A company that wants to bring a little bit of daylight to your evening might end up turning night into something closer to a very aggressive twilight, according to a new study. Reflect Orbital, a US firm, is planning to launch a test satellite called Eärendil-1 later this year, which will unfold an 18-by-18-meter mirror in orbit. The ultimate goal? Launch up to 50,000 larger satellites, each a whopping 54 by 54 meters, to reflect sunlight to Earth on demand.
The company's pitch is that this could prolong sunlight for solar panel charging, emergency response, and military activities - though the case for it remains, shall we say, a bit hazy. The Federal Communications Commission (FCC) gave the green light in July, much to the horror of astronomers and environmental groups. "This is incompatible with astronomy," says Samantha Lawler, an astronomer at the University of Regina in Canada. "There is no way you can do this and preserve dark skies."
Now, Miroslav Kocifaj, an astronomer at the Slovak Academy of Sciences, and his colleagues have crunched the numbers to see how much of the night sky would be affected. Their paper, accepted for publication in Astrophysical Journal Letters, found that within the beam's target area - a circular patch five kilometers across - a single satellite would appear about 40 times brighter than the full moon. Even 14 kilometers away from the beam's center, it would still shine as bright as the full moon.
And here's where it gets really cosmic: combining 400 satellites, which is part of the plan, would produce a light as bright as 10,000 full moons within that five-kilometer area - that's 2.4% as bright as the sun. Even 80 kilometers away, the combined beam would be visible as a "glow above the horizon," says Kocifaj. So the night sky would be altered for far more people than just those in the intended illumination zone. "Deploying these mirrors would be seriously damaging for astronomy and for the nighttime environment," he says. "The damage extends far beyond the target area."
Olivier Hainaut, an astronomer at the European Southern Observatory in Germany, isn't surprised but finds the work useful. He had previously modeled that Reflect Orbital's beams could brighten the sky up to 300% worldwide. "These two papers really cover most of it," he says.
Reflect Orbital CEO Ben Nowack, unsurprisingly, disagrees. "Some assumptions are simply inaccurate," he says, insisting that safeguards like exclusion zones account for scattering. But Kocifaj points out that the company hasn't provided any data to back these claims. "It gives no numbers, no description of the model, no assumptions, and no data," he says. "Our calculations produce concrete figures."
The satellites are intended to operate in highly inclined, pole-to-pole orbits, reflecting sunlight before sunrise and after sunset to extend daylight hours. Eventually, they might even provide 24-7 light. In August, a coalition including DarkSky International and the American Bird Conservancy urged the FCC to review its approval, citing risks to astronomy, aviation, and wildlife. They're asking for a lawful public-interest and NEPA review.
Even Reflect Orbital admits there might be risks to humans: observing Eärendil-1 with a telescope larger than 12 inches could be unsafe for eyes, though they claim significant injury is "unlikely" because the satellites aren't constantly bright.
There's a regulatory gap here - no global entity oversees such satellites, so it's left to national regulators like the FCC. Michelle Hanlon, a space lawyer at the University of Mississippi's School of Law, sees "real benefits" but notes the "legal basis is less clear than the technology." The FCC can only authorize radio frequencies, not the operation of the solar reflector itself. So Reflect Orbital might need approvals in multiple jurisdictions if the beams spread as predicted, and there could be cross-border and aviation-safety questions.
The debate rages on. "It makes me sad that astronomers are having to spend their time doing these sorts of calculations rather than actually doing astronomy," says Lawler. Indeed, who knew we'd be adding 'space mirror glare' to the list of things keeping astronomers up at night?