How satellite swarms pose a rising threat to astronomy

It’s been three years since SpaceX, a Hawthorne, California-based aerospace firm, launched its first batch of Starlink Internet-communication satellites, causing astronomers to be concerned about the streaks the spacecraft leave in images of the night sky. Since then, many more Starlink satellites have been launched: over 2,300 of them presently orbit the Earth, accounting for roughly half of all active satellites.

How astronomy photographs will be photobombed by satellite ‘megaconstellations’
Scientists have made some headway in combating the assault. For example, the International Astronomical Union (IAU) will launch a website with tools to enable telescope operators estimate satellite placements so that they may direct their equipment elsewhere in the coming days1.

However, evidence is mounting as to how much these satellite’megaconstellations’ may interfere with astronomical observatories and other skywatchers throughout the world. Satellite businesses have yet to find a solution. SpaceX attempted to remedy the issue by installing sun-blocking curtains on its Starlinks, which dimmed their appearance in the night sky. Nature, on the other hand, has learned that the firm has ceased doing so.

Thousands of additional satellites might be deployed in the coming years. “This is an unsustainable trend,” astronomer Meredith Rawls of the University of Washington in Seattle said. “For the time being, our science is OK. But when will we miss a breakthrough?”

The cost of megaconjunctions

Astronomers have gone from fretting over the satellites photobombing scientific observations to coordinating a worldwide reaction since the first Starlinks launched. Following a series of international conferences in 2020 and 2021, the International Astronomical Union established the Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference. Its soon-to-be-launched website will serve as a focal point for astronomers, policymakers, satellite operators, and the general public to collaborate on ways to lessen the affects of satellites blazing over the sky.

According to a recent research, future satellite constellations would be best visible on summer evenings at latitudes of roughly 50 degrees south and 50 degrees north, which are home to numerous European and Canadian astronomical facilities. According to the report, if SpaceX and other businesses launch the 65,000 satellites requested, bright spots would buzz over the sky all night long at certain latitudes during the summer solstice. Around one in every 14 stars visible to the naked eye between dawn and dusk will be a satellite.

“It’s actually very scary,” says Samantha Lawler, an astronomer from Canada’s University of Regina who led the research.

Astronomical observatories that investigate large areas of the sky rather than specific celestial objects would be the most impacted. The Zwicky Transient Facility (ZTF), which monitors the sky with a 1.2-metre telescope on Palomar Mountain in California, found satellite streaks in 18% of its photographs collected after twilight in August 20213. And that number has risen as the number of satellites has grown, according to lead author Przemek Mróz, an astronomer at the University of Warsaw. He conducted a preliminary review of ZTF data from April 2022 and discovered that satellite streaks impacted around 20–25 percent of twilight photographs.

Mróz claims that the ZTF hasn’t had many of its measurements ruined by satellite streaks since its image-processing technologies can identify and conceal satellite traces. Other observatories, however, confront greater hurdles, most notably the Vera C. Rubin Observatory, an 8.4-metre-wide telescope financed by the US and now under construction in Chile. It will be especially sensitive to satellite streaks following across its photographs since it will shoot the whole visible sky every three days. Rawls and other astronomers are developing methods to reduce the harm, including as algorithms to detect and remove satellite streaks from data. However, repairing the data still requires a significant amount of time and effort. “It’s definitely eating away at my career,” Rawls adds.

A crowded sky

The increasing number of satellites also threatens to harm radio astronomy and increase the quantity of space debris. Other, bigger effects might have a global impact: satellites contribute to a background light in the sky, which can disorient animals that depend on celestial navigation. Satellite streaks may also disrupt human knowing systems, such as Indigenous knowledge systems that depend on information from the night sky to record major events throughout the year4.

SpaceX is testing a dark satellite to decrease the danger of a “megaconstellation” to astronomy.
According to Karlie Noon, a PhD candidate in astronomy and an Indigeneous research associate at Australian National University in Canberra, the rising hazard of satellite constellations exacerbates other night sky degradations such as light pollution. “Our skies are being invaded in the same manner that our soils were,” she argues. “This isn’t limited to Indigenous people.” She claims that firms have launched satellites without first contacting the scientific community.

Some satellite providers have been striving to address the issue. Companies such as SpaceX, OneWeb in London, and Amazon’s Project Kuiper in Seattle, Washington, have met with the IAU and national astronomical societies on a regular basis to discuss how to lessen the effect of satellites. SpaceX has experimented with darkening their Starlinks, such as inserting sunshades. The sunshades indeed lower the brightness of the satellites5, but they seem to have been removed from the newest generation of Starlinks. These satellites, which have been deployed since September, interact with one another via lasers rather than radio waves, and the sunshades interfere with their transmissions.

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

How effectively that will function is yet being determined. An unpublished examination of 102 observations of Starlink brightness over time reveals that the current generation seems brighter than those known to have sunshades. However, without sunshades, they are not as brilliant as the original Starlinks, according to Anthony Mallama, a retired astronomer in Bowie, Maryland, who conducted the investigation.

Meanwhile, OneWeb has launched 428 of a total of 648 satellites. They orbit at a significantly greater altitude than the Starlinks – 1,200 kilometers vs 550 kilometers. The satellites are normally fainter than Starlinks due to their greater distance, although their brightness may vary greatly depending on how they capture and reflect sunlight.

According to Jeremy Tregloan-Reed, an astronomer at the University of Atacama in Copiapó, Chile, a preliminary examination of 50 OneWeb satellites in 2021 revealed that over half of them were a bit brighter above the’safe’ level stipulated by astronomers. According to Maurizio Vanotti, OneWeb’s vice-president of space infrastructure development and partnerships, the company is committed to reducing the visibility of its satellites; it uses a telescope in Sicily to measure their brightness and is using that information to design future satellites that are fainter.

Astronomers advocate for a worldwide discussion on massive satellite swarms.
Amazon’s Project Kuiper, which would add over 3,200 satellites, intends to launch the first two prototype satellites by the end of this year. One of them will have a sunshade so that the corporation can compare its capacity to lower the brightness of the satellites.

There are no regulations governing how bright satellites should look in the night sky, despite the IAU and other astronomical organizations urging the United Nations to address the issue. Representatives from several countries will address the protection of the sky during a conference of the United Nations Committee on the Peaceful Uses of Outer Space, which opens on June 1 in Vienna.

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