Skywatchers around the world could be forgiven for thinking that the heavens were more crowded than usual April 23, as dozens of bright new points of light arced slowly across the night sky.
“Alien invasion over Europe? No, it’s just SpaceX,” declared Britain’s Express newspaper. “SpaceX Starlink satellites streak across Kingston skies,” wrote Ontario’s Kingstonist.
Owned by billionaire Elon Musk, SpaceX had just launched another 60 of its Starlink mini-communication satellites — the company’s seventh such launch in just 26 months.
Starlink is one of numerous small satellite “constellations” that are expected to flock across observers’ fields of view over the next few years. Companies such as SpaceX, Amazon and Boeing want to use thousands of satellites to enhance communications on Earth.
Of course, satellites have been a part of our celestial view for more than half a century. Iridium satellites in particular were criticized for causing bright “flares,” which were rare, predictable and avoidable.
But this new generation is of more concern to astronomers. Small satellites are now more powerful and affordable than even a decade ago. As satellite popularity increases, business and astronomy interests are starting to clash in low-Earth orbit. Entities ranging from the Canadian Astronomical Society to the International Dark-Sky Association have said satellite constellations could interfere with amateur and professional observations, not to mention Indigenous cultures who use the sky as part of their store of cultural knowledge. Business owners argue they are working to reduce the satellite glare and impact as much as possible, but it is still unclear what the ultimate effects will be and who is monitoring them.
Which leaves one big question — who rules the space above the Earth?
By the numbers
SpaceX is under the most scrutiny of all the constellation providers. The company has already launched more than 400 Starlink satellites into low-Earth orbit, satellites which are described as unusually bright and thus even more difficult for observers to avoid. SpaceX has secured licenses from the United States Federal Communications Commission to launch up to 12,000, and has applied for permission to send up another 30,000. (By comparison, humans have launched about 9,400 satellites since the space age began in 1957.)
According to an April 23 SpaceX press release, the goal of Starlink’s 260-kilogram satellites is worldwide internet service.
“Starlink is targeting service in the Northern U.S. and Canada in 2020, rapidly expanding to near global coverage of the populated world by 2021,” it states.
Rob Thacker, a computational astrophysicist and professor at St. Mary’s University in Halifax, said the satellites are brightest immediately after launch, when they can shine at magnitudes of -1 or even -2. He noted they should get progressively fainter as they rise to their final orbital altitude of 550 kilometres.
Even at that height, Starlink satellites can be easily visible telescopically, especially in the first couple of hours after sunset and again in the pre-dawn hours, when the satellites reflect sunlight back down to earth.
“Once they get to their proper altitude, they should be considerably less bright, around [magnitude] 4.2 to 5.5,” Thacker said.
The Starlink website also states when the satellites are no longer in use, their on-board propulsion system pushes them to deorbit over the course of a few months. If that system stops working, they will fall into the Earth’s atmosphere within one to five years.
“They’re designed to burn up,” Thacker said.
While these satellites are set to enhance telecommunication access in remote areas, astronomers state they are already hampering the view and study of the night sky.
The International Astronomical Union issued a statement last year, warning “satellite constellations can pose a significant or debilitating threat to important existing and future astronomical infrastructures.”
Canadian astronomers are adding their voices to international concerns. In February, the Canadian Astronomical Society expressed concern over satellite constellations via a position statement written by Thacker, who was also the organization’s president.
“What really changed was the number of satellites,” Thacker said. The number of satellites that astronomers are expecting to deal with “went from a few thousand to tens of thousands in a fairly short space of time,” he said.
In the position statement, Thacker noted that the planned number of satellites “could pose an acute threat” to certain kinds of astronomy, notably wide field survey telescopes. He states the study of transients — objects that change quickly over time — could be jeopardized, and radio astronomy could be hampered.
“With no international oversight over the public commons that is Earth orbit, a likely outcome is that competition between multiple actors will push collision risks higher,” he wrote.
“Beyond this fundamental concern about the use of the Earth’s orbital resources, current analysis suggests tens of thousands of satellites deployed in orbit could pose an acute threat to wide-field, transient and radio astronomy.”
Vera C. Rubin’s woes
Chile is home to the European Southern Observatory (ESO)’s Extremely Large Telescope as well as the United States National Science Foundation’s Vera C. Rubin Observatory. These professional astronomy observatories could be vulnerable to constellation interference, according to a recent ESO report.
The Vera C. Rubin’s crown jewel is the Simonyi Survey Telescope, a wide-field 8.4-metre reflector telescope that is expected to take in its “first light” later this year. It is set to work on the Legacy Survey of Space and Time (LSST),a ten-year survey of the southern sky. It is expected to capture 30-second exposures of the sky 2,000 times per night, covering the southern sky every few days. Each frame will cover ten square degrees, roughly the area of 40 full moons.
LSST chief scientist Tony Tyson, who is also a faculty member at the University of California at Davis, estimates that during winter, 10 to 20 percent of LSST images will have satellite trails in them. The percentage will be higher in summer when twilight lasts longer.
“Satellite trails could be so bright that they could saturate the camera,” he said. “There could be a white line of saturated pixels, across the focal plane. It won’t damage the CCD, but it compromises the image quality.”
One problem is that signals may “leak” from one pixel to adjacent pixels in the detector, creating a ghosting effect on the images, and there is no quick fix through digital manipulation of the images, Tyson said.
One possible mitigation strategy is to make sure the telescope is aimed only at satellite-free portions of the sky at any one moment.
“That’s been shown to work for a thousand satellites, and to sort of work for about 5,000 satellites,” Tyson said. “But for tens of thousands of satellites, it ends up being a wild goose chase.”
SpaceX, for its part, is aware of this issue. An April 28 press release points to DarkSat, its experimental satellite with a darkened phased array and parabolic antennas. The release states brightness was reduced by about 55 per cent compared to other Starlink satellites, but because black surfaces get hot and reflect light, the company will test a sun visor instead.
“As launch costs continue to drop, more constellations will emerge and they too will need to ensure that the optical properties of their satellites don’t create problems for observers on the ground,” the release stated. “This is why we are working to make this problem easier for everyone to solve in the future.”
Tyson said he has had productive meetings with representatives from some of SpaceX’s subcontractors, andis “cautiously optimistic” that the efforts to darken the satellites will be effective. “If you can darken it enough, by a factor of 10 or 20, you can bring these trails down to the point where they won’t saturate the detectors,” he said.
He added that at that point, “we can begin to handle it.”
Many in the astronomical community — both professional and amateur — have lamented the lack of regulation regarding the night sky. While communication satellites like those launched by SpaceX require United States Federal Communications Commission approval, there are no rules regarding brightness.
“It hasn’t been an issue until now,” says Patrick Seitzer, a professor emeritus in astronomy at the University of Michigan. “But the launch of these large constellations in low-Earth orbit has brought it to the forefront.”
Seitzer also said skywatchers in Canada and elsewhere at similar latitudes may see more of the Starlink satellites in their skies, due to their 53-degree orbital inclination. While the satellites merely “pass over” countries like the United States, they linger over countries at higher latitudes as they change from a northward trajectory to a southward one, and vice versa.
Thacker said if a company’s satellites emit radio waves to be picked up by ground stations in Canada, then they need approval from Innovation, Science and Economic Development Canada and the Canadian Radio-television and Telecommunications Commission (CRTC). But no satellite needs approval to orbit 550 kilometres above the country.
“It’s a part of international treaty, that outer space is free for exploration and use by other countries,” said Ram Jakhu, associate professor at McGill’s Institute of Air and Space Law. “Once you are in space, you are free to go around. It doesn’t matter whose territory you fly over.”
Alan Dyer has been an astrophotographer for decades, and is a regular contributor to SkyNews. He said he fears what the sky of the future might look like as the number of satellites grows. He said they will impact the ability for ordinary people to enjoy the night sky, and will have a very tangible effect on the photographs that are his livelihood.
“The concern is that, as the numbers increase, there will always be some satellites in your pictures,” he said. “We’re used to having a few, but not hundreds.”
And, like Seitzer, he lamented the lack of regulation over who can put what into our skies.
“You’ve got one man, one company, unilaterally changing the appearance of the night sky, for everyone,” he said.
“At the moment, there is nothing, legally, to stop someone from doing that. There would be, for someone putting up illuminated billboards all through national parks and destroying natural scenery. But there isn’t, for the night sky … Space is like the Wild West. You can just do whatever you want.”
— With files from Allendria Brunjes