The Voyager 1 dictionary contains classes that describe aspects of the Voyager 1 mission and related instruments. The VG1 class is the container for mission-specific metadata elements. This section contains the simpleTypes that provide more constraints than those at the base data type level. The simpleTypes defined here build on the base data types. This is another component of the common dictionary and therefore falls within the pds namespace. The mission_phase_name attribute provides the mission-defined name of a mission phase. The spacecraft_clock_start_count attribute provides the value of the spacecraft clock at the beginning of a time period of interest. The spacecraft_clock_stop_count attribute provides the value of the spacecraft clock at the beginning of a time period of interest.