The Satellite Catalog Number (also known as NORAD (North American Aerospace Defense) Catalog Number, NORAD ID, NASA catalog number, USSPACECOM object number or simply catalog number and similar variants) is a sequential five-digit number assigned by USSTRATCOM (United States Strategic Command) in order of discovery to all man-made objects in Earth orbit (including rocket bodies and debris) and space probes launched from Earth. The first catalogued object, catalog number 00001, is the Sputnik 1 launch vehicle, with the Sputnik 1 satellite assigned catalog number 00002.
Objects that fail to orbit or orbit for a short time are not catalogued. The minimum object size in the catalog is 10 centimeters in diameter. As of June 23, 2019 , the catalog listed 44,336 objects including 8,558 satellites launched into orbit since 1957. 17,480 of them were actively tracked while 1,335 were lost.ESA estimates there are about 34,000 orbiting debris of the size USSTRATCOM is capable to track as of January 2019.
Initially the catalog was maintained by NORAD but starting from 1985 USSPACECOM (United States Space Command) was tasked to detect, track, identify, and maintain a catalog of all man-made objects in Earth orbit. In 2002 USSPACECOM was merged with USSTRATCOM.
Q: What criteria are used to determine whether an orbiting object should receive a catalogue number and International Designation? A: We must be able to determine who it belongs to, what launch it correlates to, and the object must be able to be maintained (tracked well).
10 centimeter diameter or "softball size" is the typical minimum size object that current sensors can track and 18 SPCS maintains in the catalog.