Satellite Catalog Number

Sequential number given by the US military to every object it tracks in orbit, starting with Sputnik 1's rocket (1) and satellite (2). It ran out of five digits on 11 July 2026, forcing the 'Alpha-5' workaround and a move to nine-digit formats.

Part of the thread Who runs the registry? precedent

built upon by

• CelesTrak project 1985 [src]
• Space-Track project 2004 [src]
• Two-line element set standard 1980 [src]

Sources

• https://en.wikipedia.org/wiki/Satellite_Catalog_Number
• https://celestrak.org/