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The International Designator, also known as COSPAR designation, and in the United States as NSSDC ID, is an international naming convention for satellites. It consists of the launch year, a 3-digit incrementing launch number of that year and up to a 3-letter code representing the sequential identifier of a piece in a launch.
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. The number reveals that it was launched in 1990 and that it was the 37th launch made that year. Spacecraft which do not complete an orbit of the Earth, for example launches which fail to achieve orbit, are not usually assigned IDs.
The designation system has been generally known as the COSPAR system, named for the Committee on Space Research (COSPAR) of the International Council for Science. COSPAR subsumed the first designation system, devised at Harvard University in 1958. That system used letters of the Greek alphabet to designate artificial satellites. For example, Sputnik 1 was designated 1957 Alpha 2. 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.