Space sustainability comes down to Earthby Jeff Foust
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| “The underlying uncertainty here is what exactly is being emitted: what, where, and how much?” Herberhold said. |
This surge in activity in the United States, China, and elsewhere has prompted questions about space sustainability. With more satellites and debris in orbit than ever before, the risk of collisions between objects creates fears of the Kessler Syndrome: a chain reaction of debris collisions that renders some orbits effective unusable.
However, the increase in launches and satellites has also created questions about terrestrial sustainability. For the last few years some researchers have pointed to potential effects of launches on the atmosphere, such as soot deposited in the upper atmosphere (see “What is the environmental impact of a supercharged space industry?”, The Space Review, February 6, 2023). Those concerns continue today, compounded by worries about what happens when those thousands of satellites being launched reenter.
Launch emission concerns
While the issues about effects of launches and reentries on the atmosphere have existed for several years, there remains little data about what impact they really have on atmospheric chemistry and climate. There are, though, ongoing efforts to get a better handle on how significant they could be.
One example is ongoing work at the German Aerospace Center, or DLR, to model emissions from launches into the atmosphere. In a talk on the final afternoon of the International Astronautical Congress in Sydney earlier this month, Moritz Herberhold of DLR noted that the total amount of propellant consumed by launches has more tripled since 2019, an increase that will continue with more, larger vehicles entering service.
“The underlying uncertainty here is what exactly is being emitted: what, where, and how much?” he said.
The project he discussed in his conference presentation was an effort to model emissions from all launches in 2024, with a goal of analyzing 95% of propellant consumed. As of the presentation, the project had modeled 88% of emissions based on publicly available data on more than 200 launches.
The study of the emissions, and their effect on climate, is not complete, but Herberhold identified one area of concern: emissions of black carbon into the upper atmosphere. Launch emissions are a tiny fraction of those from aviation, but launches deposit black carbon much higher in the atmosphere, where it can have a far stronger effect. He said some analyses estimate that black carbon from launches could be as much as 500 times more potent than the same amount emitted from aviation.
The data collected so far from the modeling of 2025 launches show that black carbon emissions are between 10 and 40% those from aviation two decades ago. If black carbon emissions from launches are 500 times worse than from aviation, he concluded, “we could already have a significant impact from spaceflight with only 250 launches.”
That assessment, he acknowledged, still needs to be confirmed by climate modeling that will be a later phase of the project, “but this, to me, shows how important it is to look into this, because we have this huge range.”
The potential for significant impacts, but also the uncertainties in existing models, have attracted more researchers to the field. Among them is Michele Bannister, a senior lecturer at the University of Canterbury in New Zealand.
| “This is an engineering problem,” Bannister concluded. “It can have an engineering solution.” |
She has done research on the impact of launch emissions on the ozone layer. With the projected growth in launches needed to deploy the many planned megaconstellations, she said during a panel at the New Zealand Aerospace Summit earlier this month, “we will see damage to the ozone layer, and we will see that most severely over latitudes like New Zealand.”
The work, she said, presented an opportunity for industry and academia to work together. “How do we think about how we make vehicles that are going to ensure that we can grow this economy in low Earth orbit but also retain the things we care about, like being able to have life on Earth?”
“This is an engineering problem,” she concluded. “It can have an engineering solution.”
“I don’t know what to do”
An emerging area of study, and concern, involves the atmospheric impacts of satellite reentries. SpaceX has launched more than 10,000 Starlink satellites, but more than 1,300 of them have reentered. Satellite operators are increasingly encouraged to deorbit their satellites as soon as possible after the end of life to avoid contributing to the growing debris problem in orbit and to ensure they “fully demise” upon reentry so no debris makes it to the ground.
That means, though, that a growing amount of material is being deposited into the upper atmosphere, where its effects on climate and atmospheric chemistry are only now starting to be studied.
“Is this really a problem, or is this a case of just a drop in the ocean?” asked José Pedro Ferreira, a researcher at the University of Southern California, in a talk last week at the Secure World Foundation’s Summit for Space Sustainability.
| “Broadly, the conclusions were that we really don’t know anything,” Young said. “We really don’t know much about what the atmospheric impact is of reentry.” |
He argued that, at the very least, the effect of satellite reentries cannot be ignored. He found that 2024 was the first year that the mass of aluminum deposited in the atmosphere from satellite reentries exceeded that from natural sources, like meteors, with a confidence level of 95%. “This doesn’t mean that there is a negative environmental impact,” he said, “but there is a change in the status quo.”
His presentation was the prelude to a panel discussion on the environmental effects of satellite reentries, where people from industry and academia examined both the potential adverse impacts but also the uncertainty surrounding them.
“When it came to reentry and the effects of reentry, we just didn’t know what exactly the impacts of those would be,” said Chris Young, space sustainability senior lead at the UK Space Agency.
The agency commissioned several studies to explore those impacts, which were recently completed and discussed at a workshop the day before the main summit. They did not necessarily alleviate much of the uncertainty on the topic. One was a study of literature on atmospheric chemistry relevant to the topic. “Broadly, the conclusions were that we really don’t know anything,” he said. “We really don’t know much about what the atmospheric impact is of reentry.”
Other studies looked at how to model atmospheric ablation of spacecraft materials in labs and various ways to optimize reentry to minimize those effects. One more concerning study found evidence of metallic material from spacecraft being deposited in the polar regions. “There is evidence that space activity is causing environmental harm in the polar regions due to the atmospheric conditions,” he said.
The limited information offers little guidance for satellite operators. On the one hand, they are being encouraged, if not required, to deorbit their spacecraft as quickly as possible to prevent debris creation in orbit, while doing so in a way to prevent debris reaching the ground. On the other hand, those same practices could damage the ozone layer or contribute to climate change.
“I’m lost,” said Vijay Thakur, technical authority in the engineering department of Eutelsat, whose fleet of spacecraft includes the OneWeb constellation, second in size to Starlink. “The difficulty that I have as a responsible operator is, in this particular case, I don’t know what to do.”
On the panel, he compared the uncertainty about atmospheric impacts from satellite launches and reentries to another environmental issue, the effect satellites have on astronomy through reflected sunlight and radio emissions. In the case of what’s commonly called “dark and quiet skies,” he said there are clear requirements on what operators need to do to minimize the impact, such as brightness limits on satellites. Companies can they take mitigation steps to try to reach those requirements.
“In this domain, it’s much more difficult,” he said. Companies have requirements to deorbit their satellites and do so with jeopardizing safety on the ground, which have clear metrics and ways to comply.
“It may be that I’m dumping too much of the wrong material—aluminum and anything else—somewhere in the atmosphere,” he said, but with little insight into how much is too much and what alternatives his company should pursue.
At the panel and other events, there was very little in the way of a push for regulations on launch or reentry emissions in the upper atmosphere, even among those concerned about potential adverse effects. Instead, there were calls for more research, from data collection in the atmosphere and in the lab to improved modeling.
Thakur, for example, said companies could provide data on what kinds of materials are in their satellites without giving up proprietary information on their designs. He also suggested that spacecraft could carry sensors designed to measure conditions during reentry, similar to radiation sensors that measure conditions in orbit.
There are some initial steps, though, that could lead to regulations. Earlier this month, the European Commission released an initial draft of a document called Product Environmental Footprint Category Rules for the space sector, or PEFCR4Space. It is part of a broader European effort to develop ways to measure the full lifecycle environmental impacts of products, from sourcing of raw material to disposal.
“Sustainability doesn’t stop at the edge of our atmosphere,” said Vera Pinto, policy coordinator for DG DEFIS, the European Commission directorate responsible for the defense industry and space, in a speech at the Summit for Space Sustainability. “The satellites that are helping us fight climate change are also becoming part of the problem.”
The PEFCR4Space guidelines are part of a long-term effort to address that issue. “If we can measure the impacts of space activities, we can manage them,” she said. “And if we can manage them, then we can make space activities more sustainable.”
| “We are not doing sustainability to the space sector. We are doing sustainability with the space sector, with you,” Pinto said. |
The draft document, open for public input until December 1, covers topics like emissions from launches and material deposited in the upper atmosphere from reentering satellites. It also covers a far broader range of impacts, from how the raw materials that go into the satellites are procured to how the employees of the satellite or rocket manufacturer commute to work, all to try to quantify the full impact of an individual satellite or launch vehicle.
The document doesn’t set out rules for limiting emissions or other impacts but instead offers an agreed-upon methodology to calculating impacts. “It makes sure we all measure the environmental performance of products or services in the same way,” said Carolin Spirinckx of Vito, a consultancy involved in the development of the PEFCR4Space guidelines, during a webinar Friday about the draft document.
Pinto noted in her speech that the rules can also help companies and policymakers make “more informed and more sustainable choices” and aligns with broader European initiatives, such as “climate neutrality” by 2050.
She emphasized that this effort is intended to be collaborative with the industry, including the ongoing public consultation and plans for pilot studies next year to see how the rules would be applied. “We are not doing sustainability to the space sector. We are doing sustainability with the space sector, with you.”
The final PEFCR4Space guidelines won’t be published until the end of 2027, she said. That is little help for now for companies who say they are interested in minimizing their environmental impact, including for launch and reentry, but have little data or guidance to help them.
“Once again, I’m lost,” Thakur said on the panel. “And, by the way, I’ve got to launch my next constellation by 2026.”
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