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Saturday, November 25, 2023

As SpaceX's Starlink Ramps Up, So Could Light Pollution

With some 1,800 satellites already orbiting Earth, providing internet access to about 100,000 households, SpaceX’s Starlink broadband service is poised to emerge from the beta testing phase this month, according to a recent tweet from Elon Musk, the company’s founder and CEO.

Just a decade ago, there were only a few thousand spacecraft orbiting Earth. Now Starlink engineers aim to build up to 12,000 satellites, and SpaceX launches scores more on its Falcon 9 rockets almost every month. (A recent FCC report states that the company applied for authorization for 30,000 more.) The massive network of satellites, known as a “mega-constellation,” currently dominates the satellite internet industry, but other players, like Amazon and OneWeb, have plans to launch thousands of satellites of their own.

As the Starlink fleet grows, SpaceX and its competitors will have to address some potential problems. One is that more orbiting bodies means that, eventually, there will be more space junk, creating more chances for collisions. And astronomers, environmentalists, and indigenous groups, among others, express concern that Starlink will irrevocably light up the night sky, thanks to the sunlight reflected off its satellites. For telescopes like the National Science Foundation–funded Vera C. Rubin Observatory, nearing completion in Chile, astronomers are trying to develop software to mitigate the effects of a sky filled with more private satellites, but they will inevitably leave streaks on their images of the cosmos.

Over the past few years, astronomers have already spotted many Starlink satellites in the night sky. “If I walk on my porch and look up at night, I’ll see a bright satellite going across the sky, and usually I’ll see several. It’s a very weird sensation: All the stars then seem to move, like an optical illusion,” says Aaron Boley, a planetary astronomer at the University of British Columbia and codirector of the Outer Space Institute. “It’s going to have a much larger effect than people appreciate.”

With the prospect of a total of some 65,000 SpaceX, Amazon, OneWeb, and Starnet/GW satellites orbiting in just a couple years, Boley and astronomer Samantha Lawler made predictions for their light pollution effects in a new research paper that’s currently going through peer review. (They aren’t affiliated with any of the satellite makers.) Based on observations and models of Starlink satellites’ brightness, they find that at latitudes near 50 degrees North and South—affecting people in Canada and Europe, for example—satellites will make up between 7 and 14 percent of lights one can see by telescope, and about one in 10 of those seen by the naked eye. 

Boley and Lawler identify tradeoffs: For example, satellites orbiting at around 1,200 kilometers above Earth linger in the sky for a while, while Starlink’s satellites move more quickly in low-Earth orbit, at an altitude of less than 600 kilometers—about as high as SpaceX’s all-civilian Inspiration4 flew. Lower satellites cover less area than higher ones, so SpaceX needs more of them to reach the same number of people. But to us on Earth, they also glow more brightly in the sky.

Other industry players, who generally stick to one or the other of these ranges of orbit altitudes, include the UK’s OneWeb and planned satellite constellations like Amazon’s Project Kuiper, China’s Starnet/GW, and Canada’s Telesat. But Starlink’s constellation will likely remain the biggest one, at least for a while: SpaceX has already shipped terminals, which include a Wi-Fi router and satellite dish, to beta users in 14 countries, mainly in Western Europe and North America, including rural and remote users, according to Musk’s tweets, and the company plans to expand the user base to at least half a million

“It’s going to be difficult to compete against SpaceX in this domain, given its obvious advantage in launch. Competitors exist and are being formed, however, suggesting that the market still sees opportunity,” wrote Matthew Weinzierl, an economist at Harvard Business School who researches the commercialization of the space sector, in an email to WIRED.

A representative from SpaceX’s communications team declined interview requests from WIRED.

But a representative from Amazon indicated the company is aware of potential light pollution issues. “Reflectivity is a key consideration in our design and development process. We’ve already made a number of design and operational decisions that will help reduce our impact on astronomical observations, and we’re engaging with members of the community to better understand their concerns and identify steps we can take,” the spokesperson wrote by email.

Katie Dowd, OneWeb’s director of government and corporate affairs in North America, wrote in an email to WIRED that the company is talking with groups, including the UK’s Royal Astronomical Society and the American Astronomical Society, to understand the effects satellites have on observations, "and to create design and operational practices that support both communities. We are also undertaking brightness measurements and will be looking at those results to explore solutions.”

SpaceX and its rivals can’t avoid light pollution; they can only reduce it. Every object in the atmosphere reflects at least some light during part of its orbit, depending on its materials, color, and size. While satellites beam information down to Earth, a tiny bit of sunlight often gets reflected down, too, both by a satellite’s body and its solar array.

Early last year, SpaceX tested a Starlink satellite nicknamed Darksat, giving it an experimental darkening coating on one side, including the antennas, to cut down on the reflective brightness, which the company claims was reduced by 55 percent. In one paper, some astronomers found that the measure did darken the satellite but not to that degree, though it made the satellite invisible to the naked eye. Others didn’t detect significant darkening at all. They found that the satellite’s measured brightness may vary, however, depending on the angle at which it’s observed and how the light scatters through the atmosphere. 

According to a post on the company’s website, SpaceX found that the dark surfaces got hot, putting the satellite’s components at risk, and that it still reflected light in the infrared. So the company later tested a different approach that it calls Visorsat, deploying a number of satellites with rectangular sun shades attached, like the one used on a car windshield. Those visors are intended to make sure that sunlight that bounces off the satellites’ antennas is reflected away from Earth. 

So far, SpaceX hasn’t publicly released any information about how well this approach works, or how it compares to Darksat. But another astronomer, in an unpublished paper posted on the academic preprint server arXiv.org, and Boley’s team in work-in-progress, both independently find that at least 70 percent of the Visorsat spacecraft were still brighter than their preferred threshold: a level that would ensure that the Vera C. Rubin Observatory’s images will be mostly unaffected.

To draw attention to light pollution concerns and to work on developing solutions, the American Astronomical Society convened a virtual workshop on satellite constellations this summer, known as SatCon2. They plan to soon issue reports and recommendations, coinciding with a meeting beginning this Sunday, called “Dark and Quiet Skies for Science and Society,” organized by the United Nations and the International Astronomical Union.

SatCon2 organizers made a priority of reaching out to a broad range of people concerned about the night sky, including amateur astronomers, astrophotographers, the planetarium community, environmentalists, and indigenous and tribal communities from the United States, Canada, New Zealand, and other countries. “Everybody wanted things to slow down. They want industry to engage more. This is something that belongs to everyone as a global commons,” says Aparna Venkatesan, an astrophysicist at the University of San Francisco and SatCon2 public engagement co-chair. 

As part of SatCon2, a working group of astronomers spoke with representatives from SpaceX and five other major satellite operators about what reflected light limits researchers propose, and how the companies could assess and reduce how reflective their spacecraft are. They also debated policy options within the US that could involve setting rules for how much light pollution internet satellites can create. These include the possibility of regulations imposed by the Federal Aviation Administration, which sets conditions for launch and reentry, or the FCC, which licenses radio frequencies in orbit. Some astronomers also would like to see the National Environmental Policy Act to end its exemption for space—that is, they see space as an environment in need of protection.

“There is a little bit of tension, but we’re still considering both approaches: A cooperative approach, where industry really tries and we talk to them, and the possibility of getting regulations that make them try to commit to a [brightness] limit,” says Richard Green, an astronomer at the University of Arizona and chair of the SatCon2 policy working group. 

In addition to light pollution, all these companies face another challenge: space junk. Their satellites could be both part of the problem and potential victims, if another spacecraft or any of the hundreds of thousands of bits of orbiting debris smashes into them.

SpaceX has the ability to move its satellites out of the way to avoid a collision, and like other companies with spacecraft in lower orbits, at the end of a satellite’s life, its engineers can bring it down into the atmosphere to burn up on reentry, says Brian Weeden, director of program planning at the Secure World Foundation, a nonpartisan think tank based in Broomfield, Colorado. “But there’s still some uncertainty there. Actively deorbiting only works if the satellite’s still functional,” he says. If, say, 2 percent of Starlink’s satellites go kaput before they can be moved or pulled down back to Earth, that still amounts to hundreds of derelict spacecraft. 

And the lack of rules about who notifies whom of a potential collision, and how close is too close, and who has to move as satellite owners play chicken in space, adds to the confusion. In April, Starlink and OneWeb satellites came uncomfortably close, and in 2019, a European Space Agency satellite fired thrusters to avoid hitting a Starlink one.

The US Space Command currently monitors all pieces of space debris 10 centimeters in size or larger and calculates the odds of a space crash. “Megaconstellations and all these launch opportunities are overwhelming that system, so there’s the need to expand the capacity,” says Dan Ceperley, founder and CEO of LeoLabs, based in Menlo Park, California. Using radar systems around the globe, his company tracks space debris, including much of the small stuff, and provides data to companies that contract with them, which he says includes SpaceX.

As Starlink and other constellations grow, Boley and his colleagues hope that these companies will better address both the light pollution and debris challenges. “I hope that as they’re modifying the satellites, that the engineering is not just a matter of retrofitting, but the actual design of the satellite as a whole takes into account brightness mitigation,” Boley says. 

As he points out, once those satellites go up, there will be no way for people on Earth to avoid their effects. “You can get out of the city, escape from city light pollution, and experience the night sky, but you can’t do that from satellite light pollution. There’s nowhere you would be able to go,” he says.

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