Thomas G. Roberts, Massachusetts Institute of Technology; Richard Linares, Massachusetts Institute of Technology
Keywords: International Telecommunications Union, spectrum allocation, geosynchronous orbital regime, collision avoidance
Abstract:
The vast majority of active satellites in the geosynchronous (GEO) orbital regime—approximately 95 percent of the annual population since 2010—perform consistent station-keeping maneuvers to stay near a particular geographic longitudinal position for their entire operational lifetimes, from orbital insertion to post-mission removal. To avoid issues of congestion due to satellites operating physically near one another at similar longitudinal positions while propagating signals that are spectrally near one another at similar radio frequencies—which can increase the threat of satellite-on-satellite collisions or harmful radio-frequency interference—satellite operators must acquire space station licenses from the the International Telecommunications Union (ITU), a specialized agency of the United Nations, prior to launch. Since 1971, the ITU has granted licenses to satellite operators to propagate signals at particular frequencies from particular orbital slots, or fractions of the geostationary belt, measured in longitudinal degrees. Although the GEO orbital regime is indeed popular, the number of space station licenses granted by the ITU far exceeds the number of real, active satellites launched to the domain.
This paper compares the ITU space station license application environment with the active on-orbit satellite population in GEO. This work describes the various information available in the ITU’s Space Network List and Space Network Systems Database, as well as the ITU Radiofrequency Bureau’s “As Received” list of published satellite notifications, which includes submissions for the notification of space stations, coordination requests, and those submissions received in accordance with various ITU agreements prior to licenses being granted. This paper describes the similarities and differences between space station licenses that are used—that is, an operator from the grantee country eventually appears to station-keep a satellite at that location—and those that are, as of yet, unused. Patterns of license use are identified across ITU operational region, operator countries, satellite purpose, and other key characteristics. The concept of “paper satellites”—the observed practice of space administrations filing license applications for the use of particular physical and spectral spaces with no intention of ever using them—as well as the history and evolution of ITU orbital slot sizes are also discussed.
The principal data source for describing the behavior of active satellites in the GEO domain for this work is the publicly available space object catalog maintained by the United States Space Force’s 18th Space Control Squadron and made public on Space-Track.org. For this application, the two-line element (TLE) time-histories available on Space-Track.org must first be converted to equal-timestep geographic position time-histories. The study period for this work is January 1, 2010, to December 31, 2020.
This paper features several case studies in which the historical station-keeping behavior of satellites that perform a relatively large number of phase change maneuvers are studied alongside their operator country’s active ITU space station licenses. When GEO satellites perform phase change maneuvers, also known as longitudinal shift maneuvers, they first appear to station-keep at one longitudinal position, then engage in a period of natural drift either eastward or westward in the geostationary belt, and finally begin a second period of station-keeping at a new longitudinal position.
Date of Conference: September 27-20, 2022
Track: SSA/SDA