‘Unsustainable’: How Satellite Swarms Pose a Rising Threat to Astronomy

'Unsustainable': How Satellite Swarms Pose a Rising Threat to Astronomy thumbnail

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

Scientists made some progress in dealing with the onslaught. The International Astronomical Union (IAU), for instance, will soon launch a website that includes tools to help telescope operators determine satellite locations so they can point their instruments elsewhere.

But, evidence is mounting that satellite’megaconstellations” will cause interference with other skywatchers and astronomical observatories around the world. Satellite companies have yet to find a solution. SpaceX had tried to solve the problem by using sun-blocking shades to dim its Starlinks’ appearance in the night sky. But Nature has learnt that the company has stopped doing so.

Tens of thousands more satellites could be launched over the next few years. Meredith Rawls is an astronomer at University of Washington in Seattle. “This is an unsustainable path.” “At the moment our science is fine. But when will we lose a discovery ?”

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The toll of megaconstellations

Since the first Starlinks launched, astronomers have gone from panicking about the satellites photobombing scientific observations to organizing a global response. After a series of international workshops in 2020 and 2021, the IAU set up a Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference. Its website, soon to be launched, is intended to serve as a hub for policymakers, astronomers, and satellite operators to coordinate efforts to reduce the impact of satellites in the sky.

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

” It’s really quite terrifying,” said Samantha Lawler, an astronomer from the University of Regina in Canada who was the leader of the work.

Astronomical observatories which study large expanses of sky rather than individual celestial objects will be most affected. The Zwicky Transient Facility (ZTF), which surveys wide swathes of the sky using a 1.2-metre telescope on Palomar Mountain, California, had satellite streaks in 18% of its images taken during twilight in August 2021. Przemek Moroz, an astronomer from the University of Warsaw, said that this number has increased as satellite numbers have increased. He ran a preliminary analysis of ZTF data from April 2022 and found that satellite streaks affected about 20-25% of twilight images.

So far, the ZTF has not had any of its measurements damaged or ruined by satellite streaks. This is due to its image-processing techniques that can detect and mask satellite trails. Other observatories face greater challenges, such as the Vera C. Rubin Observatory which is a 8.4-metre-wide telescope that was funded by the United States. It is currently being built in Chile. It will be able to see the entire visible sky every 3 days. This makes it vulnerable to satellite streaks. Rawls and other astronomers have been working to find ways to mitigate the damage. For example, algorithms that can detect and remove satellite streaks from the data. However, fixing the data takes a lot time and energy. Rawls states that it is “certainly eating my career.”

A busy sky

The increasing number of satellites could also negatively impact radio astronomy and increase the amount of space debris. Other, more general impacts could also affect the quality of life around the world. Satellites can create a background glow that can confuse animals that depend on celestial navigation. Satellite streaks can also affect human knowledge systems, such Indigenous knowledge systems which rely on information from the dark sky to mark important events throughout a year.

The growing threat from satellite constellations contributes to other degradations in the night sky, such as light pollution, according to Karlie Noon (a PhD candidate in Astronomy and an Indigenous research associate at Australian National University in Canberra). She says, “In the same manner that our lands were colonized,” our skies are being colonized. She says, “And this isn’t just Indigenous people.” She also points out that satellite launches have been made by companies without consulting the scientific community.

Some satellite operators are working to reduce the problem. SpaceX, OneWeb in London, and Amazon’s Project Kuiper, Seattle, Washington have met regularly with the IAU, national astronomical societies, and discussed ways to reduce the impact of satellites. SpaceX has tried various methods to dimming its Starlinks ,, including installing sunshades. Although the sunshades reduce the brightness of the satellites, they are not compatible with the latest generation Starlinks. These satellites, which were launched in September, communicate with each other using lasers rather than radio. The sunshades block those communications.

SpaceX is working on other mitigations, such as adding stickers to satellite mirrors to reflect sunlight away from Earth, David Goldstein (an engineer with the company) said during a webinar hosted earlier this month by the UK-based Federation of Astronomical Societies.

It is still unknown how well this might work. An unpublished analysis of 102 observations of the brightness of Starlinks over time suggests that those from the new generation seem brighter than those known to have sunshades. They aren’t as bright as the original Starlinks with sunshades, according to Anthony Mallama (a retired astronomer from Bowie, Maryland), who conducted the analysis.

Meanwhile, OneWeb has launched 428 of a planned initial set of 648 satellites. They orbit at much higher altitudes than the Starlinks do — 1,200 kilometres compared with 550 kilometres. Satellites are usually brighter than Starlinks because they are farther away. However, they can be quite different in brightness depending on how much sunlight they catch and reflect.

One preliminary study of 50 OneWeb satellites during 2021 found that 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 Copiapo, Chile. OneWeb claims it is committed to reducing visibility of its satellites. It uses a telescope in Sicily for measuring their brightnesses, and is using that information to design future satellites with fainter designs, Maurizio vanotti, OneWeb’s vice president of space infrastructure development, told 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 will have a sunshade to allow the company to compare its ability dimming the satellites’ brightness.

There is no law that regulates how bright satellites should appear in night sky. However, the IAU and other astronomical organisations have been pressing the United Nations to address the problem .. Representatives from many nations will discuss protecting the skies at a meeting of the UN’s Committee on the Peaceful Uses of Outer Space that begins in V

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