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Falcon 9 contrail
A Falcon 9 heads to orbit. Launch emissions like carbon soot are a concern to some atmospheric scientists as launch rates increase. (credit: SpaceX)

What is the environmental impact of a supercharged space industry?

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There has been a surge in the number of launches, and of satellites launched, in the last several years, thanks to the rise of megaconstellations and less expensive launch options. Last year set a record for orbital launches, with 186 attempts worldwide. This year is on a similar pace, with 16 orbital launch attempts in January alone.

“The impacts of spaceflight on climate and ozone is growing because we’re looking at this projected increase in the pace of space activity and we’re doing it in a climate-changed world,” said Rosenlof.

That growth in launch activity has created problems, primarily in space. An increase in the number of satellites, and of debris, poses space sustainability challenges that, in a worst-case scenario, would render some orbits unusable. Megaconstellations like Starlink have raised the ire of astronomers who warn those satellites will interfere with their groundbased optical and radio astronomy observations, leading to ongoing efforts to try to mitigate the problem.

However, launches themselves could create environmental hazards. A growing number of atmospheric scientists are worried that pollution from launches, particularly in the upper atmosphere, could affect atmospheric chemistry and heating. Similar concerns stem from the growing reentries of satellites that, as they burn up, deposit materials that could also affect the upper atmosphere.

“What is done by the space industry in terms of communications satellites and observing the Earth, is indispensable to the economy and it’s providing critical information for us to do climate change research,” said Karen Rosenlof, a research meteorologist at the NOAA Chemical Sciences Laboratory, during a panel at the AIAA SciTech Forum outside Washington January 27. “But the impacts of spaceflight on climate and ozone is growing because we’re looking at this projected increase in the pace of space activity and we’re doing it in a climate-changed world.”

Rosenlof moderated a panel discussion that, for more than 90 minutes, explored the potential environmental impacts of increased launches and reentries. That panel made clear that the magnitude of the problem remains uncertain, which makes it difficult to figure out how to resolve it, including whether new regulations are needed.

Potential impacts

The argument the space industry has typically used to play down environmental impacts is that emissions from launches are infinitesimal compared to other industries, such as aviation. Karen Jones of The Aerospace Corporation’s Center for Space Policy and Strategy noted there are thousands of flights worldwide daily, compared to those 186 orbital launches in all of 2022. Moreover, aviation is just a small fraction of global greenhouse gas emissions. “It’s a sliver of a sliver,” she said of the launch industry’s contributions.

However, not all emissions are equal. Of particular concern is carbon soot from launches, created from vehicles burning kerosene fuel. It is perhaps most recognizable on Falcon 9 boosters, creating a patina that, with each reflight, transforms the booster from its original white to a dark gray.

That soot, or black carbon, can locally heat the upper atmosphere, Rosenlof said, which can affect circulation and radiative transfer, although this overall impact is still not well understood.

“I cannot imagine any chemical rocket which would be considered to be clean,” Eastham said. “They will all produce emissions of some kind.”

What is known, though, is that rockets proportionally produce far more black carbon than aircraft, particularly in the upper atmosphere where the fuel is not completely combusted. “A sooty, open-cycle kerosene engine will emit a thousand times more black carbon than a jet engine will at cruise per kilogram of fuel,” estimated Martin Ross, a scientist at The Aerospace Corporation.

Those emissions in the upper atmosphere are problematic because they are long-lived, said Sebastian Eastham, associate director for the Laboratory for Aviation and the Environment at MIT. Launch vehicles, he said, “are going to be depositing black carbon up to arbitrary altitudes,” remaining in the atmosphere for years. “That lifetime alone magnifies their impact by orders of magnitude.”

There is, though, a shift in the industry underway from kerosene to methane. Vehicles like SpaceX’s Starship, Relativity’s Terran 1 and Terran R, ULA’s Vulcan Centaur and Blue Origin’s New Glenn, among others, use methane, which is designed to be cleaner than kerosene, producing less soot.

“Methane is a clean burning fuel. It’s all about where does it come from,” said Jones. Methane produced from renewable energy courses, or even harnessed from landfills, could have far less overall environmental impact than kerosene. “A methane rocket is not such a bad thing.”

Others, though, offered some caveats. “Methane is a cleaner burning fuel. It’s not clean,” argued Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies. Methane, he noted, produces carbon monoxide as a byproduct of incomplete combustion.

“I cannot imagine any chemical rocket which would be considered to be clean,” Eastham said. “They will all produce emissions of some kind.”

At the other end of the space lifecycle is spacecraft reentries, which are increasing as more satellites are launched. That can deposit materials in the upper atmosphere as well, particularly metals.

“We’re seeing an increase in species—specifically, lithium, copper, and aluminum—that can only come from the space industry at altitudes around 20 kilometers,” said Rosenlof, based on high-altitude aircraft measurements taken over the last two decades.

That increase doesn’t appear to be causing “major perturbations” in the upper atmosphere—at least not yet, she said. “However, as spaceflight grows by an order of magnitude or more, we think we’re going to start seeing impacts.”

Measuring environmental impacts

This is not the first time that people raised concerns about the environmental impact of launches. More than three decades ago, some scientists warned that emissions like chlorine from solid rocket motors, like those used on the shuttle and the Titan IV, could damage the ozone layer.

“There were some models that indicated that solid rocket motors would were going to cause a big problem for stratospheric ozone,” Ross recalled. “There were calls back in the 1990s to ban solid rocket motors.”

The US Air Force concluded they did not have enough data on the environmental impacts of solid rocket motors, and asked Aerospace to study it. That led to a campaign of measurements to see how the models compared to reality.

“We got into the plumes, measured the parameters we needed to measure, and determined at solid rocket motors were much less of a problem than some of the models were indicating,” he recalled. “We were able to take solid rocket motors off of the table for regulatory discussions at the time.”

Schmidt said that NASA would often be asked what effect a launch would have on the environment. “Up until very recently, no one at NASA knew the answer.”

He and others said that it was time to undertake a similar campaign to measure the effects of launch and reentry emissions on the upper atmosphere. “We can do this,” said Darin Toohey, a professor of atmospheric sciences at the University of Colorado who was involved in those earlier studies. “The trick here is knowing in advance what matters. Back then it was chlorine, but in the future it might be black carbon.”

NASA is starting to look into those issues. Schmidt said that the agency would often be asked, even when launching climate science missions, what effect the launch itself would have on the environment. “Up until very recently, no one at NASA knew the answer,” he said.

During a stint as the agency’s senior climate advisor in 2021, he pushed for a cross-directorate study of launch emissions, bringing together people from human spaceflight, aviation, and Earth science. “We hope to have an actual answer some time soon.”

That initial effort could lead to more detailed studies. “What we’re hoping for is that the work we’re doing here will be a sufficient proof of concept to have NASA and other agencies set up a more structured funding regime to bring in more people and more partners from industry to provide the key information we need,” he said.

Those efforts, Ross said, will likely require in situ measurements of the plumes of some kind, since ground tests aren’t sufficient. “If I tested the black carbon output of an engine on the ground, it’s going to be small,” he said, since the black carbon is consumed in the plume at low altitudes, but not at upper altitude. “Ground testing has a role, but there’s nothing like actually seeing what’s in the stratosphere.”

Jones advocated for what she called an “environmental life cycle” study for spacecraft launches, something she said would be the subject of an upcoming Aerospace white paper. “The lifecycle assessment we propose looks above the Kármán Line as well as below: there’s a lot of terrestrial impacts,” she said. “In doing these lifecycle assessments, you can start to look for efficiencies.”

Technology versus regulation

Any thought of studying launch or reentry emissions triggers fears among some in the industry of impending regulations that would slow its rate of growth or increase costs.

None of the panelists were eager to push for new regulations, saying their interest is in better understanding the impacts of emissions on the atmosphere and find ways to mitigate them. “If we understand the science, that will actually benefit the space industry,” Rosenlof said. “Part of what we want to do is with the people who are developing the technology to have the cleanest technology that is available and promote collaboration and reduce the potential for regulation that may not be desired.”

There have been initiatives elsewhere, though, to reconsider the application—or lack thereof—of environmental law for space activities. For decades, the FCC has excluded satellite licensing from reviews that would be required under the National Environmental Policy Act (NEPA), citing a “categorical exclusion” that concluded that individual satellite launches had no significant impact on the environment.

That exclusion, some believe, no longer applies in an era of satellite megaconstellations that require dozens or hundreds of launches to place thousands of satellites into orbit. Environmental concerns extend beyond launch and reentry emissions to the creation of orbital debris and interference with astronomy.

“No single agency is given responsibility for spaceflight,” Ross said. “It's a crazy meatloaf of organizations.”

The Government Accountability Office (GAO), in a report published in November, concluded the FCC needed to review if that categorial exemption still applied. “Without a documented determination from FCC as to whether licensing large constellations of satellites normally has significant effects on the human environment, Congress and the public lack reasonable assurance that FCC’s application of the categorical exclusion remains appropriate for licensing large constellations of satellites in light of technological changes and advances,” the report stated.

The GAO recommended that the FCC reexamine if the categorical exclusion to NEPA applied to satellite megaconstellations and set up a process to regularly review that exclusion. The FCC said it would accept the recommendations, but would wait until a White House body, the Council on Environmental Quality, issued updated regulations for implementing NEPA.

If the categorical exclusion to NEPA no longer applied to licensing satellite megaconstellations or even individual satellites, requiring some level of environmental review, it’s not clear how it might change the design and launch of megaconstellations. “One of the key principles of NEPA is that you have to use the best available science,” said Schmidt. “In a situation like this, the best available science is not very good.” He warned that could lead to lawsuits challenging the quality of the science done for such reviews.

Jones said it’s uncertain how environmental laws would apply to some aspects of space launches. “It’s a huge question in the industry, still.”

Toohey advised caution as well. “What is the proper signal to send to the industry so that we don’t have a disruption?” he asked, referring to changes that new research might cause. “The key here is to think about a framework that’s needed that’s correct for the problem, and try not to adopt another framework which is imperfect but we know how to use.”

Another challenge for environmental law is determining what agency is responsible. In an order in December granting partial approval to SpaceX to launch its second-generation Starlink constellation, it rejected arguments that it needed to perform an environmental review of the launches, concluding that was being done by the FAA, which licenses SpaceX launches. “We have every confidence the FAA has conducted, and will continue to conduct as necessary, thorough environmental reviews of SpaceX’s launch activities and accordingly we incorporate the FAA’s analysis into our own environmental review,” the FCC stated.

Ross blamed the fractured oversight of spaceflight by the federal government, with several agencies holding different responsibilities. “No single agency is given responsibility for spaceflight,” he said. “It's a crazy meatloaf of organizations. At some point, one might wonder if the federal government should develop an agency or sub-agency whose responsibility is space.”

Another regulatory approach could be taxation. Last April, Rep. Earl Blumenauer (D-OR) introduced the Securing Protections Against Carbon Emissions (SPACE) Tax Act that would tax commercial human launches not performing scientific research: $2 million per orbital launch and $100,000 per suborbital launch, as well as a 10% tax per ticket.

“Just as Americans pay taxes when buying airline tickets, billionaires flying into space to produce nothing of scientific value should do the same,” Blumenauer said in a statement announcing the introduction of the bill (which he teased the previous July, just after the first crewed flight of Blue Origin’s New Shepard whose crew included company founder Jeff Bezos.) “I am also concerned about the impacts of recreational space travel on carbon emissions.”

The SPACE Tax Act did not go anywhere in Congress last year, and its future prospects remain uncertain. Jones did not rule out some tax regime, analogous to taxes paid by airline passengers, that could be applied to commercial space. “Maybe some economic model involving a carbon tax could occur,” she said.

A fundamental issue, said Ross, is that industry moves at a different speed from both regulators and scientists. “Megaconstellations are an example of private industry moving much faster than not only regulatory agencies but also faster than professional science societies,” he said. “By the time we write and publish papers, there’s another 2,000 Starlink satellites up. We’re moving along, but maybe not fast enough.”

“It’s an example of technology moving so much faster than society can really respond to,” he added.

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