1. Operational Data Sharing (ODS) v1.0.0

As part of the NSF’s Spectrum Innovation Initiative: National Radio Dynamic Zones (SII-NRDZ) and Spectrum and Wireless Innovation enabled by Future Technologies - Satellite-Terrestrial Coexistence (SWIFT-SAT), NRAO has led the development of coordination techniques in conjunction with SpaceX and other non-geostationary (NGSO) satellite operators to achieve dynamic spectrum sharing and spectrum coexistence. Meanwhile, these efforts can help to achieve the requirements set by the FCC Rule Part US131.

To mitigate radio frequency interference (RFI) from satellites’ broadband internet and cellular downlink services, particularly from the Low-Earth Orbit (LEO), by radio telescopes on Earth, two primary schemes have been implemented between satellite operators and radio astronomy (RA) observatories are: Zone Avoidance (ZA) and Telescope Boresight Avoidance (TBA).

The ZA provides the basic protection approach to have satellite constellations avoid directly illuminating the RA sites (Figure 1, left). This partial solution requires no communication between telescopes and satellite operators, but simply a database of the observatory locations.

Figure 1 - A simplified illustration of the two approaches enabling spectrum coexistence between radio telescopes and satellite operators. (Left) Zone avoidance (ZA) provides the basic protection with satellites placing DL beams far away from radio telescopes residing within their 10.7-12.7 GHz internet service cells, highlighted by orange hexagonal hierarchical geospatial indexing regions in the lower insets, as reproduced from the Starlink Availability Map online in February 2025. (Right) Telescope boresight avoidance (TBA) provides an advanced protection when a satellite is passing close to the telescope main farfield beam (or boresight). The TBA consists of two modes: the inner boresight region (white dashed circle) where the satellite would briefly turn off the formation of phased array beams; and the outer boresight region (orange dashed annulus) within which the satellite places its DL beams far from the telescope site. (Credit: NRAO/SMD/Paul Vosteen).

Figure 1 - A simplified illustration of the two approaches enabling spectrum coexistence between radio telescopes and satellite operators. (Left) Zone avoidance (ZA) provides the basic protection with satellites placing DL beams far away from radio telescopes residing within their 10.7-12.7 GHz internet service cells, highlighted by orange hexagonal hierarchical geospatial indexing regions in the lower insets, as reproduced from the Starlink Availability Map online in February 2025. (Right) Telescope boresight avoidance (TBA) provides an advanced protection when a satellite is passing close to the telescope main farfield beam (or boresight). The TBA consists of two modes: the inner boresight region (white dashed circle) where the satellite would briefly turn off the formation of phased array beams; and the outer boresight region (orange dashed annulus) within which the satellite places its DL beams far from the telescope site. (Credit: NRAO/SMD/Paul Vosteen).

To help inform satellite operators of the current telescope status, the Operational Data Sharing (ODS) system was developed to provide information about current and near future observations of participating radio telescopes, including where their antennas are pointing and at what frequencies they are observing. Satellite operators can dynamically query for this information to reconfigure any satellites that may interfere with the RA observations by either activating the TBA technique or other means of reducing the downlink RFI. Note that this technique is not meant to address the unintentional electromagnetic radiation (UEMR) from onboard electronics.

1.1. How ODS Works

ODS is NRAO’s attempt to facilitate near real-time communication of telescope status to satellite operators. By design, the functionality of the ODS at the NRAO/GBO telescopes should require no special actions on the part of observers, e.g., who submit their observing schedule (e.g., Scheduling Blocks for VLA) as they always have. The NRAO systems then process these data without any intervention from observers (See ODS Data Format for the ODS JSON fields). The ODS is also capable of disabling status reporting (e.g., for proprietary reasons) for certain observations by a particular observer upon request. In return, these observations will not be informed and protected by TBA.

Currently, the satellite operators are interfacing with the NRAO ODS API endpoint using a token-based authentication (See How to interface with the NRAO ODS API). By design, the ODS framework can be adopted by any satellite operators and radio observatories if they use the same data and API standards (See ODS Adoption).

Figure 2 - A high level block diagram of the current ODS prototpye how NRAO's VLA, VLBA, and GBO's GBT report their observation schedules to the ODS server for satellite operators (Credit: NRAO/SMD).

Figure 2 - A high level block diagram of the current ODS prototype showing how NRAO’s VLA, VLBA, and GBO’s GBT report their observation schedules to the ODS server for satellite operators (Credit: NRAO/SMD).

1.2. How TBA Works

The main objective of the TBA is to help prevent extremely strong satellite downlink (DL) signals exposing the radio telescope’s main beam during occasional main-beam to main-beam interactions.

The TBA is a satellite tasking scheme developed by SpaceX and NRAO, that allows Starlink satellites to respond to the shared ODS radio telescope information (provided at some prearranged buffer time before observation starts). Once the Starlink system identifies that a satellite trajectory will pass close to a telescope boresight operating at one of its DL frequency channels, the satellite constellation takes one of three actions (as illustrated in Figures 1 & 3):

1) If the satellite passes outside of an agreed “outer boresight” region (defined as an angular separation from the boresight position on the sky), it takes no action.

2) If the satellite crosses into the “outer boresight” region, it will task its beams far from the radio telescope (typically 180 km) so that the telescope is only illuminated by the DL beam’s sidelobes.

3) If the satellite further crosses into an agreed upon “inner boresight” region, it will momentarily disable beam forming, completely quieting the phased array antenna and other related electronics.

Initial TBA results and analysis can be found in Nhan, et al. 2025, IEEE Comm. Mag.

Figure 3 - (Top) Waterfall plot for the cross-correlated visibility data in lefthanded circular polarization (LCP) at one of the VLA baseline pairs showing the Starlink passage with TBA activated for the DTC band (red dashed lines) with two shaded TBA regions (using the TBA log file provided by SpaceX), outer (yellow) and inner (red) angular cutoff regions. (Bottom) Similarly, the profile plot for the same VLA spectra is shown as a function of time for the DTC channels of the same Starlink passage with TBA activated with the same shaded regions. Evidently, the angular separation between the satellite and the boresight (black dashed curve, right y-axis), computed using public TLE data, shows the expected behavior of the TBA modes. (Credit: NRAO/SMD).

Figure 3 - (Top) Waterfall plot for the cross-correlated visibility data in lefthanded circular polarization (LCP) at one of the VLA baseline pairs showing the Starlink passage with TBA activated for the DTC band (red dashed lines) with two shaded TBA regions (using the TBA log file provided by SpaceX), outer (yellow) and inner (red) angular cutoff regions. (Bottom) Similarly, the profile plot for the same VLA spectra is shown as a function of time for the DTC channels of the same Starlink passage with TBA activated with the same shaded regions. Evidently, the angular separation between the satellite and the boresight (black dashed curve, right y-axis), computed using public TLE data, shows the expected behavior of the TBA modes. (Credit: NRAO/SMD).