The International Designator, also known as COSPAR ID, and NSSDCA ID, is an international identifier assigned to artificial objects in space. It consists of the launch year, a three-digit incrementing launch number of that year and up to a three-letter code representing the sequential identifier of a piece in a launch. In TLE format the first two digits of the year and the dash are dropped.
For example, 1990-037A is the Space Shuttle Discovery on mission STS-31, which carried the Hubble Space Telescope (1990-037B) into space. This launch was the 37th known successful launch worldwide in 1990.
COSPAR subsumed the first designation system, devised at Harvard University. That system used letters of the Greek alphabet to designate artificial satellites. This was based on the scientific naming convention for natural satellites. For example, Sputnik 1 was designated 1957 Alpha 2. The launch vehicle, which was brighter in orbit, was designated 1957 Alpha 1. Brighter objects in the same launch were given the lower integer number, and Alpha was given since it was the first launch of the year. The Harvard designation system continued to be used for satellites launched up to the end of 1962, when it was replaced with the modern system. The first satellite to receive a new-format designator was Luna E-6 No.2, 1963-001B, although some sources, including the NSSDC website, anachronistically apply the new-format designators to older satellites, even those no longer in orbit at the time of its introduction.
Designators are assigned to objects by USSTRATCOM along with satellite catalog numbers as they are discovered in space. The United Nations Office for Outer Space Affairs (UNOOSA) and the National Space Science Data Center (NSSDC), part of NASA, maintain two catalogs that provide additional information on the launchers and payloads associated with the designators. Spacecraft which do not complete an orbit of the Earth, for example launches which fail to achieve orbit, are not assigned IDs.
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).