Spaceflight, despite its Cold War arms-rattling origins, is often portrayed as a uniquely beneficial endeavor that somehow helps all of humanity: satellites provide invaluable planetary-scale situational information and communications. Space telescopes and interplanetary probes are making transformative discoveries about our place in the universe. Astronautical missions help satisfy our species’ innate exploratory urges and inspire new generations of scientists and engineers. And they all start out the same way, riding rockets through the sky.
But contrary to rosy estimates, this last detail may sooner or later harm life on earth. Simply put, the problem is that most of what goes up ends up coming back down as defunct rocket boosters and satellites that experience fiery re-entry or even crash landings. Consider China’s July 24 launch of its Wentian space station module aboard a massive Long March 5B rocket: After successfully delivering Wentian into orbit, the giant 23-metric-ton upper stage was left to fall back to Earth uncontrollably, creating a remote control. but a real threat to anyone or anything unlucky enough to be in his path.
However, dramatic death from a falling missile is not the only risk. A greater threat may come from constantly increasing amounts of space debris that burns up in our planet’s fragile upper atmosphere, leading to long-term effects on global climate and stratospheric ozone. How significant these effects might be is unclear because the problem itself has been largely unstudied. But the situation should become more relevant as the cost decreases and new profitable applications such as satellite mega constellations increase launch speed worldwide. In short, the boom in spaceflight in the 21st century could trigger a space-age “tragedy of the commons” with consequences spanning millennia, and scientists are sounding the alarm.
Stunning consequences
Recently in dz The future of the Earthresearchers from University College London (UCL), Cambridge University and MIT studied the impact of rocket launches and atmospheric entry objects.
The team reported that soot (soot) particles emitted by rockets are almost 500 times more efficient at trapping heat in the atmosphere, thus having a greater impact on global warming than airplanes and other terrestrial sources. The soot “is emitted by rockets burning hydrocarbon fuels,” says study co-author Robert Ryan of UCL. “And soot, which is ejected directly into the stratosphere, is very effective at causing heating.”
The team also studied how re-entry into the atmosphere could damage the thin layer of stratospheric ozone, which helps protect the Earth from harmful ultraviolet radiation. Falling debris or returning spacecraft produce ozone-depleting nitrogen oxides as they and the surrounding air heat up, depleting the protective gas from the stratosphere. Currently, the effect is small on a global scale, Ryan says, but already in the upper atmosphere, “the extent of ozone depletion [from spaceflight] cause for concern.” To make matters worse, the rocket components that go into the system can have complex and highly variable compositions—and the specific chemicals produced when the cocktail of ingredients are combusted are not precisely determined.
“We are currently investigating the effects of other pollutants originating from satellite materials that burn up on return to Earth,” says study co-author Eloise Marais, Associate Professor of Physical Geography at UCL. What is known, she adds, is that the space sector has “numerous impacts” on Earth’s atmosphere.
Another certainty, experts say, is that the atmospheric impact of spaceflight is bound to increase as the number of launches and returns skyrockets. The surge in activity in the space sector prompted another research team from the National Oceanic and Atmospheric Administration (NOAA) to model how the resulting rise in stratospheric soot might affect atmospheric circulation patterns. Published in Journal of atmospheric geophysical researchtheir research showed another route with which missile technology can destroy the ozone and worsen climate change.
“We looked at hypothetical scenarios in terms of the number of rockets growing over the next few decades and how the climate might respond,” said lead author Christopher Maloney, a research scientist at NOAA and the Joint Institute for Environmental Studies. in Boulder, Colorado. “We saw that there would be stratospheric warming. The overturning of the stratospheric circulation is slowing down, and that’s affecting ozone.”
Taking the problem further, Maloney says “emissions inventories” of what different rocket engines emit would be useful. This type of catalog can help create a more complete picture of the side effects of rocket technology in the stratosphere.
NOAA is also preparing to study the satellite’s return and possible effects on climate. “There are really a lot of unknowns,” Maloney says. “These are certainly topics worthy of further investigation.”
A place for surprises (and adjustments)
The growing interest is welcome news to Martin Ross, a senior engineer for civil and commercial launches at the Aerospace Corporation and a longtime advocate of elucidating the climate effects of rocketry.
“Everybody expects the space business to grow a lot, and that’s the catch,” says Ross. “Given the growth, given the changing mix of return vehicles, launches and fuels used, all of these things change during evolution, we really need to reduce the uncertainty so we can reliably predict what the future will be.”
Megaconstellations of thousands of satellites are the main concern, Ross says, because most are designed to last, constantly getting rid of old or malfunctioning spacecraft, which are then replaced by new launched batches. Leaving launches aside, this adds up to a significant “steady stream” of fiery debris falling through the atmosphere. And some of that—no one knows exactly how much—will be in the form of submicron particles that linger in the air for a long time, rather than falling out quickly. “If we assume even half [mega constellation reentry debris] becomes dust of some significance to the stratosphere, then it will compete if not larger than the launch side.’
Typically packed with electronics and solar cells containing heavy metals and exotic compounds, satellites also exhibit even greater chemical diversity than rockets, to the chagrin of researchers. “[Satellites have] all these strange metals, and we have no idea what their reactivity will be with the atmosphere,” says Ross. “There is room for surprises.”
But getting the data you need to avoid nasty surprises won’t necessarily be easy, says Laura Ratliff of George Washington University’s Space Policy Institute.
There is, for example, a lack of measurements for some of the outer layers of the atmosphere, where the gradual transition into space begins. Too low to be easily reached by satellites, too high for weather balloons to reach, this little-explored region has been dubbed the “ignorosphere.” However, it may prove crucial for quantifying the effects of vertical entrainment on the Earth’s atmosphere and climate.
“I feel involved in this issue because I feel involved in our climate crisis and the solutions to these problems,” Ratliff says. “It appears to be an area that is doing significant damage to the atmosphere without even knowing it.”
While almost everyone agrees that the Earth’s upper atmosphere and orbital environment are worthy of protection, she notes that these places generally slip through the cracks of national and global regulatory oversight. “There is no agency that deals with ‘space sustainability,'” Ratliff says. “Now it’s mostly an American problem. But it will be an international problem as a result.”
Don’t look up!
For strong evidence of the global nature of the negative effects of spaceflight, look again at the Chinese rocket booster. As of this writing, the latest forecast from the Aerospace Corporation says the Long March 5B launch vehicle should hit Earth shortly after 7 a.m. ET on July 31 (plus or minus 24 hours). This uncertainty will decrease as the missile continues to descend, but the exact time and location of its impact is fundamentally difficult to predict because seemingly insignificant variables, such as small fluctuations in the Earth’s upper atmosphere, can have major effects on launch vehicle orbital decay.
Most likely, as with most space debris, the launch vehicle (or the 20 to 40 percent of it that is predicted to reach the surface intact, anyway) will end up in the ocean, which covers about 71 percent of the globe . But the Aerospace Corporation noted on July 26 post that there is “a non-zero chance that surviving debris will fall into a populated area—more than 88 percent of the world’s population lives under the potential wake of debris on reentry.”
This small but significant risk is consistent with the findings of a recent study published in Astronomy of naturewho analyzed three decades of data estimate the probability of human casualties from uncontrolled missile inputs.
Michael Byers of the University of British Columbia and colleagues estimate that, under current practices, there is about a 10 percent chance that a rocket free-falling from orbit will cause one or more injuries or deaths within the next decade. (Most rocket boosters do not go into orbit and end up in a well-defined zone below launch. Those that do go into orbit usually fire their engines to allow a safer exit from orbit into the open ocean, and break up almost completely on reentry. Upper stage Long March 5b, however, is not designed to restart engines.)
Broadly speaking, the many and growing risks associated with the burgeoning space sector should be alarming for everyone, says Moriba Jha, co-founder and chief scientist of Privateer, a group created to “treat the space environment as our life. depends on it.” Steve Wozniak, Silicon Valley icon and co-founder of Apple, serves as president of Privateer.
“At the end of the day, we want the space environment to be more transparent,” says Jha. “What’s up there? Who does it belong to? What can it do? It should be more predictable. Now we have no way to predict not only the intended, but also the unintended consequences of our actions.”
From a regulatory perspective, whatever treaties are in place, Jah says, are so open to interpretation that the situation presents risks. “I think if countries could show leadership and demonstrate measurable ways to try to be green, other countries might be tempted to behave more appropriately,” he adds.
