Scientific American: The battle for the night sky
As plans for ever-larger satellite constellations accelerate, questions about how much activity Earth’s orbit can safely sustain are becoming increasingly urgent. AeroAstro research scientist Giovanni Lavezzi, as well as alumni Miles Lifson and William Parker, weigh in on orbital capacity in a new article from Scientific American. Read the full article on their website.
Seven years ago, when Samantha Lawler moved to rural Saskatchewan to run a farm with her partner, the glorious darkness overhead was one of the biggest perks. Undiminished by light pollution, countless stars filled the night sky. It was a pristine celestial view that city dwellers can only dream of seeing. That matters a lot to Lawler, who studies the universe as an astronomer at the nearby University of Regina when she’s not tending goats and chickens.
Yet ever since Lawler’s rural relocation, a new type of artificial star has increasingly encroached on the heavens above her homestead: satellites, constellations of them, most beaming the Internet around the globe. “Now there are many satellites all the time,” Lawler says. “I really could notice the change that was happening.”
In 2019, the same year Lawler moved to Saskatchewan, Texas-based SpaceX began launching its Starlink megaconstellation in earnest, lofting an initial 60 satellites into orbit that May. The constellation has since exploded in size. This past March, SpaceX reached a milestone of 10,000 active Starlink satellites. More than 10 million customers worldwide now use its Internet service. Other companies and countries are racing to catch up. There are plans to put nearly two million satellites in orbit. If even a fraction of those launch, it will make the current crop of about 15,000 satellites look paltry by comparison.
The rapid proliferation of satellites brings many benefits on the ground, offering faster, more reliable Internet access in remote locations than ever before. Oceanic ships and passenger planes can benefit from broadband communications wherever they are. Emergency services can better respond to natural disasters even when local Internet infrastructure fails. Soldiers on the battlefield can remotely pilot drones and coordinate with commanders half a world away. But the surge has also raised questions about just how many satellites we can safely launch, whether there might be some kind of carrying capacity for Earth orbit and where the limitations lie.
Until now we’ve managed to operate several thousands of satellites relatively smoothly, but what does the future hold? “So far it seems manageable” through active coordination, says Giovanni Lavezzi, a research scientist who specializes in orbital capacity at the Massachusetts Institute of Technology. “The problem is how much can we push.”
Experts are wary of putting a single number on how many satellites we can fit in low-Earth orbit, the region up to 2,000 kilometers above our planet that is prized for most satellite constellations. One 2022 study attempted an answer, suggesting that as many as 12.6 million spacecraft could occupy orbits between 200 and 900 kilometers in altitude. But that simplified scenario assumes an almost perfectly ordered system, something far from reality; a more nuanced appraisal published in 2024 found that the limit would be between about 10 million to 100 million satellites—an unhelpfully broad range for any policymakers seeking guidance for regulatory action.
Either way, with so many satellites, even a tiny number of mishaps would lead to chaos. Hundreds of thousands of collisions would happen every year, each unleashing its own swarm of hazardous, high-speed orbital shrapnel. Satellites could keep operating only because some of that debris would naturally, gradually drift down into Earth’s atmosphere, but some regions of orbit would essentially become unusable. The point of the 2022 study was not to rule out the sheer physical space of low-Earth orbit as the real constraint. “There probably is a capacity,” says Miles Lifson, an orbital-capacity expert at Aerospace Corporation, headquartered in Virginia, and a co-author on both studies. “But the number of satellites is a really ill-posed way to think about it.”
