============================================================================= MEX SPK Files ============================================================================= Last update: 30 MAY 2006 This "aareadme.txt" file describes the contents of the KERNELS/SPK directory of the MEX SPICE data server. It also provides the file naming conventions used for the MEX SPK kernels, and it provides identification of the most current version of each kind of SPK file. Some of these SPK files are produced by an automated system located at ESTEC, operated by the MEX Project Science Team (PST). For these we have chosen to use the ESOC naming convention for SPK files, which are converted from ESOC's DDID Orbit files. Although this convention doesn't seem very descriptive and holds some redundant information, it could be useful to use the same name style for the sake of consistency. Also, data handling performed by the PST automated system will be easier and faster. The contents and time span covered by any SPK file may be easily determined using the "brief" utility program available in all copies of the SPICE Toolkit. Examples of usage: %brief %brief <*.bsp> %brief Descriptive information about how/why/when an SPK file was created is usually available in the "comment area" of the file. This may be viewed using the "commnt" utility program available in all copies of the SPICE Toolkit. Use the "-r" option to read the comments. Example: %commnt -r All binary SPK files (*.BSP) contained in this directory are Unix binary files. These may be used as is (without format conversion) in a non-unix environment when using any recent version of the SPICE Toolkit (Version N0052 or later). [Ref 3b] Contact Jose Luis Vazquez (jlvazquez@sciops.esa.int) or Joe Zender (Joe.Zender@esa.int) if you have any questions. ============================================================================= References ============================================================================= 1. Data Delivery Interface Document (DDID) Appendix H - FD products Issue 3.0 (MEX-ESC-IF-5003) 2. SPK Required Reading. NAIF Document No. 168.10 3. Selected SPICE Tutorials from the NAIF server: ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/office/individual_docs/ a) SPK Tutorial 14_spk.ppt b) Porting Kernels Tutorial 09_porting_kernels.ppt 4. ``Astrometric Observations of Phobos and Deimos with the SRC on Mars Express'', Oberst, J. et al. Astronomy and Astrophysics. Accepted 07-Oct-2005 ============================================================================= Mars Express SPK Directory Structure ============================================================================= aareadme.txt Text file describing the directory structure, the naming conventions for the SPKs, and the current version(s) of each SPK type. former_versions Subdirectory that contains obsolete versions of the SPK files that have been updated in the Current SPK Kernels Set. ============================================================================= MEX Spacecraft SPK Naming Convention ffff__YYMMDDhhmmss_vvvvv.BSP ============================================================================= token description ------------ ----------------------------------------------- ffff Source Product Type Identifier: ORHM -- S/C Orbit, cruise, heliocentric ORMF -- S/C Orbit, Mars-centric. Long Term Planning ORMM -- S/C Orbit, operational, Mars-centric. YYMMDDhhmmss Coverage start time of the data contained in the ORMM file. In ORMF and ORHM files this token is replaced by twelve "_". vvvv version number ============================================================================= ESA Martian Satellites SPK Naming Convention MARSAT_ESA_yymmdd_Vxx.BSP ============================================================================= token description ------------ -------------------------------------------- yymmdd Coverage start date of the data contained in the file. xx version number ============================================================================= DSN Stations SPK Naming Convention EARTH_[spec]_yymmdd.BSP ============================================================================= token description --------- ------------------------------------------------------- [spec] Reference frame label: FX: EARTH_FIXED alias used. ITRF93: ITRF93 label used. yymmdd Release date. ============================================================================= Planet and Satellite Ephemeris SPK Naming Convention ============================================================================= Use original names assigned by NAIF, in uppercase. For example: DE405.BSP Planetary ephemeris MAR033.BSP Mars satellite ephemeris (Phobos and Deimos) ============================================================================= Current SPK Kernels Set ============================================================================= Note: There may be several files of a given type, each one having a different time span (e.g. the ORMM family). Note: Files EARTHSTNS_FX_yymmdd.BSP and EARTHSTNS_ITRF93_yymmdd.BSP contain the same data. These files only differ in that the second one use the reference frame label 'ITR93' instead of 'EARTH_FIXED'. 'EARTH_FIXED' alias must be map to either 'ITR93' or 'IAU_EARTH' before using the file. For high accuracy work, the EARTHSTNS_ITRF93_yymmdd.BSP is recommended (on the basis of ease of use). Name Comments --------------------------------- ----------------------------------------- BEAGLE2_SAMPLE_Vx.BSP Contains ephemeris data for the Beagle-2 lander (location relative to the center of Mars, in Mars body-fixed rotating frame.) DE405S.BSP Contains ephemeris data for planet barycenters, and for the sun, earth and moon mass centers. Spans the entire MEX mission. EARTHSTNS_FX_yymmdd.BSP Contains ephemeris data for NASA DSN stations relative to the terrestrial reference frame ITR93. In the interest of flexibility, in this file the reference frame is labeled with the alias 'EARTH_FIXED'. Any application using this file must map the alias 'EARTH_FIXED' to either 'ITR93' or 'IAU_EARTH'. This file was released on yy-mm-dd. EARTHSTNS_ITRF93_yymmdd.BSP Contains ephemeris data for NASA DSN stations relative to the terrestrial reference frame label 'ITR93'. This file was released on yy-mm-dd. NEW_NORCIA.BSP Contains ephemeris data for the ESA New Norcia station. MAR033_2000-2025.BSP Contains JPL ephemeris data for Phobos and Deimos. Spans the entire MEX mission. MAR033_HRSC_V03.BSP Contains time-shifted JPL ephemeris data for Phobos and Deimos. Spans the entire MEX mission. For further explanation, please check the "About Phobos and Deimos ephemeris" chapter in this aareadme file and the comment area of this kernel. MARSAT_ESA_yymmdd_Vxx.BSP Contains ESOC ephemeris data for Phobos and Deimos starting from 20yy-mm-dd. MEX_ASPERA_STRUCT_Vxx.BSP Contains relative locations of the ASPERA structures with respect to the spacecraft bus and each other. This SPK spans the entire MEX mission. ORHM_______________xxxxx.BSP Contains MEX spacecraft reconstructed cruise ephemeris. This ephemeris corresponds to the ESOC orbit file named: ORHM_FDLMMA_DA______________xxxxx.MEX where xxxxx designates the version number. ORMF_______________xxxxx.BSP Contains MEX spacecraft long term operational Mars centric ephemeris. This ephemeris is an approximation to that provided by an corresponds to the ESOC orbit file named: ORMF_FDLMMA_DA______________xxxxx.MEX where xxxxx designates the version number. ORMM__yymmdd000000_xxxxx.BSP Contains a MEX predicted and reconstructed ephemeris after orbit insertion, starting from 20yy-mm-dd. This ephemeris corresponds to the ESOC orbit file named: ORMM_FDLMMA_DA_yymmdd000000_xxxxx.MEX where xxxxx designates the version number. ============================================================================= About Phobos and Deimos ephemeris ============================================================================= The current Mars Express SPICE data set contains three SPKs giving ephemeris data for both Phobos and Deimos. Two out of the three files correspond to the JPL orbit solutions for both Mars' moons, and the third one to the ESOC orbit solutions. The official JPL SPK file, provided by NAIF and named MAR033_2000-2025, was used in the data analysis of HRSC/SRC images [Ref. 4]. In this analysis, the measured Phobos and Deimos positions have been compared with the JPL predictions. This comparison has shown that Phobos has advanced by approx. 12 km with respect to the JPL model, while the predicted Phobos positions in the across-track directions are off by only small amounts (+/- 1 km). Deimos observations show that this satellite has advanced by approx. 50 km, and is also off across-track by less than 1 km. The down-track offsets of 12 km and 50 km of the satellites' position can be removed by shifting in time the Phobos and Deimos ephemeris. This solution has been implemented and a new SPK kernel produced: MAR033_HRSC_V03.BSP This file solves the down-track offsets but there are still some across-track inconsistencies that remain, until a new orbit solution, more accurate, is provided. The third file, named MARSAT_ESA_040101_V01.BSP, was also used in the analysis of HRSC/SRC images [Ref. 4]. In this analysis, the measured Phobos and Deimos positions have been also compared with the ESOC predictions and the results are the following: Phobos' predicted position is 2 km ahead of the measured position, and it is off by +/- 8 km cross-track. Deimos' predicted position is 5 km ahead of the measured position, and it is off by +/-18 km cross-track. A comparison of official the ESOC and JPL orbit solutions of Phobos for epochs in 1989 show position differences over one Phobos orbital revolution ranging from 3 km to 7.5 km. These differences are mainly periodic. At the time frame of the ESOC file, 2004-2006, the same comparisons show larger differences over a Phobos orbital revolution, ranging from 6km to 22 km. It is recommended therefore to use the HRSC/JPL solution since it's the one providing more accurate values.