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. Mars Express C-Kernel Files =========================== The following file describes the contents of the DATA/CK directory of the Mars Express SPICE dataset. Sources of kernels and naming convention: ---------------------------------------- - Kernels that are produced from the ESOC Flight Dynamics attitude products. These kernels are generated by an automated system located at ESAC, and operated by the ESAC SPICE Team. The naming convention for these kernels is the same used in the Attitude products used to create them; their filename start by ATNM. - Kernels with orientation for the spacecraft solar arrays. They are created from the telemetry, by RSSD/ESA. The file name for each of these kernels start by MEX_SA_. - Kernels that represent the movement of the moving parts of an instrument (if the instrument has moving parts). These kernels are produced by the instrument Team, with the support of ESA and NAIF. The naming convention for them is left up to the teams, although the filename shall start by MEX_[INSTRUMENT_NAME], where [INSTRUMENT_NAME] is the name of the instrument. 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 available in this dataset. 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). Mars Express C-kernels contained on this data set ================================================= The following Mars Express C-kernels are provided in this data set (only name portion of the file name is shown; extension of all file names is '.BC'): ATNM_PYYMMDDhhmmss_vvvvv Provides predicted attitude for the Mars Express spacecraft. Run the ckbrief SPICE utility or refer to the label of the kernel to see the full coverage of the file. The starting of the coverage is indicated in the file name (in the field YYMMDDhhmmss). ATNM_RECONSTITUTED_vvvvv Kernel that contains reconstructed attitude for all periods of time where the predicted attitude is deemed not good enough. MEX_SA_YYYY_Vvvvv Provides measured orientation of the spacecraft Solar Arrays. Each file of this type stores the available information for one year of the mission (indicated in the file YYYY of the file name). MEX_ASPERA_SAF_YYMMDD_VV Kernel describing the ASPERA scanner motion from the telemetry. It is provided by the ASPERA Team. 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). Note that several versions of the same kernel can be provided. In that case, the file with the highest version number is the most up to date, and the one that should be used. 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).