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A recent discovery by an amateur radio astronomer has revealed that approximately 170 Starshield satellites, built by SpaceX for the U.S. National Reconnaissance Office (NRO), are transmitting signals in an unusual and potentially problematic frequency band. These emissions, sent from space to Earth, fall within a spectrum segment internationally designated for Earth-to-space (uplink) and space-to-space communications, raising significant questions about international coordination and transparency in satellite operations.
The Unconventional Discovery
Scott Tilley, an engineering technologist and amateur radio astronomer based in British Columbia, uncovered these signals in late September or early October while engaged in another project. Tilley detected strong, wideband S-band emissions across various parts of the 2025–2110 MHz band. From his location, he confirmed that 170 of the 193 known Starshield satellites were emitting these signals over Canada, the United States, and Mexico. Given the constellation’s global nature, these transmissions likely extend over many other nations.
The core issue, as highlighted by Tilley, is that this specific band is primarily allocated by the International Telecommunication Union (ITU), the United States, and Canada as an uplink band. This means satellite receivers in orbit are typically listening on these frequencies. A constellation “blasting away” with signals in the same band has the potential to interfere with legitimate ground station signals aimed at satellites, including those used by NASA and the National Oceanic and Atmospheric Administration (NOAA) for critical missions, as well as non-governmental users like TV news broadcasters for remote transmissions.
Lack of Transparency and Coordination
While there have been no public reports of harmful interference attributed to the Starshield emissions yet, Tilley emphasizes that the discovery underscores a troubling lack of transparency in how the U.S. government manages spectrum use and a failure to coordinate with other countries.
Experts suggest that the NRO likely coordinated internally with the U.S. National Telecommunications and Information Administration (NTIA) to ensure domestic non-interference. However, such decisions are often not made public. Crucially, the Canadian Space Agency (CSA) confirmed that no coordination process has been initiated with the ITU or the U.S. regarding this satellite network. The ITU itself declined to comment on the specific matter, noting that interference concerns must be formally raised by national administrations.
Rick Reaser, a spectrum consultant with extensive government experience, noted that these signals might have been approved on a “non-interference basis” domestically, meaning the operators would have to shut down if interference is reported. However, Tilley argues that such a domestic arrangement does not fulfill international requirements, especially for a global constellation of hundreds of satellites.
What Are These Signals For?
The precise purpose of these “wrong direction” signals remains unknown. Tilley’s technical paper points to signal characteristics—strong, coherent, and highly predictable carriers—that could technically enable “Positioning, Navigation, and Timing (PNT) exploitation.” While not suggesting this was the system’s primary design, the paper indicates such a network could serve as a practical foundation for PNT applications by friendly forces or third parties seeking situational awareness.
Newer Starshield satellites, launched in late September, have not yet emitted these signals while moving into their final orbits, suggesting the emissions are tied to an “operational payload” rather than basic telemetry, tracking, and control (TT&C).
Global Implications and Regulatory Gaps
The deployment of large satellite constellations, like Starshield, by various nations raises significant concerns about the future of the radio environment. Tilley argues that unilateral use of space and spectrum affects every nation, highlighting a need for greater international cooperation and cooperative disclosure without compromising legitimate security interests.
He drew a contrast with China’s Guowang constellation, which also uses unallocated spectrum but at least filed advance notices with the ITU, even if full protection wasn’t granted for non-compliant use. This, Tilley notes, suggests China consulted internationally, while the U.S. appears not to have consulted at all for Starshield’s controversial emissions.
Tilley shared his findings with various Western space agencies and Canadian government spectrum regulators, receiving acknowledgment from the Canadian government. He continues to monitor the signals and collaborate with other researchers to gather more data on their scope and impact.
This accidental discovery, prompted by a “clumsy move at the keyboard,” serves as a vital alert to spacecraft operators who might not ordinarily listen on this particular band. It urges them to assess risks and determine whether their missions have suffered or could suffer interference, emphasizing the complex challenges posed by rapidly expanding satellite mega-constellations in an increasingly crowded orbital and spectrum environment.