On August 9, 2024, SpaceX filed a petition with the Federal Communications Commission (FCC) requesting the agency initiate a rulemaking to update its rules governing spectrum sharing between non-geostationary orbit (NGSO) and geostationary orbit (GSO) satellite systems. SpaceX argues that the current equivalent power flux-density (EPFD) limits in the FCC’s rules, which were adopted over 20 years ago, are significantly overprotective of GSO systems and constrain the operations of modern NGSO systems to the detriment of American consumers.
Flawed Assumptions and Methodology Behind Current EPFD Limits
SpaceX contends that the existing EPFD limits incorporated into the FCC’s rules in Sections 25.146 and 25.289 were developed using incorrect assumptions and a flawed methodology:
- The limits were based mainly on studies of the proposed SkyBridge NGSO system in the late 1990s, which never launched. The SkyBridge system design is completely different from modern NGSO systems.
- The International Telecommunication Union (ITU) adopted the EPFD limits without reaching consensus on an appropriate long-term interference protection criterion for GSO systems. The long-term limits reflect arbitrary masks proposed by different countries.
- The GSO reference links used to derive the limits were inconsistent with typical GSO operations in terms of power levels and noise temperatures.
As a result, SpaceX argues the EPFD limits overprotect GSO systems by 3.5 to 12 times compared to reasonable interference thresholds and require NGSO systems to maintain unnecessarily large separation angles from the GSO arc.
Constraints on NGSO Systems and Negative Impact to Consumers
SpaceX explains how the antiquated EPFD limits place significant constraints on the design and operations of modern NGSO systems:
- NGSO operators must artificially limit the power and capacity of their satellites, reducing signal quality and making it harder to provide consistent high-quality service.
- Large avoidance angles away from the GSO arc restrict which NGSO satellites can serve a given location, leaving a significant portion of satellites unusable even when no GSO earth station is present. Studies show this can reduce NGSO system capacity by up to 8 times.
- The limits make spectrum sharing between NGSO systems more difficult by reducing the usable sky for coordination.
According to SpaceX, relieving these constraints by modernizing the FCC’s rules would bring major benefits to American consumers, especially those in rural and remote areas that rely on satellite broadband. More efficient use of spectrum would allow NGSO operators to dramatically improve service quality and coverage.
Proposed New Approach for GSO-NGSO Spectrum Sharing
SpaceX urges the FCC to develop a new spectrum sharing methodology for NGSO downlinks that:
- Specifies appropriate short-term and long-term interference protection criteria for GSO systems, such as an aggregate unavailability increase of 10% in the short-term.
- Identifies realistic GSO reference links based on modern GSO operations to test against the protection criteria.
- Requires NGSO systems to demonstrate they meet the protection criteria as part of their FCC applications.
This new approach would act as an alternative to the current EPFD limits for NGSO operations in the U.S. while still protecting GSO systems from unacceptable interference. SpaceX notes the U.S. is already leading efforts internationally to revise EPFD limits but says American consumers should not have to wait years for the ITU process to conclude.
By initiating a rulemaking now to update its rules, SpaceX argues the FCC can rapidly increase broadband service for Americans everywhere, unleashing the full potential of NGSO systems to connect the unconnected. The reforms are critical to fulfill the FCC’s goals to bridge the digital divide, promote competition and innovation, and ensure efficient use of spectrum.
