Greenhouse gas emissions are changing the Earth's atmosphere in surprising ways that are likely to reduce the number of satellites that can sustainably operate in orbit in future.
Researchers from MIT report that carbon dioxide and other greenhouse gases can cause the upper atmosphere to shrink, and calculated that, by 2100, the ability of the most popular regions of low Earth orbit to support satellites could be reduced by 50-66 percent due to the build-up in space junk this shrinking will cause. That’s a problem as new satellite constellations are being launched at a rapid pace, particularly to deliver broadband internet access from orbit.
“Our behavior with greenhouse gases here on Earth over the past 100 years is having an effect on how we operate satellites over the next 100 years,” says study author Richard Linares, associate professor in MIT’s Department of Aeronautics and Astronautics.
The research focused on the thermosphere, which is where the International Space Station and most satellites orbit. While greenhouse gases trap heat in the lower atmosphere, the same gases radiate heat at much higher altitudes, effectively cooling the thermosphere. With this cooling, the thermosphere should shrink, which reduces atmospheric density at high altitudes.
If the thermosphere contracts, this reduces atmospheric drag which is one of the forces that pulls old satellites and other space debris down. Less drag means space junk takes longer to de-orbit, making the potential for collisions between satellites and space junk in orbit greater.
Today, there are over 10,000 satellites in low-Earth orbit - the region of space up to 2,000 kilometers from Earth's surface. More satellites have been launched in the last five years than in the preceding 60 years combined, so MIT’s researchers wanted to see if this was sustainable.
The team simulated various greenhouse gas emissions scenarios over the next century to investigate impacts on atmospheric density and drag. They found that continuing increases in emissions would lead to a “significantly reduced carrying capacity throughout low-Earth orbit”.
They estimate that, by the end of this century, the number of satellites safely contained within the altitudes of 200 and 1,000 kilometers could be reduced by 50 to 66 percent compared with a scenario in which emissions remain at year-2000 levels. If satellite capacity is exceeded, even in one region, the researchers predict that the region could experience a “runaway instability,” or a cascade of collisions that would create so much debris that satellites could no longer safely operate there.
“We rely on the atmosphere to clean up our debris. And if the atmosphere is changing, then the debris environment will change too,” said William Parker, a graduate student in the department. “We show the long-term outlook on orbital debris is critically dependent on curbing our greenhouse gas emissions."
The paper, to be published in Nature Sustainability notes: “This effort has shown that, perhaps unintuitively, climate change and orbital debris accumulation are two pressing issues of inextricable global concern requiring unified action.”
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