SpaceX's Starlink satellite-internet project may create hundreds of visible objects that constantly move across dark night skies
- SpaceX this week launched 60 more more of its internet-beaming Starlink satellites into orbit, bringing the total to 360. Nearly 12,000 may fly before the end of the decade, though.
- Astronomer Jonathan McDowell studied the possible impacts of Starlink on dark night skies. He found that SpaceX has already doubled the number of satellites close to Earth and visible to stargazers through reflected sunlight.
- If SpaceX flies nearly all of the 12,000 planned satellites, some areas on Earth may have night skies dotted with "hundreds" of the spacecraft, all visible at once.
- Dark coatings may mitigate the issue, but mostly for stargazers and not professional astronomers. "It's not the end of ground-based astronomy - yet," McDowell said, adding some important projects may be practically "impossible" to pull off.
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If you venture beyond the glow of city lights and gaze up at a dark night sky with unaided eyes, you may see as many as 4,500 stars.
By the end of this decade, however, countless new points of light may constantly move across and invade that natural splendor: Starlink, or SpaceX's planned fleet of up to 12,000 internet-beaming satellites.
That's according to Jonathan McDowell, an astronomer at the Center for Astrophysics at Harvard and Smithsonian. McDowell meticulously follows Starlink government filings and the orbits of the 360 spacecraft that the rocket company, founded by Elon Musk, has launched into orbit to date.
This week, McDowell announced a new study that models the potential impacts of Starlink, noting that Astrophysical Journal Letters had accepted his paper for publication. His model suggests that at any moment "several hundred" of SpaceX's 12,000 planned satellites may be visible from locations with dark night skies and good visibility of the horizon.
For example, he said, a person hiking through Arcadia National Park in Maine during the summer might see some 200 Starlink satellites moving overhead - all at once.
"They'll be about the same as the fainter stars that you can make out. But I still think that's going to be dramatic," McDowell told Business Insider. "One or two you wouldn't notice, but 200 that faint moving across the sky? You'll sort of start to notice that the sky is swimming."
The ramifications aren't just for casual observers, though, but also astronomers who are trying to protect the human race from great harm.
Satellite size and location drives a lot of the problem
McDowell said the inspiration for his study was hearing a common talking point among staunch defenders of SpaceX and other satellite-internet projects that goes something like this: Humanity has about 10,000 satellites in space already, so what difference does another 10,000 or even 12,000 make? Or even 30,000 more than that? (Which SpaceX's government filings suggest is part of the long-term plan.)
While that may seem logical, McDowell says the talking point ignores how big (larger than 100 kilograms [220 pounds]), shiny, and relatively close objects can reflect much more sunlight than ones in higher orbits above Earth.
"If you're looking at objects that are both low and big, then there are only 400 pre-Starlink [satellites]," McDowell said. "So 12,000 is a huge change."
He noted that roughly 9,000 are slated to orbit in layers within a zone he calls "lower LEO," or low-Earth orbit, which he defines as lower than 600 kilometers (373 miles) above the planet. Remaining ones would layer in a zone he calls "upper LEO," or above 600 kilometers in altitude.
"The initial Starlink layer is in lower LEO, and it's large objects in lower LEO that are naked-eye visible," McDowell said, noting that small satellites, such as fist-size CubeSats, aren't as much of an issue. "Starlink is really the first big constellation to have big satellites in this low LEO region."
The model shows SpaceX is poised to dramatically boost the number of satellites visible to the unaided eye in dark skies.
"It's a doubling after only five launches, and they're only just beginning," he said.
Solutions may be expensive and not work well
SpaceX, which did not acknowledge Business Insider's requests for comment for this story, is doing its part to try and mitigate the problem. One potential solution is a prototype "dark satellite" that SpaceX recently launched. It's so-named because part of it is coated with a substance to reduce its reflectivity.
One group of astronomers recently measured the satellite's brightness from the ground, and their study suggests its about half as bright as prior designs - enough to remove it from naked-eye visibility, McDowell said. But he added that, at least anecdotally, that number seems low and more observations are required to back it up.
McDowell nevertheless praised the company for actively working with astronomers to engineer and deploy such solutions to at least mitigate the problem. But there will not be "zero" impact to future astronomy projects, as Musk claimed in early March.
Even if SpaceX's new spacecraft-darkening coating works well enough to hide Starlink from stargazers, McDowell said the project remains a significant problem to ground-based and likely even space-based observatories, especially those that survey large sections of the sky for interesting objects to target with more powerful telescopes.
"Some projects really won't mind this. Other projects we'll have to really rethink, and some will be impossible," McDowell said.
Starlink is just the beginning, though. Barring new regulations to limit the number of satellites in low-Earth orbit, Amazon's Project Kuiper, OneWeb, and governments like China may add up to a total of 57,000 satellites there by 2030.
This could have what McDowell said described as "a very bad effect" on observatories that scan the skies low to the horizon in a twilight period shortly after the sun sets.
"You're trying to see objects that are actually physically quite close to the sun, so you have to look sort of in the same direction as the sun," he said. "And what are those objects? Those objects are the near-Earth asteroids that might come and kill us."
McDowell isn't too concerned about very rare asteroids of the size that helped kill off dinosaurs, but rather "city killer" asteroids, so named because they are small enough to easily evade detection yet big enough to devastate a metropolitan area.
Special shutters can be added to telescopes to turn off a telescope's shutter and save an image from a big bright satellite streak. Alternatively, a ring of tripwire-like scouting telescopes around an observatory might scan for incoming bright satellites then, if one is seen, trigger a telescope's shutter to turn off before a sensitive image is corrupted.
But perhaps within five years, there will likely be too many satellites overhead for such solutions to matter, McDowell said. Their presence will be somewhat omnipresent.
"It's a serious and expensive impact to how we do business. It's not the end of ground-based astronomy - yet," McDowell said. "But if these constellations don't hose us, the next lot may."