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SpaceX’s dark satellites are still too bright for astronomers

Starlink, a “mega constellation” of hundreds of Internet satellites launched by the aerospace company SpaceX, has caused astronomers to have headaches by overshadowing celestial objects. Set to eventually include tens of thousands of spacecraft broadcasting high-speed internet to the entire planet, Starlink has one disadvantage for stargazing: satellites reflect enough sunlight at night to be clearly seen with the naked eye (for not to mention sensitive telescopes). Their luminosity is accentuated only by the long trains in which they are arranged, which cross the skies like dozens of luminous pearls on a celestial thread.

Since the first 60 Starlink satellites were launched in May 201

9, another 655 have been placed in orbit, influencing a number of astronomical observations. Each launch consistently held around 60 satellites, with one or two batches increasing each month since January, the latest on September 3.

Finally, in August, after more than a year of complaints from the scientific community and damage control efforts by SpaceX, the National Science Foundation (NSF) and the American Astronomical Society (AAS) released a report on the situation. It was drawn from discussions among more than 250 experts at the Satellite Constellations 1 (SATCON1) virtual workshop earlier this summer to provide recommendations to both astronomers and satellite constellation operators to minimize further disruption.

For now, many astronomers can do little more than hope the situation improves. Although SpaceX’s satellites pose a problem for astronomical observations, the company doesn’t “want to ruin astronomy,” says Meredith Rawls, an astronomer at the University of Washington. Rawls works with the upcoming Vera C. Rubin Observatory in Chile, formerly known as the Large Synoptic Survey Telescope. The constant flow of the project of panoramic images of the entire sky will help to discover the nature of dark matter and dark energy, identify countless instances of transient astrophysical phenomena and map threatening asteroids for the Earth, if, of course, the interference of the constellations satellite does not sink its delicate work.

SpaceX’s initial efforts to mitigate the spacecraft’s impact involved launching a Starlink satellite prototype known as DarkSat earlier this year that features a black anti-reflective coating. Recent ground-based observations of DarkSat in orbit have found it to be half as bright as a standard Starlink satellite – a big improvement, according to experts, but still far from what astronomers say is needed.

“I wouldn’t consider DarkSat a victory, but rather a good step in the right direction,” says Jeremy Tregloan-Reed, astronomer at the University of Antofagasta in Chile and a member of the observation team that evaluated the prototype. The team compared it to a typical Starlink sibling using a 0.6-meter telescope at the Ckoirama Observatory in Chile and found that although DarkSat’s anti-reflective coating made it invisible to the naked eye, it remains too bright to avoid. interfere with the Rubin Observatory and other large telescopes.

These results show that DarkSat is essentially a dead end, says Jonathan McDowell, a researcher at Harvard University’s Center for Astrophysics and the Smithsonian Institution, which has performed computer simulations of the effects of mega constellations on astronomical observations. However, he says, the investigation by the Tregloan-Reed team is an important step. “This study is noteworthy as one of the first significant observational studies of a Starlink satellite, something the community is now organizing to do on a much larger scale,” adds McDowell. He warns that if the satellites continue to be launched without correction, “the impact would be enormous”.

In the long run, Rawls fears that with the spread of the satellite constellations, future companies could launch them without any attempt to compromise with astronomers. “It creates a lot of systematic errors … It becomes kind of a mess,” he says.

SpaceX hopes to finally be able to put 12,000 Starlink satellites in the sky and last year asked for permission to install another 30,000. With these plans – as well as Amazon’s Kuiper Project targeting 3,236 satellites and OneWeb, a now bankrupt company recently acquired by the UK government, possibly targeting 2,000 – the scale of the astronomy satellite constellation problem will only do that. to increase.

While DarkSat’s tested dimming techniques are far from a sufficient solution, SpaceX has continued to develop other ways to further reduce the spacecraft’s brightness. The company’s second attempt at making a darkened satellite, VisorSat, uses a black parasol to reduce light reflection. The first spacecraft with this project was launched on June 3. Astronomers hope to observe VisorSat and compare it to DarkSat once the observatories reopen, following the closure of Covid-19.

Even before detailed observations have been made on VisorSat, SpaceX appears to have doubled down on the new model. All satellites in the two Starlink lots launched in mid-June and early August were VisorSats, each with their own umbrella.

Astronomers are still unsure if dimming methods like DarkSat and VisorSat are the solution. Of the 10 recommendations in the SATCON1 report, only one asks satellite operators to use blackout techniques. The others suggest deploying satellites in orbits less than 600 kilometers to minimize their night glow, checking their orientations in space to reflect less sunlight, developing ways to remove their tracks from astronomical observations, and making their information available. orbital so that astronomers can point telescopes away from them.

With a mix of approaches from this menu of options, hopefully, the problem can be handled. Even so, the advent of satellite mega-constellations may have made further degradation of the astronomical view of the night sky inevitable.

For now, Tregloan-Reed is comforted that SpaceX is taking the issues seriously. “The development of both DarkSat and the new VisorSat shows that Starlink appears to be dedicated to mitigating the impact” of its satellites on both astronomers and backyard astronomers, he says.

The spirit of collaboration at the SATCON1 seminar and the relationship building that followed is promising, according to Patrick McCarthy, director of NSF’s NOIRLab, which produced the report with AAS. “I hope the collegiality and spirit of collaboration between astronomers and commercial satellite operators will expand … and that it will continue to prove useful and productive,” he said in a statement in late August.

SATCON2, the next seminar bringing together astronomers and satellite constellation operators, is slated to start through mid-2021. It will be geared towards addressing policy and regulation. With the prospect that hundreds of satellites will be launched in the meantime, Rawls stresses the urgency and importance of the issue. “This will only speed up,” he says. “And it’s a long-term precedent. It’s a question of what kind of sky you want your grandchildren to have.”

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