General information about SPICE C-kernels ========================================= In the SPICE system, pointing data for an instrument platform, or for a specific instrument, are stored C-kernels. The pointing of a platform or an instrument is often expressed in terms of a transformation matrix from some standard inertial 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 FORTRAN 77 subroutines which are part of the SPICELIB library or C functions which are part of the CSPICE library. These subroutines/functions can be integrated into user application programs. For information on the SPICE toolkit and/or how to obtain it, please consult SPICE_INST.CAT and SOFT.CAT. To use C-kernels, a Spacecraft Clock Kernel (SCLK) is required. Also, for C-Kernels containing orientation of a project-defined frames, a Frame Definitions File (FK) is required. Refer to the 'CK.REQ' document provided with the toolkit or available from the NAIF Node of PDS to get more information on how to access C-kernel data. ROSETTA C-Kernel Files ====================== The following file describes the contents of the DATA/CK directory of the ROSETTA SPICE dataset. Some of these CK files are produced by an automated system located at ESTEC, operated by the ROSETTA Science Operations Center (RSOC). We have chosen to use the ESOC naming convention for CK files, which are converted from ESOC's DDID Attitude files. The contents and time span covered by any CK file may be easily determined using the 'ckbrief' utility program available in all copies of the SPICE Toolkit. Examples of usage: %ckbrief This utility requires additionally a SCLK file and a LSK file; use the latest versions of these files. Descriptive information about how/why/when an CK 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 the SPICE Toolkit. Use the '-r' option to read the comments. Example: %commnt -r All binary CK files (*.BC) 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). Rosetta C-kernels contained on this data set ============================================ The following ROSETTA C-kernels are provided in this data set (only name portion of the file name is shown; extension of all file names is '.BC'): ATNR_P040302093352_vvvvv Contains Rosetta nominal pointing information, covering from launch. This file contains predicted attitude, that is, the attitude that was commanded to the Spacecraft. Reconstructed or measured attitude will ONLY be provided under exceptional circumstances. Reconstructed attitude will be delivered as a separate kernel which will cover only the time period for which the nominal (predicted) attitude is known to be incorrect. If more than one file covering the same period are provided, the one with the highest version number has more precise data, and therefore should be used. vvvvv is the version number of the file. Kernels with different version numbers might have slightly different time coverages; for the time coverage of a kernel, it supersedes all the other kernels with a lower version number. ROS_HGA_YYYY_Vvvvvv Contains nominal orientation of the Rosetta High Gain Antenna. YYYY indicates the year for which the kernel contains information, and vvvvv is the version number. The kernel with highest version number supersedes all the others. ROS_SA_YYYY_Vvvvvv Contains nominal orientation of the Rosetta Solar Arrays. YYYY indicates the year for which the kernel contains information, and vvvvv is the version number. The kernel with highest version number supersedes all the others. Note that all the labels for the CK files in this dataset have SPACECRAFT_CLOCK_START_COUNT and SPACECRAFT_CLOCK_STOP_COUNT set to N/A. The authors of the dataset think that it is not appropiate to put a clock count value for a product that was generated on ground (from the Flight Dynamics products provided by ESOC). When several versions of the same kernel are provided in the dataset, the one with the highest version number supersedes the other(s). 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 utility programs COMMNT and SPACIT included into the NAIF Toolkit. At least a basic knowledge of the SPICE system is needed in order to use this kernels. The SPICE toolkit provides versions in Fortran (SPICELIB), C (CSPICE) and IDL (icy), and the user can choose any one that suits him/her. The SPICELIB routine FURNSH, CSPICE function furnsh_c, and icy routine cspice_furnsh load a kernel file into the kernel pool as shown below. CALL FURNSH ( 'kernel_name' ) furnsh_c ( ''kernel_name'' ); cspice_furnsh, 'kernel_name' In the case when two or more files contain data overlapping in time for a given object, for binary kernels, the file loaded last takes precedence. If two (or more) text kernels assign value(s) using the '=' operator to identical keywords, the data value(s) associated with the last loaded occurrence of the keyword are used -all earlier values have been replaced with the last loaded value(s).