You may have heard the growing complaints from astronomers as companies such as SpaceX add more satellites to our sky. Astronomers are not against the communication networks that the satellites provide, but they have valid concerns for the future of ground-based explorations of the universe. And there is only so much astronomers can do on their own to mitigate the problem. A report from the 2021 conference for Dark and Quiet Skies stated:
The advantages to society that the communication constellations are offering cannot be disputed, but their impact on the pristine appearance of the night sky and on astronomy must be considered with great attention because they affect both the cultural heritage of humanity and the progress of science.
How satellites harm astronomy: The problem with increasing satellites
Astronomers face a variety of problems with the increasing numbers of satellites filling low-Earth orbit. Optical and near-infrared telescopes feel the impacts from these mega constellations. Some of the biggest are on wide-field surveys, longer exposures and evening and morning twilight observations when sunlight reflects off the satellites. ESO, the European Space Organization, reported these findings from a 2021 study:
The effect is more pronounced for long exposures, up to three percent of which may be ruined during twilight. The study also found that the greatest impact of new satellite constellations will be on wide-field surveys made by telescopes such as the US National Science Foundation’s Vera C. Rubin Observatory. Up to 30-50 percent of twilight observations being seriously impacted.
And because we’re talking about scientists, of course they’ve officially started studying the issue. Studies in 2020 and 2021 showed the impact on optical and near-infrared telescopes. They found that telescopes such as the Very Large Telescope (VLT) and the future Extremely Large Telescope (ELT) will be “moderately affected” by new satellite mega constellations. Some telescopes, such as the Rubin Observatory under construction in Chile, will experience greater impacts. These telescopes scan wide areas quickly. This makes them crucial in spotting supernovae or potentially dangerous asteroids.
The impact on radio astronomy
Radio astronomy has its own particular concerns. Radio telescopes don’t look in the visible wavelengths of the electromagnetic spectrum, so it’s not the same “visibility” issue. For radio telescopes, the main problem is with the signals the satellites transmit down to Earth. Plus, radio telescopes aren’t only looking at dim lights in the night. They’re looking at the sky 24/7. So, satellites are a problem every hour of the day, not just at twilight.
But there’s more. A satellite’s signal is much, much stronger than the faint background sources that radio astronomers study. And a satellite doesn’t have to pass right in front of the object of study to cause interference. Satellite sources in a radio telescope’s “peripheral vision” also interfere.
They amount to hundreds of radio transmitters above the observatory’s horizon, which will affect the measurements made by our highly sensitive radio telescopes.
Radio astronomy has some protection against interference. Radio astronomers call this spectrum management, and the Radio Communication Sector of the International Telecommunication Union (ITU-R) create regulations that help protect astronomers studying certain frequency bands and wavelength ranges. But the recent large constellations of telecommunication satellites pose new threats.
One recommendation is for satellite designs that avoid direct illumination of radio telescopes and radio-quiet zones. Also, the cumulative background electromagnetic noise created by satellite constellations should be kept below the limit already agreed to by the ITU.
The deployment of thousands of satellites in low-Earth orbit in the coming years will inevitably change this landscape by creating a much larger number of fast-moving radio sources in the sky, which will interfere with humanity’s ability to explore the universe.
What can visual astronomers do?
It would be great if a computer program could quickly eliminate all the satellites trails or interference from astronomers’ data. But it’s not quite that easy. One recent report outlined the problem of low-Earth orbit satellites on images:
They leave traces of their transit on astronomical images, significantly decreasing the scientific usability of the collected data. Post-processing of the affected images only partially remedies the problem: the brighter trails may saturate the detectors, making portions of images unusable, while the removal of the fainter trails leaves residual effects that seriously affect important scientific programs, as, for example, statistical, automated surveys of faint galaxies.
But there are some things astronomers could do, and have been doing thus far. They can avoid observing where satellites will pass, limit observations to areas of the sky that are in Earth’s shadow and close the shutter precisely when a satellite crosses the field of view. This all takes a lot of knowledge of the paths of thousands of satellites and plenty of pre-planning. Obviously, these are not realistic possibilities for many situations.
What can satellite operators do?
Another way to mitigate the problem is for satellite operators to adjust their designs (for example, darkening the satellite). They can also operate the satellites in a way that would raise their orbits out of vision of the optical telescopes, deorbit satellites that are no longer functioning, as well as other considerations for minimizing disruption. In several cases, the satellite operators have shown willingness to cooperate on this.
Unfortunately, the companies planning these mega satellite constellations did not warn astronomers in advance. So many of these satellites were already filling the skies without any restrictions as astronomers scrambled to figure out how to save their observations and lessen the impact. Their efforts led to the creation of a new center that is collecting data from the community, astronomers and the general public, among others, to learn more about the effects on the night sky.
Official efforts to reduce harm from satellites
In June 2022, the International Astronomical Union (IAU), together with the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab) and SKAO, opened the Center for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS). The center highlights the dramatically increased risk of interference from low-Earth orbit satellites – both planned and already in orbit – that provide broadband services. On their website, you can see a running total of the number of operational constellation satellites (2,994) and the number of planned constellation satellites (431,713), among other stats.
Co-director Connie Walker from NOIRLab said:
Three years ago SpaceX launched the first 60 Starlink satellites. The number of satellites from this and other companies is increasing exponentially and impacting the field of astronomy. During the last two years, four key workshops identified issues and recommended mitigation solutions with the help of astronomers, satellite industry folk, space lawyers and people from the general community worldwide.
In the peer-reviewed journal Air & Space Law, scientists at ESO published a study in September 2021 extensively warning of the dangers of unlimited satellites on astronomy. They’re trying to address satellite constellations’ impact on astronomy. They’re making efforts to coordinate solutions so both satellites and observational astronomy can continue developing without harmful interference.
A reminder of what we’re losing when satellites harm astronomy
One of ESO’s studies estimated that in the future, up to 100 satellites could be visible to the unaided eye during twilight. Imagine how that will change your own view of the night sky. Then imagine if your profession depended upon seeing what is beyond the satellites. How will we learn about the universe or detect potential threats to Earth?
Interference of our view of the sky caused by ground-based artificial lights, optical and infrared trails of satellite constellations and radio transmission on the ground and in space is an existential threat to astronomical observations. Viewing the night sky has been culturally important throughout humanity’s history, and dark skies are important for wildlife as well.
Bottom line: Mega constellations of satellites can be harmful to astronomy. They mar optical and infrared images and interfere with radio astronomy. Astronomers are working to limit the negative impact.