============================================================================== MEX Orbit Number Files ============================================================================== Last update: 11 MAY 2006 This "aareadme.txt" file describes the contents of the KERNELS/ORBNUM directory of the MEX SPICE data server. It also provides the file naming conventions used for the MEX Orbit Number files, and it provides identification of the most current version of each kind of ORBNUM file. These are created from the SPK files converted from the ESOC's DDID Orbit Files. Orbit Number files (*.ORB) contained in this directory are unix text files. These may be used in a non-compatible text environment by using the ASCII mode of FTP to port the files. [Ref 2a] Contact Jose Luis Vazquez (jlvazquez@sciops.esa.int) or Joe Zender (Joe.Zender@esa.int) if you have any questions regarding this file. ============================================================================== References ============================================================================== 1. Data Delivery Interface Document (DDID) Appendix H - FD products Issue 3.0 (MEX-ESC-IF-5003) 2. Selected SPICE Tutorials from the NAIF server: ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/office/individual_docs/ a) Porting Kernels Tutorial 09_porting_kernels.ppt b) Derived Quantities Tutorial 21_derived_quant.ppt ============================================================================== Important Note Regarding Orbit Number Files ============================================================================== In the Mars Express orbit number files produced by NAIF's ORBNUM utility program each of the records contains the time of THAT orbit's pericenter and the time of the NEXT orbit's apocenter. For example, the line for orbit ``3'' provide UTC and SCLK of orbit ``3'' pericenter and UTC of orbit ``4'' apocenter. Since the project accepted orbit numbering scheme dictates the orbit number change to occur at apocenter, the time boundaries for a given orbit can be determined by taking the apocenter time from the PREVIOUS orbit record and the apocenter time from THIS orbit record. Orbit number 1 corresponds to the first mapping orbit,2004 JAN 13 All derived quantities provided on each record -- sub-solar lon/lat, sub-spacecraft lon/lat/alt, and orbital elements -- are computed for the time of pericenter. ------------------------------------------------------------------------------ Example ------------------------------------------------------------------------------ This is an example of MEX orbit number file (spacing was altered to fit the page): No Event UTC PERI Event SCLK PERI OP-Event UTC APO ... == ==================== ================ ==================== ... 1 2003 DEC 30 14:31:08 1/031415532.6386 2003 DEC 30 18:18:32 ... 2 2003 DEC 30 22:05:53 1/031442817.0170 2003 DEC 31 01:53:20 ... 3 2003 DEC 31 05:40:46 1/031470110.0775 2003 DEC 31 09:28:11 ... 4 2003 DEC 31 13:15:33 1/031497397.5425 2003 DEC 31 17:03:01 ... ... Given this example one can determine that: -- orbit 3 pericenter time is ``2003 DEC 31 05:40:46'' -- orbit 3 time boundaries are from ``2003 DEC 31 01:53:20'' to ``2003 DEC 31 09:28:11'' ============================================================================== Mars Express Orbit Number Directory Structure ============================================================================== aareadme.txt Text file describing the directory structure, the naming conventions for the ORBNUMs, and the current version(s) of each file. former_versions Subdirectory that contains obsolete versions of the ORBNUM files that have been updated in the Current ORBNUM File Set. ============================================================================== MEX Orbit Number Naming Covention ffff_______________vvvvv.ORB xxxx_MERGED_vvvvv.ORB ============================================================================== token description ------------ -------------------------------------------------- ffff Source Product Type Identifier: ORMF -- S/C Orbit, Mars centric. Long Term Planning xxxx Source Product Type Identifier: ORMM -- S/C Orbit, operational, Mars centric. vvvvv version number ============================================================================== Current Orbit Number File Set ============================================================================== Name Comments ----------------------------- -------------------------------------------- ORMF_______________xxxxx.ORB Contains Mars Express orbit pericenter and apocenter times, orbital elements, and additional geometry parameters computed from the SPK file named: ORMF_______________xxxxx.BSP where xxxxx designates the version number. ORMM_MERGED_xxxxx.ORB Contains Mars Express orbit pericenter and apocenter times, orbital elements, and additional geometry parameters computed from the latest set of ORMM SPK files available in the FTP server. xxxxx designates the version number.