PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2011-09-07 NOTE = "C-Kernel Information" END_OBJECT = TEXT END General information about SPICE C-kernels ========================================= In the SPICE system, pointing data for an instrument platform, or for a specific instrument, are stored as C-kernels (CK). The pointing of a platform or an instrument is often expressed in terms of a transformation matrix from some standard base reference frame to a instrument-fixed frame. In the past, the instrument was often a camera, and the transformation was thus dubbed the ``C-matrix''; hence the choice of C as the name for the pointing kernel. The data contained in C-kernel files can be accessed and manipulated by a collection of subroutines that are part of the SPICELIB library, the major component of the NAIF Toolkit. These subroutines can be integrated into user application programs. Information about obtaining the SPICE Toolkit is located in the "software" subdirectory of the main directory of this dataset. To use C-kernels, a Spacecraft Clock Kernel (SCLK) is required. Also, for C-Kernels containing orientation of project-defined frames, a Frame Kernel file is required. Refer to the CK Required Reading (ck.req) document provided with the Toolkit or available from the NAIF Node of the PDS, to get more information on how to access C-kernel data. EPOXI C-kernels Contained in This Data Set ========================================== This directory contains the SPICE C-kernel files for the EPOXI mission. All files are in IEEE big endian binary format and suitable for use on UNIX workstations and MACs. The following CK files are provided in this directory (only the leading portion of the file name is shown; the extension of all CK file names is ".bc"): dif_sc_050823_081231 Deep Impact Flyby (DIF) reconstructed dif_sc_090101_110228 spacecraft orientation CK files based on the low rate real-time attitude telemetry and covering the EPOCh and DIXI parts of the mission. These files have numerous gaps in coverage. Many of these gaps are very large in size (days) and happen at the times when the spacecraft transitioned from one attitude mode to another. For this reason changing the interpolation interval information to "close" gaps in these files with CKSPANIT or similar utility is not recommended. dif_sc_050823_081231_v2 Deep Impact Flyby (DIF) reconstructed dif_sc_090101_110228_v2 spacecraft orientation CK files based on the low rate real-time attitude telemetry and covering the EPOCh and DIXI parts of the mission, with internal time tags corrected for mismatch between on-board clock format defined by SCLK kernels and actual on-board clock format in telemetry. These files supersede the original low rate CKs shown above. The note about gaps and CKSPANIT also applies to these CKs. dif_sc_101104_highrate Deep Impact Flyby (DIF) reconstructed spacecraft orientation CK file based on the high-rate recorded attitude telemetry covering an 8 hour window around the closest encounter with Hartley 2. This version 1 CK has internal time tags truncated by up to 2 milliseconds, introducing attitude errors of almost 30 microradians during the fastest spacecraft turn rates in the ~200 second interval around the closest approach to Hartley 2 (at other times attitude errors due to this truncation are negligible). dif_sc_101104_highrate_v2 Deep Impact Flyby (DIF) reconstructed spacecraft orientation CK file based on the high-rate recorded attitude telemetry covering an 8 hour window around the closest encounter with Hartley 2; version 2 with corrected time tags. dif_sc_071103_090126_p_to DIF predicted spacecraft orientation CK file based on the planned attitude profile and providing coverage only for the target observation periods during the EPOCh part of the mission. In most cases this file provides the predicted orientation that is close to the reconstructed orientation and, therefore, can be used to process observations that fall within gaps in the reconstructed CK files. dif_sc_090327_100517_p_to DIF predicted spacecraft orientation CK file based on the planned attitude profile and providing coverage only for selected target observation periods during the DIXI part of the mission. In most cases this file provides the predicted orientation that is close to the reconstructed orientation and, therefore, can be used to process observations that fall within gaps in the reconstructed CK files. dif_sc_071103_090127_p DIF predicted spacecraft orientation CK file based on the planned attitude profile and providing a complete, gap-less coverage for the EPOCh part of the mission. This file should be used with great caution and only in cases when neither the reconstructed CK nor the predicted target observations only CK provide coverage for the time(s) of interest. Users should remember that attitude computed using this file is suspect because of the idealistic attitude modeling rules, incorrect timing of attitude mode transitions, and lack of modeling of some spacecraft activities altogether. dif_hga_071123_081231_vch DIF High Gain Antenna (HGA) orientation dif_hga_071123_081222_bch CK files produced from channelized dif_hga_090101_110228_vch telemetry, each covering either the EPOCh dif_hga_090106_110228_bch or DIXI part of the mission. The "vch" files are based on the "measured" gimbal angles while the "bch" files are based on the commanded channels. Ideally, only the reconstructed CKs with corrected internal time tags and the high-rate CK for encounter dif_sc_050823_081231_v2.bc dif_sc_090101_110228_v2.bc dif_sc_101104_highrate_v2.bc should be loaded into a user application. But since these files have too many, too large gaps, to get a better coverage they may have to be loaded together with the predicted files covering only the target observation periods, with the reconstructed CKs loaded last to take precedence, like this: dif_sc_071103_090126_p_to.bc dif_sc_090327_100517_p_to.bc dif_sc_050823_081231_v2.bc dif_sc_090101_110228_v2.bc dif_sc_101104_highrate_v2.bc EPOXI CK File Naming Scheme ================================= The EPOXI CKs provided in this data set are named according to the following scheme: dif_struct_YYMMDD[_yymmdd][_ident][_vX] where: struct is the name of the spacecraft structure: "sc" for spacecraft itself; "hga" for the High Gain Antenna; YYMMDD is the file coverage start date; yymmdd is the file coverage stop date (optional; provided only if the file covers more than one day); ident is a token further identifying the data in the file (optional). Examples: "p" for predicted data, "p_to" for predicted data for target observations only; "highrate" for high-rate data, "bch" for "B"-channel based attitude, etc. vX is the file version number (optional; if omitted, the file version is "0"). The file with the highest version number supersedes all files with the same name but earlier version numbers. Kernel File Details =================== The most detailed description of the data in a binary CK file is provided in metadata included inside the comment area of the file. This information can be viewed using the utility programs COMMNT and SPACIT included in the NAIF Toolkit. The Toolkit is available from the NAIF website. Contact Information =================== Regarding EPOXI project specific information provided in this data set and for general information about the SPICE system: Boris Semenov (818)-354-8136 Boris.Semenov@jpl.nasa.gov or Chuck Acton (818)-354-3869 Chuck.Acton@jpl.nasa.gov address: Navigation and Ancillary Information Facility (NAIF) Jet Propulsion Laboratory MS 301-125L 4800 Oak Grove Drive Pasadena CA 91109 USA