The Tracking Data File (TDF, or sometimes Archival Tracking Data File -- ATDF) is produced by JPL multi-mission support personnel for use in determining spacecraft trajectories, gravity fields affecting them and radio propagation conditions. The typical TDF has a single File Identification Logical Record (Table), one Transponder Logical Record (Table), a Tracking Data Table of many records, and one or more padding records to fill out a data block. Some TDFs may be missing the Identification, Transponder, and/or padding records. Each TDF logical record contains 288 bytes; 28 logical records are packed into each block of 8064 bytes. Each TDF is an integer number of these blocks. Tracking Data Table format and content until early 1997 were described by JPL/DSN Document 820-13, Rev A, TRK-2-25. Formats and content after early 1997 were described by SFOC-NAV-2-25. These may be included with the archive in the DOCUMENT directory as TRK_2_25.TXT and/or NAV_2_25.TXT, respectively.