrestrial Civilizations

• Minniti et al. (2004), A New Search for Dyson Spheres in the Milky Way

• Sviatoslavsky (1993), The Challenge of Mining He-3 on the Lunar Surface

Suggested Reading

1. Asteroids: How love, fear, and greed will determine out future in space, Martin Elvis, 2022, Yale University Press

2. Mining the Sky: Untold riches from the asteroids, comets, and planets, John S. Lewis, 1996, Helix Books

3. The Value of Science in Space Exploration, James S.J. Schwartz, 2020, Oxford University Press (specifically: Chapter 5: The need for forbearance in space resource exploitation)

Hence, it becomes important to understand its causes and its effects in order to tackle it efficiently and to focus our efforts on where it truly matters:

• Causes: Track the origin and distribution of the main sources of climate change such as emissions from fossil fuels, livestock farming, landfills, but also deforestation.

• Effects: Monitor the occurrence of events and parameters such as floods, droughts, heat waves, wildfires, sea levels, air quality, and melting of glaciers just to name a few.

Something that encompasses both these points are the essential climate variables. The Global Climate Observing System (GCOS) has identified a set of 54 atmosphere, land, and ocean variables which are key markers of our planet’s evolving climate. These are called Essential Climate Variables (ECVs), and around 60% of them can solely be tracked through the aid of satellites, as highlighted by the Global Climate Observing System. An example of this contribution is the European Space Agency's Climate Change Initiative, which furnishes reliable and long-term data concerning 21 ECVs (ESAECV).

The following chapters try to give a list of examples where satellites can provide useful data. It is clear that separating causes and effects is not always possible since many phenomena in climate change are a vicious cycle of causes and effects. As EPOPS develops further, more articles about the detailed contribution of satellite data will be published (and directly linked in this article).

Causes

There are several causes behind climate change, and covering them all is beyond the scope of this article, so we will only scratch the surface and mention the main drivers.

Greenhouse gases (GHG) emissions

While measuring the levels of CO2 or other greenhouse gases at a specific location is simple, the main challenge with GHG emissions is being able to track where they are generated exactly. Only this way, a country can be held accountable for not respecting its previous climate agreements. High-resolution GHG measures are now available from many satellite platforms, including NASA’s OCO-2 and OCO-3, the European Space Agency’s METOP-A and TROPOMI (Sentinel-5P) platforms, China’s TANSAT, and the Japan Space Exploration Agency’s GOSAT and GOSAT-2 (BrookingsEdu).

As an example, this image from NASA shows the concentrations of CO2 worldwide in 2006. The difference between the two hemispheres is very clear.

Another interesting example of GHG emissions tracking is the startup AIRMO which is able, thanks to their new LiDAR system, to track and measure emissions with unprecedented accuracy, and even to detect leakages in gas pipelines.

Deforestation, ocean pollution, and biodiversity

Land and oceans absorb half of human emissions every year. Preserving them is essential. Satellites can be used to track deforestation. Some example platforms are Global Forest Watch and Restor, which track forests and reforestation sites.

In the US, the NOAA (National Oceanic and Atmospheric Administration) is mainly responsible for monitoring the oceans and the atmosphere. NASA often used satellites to monitor oil spills, such as at the Mississippi River delta or at the Gulf of Mexico, which is essential to minimize the spread and damage to the aquatic environment.

From ESA’s side, the SMOS satellite mission launched in 2009 monitors soil moisture and ocean salinity, which are essential parameters both for the terrestrial and aquatic environments and their vegetation.

Effects

According to the World Meteorological Organization (WMO), climate and weather-related disasters surged five-fold between 1970 and 2019 (WMOReport).

A disaster is recorded in their database if any of the following criteria are fulfilled: 10 or more people reported killed, 100 or more people reported affected, declaration of a state of emergency, or call for international assistance. These recorded disasters mainly consist of storms, floods, wildfires, heatwaves, droughts, and landslides (UNClimate). The following plot shows a summary of the reported extreme events in Europe in 2022. 40 such disasters were recorded, which caused 16’365 deaths and US$ 2.13 billion in damages. While extreme storms caused 98% of all economic damages, heat waves caused 99.6% of all deaths (the record-breaking heat waves in summer 2022). Wildfires also affected many people (and also destroyed large forests, which as we mentioned are important CO2 sinks).

The picture looks much different in other regions of the world. First of all, 90-91% of all climate and weather-related deaths between 1970 and 2019 happened in developing countries1. This table gives a short summary of the different world regions and the effect of the disasters in the 1970-2019 period2.

The economic losses are difficult to compare since regions have much different infrastructures. Floods and storms accounted for most of the recorded disasters, but for example, in Africa and Europe most deaths were caused by heat waves and droughts (well-known is the drought that hit Ethiopia and Sudan in 1983 and caused 450’000 deaths).

From the numbers, it’s clear that the effects highly depend on the region. So why and how can satellites help?

Well, even though the extreme events and economic losses increased worldwide, the number of deaths per decade decreased. Damages caused by storms are also steadily increasing. Other than that, it is difficult to make predictions right now: while we might get better at avoiding deaths from droughts (which heavily impacted the numbers from the past, making us now think that deaths are decreasing overall), we should not underestimate the deaths caused by other types of disasters.

The reason for this trend is explained by the WMO Secretary-General Petteri Taalas:

Economic losses are mounting as exposure increases. But, behind the stark statistics, lies a message of hope. Improved multi-hazard early warning systems have led to a significant reduction in mortality. Quite simply, we are better than ever before at saving lives.

This once again shows the importance of satellite data: it can help in prediction and prevention, disaster relief, and emergency response planning, which can all save thousands of lives.

The fact that deaths are currently decreasing does not mean that they will continue to do so: on the contrary, the full extent of the effects of global warming scenarios, such as a 1.5°C increase in temperature, is yet to be witnessed. Disasters and deaths will increase and satellites will play a crucial role even more than they already do today.

Further, only looking at big disasters is not enough to properly evaluate the effects of climate change. For example, slowly rising sea levels, and slowly increasing temperatures, will cause damage (not only purely economical but also directly to food production) and deaths over longer periods of time, which are not captured by disasters.

Types of disasters

This list provides a more detailed description of how satellite data can help in tracking extreme weather and climate events:

• Wildfires: satellite data not only assist in the delineation of fire-prone areas but also enables the prediction of potential fire outbreaks. The advent of satellite technology has ushered in an era of heightened efficacy in monitoring wildfires, with real-time observations spanning vast regions becoming an attainable reality. Satellites operated by the US NOAA, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), and NASA's polar orbiters and geostationary platforms have emerged as sentinels in the detection and tracking of fires on a global scale. As an example, the European COPERNICUS EMS system allows us to track wildfires in real-time and to predict them.

  

• Floods: Satellites, equipped with the capability to provide a comprehensive view of flood occurrences globally, lend invaluable insights into the scale and extent of these events. By utilizing weather patterns and analyzing ground conditions, satellites contribute to the development of predictive models for flood forecasting and the high-resolution imagery plays a pivotal role in expanding our comprehension of the dynamics governing flood formation, thereby enhancing flood models and optimizing adaptation strategies. They also contribute to monitoring rising sea levels, a consequence of climate change that poses substantial risks to coastal communities and ecosystems. Satellites equipped with altimeters can precisely measure changes in sea level by monitoring the height of the ocean surface. This data aids in understanding the magnitude and spatial distribution of sea level rise, enabling coastal planning, hazard assessments, and the development of adaptation strategies to protect vulnerable areas.

• Heatwaves: these pose significant risks to human health, ecosystems, and infrastructure. Satellites provide valuable data that helps us track and analyze heatwave events. By monitoring temperature patterns from space, satellites contribute to the identification of regions experiencing extreme heat conditions. This information aids in assessing the frequency, duration, and intensity of heatwaves, allowing for better preparedness, targeted interventions, and the implementation of heatwave management strategies.

• Droughts: droughts have severe implications for water availability, agriculture, and ecosystems. By measuring soil moisture levels, vegetation health, and precipitation patterns, satellites contribute to the early detection and tracking of drought-prone regions. This data assists in water resource management, crop planning, and drought mitigation efforts.

Further efforts

A very interesting application of all satellite data is a so-called “Earth digital twin”: a digital twin is a model that tries to simulate the dynamics of a complex system. To create such a model, tons of data, known physical relations (formulas from physics, chemistry, etc.), as well as a powerful computation platform (like a supercomputer) are needed. Both ESA and NASA are working to develop an Earth digital twin (ESA, NASA).

The following video from ESA provides an example of some of the measurements that ESA’s satellites are able to take.

A very detailed Earth digital twin allows us to simulate different scenarios (e.g. pollution levels), understand some effects, and better predict their occurrence.

Conclusion

Looking at the examples brought, we believe that satellites are an essential tool to better understand climate change and the extreme weather events that it causes. As María Fernanda Espinosa Garcés, President of the UN General Assembly, nicely said at COP 24 about satellite data:

If you can’t measure it, you can’t manage it.

Both ESA and NASA spend slightly more than 20% of their yearly budget for Earth observation and/or planetary science. This corresponds to the biggest expense category for ESA, and the second biggest for NASA (depending on which categorization is used). This is an undeniable signal of how important Earth is for both agencies. The ESA Earth Explorer missions, of which the previously mentioned SMOS is also part, are pivotal toFutureEO, ESA’s Earth observation research and development program.

Bibliography

• ESA, Essential Climate Variables

• Brookings Edu, Deploying ‘sentinel satellites’ to monitor greenhouse gas emissions

• NASA CO2 concentrations 2006

• AIRMO

• Global Forest Watch

• Restor.eco

• Mississippi River delta

• Gulf of Mexico

• Full WMO Report

• WMO Atlas of Mortality and Economic Losses from Weather, Climate and Water Extremes (1970–2019)

• ESA Earth Digital Twin

• NASA Earth Digital Twin

• ESA, View from above

• ESA Earth Explorer missions

Why are space debris relevant?

Over the past six decades of space exploration, countless rockets, defunct satellites, and fragments from collisions have accumulated in Earth's orbit. The European Space Agency estimates that there are approximately 30’000 objects larger than 10 cm, and 670’000 objects larger than 1 cm hurtling through space (ESACleanSpace). The greatest risk to space missions is usually from untracked debris between 1 and 10 cm in size. Larger pieces can be tracked and then avoided, and the impact from smaller pieces is usually survivable.

The impact

Space debris presents a serious threat to both operational satellites and human space exploration. The average speed of any object in LEO is approximately 28’000 kilometers per hour. At these speeds, even a small fragment can cause catastrophic damage to an active satellite (or to the ISS). Collisions with space debris can lead to the destruction of vital communication networks, and weather forecasting systems, and even jeopardize astronaut safety.

The Kessler Syndrome, proposed by NASA scientist Donald J. Kessler in 1978, suggests that the sheer quantity of space debris may eventually reach a point where collisions become self-sustaining. Each collision generates more debris, increasing the chances of further collisions, and potentially rendering certain regions of space unusable. Such a scenario would severely impede future space missions, including the deployment of satellites, space telescopes, and crewed missions.

Some basic concepts

Before delving into the topic of space debris, it's useful to explain a few concepts: which main orbit categories exist? Where are most satellites located? Which disposal strategies exist? This section will provide a brief overview. If you have a good knowledge of satellite orbits and operations, feel free to jump to the next section “Increase of space debris”.

Orbital heights

Satellites are deployed in different orbits depending on their intended purpose.

• Low Earth Orbit (LEO) is the closest to Earth, ranging from a few hundred to 2’000 kilometers in altitude. Here is where the vast majority of satellites are. As an example, the International Space Station (ISS) is at around 400km of altitude. Objects in LEO orbit the earth in 90-120 minutes with a velocity of around 7 km/s. Since LEO is the closest to earth, it is also the one where air drag is the most relevant. Even though the air density is much smaller than at sea level, it is still able to slow down a satellite enough over time, in a period ranging from a few weeks to a few decades, depending on orbit altitude and object. When a satellite is slowed down enough, it re-enters the thicker parts of the atmosphere and it burns up, leaving nothing behind. More about this will follow in the section on disposal strategies.

• Medium Earth Orbit (MEO) lies between LEO and GEO. It is not used so often because it does not give the advantages of LEO (easier launch), and neither that of GEO (geosynchronous). Further, in MEO there are usually more intense radiations (see Van Allen radiation belts).

• Geostationary Orbit (GEO)1, is approximately 35’7862 kilometers above the equator3. GEO is interesting because the orbital period is of around 24 hours. This means that a satellite in GEO always follows the same point on Earth. Hence, satellites there have a much smaller orbital velocity, compared to LEO, of around 3 km/s.

Each orbit serves specific functions, such as Earth observation, communication, and navigation. The figure below provides an overview of the active satellites in orbit. Debris are not shown.

Satellite life phases

The life of a satellite usually consists of three main phases:

• Launch: A rocket is launched and releases multiple satellites at their target orbits. Thanks to complex deployment mechanisms, a single launch can deploy dozens of satellites in slightly different orbits.

• Operations: The satellite is operated. The lifetime can generally vary between a few months and a few decades. The operation phase generally includes small adjustment maneuvers which have to be performed by the on-board propulsion system, in order to maintain the right position. Due to different effects (solar pressure, Earth oblateness, air drag, etc.), the satellite would otherwise slowly drift and change position over time, leaving its operational orbit.

• Disposal: This last step is not always performed, especially during the first years of space exploration. A satellite reaching its end of life can just be left floating in space at its operational orbit, but this creates a big risk of collisions with future satellites. Hence, responsible disposal strategies are employed to mitigate these risks of debris accumulation.

Disposal strategies

The following provides an overview of the three most common disposal strategies.

• De-orbiting is a common approach where satellites use their propulsion systems (or simply drag if the orbit is already low enough) to lower their altitude, allowing them to re-enter Earth's denser atmosphere and burn up. This minimizes the risk of debris reaching the Earth's surface. Isn’t it bad to just burn up things in the atmosphere? Well, this was covered by different studies which showed that the effect on climate change of re-entry burn-up, even in the worst-case scenarios considered, is essentially completely negligible (ReEntryBurnUpStudies).

• For satellites in higher orbits like GEO, a common strategy is to move them to a graveyard orbit after their operational lives. These retirement orbits are designated regions where retired satellites and space debris are intentionally moved. This stable orbit above the GEO belt reduces collision risks and minimizes debris creation.

• Passivation is another strategy, involving depleting a satellite's remaining fuel and releasing stored energy to render it inert. This mitigates the risks associated with uncontrolled or accidental explosions in orbit.

Increase of space debris

The escalating number of space debris is a result of several factors:

• Overall growth in satellite launches: If before 2010 there were less than 1’000 active satellites, as of May 2023 there are almost 8’000. It is also for this reason that SpaceX and OneWeb, the two companies with the largest number of satellites in orbit, pledged to de-orbit all their satellites at the end of their operational life. More launches also mean more remnants of space missions, such as spent rocket stages and, with time, inactive satellites if they are not disposed.

• Collisions: Those can take place between any object in orbit (active or inactive satellites, space debris, etc.). Since space debris larger than a few cm can usually be tracked (the minimum size depends on the orbit), warnings of possible imminent collisions can be issued. For example, the ISS has a defined probability threshold of 1/ 10’000. If any object is expected to collide with the ISS with a probability above that, a collision-avoidance maneuver is performed. During the first years of the ISS, one maneuver per year was performed. In 2011, it was already closer to 6 maneuvers per year (NASAOrbitalDebrisNews). Even a 1 cm debris, could cause severe damage to the shield of the ISS. Clearly, these avoidance maneuvers can only be performed by satellites with a propulsion system, which is not the case for all satellites in orbit. After a collision, debris can spread out over a large range of altitudes (even up to one hundred km around the orbit of the object).

• Unwanted explosions: these can generally happen due to batteries malfunctioning, or due to propellant left in the tanks of the spacecraft.

• Anti-satellite weapons (ASAT): ASAT missiles are missiles launched from Earth designed to destroy satellites for strategic or tactical purposes. The only countries to conduct ASAT tests so far are the USA, Russia, China, and India. Interestingly, these tests often involve targeting the country's own satellites. This practice allows nations to showcase their technological capabilities and assert their strength and power in space.

Why are ASAT tests a thing?

Satellites play a crucial role in defense and security. In the realm of nuclear deterrence, satellites equipped with advanced sensors enable early detection of missile launches, providing critical warning time for potential targets to initiate necessary defensive measures. This is only an example, but there are dozens more related to secure and real-time communication of military forces, monitoring activities of adversaries, surveillance and reconnaissance, etc. The fact that the U.S. Space Force was established in 2019 (the first new branch of the armed services since 1947) is a testament to the growing relevance of space in the defense sector. And ASAT tests are, simply put, a show of strength, like all the missile tests performed each year in the middle of the sea.

How are space debris tracked and monitored?

Efforts to track and monitor space debris are crucial for ensuring the safety of operational satellites and spacecraft. Tracking systems, such as radar and optical telescopes, are employed to identify and catalog space debris. For example, the United States Space Surveillance Network (SSN) constantly monitors the trajectories of thousands of known objects in space.

In recent years, advances in tracking technology and data analytics have improved our ability to identify and track smaller debris. These systems help provide early warnings of potential collisions, allowing satellite operators to perform avoidance maneuvers to safeguard their assets.

A closer look at the numbers

If we take a closer look at the number of objects tracked, we notice a few interesting things: while spacecrafts, rocket bodies, and mission-related debris see steady but controlled growth, the line of fragmented debris clearly shows sudden jumps.

Notable increases in debris, with more than 500 pieces of trackable debris recorded, corresponding to:

• 1986, 506 pieces, residual propellant explosion: SPOT 1 rocket body

• 1996, 756 debris, residual propellant explosion: STEP 2 rocket body

• 2007, 3549 debris, ASAT test: performed by China on its Fengyun-1C satellite

• 2008, 511 debris, end-of-life self disintegration: Kosmos 2421

• 2009, 2375 debris, accidental collision: between Kosmos 2251 and Iridium 33

• 2021, 1652 debris, ASAT test: (not shown in plot) performed by Russia on its inactive Kosmos 1408 satellite. The event triggered an alarm procedure on the ISS. The seven astronauts and cosmonauts aboard were instructed to retreat to their spacecraft ready for a possible evacuation should the ISS be struck. ISSwarn

It should be noted that all these notable debris formations took place in LEO. A more complete list is available on Wikipedia, List of space debris-producing events.

Additional challenges

In the introduction, we saw how most satellites are located in LEO. Hence, as expected, many notable accidents happened in LEO. However, there is an additional challenge that mostly applies to GEO: the orbit has to be very close to the previously mentioned 35’786km of altitude in order to maintain a fixed position with respect to the ground. Satellites in LEO can change their altitudes by dozens of km with little effect on their mission. A satellite in GEO decreasing its altitude by 10 km, would cause a shift of the satellite over a period of one month equal to the distance Paris-Munich. I guess that Les Parisiens are not interested in getting the weather forecast for Bavaria instead of theirs. This means that every satellite operator tries to put their satellites as precisely as possible in the GEO region, which is getting overcrowded over time. This is why GEO is considered a hot spot in terms of debris, as there are no other orbits which such characteristics.

Conclusion - What does the future hold?

Regulations

With the improvement of tracking and maneuvering techniques, the probability of accidental collisions decreases. However, with 2 of the 3 events with the most debris generated being ASAT tests, it is clear that more regulations are needed. Last year, US Vice President Kamala Harris announced that the United States government is committed to ending the practice of anti-satellite missile tests, urging other nations to follow (USAendingASAT).

Additionally, international guidelines and regulations have been established to promote responsible space operations. For instance, the Inter-Agency Space Debris Coordination Committee (IADC) provides recommendations on spacecraft design, disposal practices, and collision avoidance measures.

Time decay

A positive point is that the number of space debris tends to decrease over time if no new collisions take place, as some debris decay and burn up. As we saw, most satellites (and hence space debris) are in LEO, where they can usually decay and burn up more quickly. However, it is clear that the space debris strategy should not count on this, mainly because above certain heights, the orbit decay to re-entry can easily take hundreds of years.

Active debris removal

Several initiatives are also underway to actively remove space debris from orbit. Concepts like space-based robotic systems and large nets to capture debris are being explored. One such project, ClearSpace, based in Lausanne, has a first mission planned in 2025 for the removal of a 100 kg space debris, and the launch contract was already signed in May 2023 (ClearSpace-1).

Final words

Overall we believe that ASAT tests should be prohibited as the debris caused can affect any object in orbit without distinction, and not only those of the space powers involved. Further, spacecraft and mission design laws (rather than guidelines only) should be established. And finally, active space debris removal missions should be launched to test the technology. Every old piece of space junk removed decreases the possibility of a collision which could generate thousands of debris.

Bibliography

• On the atmospheric impact of spacecraft demise upon reentry

• ESA, How many space debris objects are currently in orbit?

• NASA, Orbital Debris - Quarterly News

• Seradata, ISS alarm

• Wikipedia, List of space debris producing events

• CNBC, U.S. commits to ending anti-satellite missile testing

• SpaceflightNow, ClearSpace-1 launch contract

What is crystallization?

Crystallization is the process of forming a solid material with a regular, repeating arrangement of atoms, ions, or molecules. It involves the transformation of a substance from a liquid or gaseous state into a solid state, where the particles come together in an organized pattern to create a crystal structure. During solidification, various materials can undergo crystallization. This includes minerals such as quartz and calcite, metals like iron and copper, salts such as sodium chloride (table salt), organic compounds like sugars, amino acids and last but not least proteins. The resulting crystal structures provide unique properties and play a crucial role in the functionality and characteristics of these materials. It should be noted, that not all materials which solidify undergo crystallization.

Advantages of microgravity-grown crystals

Already in 1981, Littke conducted the first crystallization experiments (Protein Single Crystal Growth Under Microgravity, Littke et al. 1985). Since then, a multitude of experiments have been conducted on the topic. For example, Merck alone conducted experiments on 10 separate shuttle flights (NASA, 2015). Why are such crystals needed though? These larger, purer crystals grown in microgravity offer better insights into the complex crystalline structures, which are difficult to grow on Earth. Most notably, the structure of proteins can be better understood. Understanding these structures helps to find new drugs that fit better to the proteins at hand, a process called structure-based drug design. Enhancing their specificity and reducing side effects. (NASA, 2015)

The image above shows the clear difference that was achieved between crystals grown on Earth to crystals grown in space. Such crystals are then hit with X-ray beams. Depending on the diffraction or bending of the beams, the protein structure can be determined (Lab Chat with Steven Almo, Ph.D.). One such protein, the protein which binds penicillin, is shown below. By understanding the structure of these proteins, drugs can be engineered that fit to this specific protein.

Going into detail here about how structure-based drug design works exactly would be too exhaustive. However, within literature, there are great sources that explain more in detail how the current state of the art works. One such example is linked in the bibliography (Cao et al. (2022)).

New effects start to play a role

Surprisingly, even to the scientific crystallization community, new effects, which were previously neglected, started to dominate in microgravity environments. Notably, the Marangoni effect starts to influence the growth of crystals, as they become the dominating effect in the absence of convection. (E. H. Snell & J. R. Helliwell (2021)).

The Marangoni effect stems from mass transfer due to gradients of surface tension along an interface of two phases. In wine glasses, this effect is often visible. As shown in the image above, alcohol tends to evaporate more on the edge, which causes a decrease in alcohol concentration and a subsequent increase in surface tension. Due to this, more of the high percentage alcohol liquid is pulled up by the meniscus. Eventually, gravity will overtake again and pull down the liquid, forming the commonly known wine tears. Important here is not to confuse this effect with the capillary forces, which are what drives the initial shape of the meniscus on the wine glasses wall. (COMSOL (2017))

Even in space, gravity still exists

Another influence on crystal growth, which might come as a surprise, is the non-complete absence of gravity aboard space missions, hence the reason these environments are called micro and not zero gravity. An effect commonly called G-jitter, which denotes the period of quasisteady residual acceleration encountered within spacecrafts. Reasons for such accelerations can be as benign as fans, orbital maneuvers, or even just the movement of astronauts within the spacecraft, the latter of which had been shown to directly impact crystal growth rates.

In the above figure, after an initial settling time, spikes are visible in the growth rate at the points where it was found that the crew exercised during these times. Through their movement alone, they generated prolonged periods of up to 500µg. (Snell et al. (1995))

Crystallization in microgravity proving space is a viable option for manufacturers

The examples mentioned earlier show, that protein crystals grown in microgravity can have an impact down here on earth. Furthermore, given the large track record of experiments done in space on this topic, protein crystallization in microgravity is proof that space can and has already been used as an end to end manufacturing site, with samples being tested in space and safely being returned to Earth again. Snell et al. have mentioned, that for the most part damage done to the product during return can be neglected (E. H. Snell & J. R. Helliwell (2021). This opens up new possibilities for manufacturers, using the environment of microgravity to manufacture high-quality goods, which would not be possible on Earth.

Bibliography

Why Protein Structure Matters in Drug Development: Lab Chat with Steven Almo, Ph.D.

Crystallizing Proteins for Drug Discovery, Then and Now, D’Arcy, PSI (Paul Scherrer Institute)

Protein Single Crystal Growth Under Microgravity, Littke et al. 1985

Protein Crystals in Microgravity, NASA, 2015,

Design of protein-binding proteins from the target structure alone, Cao et al. (2022)

Microgravity as an environment for macromolecular crystallization – an outlook in the era of space stations and commercial space flight, E. H. Snell & J. R. Helliwell (2021)

CCD video observation of microgravity crystallization of lysozyme and correlation with accelerometer data, Snell et. al (1995)

Marangoni Effect, COMSOL (2017)

After the decrease of yearly space launches in the 90s, caused by the fall of the Soviet Union and then the end of the Space Shuttle Program, the number picked up again and it reached a new record in 2021, immediately surpassed again in 2022 with around 180 orbital launches. One-third of these 180 launches, were Falcon 9 from SpaceX (GunterSpacePage).

CO2 emissions from rocket launches compared to aviation

One Falcon 9 launch emits around 400 tons of CO2 per launch1. CO2 represents 70% of the total mass emitted, followed by 25% of water vapor. That's a bit more than an Airbus A330 round-trip flight from Paris to San Francisco (340 tons).2

However, there are around 30-40 million flights per year. This puts the space industry at about 0.01% of the total CO2 emissions from aviation (StatistaEmissionsAviation)3. Aviation alone represents around 3% of man-made CO2 emissions globally. The impact of manufacturing space launch systems is also equally very small compared to aviation (purely based on the proportion between rockets manufactured and airplanes manufactured, which usually require similar types of materials and masses).

To put these CO2 emissions in perspective, the entire space industry worldwide in one year polluted almost half the CO2 emissions of private jets in Switzerland alone (166’000 tCO2 as per SwissInfoJets).

This seems to indicate that rocket launches are almost negligible compared to other sectors, but...

The problem with rocket launches’ emissions

Even though we assessed that the CO2 emitted from rocket launches is an order of magnitude smaller than other sources, the effect of rocket launches is more complex, mainly for two reasons:

•Emissions generated at higher altitudes are worse, since they can't be directly absorbed, but instead stay in the troposphere and stratosphere for longer.

•Further, rocket engines do not only emit CO2 or water vapor.

What do rockets actually pollute?

The exact pollution caused by a rocket depends on the propellants used by the rocket engine. EARocketsPollution provides a good overview. Rocket engines can generally either use a “liquid” mixture, where both oxidizer and fuel are liquids, or a “solid” mixture, where both are solids (like a firework).

The typical propellant mixtures, ordered by the “greenest” to the “dirtiest” are:

• Hydrogen (H2) + Oxygen (O2): produces only water vapor (H2O)

• Methane + Oxygen: only CO2 and H2O

• Kerosene + Oxygen: CO2, H2O, but also soot, which we will cover later

• More "exotic" mixtures, both bad but in different ways, like:

  • Nitrogen Tetroxide + Hydrazine

  • Solid rocket engines

What are the effects of some pollutants? Toxic chemicals

The effect of some toxic pollutants can be very strong: hydrazine is highly carcinogenic to humans and is known for polluting some areas of Kazakhstan for decades due to failed Soviet rocket launches (Carlsen2007, AbdrazakMusa2015).

Solid rocket engines often use ammonium perchlorate. Once combusted it can form hydrochloric acid, which is toxic too.

The good news is that these are not being used frequently anymore. Hydrazine is used in the west only for orbital stages (which do not get in contact with the atmosphere), and is only used by China for first stages. Since the retirement of the Space Shuttle, solid rocket engines use has declined by about 60% globally (RossSheafer2014), mainly because they don't allow propulsive and/or complete reusability (and they have lower performances than liquid engines), but they are unfortunately still used in some major rockets such as NASA's SLS and Ariane 5/6.

What are the effects of some pollutants? Radiative forcing

Radiative forcing is the change in the net radiative flux at the top of atmosphere or simply said "how much earth absorbs of the incoming sun radiation", which is a big drive in earth's warming. Certain pollutants have a higher impact than others.

Soot (also called black carbon), produced by the incomplete burn of kerosene, has a much stronger effect than CO2 or other pollutants. Even though soot represents only 2% of all rocket engine exhausts, it still constitutes 70% of the total radiative forcing from rocket launches. Soot is followed by alumina (from solid rocket engines) with 28% (RossSheafer2014). Even though H2O and CO2 account for almost 90% of the total emissions in terms of mass, they have a negligible radiative forcing effect.

Because of soot and alumina, the radiative forcing from space launches is only 4 times smaller than that of aviation, even though the total emissions from aviation are 10'000 times higher (RyanMarais2022).

The good news is that the biggest rockets currently planned, SpaceX’s Starship, Blue Origin’s New Glenn, and China’s Long March 9 (WikiLM9) are all reusable methane fueled with no soot or alumina emissions, and many launchers startups that still use kerosene as fuel, are developing engines with closed combustion cycles which emits much less soot compared to open cycles.4

Rocket emissions: Summary

While during the first few decades of spaceflight, there was not a lot of regard for rocket emissions, the future looks better even when considering a relatively high launch cadence of one launch per day for each of the 3 largest reusable rockets currently being developed (Starship, New Glenn, and Long March 9). In this scenario, the total emissions would still only represents 0.25% of the total aviation emissions, and the total effect from radiative forcing would be much less than it currently is due to the usage of a Methane + Oxygen mixture. It should be mentioned that in a 2020 interview (StarshipCadence), Elon Musk announced a target of 3 Starship launches per day. At the moment, this seems simply unrealistic since it would be the same mass to orbit as launching five complete International Space Stations every week, and there is absolutely no market request to do so. But if humans really were to establish a lunar or Marsian colony, that could one day require such a high launch cadence.

However, it is essential that the launch industry continues to phase out solid rocket motors, toxic pollutants, and kerosene-based engines with open cycles in order to limit the toxicity and the radiative forcing of its emissions. We also believe that, especially during periods of strong impacts from climate change, rocket launches should be pursued for science and research missions first, and not driven by space tourism.

Bibliography

Growth of space launches:

• Gunter Space Page, Launches 2022

CO2 emissions from rocket launches compared to aviation:

• Everyday Astronaut, How much do rockets pollute

• SpaceFlightInsider, Falcon 9 Specifications

• Engineering toolbox, combustion of fuels

• Wikipedia, Fuel economy in aircraft

• Airmilescalculator, flight distance CDG-SFO

• Statista, CO2 emissions from commercial aviation

• SwissInfo, Switzerland is a paradise for private jets, says report

What do rockets actually pollute?

• Everyday Astronaut, How much do rockets pollute

What are the effects of some pollutants? Toxic chemicals

• Carlsen, 2007, A preliminary assessment of the potential environmental and human health impact of unsymmetrical dimethylhydrazine as a result of space activities

• Abdrazak, Musa, 2015, The impact of the cosmodrome «Baikonur» on the environment and human health

• Ross, Sheafer, 2014, Radiative forcing caused by rocket engine emissions

What are the effects of some pollutants? Radiative forcing

• Ross, Sheafer, 2014, Radiative forcing caused by rocket engine emissions

• Ryan, Marais, 2022, Impact of Rocket Launch and Space Debris Air Pollutant Emissions on Stratospheric Ozone and Global Climate

Rocket emissions: Summary

• Techcrunch, Elon Musk shares details about SpaceX’s Starship