Washington, D.C., August 27, 2025
In the Matter of Modernizing Spectrum Sharing for Satellite Broadband Revision of the Commission’s Rules to Establish More Efficient Spectrum Sharing between NGSO and GSO Satellite Systems, SB Docket No. 25-157, RM-11990 (Terminated)
The American Astronomical Society (AAS) appreciates the opportunity to provide reply comments on this Federal Communications Commission (FCC) Notice of Proposed Rulemaking (NPRM), which seeks to revise equivalent power flux density (EPFD) limits and other elements of the spectrum sharing framework between non-geostationary orbit (NGSO) and geostationary orbit (GSO) satellite systems in the 10.7-12.7 GHz, 17.3-18.6 GHz, and 19.7-20.2 GHz bands, and in other frequency bands more generally.
The AAS fully recognizes the need to expand broadband access and appreciates the FCC’s ongoing efforts to modernize spectrum policy in a way that supports innovation. However, proposals to substantially alter regulatory mechanisms that have, until now, provided a workable balance between commercial growth and protection of incumbent services must be approached with extreme caution. Furthermore, the established regulatory framework is globally recognized through its codification in Article 22 of the International Telecommunication Union’s Radio Regulations (ITU RR), including standards and methodology based on decades of technical analysis that apply uniformly across international borders. Given that satellite service operations are inherently global, unilateral changes to the existing sharing framework that apply only within the United States will misalign U.S. satellite services with the rest of the world, risking increased harmful interference for which U.S. entities will be held liable.
The NPRM rightly acknowledges that changes to the NGSO-GSO sharing regime may affect incumbent services, including the Radio Astronomy Service (RAS) [1]. Specifically, the NPRM asks if “any additional considerations with respect to NGSO FSS operation [would] be necessary to protect radio astronomy operations, beyond the current existing PFD limits.” [2] As was noted in a number of comments submitted to this NPRM by terrestrial service interests (e.g., CTIA and AT&T), the EPFD limits and methodology in RR Article 22 are inextricably intertwined with terrestrial system PFD limits codified in other ITU publications, as the same underlying technical and operational assumptions informed development of both sets of limits and their applicability. While many of these assumptions based on 1990s satellite operations appear obsolete in the new era of large satellite constellations-a view held by both proponents and opponents of changes to the NGSO-GSO sharing regime-reconsideration of EPFD limits under the new technological reality may instead find that established PFD limits for terrestrial systems are no longer sufficient to protect their operations from harmful interference when considered in the aggregate.
Recommendations ITU-R RA.769-2 and ITU-R RA.1513-2 define protection criteria for RAS systems from various sources of harmful interference, both terrestrial and space-based, and Rec. ITU-R S.1586-1 specifically examines unwanted emissions at RAS sites from NGSO Fixed- Satellite Service (FSS) systems. Although only the PFD limits required to protect RAS observations are explicitly stated in Tables 1-3 of Rec. ITU-R RA.769-2, all three of these Recommendations (i) explain that the recent proliferation of low-Earth orbit (LEO) NGSO systems, with potentially thousands of satellites per system, necessitates consideration of combined harmful interference into RAS receivers from multiple space vehicles and emission sidelobes as an EPFD, and (ii) describe a methodology to convert the single-satellite PFD limits into aggregate EPFD at a given site. Given the limits and methodology established decades ago in the above ITU Recommendations, we were surprised at the comment from Amazon Kuiper on this NPRM that states, “In Amazon’s experience, the ITU EPFD limits have not been a particular subject of discussion in coordination efforts.” [3] In fact, disagreement on EPFD limits was an impediment to reaching consensus agreement on a document as recently as the Spring 2025 ITU- R Working Party 7D (Radio Astronomy) meeting, and Amazon Kuiper’s own reply to the
“Satellite Spectrum Abundance” NPRM (FCC 25-29) admits that “RAS operations have been sufficiently protected from FSS operations through the adoption of PFD and equivalent PFD (“EPFD”) limits for more than twenty years.” [4] We reiterate that the RAS PFD limits and means of calculating aggregate EPFD described in these Recommendations are based on the existing RR Article 22 EPFD methodology, and departure from this established framework would require revising these Recommendations to ensure continued protection of extremely sensitive RAS systems, including potentially making PFD limits more stringent to account for aggregate effects.
Should the FCC decide to proceed with revising EPFD limits for NGSO-GSO sharing, the AAS urges that NGSO operators be required to demonstrate continued protection for incumbent services-including radio astronomy-from aggregate harmful interference. This demonstration must entail defensible technical analyses based on real-world NGSO and other operational assumptions, including for numbers of visible satellites and their approach angles, transmitter and receiver characteristics, aggregation calculations, etc. We would also appreciate the continuation of the FCC licensing requirement that satellite system applicants must coordinate mutually agreeable operations with the U.S. National Science Foundation (NSF) Electromagnetic Spectrum Management office prior to commencing service. Finally, recalling the inherently global natures of both satellite and scientific radiocommunication services, we urge the FCC to carefully consider how any domestically applied changes to the established ITU EPFD framework can be harmonized with spectrum operations in the rest of the world. Regarding the bands being immediately considered for changes, we note that:
• 10.7-12.7 GHz is adjacent to the 10.68-10.7 GHz band, which is an RAS primary allocation and is protected from all emissions by footnote US246 to the United States Table of Frequency Allocations (47 CFR 2.105) and RR 5.340; # 10.7-12.7 GHz is co-channel with the 10.7-11.7 GHz band, for which footnote US131 requires that NGSO FSS licensees coordinate with radio astronomy observatories to achieve a mutually acceptable protection agreement prior to commencing operations;
• The first harmonic of the 10.7-12.7 GHz band ranges from 21.4-25.4 GHz, within which:
⁃ the 22.21-22.5 GHz and 23.6-24.0 GHz bands are RAS primary allocations;
⁃ in the 23.6-24.0 GHz band, all emissions are prohibited under footnote US246 and RR 5.340; and
⁃ in the 22.01-22.55 GHz, 22.81-22.86 GHz, 23.07-23.12 GHz, and 24.0-24.05 GHz bands, it is urged that all practicable steps be taken to protect radio astronomy from harmful interference under footnotes US211 and US342, and RR 5.149; and
• The first harmonic of the 17.3-18.6 GHz band ranges from 34.6-37.2 GHz, which contains the 36.43-36.5 GHz band, for which it is urged that all practicable steps be taken to protect radio astronomy from harmful interference under footnote US342 and RR 5.149.
The NPRM also seeks comments on updating the sharing regime in other frequency bands subject to ITU EPFD limits, including C-, Q-, and V-band frequencies. [5] In the absence of specific intentions for these bands or subsets of them, we simply urge that coordination between relevant satellite and terrestrial stakeholders be required on a case-by-case basis prior to commencing operations. We also fully endorse the comments submitted by the National Academies’ Committee on Radio Frequencies (CORF) and the National Radio Astronomy Observatory (NRAO) on this NPRM. We look forward to engaging in the continued development of spectrum sharing, which requires great care and consideration from many potentially impacted stakeholders.
On behalf of the American Astronomical Society,
Dara Norman, PhD
President, American Astronomical Society
1. Modernizing Spectrum Sharing for Satellite Broadband and Revision of the Commission’s Rules to Establish More Efficient Spectrum Sharing between NGSO and GSO Satellite Systems, Notice of Proposed Rulemaking, FCC 25-23, SB Docket No. 25-157, at 9 ¶ 16 (Apr. 29, 2025) (“NPRM”)
2. NPRM at 14 ¶ 32
3. See Comments of Kuiper Systems, LLC on NPRM at 21
4. See Comments of Kuiper Systems, LLC on Satellite Spectrum Abundance et al., Notice of Proposed Rulemaking,
FCC 25-29, SB Docket 25-180 at 6
5. NPRM at 15 ¶ 36