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Theodolite Thursday: Satellites Interfere With Astronomy

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Earth Satellites Image One
Image Credit: NOIRLab
NSF
AURA
P. Marenfeld
Science Magazine

“A report warns that fleets of new communication satellites in low-Earth orbit will spoil some astronomical observations, even if all known mitigation strategies are taken.”

Astronomers and the operators of new, thousands-strong […] low-orbiting 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 [recent] report […]. Even then, there is no escaping some harm from the fleets of commercial orbiters.

“All optical and infrared observatories will be affected to some degree,” [stated] astronomer Anthony Tyson of the University of California, Davis, […] at a briefing on the report.

“No combination of mitigation will eliminate their impact,” added astronomer Connie Walker of the U.S. National Optical-Infrared Astronomy Research Laboratory.

The satellites, designed to provide internet access in remote areas, now number in the hundreds. [Following] the launch of the first batch by SpaceX in May 2019, astronomers were alarmed by how bright they appear in the sky. If all the planned [launches] go ahead, the number of satellites will grow beyond 100,000. Since last year, there have been a number of independent studies of [satellites’] possible impact. [The] workshop’s report is the first time the satellite companies, and those who would be affected (astronomers to the agencies that fund them and their telescopes), have pooled their results and worked out a strategy for the future.

NASA Satellite Image Two
Photo Credit: NASA on Unsplash

The satellite trails are very bright, and out of focus slightly, so they’re wide and cover several pixels on images taken with a test version of the (soon to open Vera C.) Rubin Observatory’s camera, notes Tyson. [Telescopes] that need to work during twilight will also run into problems. Because the satellites are in low orbits, they will often be seen close to the horizon and will be most visible when they are still in sunlight but, the observer is not. If, however, satellite operators choose orbits above 600 kilometers, the situation gets worse because, then, their spacecraft are visible for more of the night, and in [the] summer, all night long. Astronomers should also develop software tools to remove satellite trails from images and the companies should make accurate orbital data available for their orbiters so telescopes can try to avoid them.

The only measure the report could offer to totally eliminate the damage to astronomy was to launch fewer or no low-orbiting satellites…likely not an option given the financial investments the companies are making in the [satellites] and the lucrative market they foresee.

Tyson and his colleagues have been working with SpaceX engineers to modify their satellites to reduce their brightness. His team has also modeled trying to steer the Rubin Observatory telescope to avoid passing satellites but, Tyson says there are simply too many. Astronomers are already actively pursuing image processing solutions but, he says “the jury’s out” on how much that can help.

Daniel Clery
Science Magazine
August 25, 2020

Addtional Reading:
Report Offers Roadmap (American Astronomical Society)
SATCON Report (NOIRLab)
Satellites Could Spoil View of Giant Sky Telescope (Science Magazine February 27, 2020)