A report warns that fleets of new communications satellites in orbit with low Earth will spoil some astronomical observations, even if all known mitigation strategies are taken.
NOIRLab / NSF / AURA / P. Marenfeld
By Daniel Clery
Astronomers and the operators of new, thousands of strong constellations of low-orbit satellites will have to work together to prevent them from having a devastating impact on ground-based observations of planets, stars and other celestial objects, says a report released today. Even then, there is no harm in escaping the fleets of commercial orbiters. “All optical and infrared observatories will be affected to some degree,” said Astronomer Anthony Tyson of the University of California, Davis, in a briefing on the report. “No combination of mitigation will eliminate its impact,” added astronomer Connie Walker of the U.S. National Optical-Infrared Astronomy Research Laboratory.
The report is the product of a virtual workshop that brought together 250 astronomers, engineers and satellite operators in late June and early July. The satellites, designed to provide internet access in remote areas, are now hundreds. But after the launch of the first party by SpaceX in May 2019, astronomers were worried about how bright they appear in the sky. If all planned constellations continue, the number of satellites will grow further than 100,000. Observatories, which already have remote locations to prevent light pollution, will have no effect to prevent their effects, says Phil Puxley of the Association of Universities for Research in Astronomy. “There is no place to hide.”
Since last year, there have been a number of independent studies on the possible impact of constellations. But the workshop report is the first time that satellite companies and those affected, from astronomers to the agencies that fund them and their telescopes, have bundled their results and worked out a strategy for the future.
Once SpaceX’s first Starlink satellites hit orbit, astronomers soon realized the upcoming Vera C. Rubin observatory in Chile, which would begin operations next year, would be least affected. With its combination of a wide field of view and sensitive 8.4-meter mirror, “It’s a perfect machine to counteract these things,” says Tyson, the project’s lead scientist. The satellite paths are very bright and small out of focus, so they are wide and cover several pixels on images made with a test version of the Rubin Observatory’s camera, he notes. “It complicates data analysis and reduces discovery.”
Other observatories are likely to be less affected, but the workshop’s report, known as Satellite Constellations 1, said telescopes that have to work in the twilight could also cause problems. Because the satellites are in empty orbits, they are often seen near the horizon and will be most visible when they are still in sunlight, but not by the observer. Search for asteroids that potentially threaten the Earth and rapidly changing astronomical phenomena, such as visible signals of gravitational wave events, should often work in those circumstances.
However, when satellite companies make orbits above 600 kilometers, the situation becomes worse because their spaceship is visible more of the night, and in the summer all night. One operator, OneWeb, planned to use 1200-kilometer lanes. Although the company filed for bankruptcy earlier this year, plans are underway to reopen it. According to Patrick Seitzer of the University of Michigan, Ann Arbor, if OneWeb launches its full 47,000-strong constellation, every 30-second exposure of the Large Magellanic Cloud, the largest satellite system around our Milky Way, would have at least one satellite flare in there.
Workshop participants made a number of recommendations to reduce the impact of constellations, including keeping orbits below 600 kilometers, obscuring satellites, or checking their orientation in space to reduce reflections (which SpaceX is already testing). Astronomers also need to develop software tools to remove satellite paths from images, and companies need to make accurate orbital data available to their orbiters so that telescopes can try to avoid them. The only measure the report could offer to completely eliminate the damage to astronomy was to launch less than no low-orbit satellites – probably no option given to the financial investments the companies make in the constellations and the lucrative market they envision.
Tyson and his colleagues have worked with SpaceX engineers to modify their satellites to reduce their brightness. “We’ve explored every parameter space through physics,” he says. “Now we need to figure out which one is most effective.” His team has also made a model to steer the Rubin Observatory telescope to avoid passing satellites, but Tyson says there are just too many. ‘It gets stuck. You can not avoid them. “Astronomers are already actively striving for image processing solutions, but, he says,” the jury is out, “on how much that can help.
