The International Designator, or NSSDC ID, was a classification system used on Earth in the 20th and 21st centuries for manned and unmanned spacecraft. The system was divided into three parts: the year of launch, a sequential launch number, and a letter code identifying if the vessel was the booster rocket or the spacecraft. For instance, the International Designator for Nomad was 2002-045b, which identified the probe as the 45th launch of 2002 and that it was the second component of the launch. The first component would have been the unspecified rocket, labeled a, which lifted the probe into space. (TOS: "The Changeling" )