As our skies become richer with more and more satellites, an unexpected space battle is happening between their operators and astronomers trying to observe what’s going on in the universe, but finding it difficult as satellites reflect sunlight back to their telescopes.
Specifically, this is exactly what occurs whenever a satellite passes through the view of a ground observatory and the reflected sunlight creates bright streaks in the resulting pictures that can obscure astrophysical phenomena or even mimic them, according to a report by Scientific American on August 6.
As it happens, with over 13,000 spacecraft orbiting Earth at all times and proposals for more than a million new satellites pending, a large part of them belong to SpaceX as part of its growing Starlink network to provide high-speed broadband service to customers anywhere on the planet.
But Starlink isn’t the only satellite constellation to blame. There’s also Amazon’s Project Kuiper with more than 3,200 planned satellites, Eutelsat’s OneWeb with close to 650 units, and Chinese projects like Guowang, Qianfan, and Honghu-3, each planning to have thousands of satellites in the sky.
In fact, Starlink is leading the effort to carve out a peaceful coexistence and reduce the optical impact of its satellites. These attempts have included using dark materials and sun visors to absorb more sunlight and reduce visibility of the satellites from Earth. However, the sun visors were dropped due to creating too much drag.
Finding the middle ground in the space battle
In the second-generation design, SpaceX focused on strategically reflecting the light away from Earth instead of absorbing it, deploying a dielectric mirror film on any flat surfaces, in addition to developing black paint to reduce the possibility of glints from other components where possible.
According to a recent study that included J. Anthony Tyson, the Vera C. Rubin Observatory’s chief scientist and an astronomer at the University of California, Davis, and two SpaceX employees, who analyzed the impact of these innovations on the optical interference of the satellites, there’s room for further improvement.
Indeed, the Starlink satellites usually operate at a height of about 550 kilometers (342 miles), but the researchers also simulated the satellites’ optical interference in orbits as low as 350 kilometers (217 miles). In the simulations, lowering the altitude resulted in a 40% reduction in the number of satellites entering the telescope’s field of vision, with only a 5% increase in brightness.
However, reducing the altitude of a satellite’s orbit could mean trouble, as it experiences more atmospheric drag, but countering it hastens its orbital decay and the resulting atmospheric reentry. For now, the Rubin Observatory continues to recommend that satellites orbit below 600 km (373 miles).
Meanwhile, initiatives like the United States National Science Foundation’s (NSF) satellite coordination agreements with satellite operators are trying to achieve some middle ground as well, and the agency has signed them with Project Kuiper, OneWeb, Starlink, and AST SpaceMobile. Per these deals, companies promise to follow certain guidelines and minimize interference with partner observatories.
Elsewhere, the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) hasn’t proposed any regulations or standards for broader adoption of specific rules but has recommended that member nations encourage and support collaboration between satellite manufacturers and the scientific community.
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