Originally posted March 12, 2020 by sciencenews.org

Global internet satellites are photobombing telescopes and messing with astronomers’ research 

Astronomer Cliff Johnson was peering into deep space before dawn when something close to Earth interrupted his view.

He and colleagues were searching for dwarf galaxies snuggled up to the Milky Way using the Victor M. Blanco 4-m Telescope in Chile. The team was remotely operating the scope from a room at Fermilab in Batavia, Ill., about 8,200 kilometers away.

“We had a nice clear night,” says Johnson, of Northwestern University in Evanston, Ill. Through outdoor webcams at the observatory, the team could spy on the scene in the high Chilean desert. The sky was immaculate: inky black with dots of white starlight.

“All of a sudden, through this webcam, we started seeing these streaks popping through,” Johnson says. Dashes of white light shot across the view, like laser fire from a sci-fi battle cruiser. The intruders flew right across the telescope’s gaze: In a five-minute exposure with the scope’s camera, 19 white lines defaced the picture. It didn’t take long to realize the culprit.

A week earlier, on November 11, 2019, the aerospace company SpaceX had launched 60 Starlink satellites to join its growing fleet of satellites built for global broadband internet access. That flock of satellites in low Earth orbit had photobombed Johnson’s image.

SpaceX plans to send up more than a thousand satellites in its first round of launches to provide near-continuous internet service to the United States and Canada by the end of 2020 and to all corners of the globe in 2021.

These “mega-constellations” of satellites have triggered alarm bells: “Elon Musk’s satellites threaten to disrupt the night sky for all of us,” warned the Washington Post, calling out SpaceX’s celebrity CEO.

Researchers have begun to quantify the scale of the problem, and the news is mixed. Most of the new satellites will stay hidden to unaided eyes for much of the night, and small telescopes won’t often notice much difference. But large telescopes, especially those dedicated to sweeping the entire sky, may run into problems, reports a study posted on arXiv.org on March 4.

Astronomers discussed the issue on January 8 during panel sessions at an American Astronomical Society meeting in Honolulu. The group is concerned that hunting for asteroids that might impact Earth will be hampered, and flickering satellites could be mistaken for exploding stars.  

“The issue of mega-constellations in astronomy is a serious issue,” said Patrick Seitzer, an astrophysicist at the University of Michigan in Ann Arbor who studies orbital debris. Tens of thousands of new internet satellites could blanket Earth in the coming years, many of them brighter than nearly every other artificial object circling the planet. Or as Seitzer put it: “Cheer up, the worst is yet to come.” 

Shockingly bright

Artificial satellites have been getting in astronomers’ way since the launch of Sputnik 1 in 1957 (SN: 10/19/57, p. 245). Today, NASA estimates that roughly 20,000 known human-made objects larger than a softball — satellites, rocket bodies and other flotsam — are orbiting Earth. The number will keep growing, despite concerns about the risk of collisions that could put equipment and astronauts in danger. From observatories in Chile, Seitzer noted, there are about 600 to 700 overhead objects visible at any given time at night.

Sunlight reflected off metal surfaces and solar panels on those satellites can shine into a telescope and either mimic or hide things in deep space. Astronomers so far have been able to deal with that interference by taking multiple images and combining them for a cleaner composite picture. In some cases, image-processing algorithms can also recover data lost to intruding light. That’s getting harder, though, as more satellites are put into space. Plummeting launch costs, largely due to reusable rocket technology, have made low Earth orbit more accessible than ever.

SpaceX, based in Hawthorne, Calif., launched its first 60 Starlink satellites in May 2019. A second batch went up in November and three more batches were sent aloft in the first two months of 2020. Eventually, the company says, it will have an initial fleet of 1,584 Starlinks in orbit, providing near-­continuous internet service to most of the world’s populated areas.

“It’s estimated that 3.6 billion people don’t have access to the internet, and the U.N. considers broadband access as a key enabler to economic development,” Patricia Cooper, vice president of satellite government affairs at SpaceX in Washington, D.C., said at the January meeting. “We think space-based internet could be of real use to those goals.”

That internet service will be delivered via pizza box–sized ground devices that relay information back and forth to the satellites. To reduce delays in data transmission, the satellites will fly relatively close to Earth — several dozen times closer than typical communication satellites in geosynchronous orbit, an orbit in sync with Earth’s rotation. That connectivity comes with a cost, astronomers say — the clarity of our night skies.

“There is nothing bad about having internet delivered through these satellite mechanisms,” said Chris Impey, an astronomer at the University of Arizona in Tucson. “But of course, we’re worried about the side effects.”

Astronomers immediately noticed that the Starlink satellites launched in May were shockingly bright, much brighter than similarly sized objects already in orbit. Even SpaceX was surprised, Cooper said. The culprit seems to be surfaces that scatter light diffusely, but the company is still trying to figure out precisely what makes the satellites so dazzling against the sky.

When a batch is launched, the satellites appear to people on the ground as a “string of pearls” tracing the sky. But that effect is temporary. SpaceX launches its satellites into a relatively low orbit so that engineers can run diagnostics for a few weeks before moving the satellites to a higher operational orbit, where they spread out around the globe and appear fainter. Still, that distance may not be enough for the satellites to fully fade into the background.

Even when farther away, Starlink satellites “are brighter than 99 percent of all objects that are now in Earth orbit,” Seitzer said. He has been running computer simulations to quantify how much these satellites might affect astronomical observations. For SpaceX’s initial planned fleet of 1,584 Starlink satellites, Seitzer estimated that up to nine satellites would be visible to telescopes at the Cerro Tololo Inter-American Observatory in Chile for about an hour after twilight and an hour before dawn — and likely for longer during summer nights. In the middle of the night, the satellites vanish in Earth’s shadow.

“Astronomers could handle that” and work around the interference in their observations, Seitzer said — if only that was the total number of new satellites expected to launch. But 1,584 satellites is just the beginning for SpaceX, and other communication companies have their own internet satellites planned.

Continue Reading