COMPASSE comments on proposed FCC rulemaking on Supplemental Coverage From Space (SCS)

June 2024

In regards to the Report & Order and Further Notice of Proposed Rulemaking FCC 24-28; GN Docket No. 23-65; IB Docket No. 22-271

The American Astronomical Society is a major international organization of approximately 8200 professional astronomers, astronomy educators, and amateur astronomers. The mission of the AAS is to enhance and share humanity’s scientific understanding of the universe as a diverse and inclusive astronomical community. In keeping with this mission, the AAS Committee for the Protection of Astronomy and the Space Environment (COMPASSE) urges the FCC to recognize the serious threat posed to radio astronomy by Supplemental Coverage from Space (SCS) and require SCS operators to clearly demonstrate that they will not cause harmful interference with radio astronomy facilities during the licensing process.

Radio astronomy is a crucial means for astronomers to gain a view of the universe that is often impossible with observations at other wavelengths, enabling unique science and complementing other areas of astronomy to develop a multi-wavelength and multimessenger picture of the universe. Radio observations allow us to measure the gas from the early universe and learn about the time when the first stars formed, to look through the dust surrounding the central parts of galaxies, and to search for signs of life elsewhere in the universe. Beyond basic research, radio observations of quasars enable GPS calibration through Very Long Baseline Interferometry. The radio quiet zone used by the National Radio Astronomy Observatory to enable these discoveries is also crucial for other parts of the government, including the Sugar Grove NSA communications site. With the implementation of Supplemental Coverage from Space (SCS), the large investments made by the government and scientific community in radio astronomy may be significantly impacted, especially as SCS could interfere with the active and upcoming missions of multiple governmental agencies. SCS directly conflicts with the precedent set by the National Radio Quiet Zone (NRQZ), and risks causing great damage to sensitive ground-based radio astronomy receivers. It is imperative that these risks be mitigated as much as possible.

Radio astronomy faces a serious threat from SCS. The above discoveries and advancements were enabled by clear access to the broad radio spectrum, whether through the establishment of a radio quiet zone or the placement of observatories in remote locations. This will no longer be possible with persistent interference from overhead satellite transmissions. Without access across the broader spectrum, astronomical research will only be possible to carry out in the small sliver of spectrum allocated specifically for this purpose, greatly limiting the discovery potential.1 The likely interference from SCS communications will impact the fundamental missions of agencies who carry out operations within the NRQZ, such as the NSF, the NSA, and the US Navy. Such threats to the mission requirements of the U.S. national defense, security, and scientific sectors through harmful interference constitute a determining factor to preserve existing uses of the crowded radio spectrum.2 The primary tenet of spectrum management is that “normal assignment of radio frequencies for transmission purposes is the avoidance of harmful interference.”3 As such, the FCC has agreed to coordinate with the National Telecommunications and Information Administration (NTIA) when its actions can “potentially cause interference to government operations”.4 The FCC has a history of implementing regulatory law for new and emerging technology that allows the FCC to manage spectrum in the spirit of its mandate and to allow for a diversity of spectrum users.5

SCS will negatively impact radio astronomy research in a multitude of ways. First, satellite operators could potentially transmit into radio quiet zones and remote observing sites from overhead. Even if operators take measures to limit transmissions when passing over radio quiet zones and observatories, the terrestrial mobile bands in which these systems operate (less than approximately 5 GHz), have more sidelobe propagation, causing messier spatial beams which could physically leak into radio quiet zones and observing sites, causing harmful interference. Such interference certainly limits the ability of the astronomical community to carry out research in the transmission bands, but interference from SCS could also be harmful to the entire receiver passband of the radio telescope, as SCS signals are significantly stronger than other satellite signals. Such strong signals could lead to saturation of the electronics in radio telescopes, causing the whole receiver passband to be lost6. Moreover, additional interference is also caused by electronic noise from satellite  components at frequencies well below the satellite downlink frequencies 7. While this radiation
is unintended, the lack of regulation for such unintended electromagnetic radiation can have 
dire consequences when considering the aggregate effects of all satellites planned for LEO8. Finally, astronomers have been observing interference from satellite transmissions with the bands that are specifically allocated and protected for radio astronomy.9 While this out of band leakage is also unintended, i.e., the FCC is respecting the protected radio astronomy bands in its allocation, this bleedover further negatively impacts the ability to carry out astronomical research. For a detailed assessment of the impacts of SCS on astronomical research, including the potential interference at specific research facilities, we strongly recommend that the FCC refer to the NSF white paper, A Preliminary Assessment of Potential Impacts to Radio Astronomy Systems from Supplementary Coverage from Space.

We urge the FCC to adopt measures to protect radio astronomy from the significant interference arising from SCS communications. Radio quiet zones, including the NRQZ covering Green Bank Observatory and the Table Mountain Field Site, were instituted to enable radio astronomy and other research areas to observe and use the radio spectrum beyond their very limited allocations. The NRQZ, however, was created by the FCC prior to the emergence of significant space-based operations and therefore lacks specific protections from space-based radio interference. SCS communications will make much of that research impossible unless clear measures are taken to protect radio quiet zones from interference. We urge the FCC to extend the protection of radio quiet zones to also include interference from above, such as satellite systems passing overhead, so that the observatories can continue to work in all the frequencies in which they have previously operated.10 This involves both avoiding direct illumination of the main beam from satellites, and ensuring that the noise level per transmitter is comparable to that applied to ground-based ones as a function of frequency. We note that many radio observatories in the U.S. and with international partners around the world do not have the safeguard of a radio quiet zone, instead operating in remote locations, where ground-based interference is limited, but interference from space-based SCS systems is likely to be significant. We ask that the FCC take steps to ensure that the scientific activities of all observatories are able to proceed without harmful interference from SCS communications

The AAS is very appreciative of the efforts that the FCC has taken to require coordination agreements between satellite operators and the NSF, and we urge the FCC to continue this practice with coordination agreements that protect the interests of both optical and radio astronomy. Effective mitigation of the negative impact of SCS communications on the national radio astronomy enterprise as a whole would include extending the concept of radio quiet zones to SCS with the same limits on spectral power flux density transmitted per SCS satellite to those zones from any orbital location. The appropriate limits are the protection thresholds in Recommendation ITU-R RA.769 Table 1 for the Green Bank Telescope and the Very Large Array.11 Minimal disruption to the missions of such agencies as the NSF or DoD would be imposed if those limits are applied to all locations with radio telescopes supported by federal funds. We urge the FCC to require in its SCS licensing process, in coordination with the NTIA and the NSF, a detailed analysis with specific proposed implementations of SCS (both actual antenna patterns and satellite orbital configurations) using Monte Carlo equivalent power flux density simulations and field testing to more fully understand the impact to radio astronomy systems, per the NSF white paper. Such pre-licensing testing must include a demonstration that SCS signals will not saturate receiver chains, as the strength of these signals could lead to the entire receiver passband being lost, beyond just the SCS bands that are impacted. Further testing of the spatial beams, including the sidelobe propagation, will be necessary before licensing these systems to ensure that the boundaries of radio quiet zones can be respected, and that these systems are able to avoid harmful interference with other radio astronomy observatories. We also strongly recommend that SCS systems are tested for electronic noise from their satellite components, as such noise can cause leakage into protected radio astronomy bands. Throughout this process, the FCC must consider the aggregate effects of SCS satellite systems, especially as the leakage from an individual constellation might fall below the noise floor for radio observatories, but the combined effects from all operating constellations are likely to be much larger, leading to significant data loss. We further urge the FCC to work with community groups, industry, and federal agencies to provide funding to develop technical solutions to these issues, including sidelobe propagation and electronic noise.

In addition to the existential threats posed by SCS to radio astronomy, satellite systems used for SCS are likely to significantly impact optical astronomy carried out from ground-based telescopes. SCS requires satellites to carry large antennas to generate a signal powerful enough for cellular phones to pick up. While developing larger antennas will enable more steerable beams which will help mitigate interference in radio quiet zones, these larger antennas will lead to brighter satellites and greater interference with optical astronomy with the increased satellite area which reflects sunlight towards the Earth. For example, the Starlink V2 minis have 11 square meter antennas (note that Starlink Gen 2 satellites are larger than this, approximately, 25 square meters, to fully enable SCS capabilities), while AST SpaceMobile’s BlueWalker3 satellite used a 64.3 square meter phased-array antenna. Notably, with its unfolded antenna, BlueWalker3 was one of the brightest objects in the night sky, reaching an apparent magnitude of 0.4, nearly 400 times brighter than the current International Astronomical Union recommendation of magnitude 7 for artificial satellites12. AST SpaceMobile’s full constellation as planned will have hundreds of satellites each with much larger antennas, approximately 330 sq m. Without significant brightness mitigation measures, these satellites could lead to substantial data loss by saturating the amplifiers of the CCDs used by optical observatories. As SCS capabilities proliferate, it will become increasingly difficult, and quite likely impossible, for ground based observatories to avoid these bright satellites, which will certainly lead to a loss in data collected. These bright satellites will also fundamentally change the night sky, impacting stargazing activities and leading to the loss of intangible cultural heritage. We urge the FCC to recognize that any proposed RFI mitigation measures for SCS systems should also consider the potential for harm to other areas of astronomy.

In response to the inquiry about early coordination efforts, the AAS recommends that operator applicants engage as early in the process as possible with the Industry and Technology Hub of the International Astronomical Union’s Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS)13. The Hub with its space industry members is actively exploring the tools and resources needed to assess satellite systems and effective, affordable and accessible solutions to mitigate effects on astronomical discovery.

Both the scientific community and the US government have invested significant time, effort and funds in the creation of radio astronomy facilities that allow us to better understand the history and composition of our universe. SCS operations, if unregulated, will completely undermine these efforts and undercut American scientific competitiveness. One of the mandates of the FCC is to serve the public interest, including the progress of knowledge. While SCS may advance connectivity across the nation, it must also be recognized that it will simultaneously interfere with our ability to explore and learn about our universe. It is crucial that the FCC take steps to ensure that the SCS transmissions do not interfere with radio observatories, by both respecting radio quiet zones and ensuring protections are in place for remote observatories outside these zones.

On behalf of the American Astronomical Society’s Committee for the Protection of Astronomy and the Space Environment,

Aparna Venkatesan, Co-chair 
Teznie Pugh, Co-chair


1 On the diverse forms of observations and objects of study through the use of radio waves, see: National Research Council. 2007. Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses. Washington, DC: The National Academies Press.

 2 U.S. Department of Commerce, National Telecommunications and Information Administration, Manual of Regulations and Procedures for Federal Radio Frequency Management (2021), p. 2-6.

3 Ibid., p. 2-5. Related to this provision is the historical trajectory of interference mitigation between governmental entities. The Telecommunications Act mandates that the FCC “help attain coordinated and efficient use of the electromagnetic spectrum and the technical compatibility of the communications satellite system with existing communications facilities both in the United States and abroad.” This language originally appeared in the Communications Satellite Act of 1962 and implemented in Executive Order 11191. These functions were then transferred to the Secretary of Commerce in Executive Order 12046. According to the Manual of Regulations and Procedures for Federal Radio Frequency Management, radio spectrum allocations shall be made in the following order of priority: 1) national security and defense, 2) the “safeguard[ing] of life and property in conditions of distress, 3) “safeguard[ing] of life and property” outside of conditions of distress when no “other means of communication are available”, 4) scientific research, and lastly, 5) uses “judged upon the merits of the intended use.” U.S. Department of Commerce, National Telecommunications and Information Administration, Manual of Regulations and Procedures for Federal Radio Frequency Management (2021), p. 2-5.

4 U.S. Department of Commerce, National Telecommunications and Information Administration, Manual of Regulations and Procedures for Federal Radio Frequency Management (2021), p. 2-8. The aim of this provision is that the FCC and NTIA will seek consensus to “resolve technical, procedural, and policy differences by consensus whenever possible.” Ibid.

5 Jessica Rosenworcel (FCC), ”2023 in Review: A Note from the Chairwoman”, 29 December 2023,

A Preliminary Assessment of Potential Impacts to Radio Astronomy Systems from Supplementary
Coverage from Space,

7 Di Vruno et al. “Unintended electromagnetic radiation from Starlink satellites detected with LOFAR
between 110 and 188 MHz.”
Astronomy and Astrophysics, 10 August 2023.

Falle et al. “One million (paper) satellites.” Science, 12 October 2023.

9 Chris De Pree (NRAO), Anthony Beasley (NRAO), Sheldon Wasik (NRAO), Urvashi Rao (NRAO), Rob
Selina (NRAO), Will Armentrout (GBO), Harvey Liszt (NRAO), “Strategies for Spectrum Coexistence
Between Radio Telescopes and Satellite Networks,” International Astronomical Union Symposium 385:
Astronomy and Satellite Constellations: Pathways Forward (2-6 October 2023),

10 47 CFR § 1.924 specifies that permanent stations cannot be constructed or operated within these
zones. A station is defined as equipment used to “engage in radio communication or radio transmission of
energy.” 47 CFR § 153. Satellites would fall under this definition of station, but would not fall under current
regulations due to their mobile nature. However satellites do follow defined orbits that are known to the
FCC, considering systems whose orbital plan intersects with the NRQZ as permanent stations may be a
possible avenue through which the FCC can extend radio quiet zone protections. 

11 Recommendation ITU-R RA 769 

12 Nandakumar et al. “The high optical brightness of the BlueWalker 3 satellite.” Nature, November 2023.

13 IAU CPS Industry and Technology Hub,