This post is part of a series on understanding the meaning behind the values contained in a Two Line Element set, or Keplerian Elements. The main article is here.
International Designator (Launch Number)
This is a three digit number showing launch number for the year. These numbers are designated by the World Warning Agency (WWAS).
In most cases, the first launch of the year is numbered 001 and then incremented sequentially until the last launch of the year.