Astronomy vs. Space-Based Internet. Is There a Win-Win?
By Richard A. Lovett
One of the fun things about watching the skies is that occasionally, you get a surprise. And in late May 2019, sky-watchers around the globe got a big one when they spied a train of about sixty bright dots following each other across the twilight sky like a string of pearls, each as bright as the main stars in the Big Dipper or the Southern Cross.
“I was shouting, ‘Owowowow,’” Dutch astronomer Marco Langbroek—who knew what they were and was looking for them—told space.com. “They were brighter than I had anticipated.”
Others had no idea what they were. The internet erupted in chatter, and briefly, it looked as though ET had finally arrived, complete with an entire invasion fleet. Speculation ran rampant.
The true answer was a lot more mundane. The bright dots were the vanguard of a “constellation” of satellites being deployed by SpaceX as part of a project called Starlink—an ambitious plan to blanket low Earth orbit with thousands of such satellites in order to provide inexpensive, space-based internet to the entire globe.
It’s an idea straight out of a science fiction dream. I myself have written stories where characters easily get onto the web from anywhere on Earth, via orbiting satellites. There’s just one problem. These satellites really are bright—about 100 to 250 times brighter than anyone had expected, based on the brightness of other satellites and space debris, says Pat Seitzer, an astronomer at the University of Michigan, Ann Arbor, who specializes in studying space debris. “The new satellites could be brighter than 99% of all the objects in orbit today,” he says.
Prior to the Starlink launches, he adds, there were maybe two hundred objects in Earth orbit visible to the naked eye. (Not that more than a few can be seen at any given time.) But at the rate SpaceX was launching Starlink satellites, the number had already doubled in early 2020—with nearly 1,600 more planned for the end of 2020. “That’s a nine-fold increase in less than one year, by one operator,” Seitzer said at the time.
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Why does it matter?
Part of the concern is philosophical. Not all that long ago, our ancestors lived under skies where the stars gleamed unimpeded, inspiring them to ponder not only what’s out there, but humanity’s place in it. It was one of the original—if not the original—sources of the “sense of wonder” that science fiction so often tries to evoke.
But today, says Ruskin Hartley, executive director of the International Dark Skies Association (headquartered in Tucson, Arizona), a full 80% of the world’s people live under light-polluted skies where it is impossible to see the views that tantalized our ancestors. In fact, he says, billions have never seen the arc of the Milky Way across a truly dark sky.
And now, he asks, if even the darkest places have skies strewn with moving dots that speak not of the vast reaches of space, but rather the reach of human technology, “how will it change our relationship to the world and the Universe?”
It’s not just a metaphysical question. In much of science fiction, these ancient, unimpeded views are the very things that draw characters to space in a quest not only to see what’s out there, but to answer the critical question of whether we are alone in the Universe. And it’s not just the bold travelers of the future who need to hear this call. “No one is born an astronomer,” Hartley says. “The spark is looking out and seeing the stars above.”
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Which brings us to the difficulties these satellites pose for the immediate future. They are going to be an enormous problem for ground-based telescopes, including not only telescopes currently in operation, but such behemoths as the European Southern Observatory’s 39.3-meter Extremely Large Telescope (ELT), now under construction on a mountaintop in Chile at an anticipated cost of $1.4 to $2 billion.
“Astronomers have been concerned for decades about light pollution, where light from towns and cities reflects off the atmosphere and into their instruments,” says Phil Puxley, vice-president for special projects at the Association for Universities for Research in Astronomy. That’s why telescopes are built in remote locations with the darkest possible skies. But now even the most remote locations are no longer pristine. “There is no place to hide,” Puxley says.
The problem is that astronomers use time exposures to peer deeply enough into the night sky to see the dimmest possible objects. If a satellite happens to pass through at the wrong time, it leaves a bright streak—often broad and fuzzy—ruining part of the image.
Worse, if it’s bright enough, it saturates the telescope’s detectors, messing up their electronics. That can do everything from producing ghost images parallel to the satellite trail to burning out the detector so that it produces residual trails the next time it is used. “Even if [satellites] are not visible to the unaided eye, they could still cause problems,” Seitzer says.
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For narrow field-of-view telescopes, such as the ELT, the problem is relatively minor, though in a paper published last April in Astronomy & Astrophysics, a team led by Olivier Hainaut, of the European Southern Observatory, estimated that as many as 3% of ELT time exposures lasting one thousand seconds or more (about 16 minutes) would be wrecked by satellite trails.
Harder hit will be less narrowly focused instruments.
In an as-yet unpublished study, another team, led by Seitzer, has calculated that completion of the most ambitious of the plans for space-based internet constellations—a 47,000-satellite plan by OneWeb—will mean that astronomers studying one of the Southern sky’s iconic objects, the Large Magellanic Cloud (about twenty times the width of the full Moon) will find that every thirty-second exposure will have at least one satellite trail passing through it. “That is a great challenge for astronomers,” he says.
Nor is the Large Magellanic Cloud anywhere close to the biggest thing astronomers want to study. America’s Vera C. Rubin Observatory, now nearing the end of construction and expected to be operational in 2021, is designed to monitor the entire heavens (or at least those parts that can be seen from its mountaintop in Chile) in search of transient objects like supernovas that might be of interest for more detailed study. “The Rubin Observatory is making a digital moving picture of the Universe, so it’s a perfect machine to run into these things,” says Tony Tyson, an astronomer from the University of California, Davis, who is the Rubin’s chief scientist.
Hainaut agrees. The problem is bad enough, he says, that his estimates—based on a mere 26,000 of the 107,000 satellites proposed to be launched in the next decade—show that 30–50% of the Rubin’s observations would be “severely affected” by satellite trails. (Similar problems will apply to telescopes designed to spot the tracks of potentially dangerous asteroids.)
And it’s all happening very quickly. “There is a rapid phase change where nighttime images without a satellite will no longer be the norm,” says Richard Green, assistant director for government relations at the University of Arizona’s Steward Observatory.
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Worried about what has been called an existential threat to the future of astronomy, the U.S. National Science Foundation (NSF) and the American Astronomical Society (AAS) convened a workshop to address the problem in the summer of 2020. Called SATCON1, it included Puxley, Seitzer, Green, Tyson, and 250 other scientists, engineers, astrophotographers, and dark-sky enthusiasts, including representatives of national and state parks.
SpaceX was also involved and was praised for its cooperation. “SpaceX has set an excellent example of a collaborative effort between the industry and astronomy,” says Jeff Hall, director of Lowell Observatory, in Flagstaff, Arizona. “This has been a really collaborative and cooperative process.”
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The basic finding, says Connie Walker, a scientist at NSF’s NOIRLab in Tucson, Arizona, who with Hall cochaired the workshop, was that no feasible combination of control measures can eliminate the impact of satellite constellations on astronomy.
But that does not mean all is lost, because there are a number of ways to mitigate the problem.
The most straightforward is to darken the satellites—though that’s not as easy as just painting them all so black that they simply can’t be seen. “If a satellite is completely black, it would get too warm,” says Hainaut, “so the idea is to darken the part of the satellite that is facing down.”
In fact, SpaceX has already tried this with a Starlink satellite called DarkSat. Viewed from the ground as it passed overhead, it proved to be only 40% as bright as other Starlink satellites, says Lori Allen, also of NOIRLab.
That’s definitely a good start. Also important, the SATCON1 workshop found, is to orient satellites to be edge-on when seen from the ground and to design them to avoid shiny surfaces positioned in such a manner that they can reflect bright glints of sunlight down toward Earth. Engineering constellations to need fewer satellites would also help, Tyson says, adding: “There are probably ways of doing that.”
Another big help would be for constellations to be designed so that no satellites are launched into high orbit, where, especially during summer, some catch sunlight all night long. (At lower altitudes, fewer are visible except at dawn and dusk, allowing astronomers a middle-of-the-night window still fairly clear from interference.) That, Tyson adds, is the problem with the OneWeb constellation, because its satellites are currently planned to orbit at an altitude of 1,200 kilometers.
“We need to make them as low as possible,” says Green. (The SATCON1 report recommends an altitude of no higher than six hundred kilometers.)
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There are also things astronomers can do on their own, especially with a little help from the satellite companies.
To start with, Tyson says, SpaceX has suggested that an app could be created that would tell astronomers precisely when something is going to come across their fields of view. “That’s quite achievable,” he says.
Armed with that knowledge, astronomers could do one of two things: time their observations to be pointing at a part of the sky where there are no satellites to interfere with them, or shutter their telescopes so that they, in essence, blink when a satellite is passing through.
“The satellites are moving very fast,” Hainaut says, “So the interruption would be very short.”
That’s a good solution for narrow to medium field-of-view instruments, he says. “[But] for large field of view, it becomes problematic. The number of satellites crossing the field of view could be large so that you need to interrupt too often.” Also, he says, for very wide field-of-view cameras, the shutter is actually a very large mechanical piece. “Opening/closing/opening it very often could become problematic,” he says. Efforts are also underway to develop software that can remove or mask satellite trails from an image (or at least minimize their impact). The dimmer the satellites can be made, the easier that will be, but it still may not be feasible for many observatories, Walker says.
Nobody, however, is calling on SpaceX, OneWeb, and Amazon (which is also in the hunt) to give up on the dream of space-based internet. Walker simply says that the plan “has merits.” Dark-sky advocate Hartley goes further. The dream of internet connectivity is a gift to humanity, he says. “It’s democratization.”
And happily, adds Hall, no one is likely to be scared off by the difficulty of finding a win-win solution. “Neither astronomers nor space scientists are strangers to difficult problems,” he says.
Meanwhile SATCON2 is already being planned for the first half of 2021. And that’s none too soon, because by that time, SpaceX’s plans call for the launch of as many as 1,560 more Starlinks, more than doubling the number in orbit at the time of SATCON1.
Richard A. Lovett is one of the most prolific contributors in Analog history, both as a writer of fact and fiction. A former professor turned journalist and running coach, he has written thousands of articles for more than 150 magazines and newspapers. His latest book, Neptune’s Treasure: The Adventures of Floyd and Brittney is a novel-length rendition of his award-winning Floyd & Brittney series, which first appeared in Analog.
Copyright © 2021 Richard A. Lovett