The threat posed by Elon Musk’s satellites also affects space telescopes like Hubble

First came some curious lights in the sky after nightfall, which surprised astronomy enthusiasts. The most excited about the new phenomenon — caused by Elon Musk’s Starlink satellite network — encouraged everyone to go out and watch the spectacle of the luminous trains created by these satellites as they ascended. Then came the protests from astronomers, who saw how those lights ruined images from their telescopes, streaking them with intense white lines.

In response, Musk promised to minimize these effects — with improvements that he never actually implemented — and urged scientists not to limit themselves to ground-based observatories: they would need to venture further into space. Now, a NASA study warns that not even space telescopes like Hubble will be safe from the threat that satellite constellations pose to astronomy.

The new research, led by Spanish astrophysicist Alejandro Serrano Borlaff, shows that at least one in three Hubble images will be contaminated by satellite light if the projects planned for the next decade for large constellations like Starlink are completed. These constellations have already requested authorization to launch more than 500,000 satellites. “This is the first scientific study whose main objective is to investigate the effects of light pollution on space telescopes, taking into account these plans announced by the industry,” says Borlaff from NASA’s Ames Research Center in Mountain View, California.

The consequences would be even worse for the new generation of space telescopes that are just beginning to launch. One of them is ARRAKIHS, the first mission of the European Space Agency (ESA) to be scientifically led by Spain. According to the study by Borlaff’s team — published on Wednesday in the prestigious journal Nature — the white streaks of satellites, which are so disruptive to astronomers, will appear in 96% of the images from this future European space telescope.

The veteran Hubble Space Telescope and the newcomer SPHEREx — launched in 2025 — are two of the space telescopes that NASA has in low Earth orbit, the region of space currently populated by more than 9,000 of Musk’s Starlink satellites, with most orbiting about 340 miles above the Earth’s surface. The new research predicts that, with 560,000 satellites deployed in orbit, almost 40% of Hubble’s images will contain at least one satellite streak; in the case of SPHEREx, up to 99% of the astrophotographs would be contaminated.

Borlaff explains that the impact of those artificial streaks predicted by his study on images from both NASA telescopes, “will depend on the scientific objective of each investigation. If the observations can be repeated or combined, it is possible to partially correct the data, though not without some cost. If the satellite streaks contaminate an observation that depends on the time at which they are obtained, or if they need to search for moving objects like asteroids, then the effect could be significant.” The Spanish astrophysicist emphasizes that, in any case, all telescopes would lose some image quality or depth, regardless of the type of observation. “One of the fields that could be most affected is the search for asteroids potentially hazardous to Earth,” he warns.

This is not the case with ARRAKIHS, which will point toward the zenith of its sky in space to search for new clues to study dark matter. This space telescope project, selected by the ESA for launch starting in 2030, was conceived by scientists from the Institute of Physics of Cantabria in Spain. The leader of that team, Rafael Guzmán, praises the scientific quality of Borlaff’s new research, which is now being published, and agrees with the need for the warnings its conclusions raise: “As an astronomer, I couldn’t be more concerned about the direction in which certain multinational corporations are leading us.”

“He is mistaken about ARRAKIHS”

However, Guzmán points out that “unfortunately, Borlaff’s article is wrong about ARRAKIHS. If we look at the diagram published by Nature, our binocular camera appears oriented tangent to the Earth’s limb: thus, it would be observing a great many satellites, and those are the numbers he derives. But that won’t be the case.”

Guzmán explains that this was true for an initial prototype, but in the final ESA-selected version, the space telescope will be oriented perpendicular — facing away from Earth — and will rotate a maximum of 60 degrees to each side. “Since it will be looking towards the Earth’s zenith, the number of satellites passing through its field of view will be much smaller than he estimates,” Guzmán notes.

Carlos Corral, head of the ARRAKIHS project at the ESA, agrees with Guzmán that the brightness of satellites like Starlink will not be a problem for this scientific mission and expresses surprise at the data calculated by Borlaff in his article. “Our previous estimates indicate a much smaller impact, on the order of 1% of the images,” says Corral, who also points out that “ARRAKIHS is a very robust mission. It is prepared to deal with natural interference — that of cosmic rays — which is indeed of the magnitude that this new research attributes to satellites. We are going to take 900 images of each galaxy studied, over a total of 150 hours. If a satellite, or a cosmic ray, happens to cross an area of interest in those images and invalidates them, we simply take more images, and they will no longer be there.”

However, Corral emphasizes that “this affects us in other missions and, in general, due to the increase in space debris and the possibility of collisions. Clearly, filling the sky with tens of thousands of satellites is not a good idea. It’s a problem especially for ground-based telescopes, but you can’t escape that problem even by going into space,” he concludes.

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