Starlink FSS: NCAT5 filter modifications

It was mentioned previously that, as LEO constellations densify, modifications to the NCAT server filters may be required. Over this weekend, the NCAT5 server introduced modifications to the Starlink filters to more precisely associate orbiting satellites with their nominal (filed) definitions.

The chart displays how satellites are instantaneously distributed in inclination and altitude (sub-satellite point) for the three 53-degree constellation shells. As of November 4th, 2024, NCAT5 counts 3,353 satellites orbiting within 53 degrees of inclination. This is more than 50% of all FSS-band (non-DTC) Starlink satellites considered in orbit by the NCAT algorithms.

Due to the extensive use of 53-degree orbits in the Starlink constellation, it can be tricky to categorize the (filed) shell that operating satellites belong to. The NCAT5 server updates orbital readings daily for all Starlink shells by simultaneously inspecting both the orbital radius and inclination to place each orbiting satellite into the appropriate (most likely) nominal shell. Those satellites that have not yet reached their destination altitude (within certain margin) are not considered “in orbit” and thus not used for the visibility and dynamic bandwidth supply-demand calculations.

Notes:

• ?Of the three 53-degree Starlink shells, the one that continues to present more variability in satellite altitude is the Gen2 shell filed with a nominal altitude of 525 kilometers. As NCAT5 users may notice, this modification in the parameters of orbital readings has increased the total count of in-orbit Starlink satellites, particularly for the 525 km shell.
• ?SpaceX does not disclose which satellites are operational, so there is a chance, that NCAT may be slightly overcounting active satellites. Satellites that are not in their destination orbits, can be in ascending (or decay) mode. However, it appears that V2-mini satellites have more variability in how they are placed into orbit.
• ?Earth is modeled as a (WGS-84) oblate spheroid. Thus, the altitude of each satellite varies based on its instantaneous location (Earth's radius is several kilometers greater at the equator than at the poles). Also note that circular orbits of operational systems are not perfectly circular. The ' eccentricity also influences the satellite altitude relative to their nominal (filed) parameters.

The Non-GEO Constellations Analysis Toolkit (NCAT) is an assembly of easy-to-use analytics models to assess and benchmark LEO and MEO satellite constellations. To learn more about NCAT:

• Watch brief videos on YouTube
• Read more use cases here on Linkedin
• Visit the NCAT info page on the Analysys Mason website
• Contact Analysys Mason