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how satellite swarms are a growing threat to astronomy

how satellite swarms are a growing threat to astronomy

A super wide angle view of Starlink satellites traversing a night sky

Starlink satellites scan (vertically) a time-lapse photo of the night sky near Carson National Forest, New Mexico.Credit: M. Lewinsky (CC BY 2.0)

It’s been three years since SpaceX, an aerospace company in Hawthorne, Calif., launched its first batch of Starlink internet communications satellites, sparking concern among astronomers about the trails the satellites leave in photographs of the night sky. Since then, many other Starlinks have been launched: more than 2,300 of them now orbit the Earth, almost half of all operational satellites.

Scientists have made some progress in dealing with the onslaught. For example, in a few days, the International Astronomical Union (IAU) will launch a website including tools to help telescope operators predict the locations of satellites so they can point their instruments elsewhere.1.

But mounting evidence reveals just how much these satellite “megaconstellations” will interfere with astronomical observatories and other skywatchers around the world. And the satellite companies have not yet found a solution. SpaceX had tried to fix the problem by putting sun-blocking shades on its Starlinks to dim their appearance in the night sky. But Nature learned that the company had stopped doing so.

Tens of thousands of new satellites could be launched in the next few years. “It’s an unsustainable trajectory,” says Meredith Rawls, an astronomer at the University of Washington in Seattle. “At the moment, our science is doing well. But when are we going to miss a discovery?

The balance sheet of megaconstellations

Since the launch of the first Starlinks, astronomers have gone from panicking about satellites photobombing scientific observations to organizing a global response. After a series of international workshops in 2020 and 2021, the IAU has set up a Center for the protection of dark and calm skies against interference from satellite constellations. Its soon-to-be-launched website is intended to act as a hub for astronomers, policymakers, satellite operators and the public to coordinate how to reduce the impacts of satellites traversing the sky.

A recent study suggests that future satellite constellations will be most visible during summer nights at latitudes around 50 degrees south and 50 degrees north, where many European and Canadian astronomical facilities are based.2. If SpaceX and other companies launch the 65,000 satellites they have proposed, bright spots will buzz across the sky all night at those latitudes around the summer solstice, the study found. At sunrise and sunset times, approximately one out of every 14 stars visible to the naked eye will actually be a satellite.

“It’s really quite horrifying,” says Samantha Lawler, an astronomer at the University of Regina in Canada, who led the work.

Astronomical observatories that study large swaths of the sky rather than focus on individual celestial objects will be hit the hardest. The Zwicky Transient Facility (ZTF), which surveys large swaths of the sky using a 1.2-meter telescope on Palomar Mountain, California, had satellite trails in 18% of its images taken at dusk in August 20213. And that number grew as the number of satellites grew, says lead author Przemek Mróz, an astronomer at the University of Warsaw. He did a preliminary analysis of ZTF data from April 2022 and found that satellite trails affected about 20-25% of twilight images.

So far, the ZTF hasn’t seen many of its measurements damaged by satellite trails, in part because its image processing methods can detect and mask satellite trails, Mróz says. But other observatories face bigger challenges, especially the Vera C. Rubin Observatory, an 8.4-meter-wide US-funded telescope under construction in Chile. Because it will photograph the entirety of the visible sky every three days, it will be particularly vulnerable to satellite trails passing through its images. Rawls and other astronomers are working on ways to mitigate the damage, such as algorithms that can identify and erase satellite trails from data. But repairing the data still takes a lot of time and energy. “It’s eating up my career,” Rawls said.

A cloudy sky

The growing number of satellites also threatens to negatively affect the field of radio astronomy and increase the amount of space debris. Other broader impacts could affect life around the world: the presence of satellites contributes to a background glow in the sky that can disorient animals that rely on celestial navigation. Satellite trails can also interfere with human knowledge systems, such as indigenous knowledge systems that rely on information from dark skies to mark important events throughout the year.4.

The growing threat from satellite constellations comes on top of other night sky degradations such as light pollution, says Karlie Noon, a PhD student in astronomy and Indigenous research associate at the Australian National University in Canberra. “In the same way that our lands were colonized, our skies are now colonized,” she says. “And it’s not just about indigenous peoples. She points out that companies have launched satellites without necessarily consulting the scientific community.

Some satellite operators have worked to alleviate the problem. Companies such as SpaceX, OneWeb in London and Amazon’s Project Kuiper in Seattle, Washington have met regularly with the IAU and national astronomical societies about ways to reduce the impact of satellites. SpaceX has been testing methods of dimming its Starlinks, including installing sun visors. Sun visors reduce satellite brightness5, but they seem to have been left behind by the latest generation of Starlinks. These satellites, launched since September, use lasers instead of radio to communicate with each other, and the sun visors interfere with these communications.

Instead, SpaceX is working on other mitigations such as adding stickers or other materials to satellite mirrors to reflect light away from Earth, company engineer David Goldstein said during a webinar. by the British Federation of Astronomical Societies (FAS). earlier this month.

How that might work is still being sorted out. An unpublished analysis of 102 observations of Starlinks’ brightness over time suggests that the newer generation ones appear brighter than those known to have sunshades. However, they aren’t as bright as the original Starlinks without a sunshade, says Anthony Mallama, a retired astronomer from Bowie, Maryland, who led the analysis.

Meanwhile, OneWeb has launched 428 of an initial planned set of 648 satellites. They orbit at much higher altitudes than Starlinks – 1,200 kilometers versus 550 kilometers. Satellites are generally dimmer than Starlinks simply because they are farther away, but their brightness can vary greatly depending on how they catch and reflect sunlight.

A preliminary study of 50 OneWeb satellites in 2021 found nearly half of them were a little brighter than the “safe” limit specified by astronomers, says Jeremy Tregloan-Reed, an astronomer at the University of Atacama in Copiapó, Chile. OneWeb says it is committed to reducing the visibility of its satellites; it uses a telescope in Sicily to measure their luminosities and uses that information to design future dimmer satellites, said Maurizio Vanotti, vice president of space infrastructure development and partnerships at OneWeb, at the FAS webinar.

Amazon’s Project Kuiper, which would add more than 3,200 satellites, plans to launch its first 2 prototype satellites by the end of this year. One of them will contain a sunshade so the company can compare its ability to attenuate the brightness of satellites.

There are no laws regulating the brightness of satellites in the night sky, although the IAU and other astronomical organizations have pushed the United Nations to recognize the problem. Representatives from many countries will discuss protecting the skies at a meeting of the United Nations Committee on the Peaceful Uses of Outer Space which begins in Vienna on June 1.

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