Could the next big environmental problem come from space?

By Tereza Pultarova,
Published by Aerosociety, 10 January 2025

Could satellite mega-constellations trigger climate change 2.0?

Air pollution from rocket launches and satellites burning up in Earth’s atmosphere could bring about the world’s next big environmental emergency. The space industry is pulling together to find a solution before it gets too late.

Humankind may once again be playing with fire, thinks Sebastian Eastham, a sustainable aviation researcher at Imperial College London. An expert in effects of aircraft emissions on the Earth’s climate and ground-based air-pollution levels, Eastham has recently begun unpacking an entirely new Pandora’s Box – the impact of rocket emissions and chemicals that arise during atmospheric incineration of re-entering satellites on the chemistry of the upper atmosphere.

It is a nascent field of science but experts already know enough about these processes to worry. “We are putting things into places we aren’t used to putting them,” Eastham told AEROSPACE. “We are talking about an untested territory in terms of environmental impacts.”

Problematic plumes

Hundreds of tonnes of dead satellites could be burning up in Earth’s atmosphere every year within the next decade. (University of Warwick/Mark Garlick)


Rockets, unlike any other combustion technology invented by humankind, inject exhaust full of soot, carbon dioxide and other nasty materials throughout almost the entire column of the atmosphere. Satellites that spiral back to the Earth at the end of their missions burn up at altitudes between 60-80km, leaving behind clouds of metallic ash. The high altitude at which these chemicals accumulate means that their survival in the atmosphere is much longer than that of similar chemical compounds emitted by cars or gas fired power plants. As a result, the impact of those emissions is far less predictable than that of emissions released close to the Earth’s surface.

“Our understanding of the consequences of an emission decreases the further you get from the surface,” said Eastham. “Anything you emit into the middle atmosphere, we would still expect most of it to have impacts in the order of up to a decade later. The factor by which you have to scale up their effects to account for the fact that they do last longer is essentially unknown. We just don’t know how much more impact you get per unit of emission.”

Expanding industry


Minkwan Kim (L) and Sebastian Eastham (University of Southampton & Imperial College London) 

Rockets have been soaring through the atmosphere since 1944 (the German V-2) and launching material into orbit since 1957 (the USSR’s Sputnik). Old satellites, used rocket stages and various fragments of space debris have been undergoing their fiery atmospheric demise for just as long. Until a few years ago, no one was bothered. Rocket emissions, experts maintained, were a drop in the ocean compared to emissions from aviation, which, they emphasised, make up only 2.5% of the world’s total greenhouse gas output.

Then the era of New Space arrived with its small, cheap satellites and the doctrine of universal access to space. Constellations of small satellites, a few hundred kilograms in mass, began pushing out the bus-sized spacecraft worth hundreds of millions of dollars that had dominated Earth’s orbits for decades. While those orbital giants frequently remained in service for up to 20 years, the philosophy behind the small satellite revolution is to replace older craft with newer, more powerful tech every few years. Eventually, the idea of internet-beaming mega-constellations took off and the number of satellites began to skyrocket. In 2010, fewer than 1,000 satellites were orbiting the Earth. By mid-2024, the number of active spacecraft climbed to more than 11,000, according to Statista. The number of rocket launches has grown in proportion, having nearly doubled over the last five years.

The amount of space debris incinerated in the atmosphere has doubled as well, says Minkwan Kim, Associate Professor in Astronautics at the University of Southampton. Kim leads an international research project, funded by the UK Space Agency, that intends to better assess the hazards posed by satellite pollution to our planet but also to outline how to mitigate the risk to avoid another major environmental problem further down the line.

“If we start dealing with this early, we have a better chance to prevent a serious problem,” Kim told AEROSPACE. “It’s similar to the carbon dioxide emissions situation. If it had been done earlier, we wouldn’t have had the global warming that we have now.”

Predictions for the space industry’s growth make Kim particularly uneasy. Satellite operators from all over the world have filed spectrum applications for more than a million spacecraft with the International Telecommunications Union, which manages the available radio frequencies. Although not all those plans will come to fruition, experts think that between 60,000 and 100,000 satellites may be launched by 2030. Most mega-constellation operators expect to replenish their fleets with new satellites every five years. As a result, thousands of tonnes of dead satellites and other debris could be perishing in the atmosphere every year within the next ten years.

What does it mean for the atmosphere?

As the skies turn extremely crowded, just like the traffic on our regular roads, experts predict an increasing threat of space debris falling back on Earth. (McKinsey)

The amount of re-entering space debris might seem low, compared to the quantity of natural, meteoric material that has been bombarding the Earth since the planet’s formation. For example, some estimates show that by 2033, some 3,600 metric tonnes of space debris could be burning up in the atmosphere annually. That is about one-fifth of the amount of the natural stuff that the Earth’s gaseous coat absorbs every 12 months. There is, however, a major difference. Most meteorites consist of rocky material, such as silicon, some iron and only a smattering of other metals. Spacecraft, on the other hand, are mostly made of aluminium. The burning of aluminium produces aluminium oxide, also known as alumina. Researchers have known for years that alumina could be bad news for the stability of the Earth’s atmosphere.

The white powdery substance acts like “sunscreen” in the atmosphere, said Kim, reflecting sunlight and, thus, reducing the amount of energy the Earth absorbs. That, Kim said, might sound like good news in the age of out-of-control climate change, but there is a catch. This temperature reduction would be equally out of control and could have unpredictable consequences. Alumina is also known to damage ozone. With the predicted increase of satellite numbers and subsequent re-entries, the concentrations of alumina in the stratosphere – the atmospheric layer harbouring the protective ozone shield – could easily increase by more than 650%, compared to natural levels, resulting in “significant ozone depletion,” concluded a study published in the journal, Geophysical Research Letters in June 2024.

Compounds in rocket exhaust could also throw the Earth’s equilibrium off-kilter. Soot, abundant in the emissions of rockets burning the kerosine-based RP-1, acts in the opposite manner to alumina – absorbing heat and increasing atmospheric temperature. RP-1 fuels the world’s currently most used rocket – SpaceX’s Falcon 9, among others. Soot also contributes to ozone depletion. A study led by researchers from the US National Oceanic and Atmospheric Administration (NOAA) and published in Geophysical Research Letters in 2022 found that a ten-fold increase in soot-producing rocket launches would have a measurable impact on the ozone layer.

“We are looking at this sudden growth, but we still don’t know what happens,” said Eastham. “We don’t know how much ozone loss we get from one launch, we don’t really know what’s emitted during a launch nor do we really know what we should expect from lots of launches.” The same applies to by-products of satellite incineration, he added.

Kim says the metallic dust could have other, less understood impacts. It could alter the Earth’s magnetic field, result in the increase in thunderstorms, disturb satellite communication links and obscure the view of Earth-observing satellites.

The space industry’s dilemma

ESA space junk map. (ESA)

The emerging research into the effects of satellite pollution presents a major dilemma for the space sector. After decades of discussions, the global space community has in recent years reached a consensus on the problem of space junk. Nearly seven decades of space utilisation have left Earth’s orbit cluttered with debris. A few devastating anti-satellite missile tests, a handful of collisions and the general wear and tear of leftover junk has produced over 35,000 space debris pieces larger than 10cm and millions of smaller fragments. Both numbers keep rising. This orbiting shrapnel hurtles through space at mind-boggling speeds of nearly 30,000km/h, threatening to destroy everything in its path.

The space community has, therefore, agreed that satellites need to be removed from orbit within 25 years from their missions’ end. The US Federal Communications Commission requires US satellite operators to remove their junk from orbit even faster — within five years. The stricter rule is fantastic for keeping near Earth space in order but troublesome for the cleanliness of the upper atmosphere. Active space debris technologies are also being developed that could pull down into the atmosphere even the peskier junk in higher orbits that would otherwise take centuries to spiral down naturally.

Legal loopholes

An artists rendering of a satellite reentering Earth’s atmosphere. (ESA)

Eastham says rocket flights exist in a legal loophole that is hard to justify in the era of progressing climate change. “Launch vehicles, unlike anything else, are not consistently regulated when it comes to environmental impacts,” he said. “They don’t go through the same sort of regulation as aviation, for example, where we have specific emissions requirements.” Pollution from re-entering satellites, too, seems to evade all laws ever conceived on Earth.

Speaking at a workshop on Protecting Earth and Outer Space from the Disposal of Spacecraft and Debris held at the University of Southampton in September, Rachael Craufurd-Smith, a space and policy law expert at the University of Edinburgh, said that none of the international treaties governing space utilisation and exploration considers environmental harm to the Earth’s environment.

The Liability Convention, in place since 1972, requires launching states to compensate other countries if their satellites or rocket parts crash on other nation’s territories. The convention also covers damage to aircraft and other satellites in orbit.

The 1967 Outer Space Treaty is mostly concerned with a possible contamination of other celestial bodies with matter from Earth and vice versa.
Space sector pollution is equally elusive for existing international treaties protecting air quality, oceans and soil.

Kim thinks that amendments to documents, such as the 1987 Montreal Protocol that banned ozone depleting substances used in the past in aerosol sprays and refrigerants, will be needed to prevent another future environmental disaster.

“I think we need to do something similar as we have done for the ozone layer before,” said Kim. “We can just add that extra thing – the satellite disposal – [to the Montreal Protocol]. But we need to do more research before that can happen.”

Is there a way out?

Experts calculate there are over 35,000 space debris pieces larger than 10cm orbiting the Earth along with millions of smaller fragments. (ESA)



Eastham finds it hard to justify the space industry’s environmental exemption in the age of full-blown climate change. As beneficial as satellite applications are for humankind, he thinks the industry will in the future have to think more carefully about what it really needs to launch and what it doesn’t.

“I would say that we don’t count the environmental harm per unit of benefit at the moment,” he said. “It’s not like in aviation where people are now quite comfortable to make an internal calculation and decide whether, for example, they should fly a certain route or not.”
Kim thinks that reductions in the impact of atmospheric satellite incinerations are possible through careful engineering of re-entry trajectories.

“If we put the particles at a very high altitude, they’re going to stay there for very long,” he said. “But if we burn them at lower altitudes, like 20 or 30km, the metal oxides produced will drop to the ground faster and their impact will be less significant.”

By modifying the re-entry angle of satellites, operators can adjust not just the altitude at which the spacecraft body disintegrates and burns up, but also the temperature at which these processes occur. That, too, can affect how harmful the resulting pollution will be, added Kim.

“We found scientifically that, when metal is burned, not all of it turns into metal oxide,” said Kim. “Some of it turns into metal particles and those particles don’t seem to be as harmful to the environment as the oxides. When we change the re-entry angle of those satellites, we can make more of it turn into particles rather than oxides.”

Ultimately, new materials that would replace the offending aluminium need to be invented to allow the space industry to expand as it wishes, says Kim. Other, more ambitious solutions could solve the problem in the future.

Start-ups and visionary early-stage companies are mulling over concepts for orbiting recycling stations that would reprocess old junk into new satellites or satellites capable of surviving the atmospheric re-entry to be refurbished on the Earth and sent back to space.

One thing is certain, if the space industry wants to avoid becoming the next big perpetrator of environmental harm, its future will have to be quite different from what it currently envisages.

See: Original Article