Direct-to-Device Proposal to Disrupt Radio Astronomy

A new Federal Communications Commission proposal could interfere with astronomy by introducing a massive amount of radio emissions in important spectrum bands, scientists say.

The proposal, published in early September, would allow billions more devices in the “Internet of things” to send signals to satellites using the 2.4 and 5.8 gigahertz spectrum bands. Human signals interfere with astronomical observations in nearby bands, making it more difficult to study space objects and phenomena.

As space launches become easier, the FCC is more frequently adopting rules with “game changing” implications for astronomy, said Greg Hellbourg, spectrum manager of the Owens Valley Radio Observatory. Companies’ push for satellite megaconstellations, including for direct-to-device networks, is increasingly placing them at odds with astronomers who need dark and quiet skies.

Aaron Boley, an astronomy professor at the University of British Columbia, expressed worry about a “larger trend” of putting more and larger objects in space and opening spectrum bands to more uses. “If care is not taken, then radio astronomy can actually be severely curtailed from Earth,” he said.

Radio telescopes are vulnerable to interference from human-made radio emissions. The telescopes need to be highly sensitive to detect “extremely faint” radio signals from space, Boley said. Any human transmissions creating a signal at similar frequencies can drown out the faint astrophysical source, Boley said.

Though some spectrum bands are protected for radio astronomy, telescopes must operate far outside these bands to achieve higher sensitivity, which means sharing bands with emitters built by humans. “Astronomers don’t get to pick where astrophysical sources emit, and therefore, in principle, want to be able to observe over the entire electromagnetic spectrum,” Boley said.

To minimize interference, scientists have chosen more protected locations for telescopes: in valleys, surrounded by mountains, or far away from populated areas. For example, the Green Bank Observatory, which is partially funded by the National Science Foundation, is located in a 13,000-square-mile radio quiet zone along the Virginia-West Virginia border.

But in 2024, the FCC adopted a rule that allowed communication between cell phones and satellites. Cell signals that previously came from ground-based towers can now come from space, so remote locations no longer protect telescopes from cell phone interference.

“All the telescopes in the world are built away from cell towers, and suddenly cell towers are in the sky,” Hellbourg said. “So, unavoidable, and even worse, precisely where we’re looking at with our telescopes.”

The current proposal, which would allow many more devices to start transmitting signals to space, will certainly lead to the loss of more frequencies, Hellbourg said. Flagship radio telescopes in the US, including the NSF-funded Very Large Array and Very Long Baseline Array, use the 2.4 and 5.8 gigahertz bands in their observations. The 5.8 band is crucial to geodetic radio astronomy, Hellbourg said, which includes measuring the position of satellites relative to Earth — essential information for satellite operators.

The proposal is open for comments until Nov. 9.

Hellbourg also voiced concern about what other rules could be on the horizon. The proposal seeks input on space-to-Earth transmissions, which can be more damaging than Earth-to-space because they can impact telescopes that are not even pointed at the transmitting satellites. Furthermore, the expansion of direct-to-device transmissions to new bands “kind of opens the floor to potentially any other frequencies that are currently only allocated to terrestrial transmitters to be open to space,” Hellbourg said.

During the 2024 rulemaking, spectrum managers like Hellbourg simulated the impacts of the rule on radio telescopes, commenting on the FCC proposal and coordinating with NSF. The FCC did require satellite companies to minimize impacts on radio astronomy, and NSF has established cooperation agreements that include full-time sharing of satellite locations and commitments not to send signals toward telescopes.

However, Hellbourg said current emission levels from satellites, which number more than 16,000, are already exceeding the levels the FCC set for protected radio astronomy bands. “With the rise of satellite megaconstellations, we’re talking about millions of satellites eventually,” Hellbourg said.