Washington, D.C., April 28, 2025
Marlene H. Dortch, Secretary
Federal Communications Commission
45 L Street, NE
Washington, DC 2055
Re: Reply Comment in the Matter of GN Docket No. 25-133 In Re: Delete Delete Delete
Dear Ms. Dortch,
A group of concerned professional radio astronomers, writing as members of the U.S. astronomical community, appreciates the opportunity to provide a reply to a comment in response to this Public Notice.
On April 11, 2025, satellite operators including SpaceX, Amazon, Intelsat, and Logos Space Services filed individual public comments seeking to eliminate, weaken, or bypass a range of long-standing spectrum protections, procedural safeguards, and technical limits that are vital for the continued success of radio astronomy in the United States and around the world.While we recognize the satellite operators concerns, we oppose various aspects of their proposals as detailed in the remainder of this letter.
Radio astronomy depends on detecting incredibly faint natural signals from celestial sources. These signals are often millions of times weaker than those emitted by satellites or terrestrial transmitters. As a result, even marginal increases in out-of-band or spurious emissions can permanently compromise observations, introduce harmful interference, and degrade our ability to pursue fundamental research in astrophysics, planetary science, and cosmology.
We are deeply concerned by proposals to abandon power flux density (PFD) limits adopted through international consensus at the International Telecommunication Union (ITU), particularly those in ITU-R RA.769 and RA.1513. These limits, while already lenient compared to the intrinsic sensitivity of modern observatories, are the only internationally coordinated measures that offer minimal baseline protections for passive science services. Amazon’s proposal
to discard PFD limits on the grounds that they are unnecessary in certain bands is unsupported by science and places critical research at serious risk. Protected bands for scientific use offer rare opportunities to study specific astronomical sources and emission mechanisms (such as the 1.4 GHz hydrogen line, the 22 GHz water maser, and molecular transitions between 60 and 70 GHz). However, achieving the sensitivity levels required for scientific discovery relies primarily on continuum observations spanning wide bandwidths on the order of gigahertz.
Similarly, multiple commenters have asked the Commission to sunset equivalent power flux density (EPFD) protections for legacy geostationary systems, dismissing their relevance for next-generation non-geostationary (NGSO) systems. However, these EPFD protections were specifically designed to mitigate the aggregate interference from large constellations, where the combined signals of many individually low-power satellites can amount to disruptive levels of interference, equivalent to or even exceeding those of a single powerful transmitter. Far from being outdated, EPFD limits are becoming increasingly critical in the era of mega-constellations, where thousands of satellites are simultaneously active across the sky. Removing these protections would leave current and future observatories exposed to dynamic, cumulative satellite interference that is extremely difficult to predict, model, or mitigate, and would jeopardize the integrity of passive scientific observations on a global scale.
The request to eliminate site-by-site licensing and shift toward a fully self-coordinated “light licensing” regime, as advocated by SpaceX and others, would remove one of the last tools the Commission retains to assess and limit harmful interference from large-scale deployments. If permitted, this change would render it virtually impossible for stakeholders to meaningfully review, challenge, or prepare for the interference environment introduced by new entrants.
Amazon and Intelsat have also proposed the deletion of various coordination and notification procedures, including waiving deployment milestone reviews and removing requirements to notify the Commission of orbital repositioning or in-orbit testing. These procedures serve an important function in allowing federal agencies, including NASA and the NSF, to track and respond to changes in the orbital environment and their potential spectrum impact.
The collective goal of these proposals appears to be the streamlining of satellite deployment and licensing at the expense of rigorous review and scientific due process. While we support responsible and efficient commercial innovation in space, this must not come at the cost of the public good, including access to Dark and Quiet Skies.
We also highlight that the United States has long maintained a global leadership role in astronomy, thanks in part to landmark facilities such as the Very Large Array, the Green Bank Telescope, and the forthcoming Next Generation Very Large Array. These facilities are routinely used in international collaboration, contribute to Nobel Prize-winning research, and support the STEM training of countless students and early-career scientists.They have enabled iconic discoveries such as the imaging of the first black hole shadow, the detection of Fast Radio Bursts
(FRBs) from distant galaxies, and the discovery of the first binary pulsar, which provided the first indirect evidence for gravitational waves.
Jeopardizing these assets by relaxing satellite emission limits or procedural oversight would not only undermine U.S. science but also damage our nation’s leadership in a highly visible and strategic domain of international cooperation.
The proposed deregulations also neglect the fact that many observatories are located in federally protected radio quiet zones, such as the National Radio Quiet Zone (NRQZ) and coordination zones established around federally funded facilities. Removing or diminishing oversight mechanisms without equivalent safeguards would make these zones effectively unenforceable.
We acknowledge that some operators, including SpaceX, have engaged in productive discussions with the NSF and radio observatories to voluntarily mitigate their impact. However, voluntary agreements cannot replace enforceable protections. Without clear and enforceable rules, there is no accountability nor assurance that future operators will follow suit.
Efforts to reduce the notification burden on operators must not come at the cost of transparency or scientific oversight. The growing use of passive services, including radio astronomy, Earth remote sensing, and space weather monitoring, relies on reliable data about active spectrum users. Removing these sources of transparency deprives scientists of their ability to plan, adapt, or appeal when harmful interference occurs.
The Commission has an opportunity to lead in crafting a spectrum policy that balances innovation with stewardship. But leadership also requires restraint and an honest acknowledgment that not all interference can be mitigated through filtering techniques. The myth that filtering or beam steering alone can protect radio astronomy has been repeatedly disproven in both theory and practice. Contrary to some claims in the record, no advanced filtering technique today can effectively recover signals that are millions of times weaker than the noise floor established by active transmissions. Such techniques, even when successful at removing bulk interference, introduce artifacts that corrupt the very scientific signals we seek to preserve. For this reason, these methods are not used operationally on any major observatory.
The erosion of protections for radio astronomy would have global consequences. The FCC’s regulatory decisions are closely watched by peer agencies worldwide. A decision to relax emission protections or eliminate coordination processes would signal to other administrations that passive services are no longer a priority in U.S. spectrum management.
In summary, we urge the Commission to reject calls to delete power flux density limits, remove site-specific coordination procedures, or discard milestones and reporting requirements. Instead, we encourage the Commission to uphold its commitment to scientific integrity, inter-agency coordination, and responsible stewardship of the spectrum.
Thank you for your consideration.
Gregory Hellbourg, Radio Astronomy department, California Institute of Technology
Samantha Lawler, Physics Department, University of Regina
Teznie Pugh, McDonald Observatory at The University of Texas at Austin