Satellite Catalog Number

The Satellite Catalog Number (SATCAT, also known as NORAD (North American Aerospace Defense) Catalog Number, NORAD ID, USSPACECOM object number or simply catalog number, among similar variants) is a sequential nine-digit number assigned by the United States Space Command (USSPACECOM) in the order of launch or discovery to all artificial objects in the orbits of Earth and those that left Earth's orbit. The first catalogued object, catalog number 1, is the Sputnik 1 launch vehicle, with the Sputnik 1 satellite having been assigned catalog number 2.

Objects that fail to orbit or orbit for a short time are not catalogued. The minimum object size in the catalog is 10 cm in diameter. , the catalog listed 58,010 objects, including 16,645 satellites that had been launched into orbit since 1957 of which 8,936 were still active. 25,717 of the objects were well tracked while 2,055 were lost. In addition USSPACECOM was also tracking 16,600 analyst objects. Analyst objects are variably tracked and in constant flux, so their catalog and element set data are not published. ESA estimated there were about 36,500 pieces of orbiting debris that are large enough for USSPACECOM to track. Space Command shares the catalog via space-track.org, which is maintained by the 18th Space Defense Squadron (18 SDS).

History
Initially, the catalog was maintained by NORAD. From 1985 onwards, USSPACECOM was tasked to detect, track, identify, and maintain a catalog of all human-made objects in Earth orbit. In 2002, USSPACECOM was disestablished and merged with the United States Strategic Command (USSTRATCOM). However, USSPACECOM was reestablished in 2019.

Before 2020, the catalog number was limited to five digits due to the TLE format limitation. In 2020, Space-Track started to provide data in CCSDS OMM (Orbit Mean-Elements Message) format, which increased the maximum catalog number to 999,999,999.