PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 OBJECT = TEXT PUBLICATION_DATE = 1996-10-31 NOTE = "Description of contents of GEOMETRY directory" END_OBJECT = TEXT END The GEOMETRY directory holds ephemeris and spacecraft attitude data for Magellan bistatic radar experiments. Ephemeris Data -------------- Most ephemeris data are provided in the form of NAIF SPK files. Each SPK file is a data module which can be read and interpreted using software provided by the PDS Navigation and Ancillary Information Facility (NAIF). That software is described briefly in TK_FTP.TXT, TK_DESCR.TXT, and TK_INSTL.TXT in the DOCUMENT directory. There are two formats for the NAIF SPK data. The NAIF 'text' format is used for all experiments except those on 31 May 1994; these files can be identified by the suffix 'TSP'. They contain information on both the Magellan spacecraft trajectory and the solar system bodies of interest. A single file of NAIF 'transfer' format data is included. This file (PEPH8996.XSF) provides ephemeris data on solar system bodies from late 1989 through early 1996. Both formats (TSP and XSF) can be converted to the local binary format using the NAIF utility SPACIT. Each line in each SPK file is delimited by an ASCII carriage- return line-feed pair. Users may need to remove one of these before using the file with the NAIF software. For example, most Unix users will need to convert the carriage-return line-feed pair to a single line-feed. A single table of Keplerian orbital elements (KEPELEMS.TAB) defines the spacecraft orbit near the time of each experiment. It can be used in conjunction with PEPH8996.XSF to obtain the complete geometrical configuration during those observations. Since there is no SPK file for the experiments on 1994-05-31, the Keplerian elements are required for analysis of those data. Attitude Data ------------- Attitude data during spacecraft maneuvers are provided as files of quaternion polynomial coefficients (file name suffix 'QPC'). The file QTERNION.TXT in the DOCUMENT directory describes the format and application of these coefficient files. QTERNION.TXT also includes the reference (or offset) times and fixed quaternion values for pre- and post- experiment Earth-pointing periods. Labels ------ Each SPK and QPC data file is accompanied by a detached PDS minimal label. The Keplerian element table is accompanied by a detached full PDS label. If the name of the data file has the form NNNNNNNN.XXX, where 'XXX' is a three character extension, then the label file has the name NNNNNNNN.LBL.