Why SpaceX’s Starlink satellites caught astronomers off guard

Astronomers have had five years to brace for the impact of SpaceX’s Starlink internet-satellite megaconstellation, but the first few batches of the spacecraft still managed to catch the community off guard.

SpaceX founder and CEO Elon Musk announced the Starlink concept (though not the name) back in January 2015, explaining that the company intended to launch about 4,000 broadband satellites to low Earth orbit to provide low-cost internet service to people around the world. 

The envisioned numbers have grown since then. SpaceX now has permission from the U.S. Federal Communications Commission to loft about 12,000 Starlink craft, and the company has applied to an international radio-frequency regulator for approval of up to 30,000 additional satellites. (For perspective: There are only about 2,000 operational satellites in orbit today, and humanity has launched only around 9,000 craft into space in all of history, according to the United Nations’ Office of Outer Space Affairs.)

Related: In Photos: SpaceX Launches Third Batch of 60 Starlink Satellites

Nearly 200 Starlink craft are already circling Earth. SpaceX lofted the first batch of 60 satellites last May and performed similar launches in November and this past Monday (Jan. 6). 

These three missions have been eye-opening for skywatchers and professional astronomers alike. Shortly after deployment, the Starlink craft look like a bright string of pearls as they race together across the sky. This formation disbands as the 500-lb. (225 kilograms) satellites disperse and climb to their final operational altitude about 340 miles (550 kilometers) above Earth’s surface — but the individual spacecraft remain visible to the naked eye, even way up there.

“What surprised everyone — the astronomy community and SpaceX — was how bright their satellites are,” Patrick Seitzer, an astronomy professor emeritus at the University of Michigan, said Wednesday (Jan. 8) during a special news conference at the 235th meeting of the American Astronomical Society (AAS) called “Astronomy Confronts Satellite Constellations.” 

Related: SpaceX’s 1st Starlink Satellite Megaconstellation Launch in Photos

“We knew these tens of thousands[-strong] megaconstellations were coming, but based on the sizes and shapes of things currently in orbit, I thought maybe 8th or 9 magnitude,” Seitzer added. “We were not expecting 2nd or 3rd magnitude in the parking orbits, and we were certainly not expecting 4th to 5th magnitudes in the [operational] orbits.”

The magnitude scale used by astronomers assigns lower numbers to objects that appear brighter in the sky. For example, the brightest object in our sky, the sun, has a magnitude of minus 27, whereas the faintest objects you can see with binoculars are around plus 10. Only objects about plus 6 or brighter can be seen by the naked eye under clear, dark skies.

This surprising brightness has many astronomers worried. The huge number of coming Starlink satellites — and SpaceX plans to launch nearly 1,600 more just by the end of this year, according to Seitzer — could severely compromise the ability of ground-based scopes to do their work, some researchers have said.

The high-profile project most likely to be affected, Seitzer said, is the Vera Rubin Observatory. This big instrument, which was until Monday known as the Large Synoptic Survey Telescope (LSST), is scheduled to come online a few years from now in the Chilean Andes. 

“The survey is the most impacted by bright satellite trails because of its wide field of view and extreme sensitivity,” Seitzer said, citing a statement provided to him by Vera Rubin Observatory chief scientist Tony Tyson. “The original Starlinks will saturate the LSST’s detectors.”

But Starlink’s effects will be felt beyond the astronomical research community —  indeed, by pretty much everyone around the world, dark-sky advocates have stressed. The star-filled night sky is an international resource and one of the only ways that many people commune with nature in our increasingly urban and technological world, said Ruskin Hartley, executive director of the International Dark Sky Association. So, we should think hard about how we manage that resource, he said.

“The night sky is the ultimate public good; it’s our ultimate commons,” Hartley said during Wednesday’s news conference. “No one individual can protect it. And the flip side, I believe, [is] no one individual should be allowed to despoil that.”

Astronomers have voiced their concerns to SpaceX and found a receptive audience, said Jeffrey Hall, the director of Lowell Observatory in Flagstaff, Arizona. 

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“We have not had to cajole SpaceX in any way; they’ve been very receptive, very proactive, in holding roughly monthly telecons with us,” Hall said during Wednesday’s news conference. 

So far, he added, those telecons have mostly been informational, telling the astronomical community when the company plans to launch and deploy more Starlink satellites, and into which orbits. 

“It’s been a little more staying in touch than making a lot of progress on mitigation,” Hall said. (He added that astronomers plan to speak soon with OneWeb, which has launched the first half-dozen members of its own big internet-satellite constellation. A few other companies, including Amazon, are planning similar networks of their own, but none will be as big as SpaceX’s is envisioned to become.)  

But SpaceX representatives have expressed a desire to mitigate, and they’ve recently taken some action toward this end. For example, Patricia Cooper, SpaceX’s vice president of satellite government affairs, presented a paper during a special AAS scientific session about megaconstellations on Wednesday (though the company didn’t participate in the news conference that day). 

And one of the 60 spacecraft that launched on Monday sported a special coating designed to reduce its brightness. If everything goes well, and the coating doesn’t seriously affect the satellite’s performance (through increased solar heating, for example), this mitigation measure could eventually become widespread across the Starlink fleet.

Not everyone is satisfied by such steps. Consider the question asked by astrophysicist and science communicator Ethan Siegel, who was in the audience at Wednesday’s news conference.

“I apologize for this question, because I’m having difficulty controlling my fury at this situation,” Siegel began. “Why should astronomers trust SpaceX — which knows about this [brightness] problem but is deliberately worsening this instead of addressing it before additional launches — instead of seeking a legal or international mandate for regulation? Are we Elon Musk’s Neville Chamberlain?”

In response, Hall explained that the astronomy community doesn’t really have much choice.

“The launches are underway right now. I think regulation of the Wild West up there is necessary; that is going to take a great deal of time to implement, just because of the nature of that beast,” Hall said.

“Therefore, there is no advantage or upside to distrusting what SpaceX colleagues have told us,” he added. “We will simply take them at face value and work as best as we can and honestly with them to try to solve the situation. They are on the record saying they want to solve the situation for astronomy. We are working to identify the targets they will need to hit to make that happen, and then we’ll see what happens.”

Mike Wall’s book about the search for alien life, “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook

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Source: space.com

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