CASSINI CK files =========================================================================== This ``aareadme.txt'' file describes contents of the kernels/ck directory of the CASSINI SPICE data server. It was last modified on October 4, 2006. Contact Chuck Acton (818-354-3869, Chuck.Acton@jpl.nasa.gov) or Boris Semenov (818-354-8136, Boris.Semenov@jpl.nasa.gov) if you have any questions regarding the data files provided in this directory. Brief Summary -------------------------------------------------------- This directory contains SPICE C-Kernel (CK) files providing predicted, reconstructed, and image navigated (``c-smithed'') attitude of the CASSINI spacecraft. The spacecraft attitude data are stored in the CK files as spacecraft attitude quaternions and spacecraft angular rates tagged with spacecraft clock time tags. The CK files provided in this directory use the IEEE big-endian binary standard. Also contained in this directory are reports showing comparisons between various predicted and reconstructed CK files, logs of angular differences between c-smithed and reconstructed CKs, and TAR/GZIP archives of the graphic images that resulted from the c-smithing process. The reports take the form of text and Portable Document Format (PDF) files that contain information, including statistics, on comparisons between predicted and reconstructed CKs. The logs of angular differences between c-smithed and reconstructed CKs are provided in text format. The TAR/GZIP archives contains images in JPEG format. Most of the files in this directory have been copied from the CASSINI Project Database (DOM). The predicted and reconstructed CKs produced by the Spacecraft Operation Team are copied automatically, within minutes of their delivery to the DOM. The c-smithed CKs produced by the ISS team are copied manually in batches -- each batch covering a three month interval -- shortly prior to the Cassini SPICE PDS archive releases, in which these CKs are included. Each CK file has internal comments (stored in the file's comment area, which is accessible using SPICE utility COMMNT) providing information about the file. In the reconstruction CK files this information includes the CK production program setup parameters and CK interpolation interval summary. In the predicted CK files it includes only the CK production program setup parameters. Comments in each c-smithed CK file include descriptions of the data in the file and c-smithing and validation processes as well as the complete list of ISS images that were used in generating that c-smithed CK. CK File Naming Scheme -------------------------------------------------------- This section describes the CASSINI CK file naming convention. Components of the name in square brackets [] are required. Components in parentheses () are optional. CKs Produced Beginning Nov 6, 2003 (03309) The CKs generated after Nov 6, 2003 follow the naming scheme: [StartDate]_[EndDate][Type][V](_xxxxxxxx).[Ext] where: [StartDate] File coverage start date (YYDOY); [EndDate] File coverage stop date (YYDOY); [Type] Type of the data stored in the file: ``r'' = reconstruction, ``p'' = predict, ``c'' = c-smithed; [V] File version. The first file generated for a specific time frame is version ``a''. Subsequent files containing revised information for the same time period are given the next higher version letter -- ``b'', ``c'', etc; [_xxxxxxxxx] Optional for reconstructions, required for predicts and c-smithed CKs. [Ext] Standard SPICE extension for CK files: ``bc'' for IEEE binary CK files, ``xc'' or ``tc'' for transfer format CK files. For reconstructions xxxxxxxxx is a freeform text that can be included to provide the user additional clues about the contents. For c-smithed files the xxxxxxxxx is always set to ``_ISS''. For predict files the xxxxxxxxx contains the following: Waypoint -- Dual sequence SOP Implementation Waypoint port1 -- Dual sequence SOP Implementation Port 1 port2 -- Dual sequence SOP Implementation Port 2 port3 -- Dual sequence SOP Implementation Port 3 sopu -- Single sequence SOP Update Port1 or 2 depending upon the version psiv1 -- PSIV1 psiv2 -- PSIV2 fsiv -- FSIV In some cases additional suffix ``_lmb'' (stands for ``live movable block'') may be added to indicate that the predicted attitude in the file includes these blocks. For example, files for S23/S24 would be named: 06231_06295pa_waypoint.bc -- S23/S24 SOP Implementation Waypoint 06231_06295pb_port1.bc -- S23/S24 SOP Implementation Port 1 06231_06295pc_port2.bc -- S23/S24 SOP Implementation Port 2 06231_06295pd_port3.bc -- S23/S24 SOP Implementation Port 3 06231_06269pa_sopu.bc -- S23 SOP Update Port1 06231_06269pb_sopu.bc -- S23 SOP Update Port2 06231_06269pc_psiv1.bc -- S23 PSIV1 06231_06269pd_psiv2.bc -- S23 PSIV2 06231_06269pe_fsiv.bc -- S23 FSIV For additional information on how various predicted CKs relate to the stages in sequence planning refer to the ``Appendix 1: C-Kernels and Sequence Versions'' provided at the end of this file. CKs Produced Prior to Nov 6, 2003 (03309) The names of the earlier CKs followed this naming scheme: [StartDate]_[EndDate][Type][V].[Ext] where: [StartDate] File coverage start date (YYMMDD); [EndDate] File coverage stop date (YYMMDD); [Type] Type of the data stored in the file: ``r'' = reconstruction, ``p'' = predict, ``i'' = improved, etc.; [V] File version. The first file generated for a specific time frame is version ``a''. Subsequent files containing revised information for the same time period are given the next higher version letter -- ``b'', ``c'', etc. [Ext] Standard SPICE extension for CK files: ``bc'' for IEEE binary CK files, ``xc'' or ``tc'' for transfer format CK files. For example, the file: 971015_971025ra.bc is a binary CK containing reconstructed data and covers the time period of 10/15 - 10/25/97. It is the first version created for this time period. Other CKs The CKs that don't follow the naming schemes described in the previous section are special products created by AACS Team or NAIF. The naming scheme for these special files is TBD. Supplementary/Meta Information Files -------------------------------------------------------- A few types of supplementary/meta information files are provided with the CK files including detached label files, comparison reports, c-smithed vs. reconstructed difference logs, and TAR/GZIP archives with images resulting from the c-smithing process. Label Files Detached label files have the same names as the corresponding CK files with the additional extension ``.lbl'' appended at the end. The labels file do NOT have any specific structure and they contain rather ``raw'' information combined from the following sources: file SFDU label (if such was present) and contents of the comment area. Most of these labels are created automatically ``on the fly'' and are planned to be re-processed before final data archiving with the PDS. Comparison Reports Reconstructed/predicted comparison report files have the same names as the corresponding CK files with the additional extension ``.txt'' or ``.pdf'' appended at the end. The ``.txt'' files contain numerical values for comparison statistics as well as interval and gap start and stop times. The ``.pdf'' files contain graphical representations of the differences. C-smithed Logs and TAR/GZIP Image Archives. Each of the c-smithed CKs is accompanied by two supplementary files -- a text log of angular differences between c-smithed and reconstructed CK and a TAR/GZIP archive of the graphic images that resulted from the c-smithing process. Both files have names that start with the CK name. The log name ends with ``_bc_err.txt'' while the TAR/GZIP archive name ends with ``_JPGs.tar.gz''. Appendix 1: CKs and Sequence Version -------------------------------------------------------- This description of the relationship between predicted CKs and sequence versions was provided by Tom Burk, Cassini AACS Uplink Team Lead. ``Waypoint'' refers to the preliminary sequence design -- before all the observations are added. Normally, each observation begins at, and returns to, a ``waypoint'' which is a defined attitude like ``XBAND to Earth'' or ``ISS_NAC to Saturn'' or something similar. In the early design stage, we produce a CK that contains only waypoints so that preliminary thermal analysis can be done before more detailed observations are added. Sequence design begins very early -- typically a year or two ahead of the actual event. This is called the ``SOP Implementation'' phase (SOP is Science Operations Plan). SOP Update then occurs several months before the actual event. It includes revisions that are added by Science after SOP Implementation is complete. Both SOP Implementation and SOP Update can have more than one ``Port'' -- meaning Port 1 is the ``baseline'' sequence for that phase, and ``Port 2'' is a later, revised version. Each port is a complete sequence of commands where all observations are merged together into one big package. After this, we move into SSUP (Science and Sequence Update Process) phase where the sequence is handed off from the Science Planning team to the Sequence Virtual Team. This typically occurs in the last 6-8 weeks before uplink. The SVT process has several ``ports''. These are called PSIV1, PSIV2, and FSIV. PSIV means Preliminary Sequence Integration and Validation. FSIV is Final Sequence Integration and Validation. The PSIV1 sequence is, hopefully, the ``final'' version of the sequence. In the real world, the SVT Lead often approves ``SCRs'' (Sequence Change Requests) that modify the sequence relatively late in the process. These changes are incorporated into the ``PSIV2'' product. Again, this is intended to be the ``final'' sequence design. In rare cases, the project can even edit this sequence, in the last weeks before uplink, if a vital change is needed. This is called the FSIV phase and is the sequence actually uplinked. In some cases, pointing is even changed after the sequence has been uplinked. This is called ``Live IVP Update'' (IVP is inertial vector propagation) and involves overlaying pointing vectors that immediately supersede (and take precedence) the background sequence vectors. Usually this is based on a new spacecraft ephemeris. The update is typically a ``mini-sequence'' that is uplinked after the background sequence is already running and runs concurrent with part of the background sequence.