PDS_VERSION_ID          = PDS3
RECORD_TYPE             = STREAM

OBJECT                  = TEXT
   INTERCHANGE_FORMAT   = ASCII
   PUBLICATION_DATE     = 2012-08-30
   NOTE                 = "This file describes the files in the
                           extras/mk directory of this volume."
END_OBJECT              = TEXT

END

Meta-kernels for the MESSENGER Mission
======================================

   This directory contains the meta-kernel files (a.k.a "furnsh" files)
   that provide lists of the archived kernels included in this data set
   suitable for loading into a SPICE-based application via the high
   level SPICE data loader routine FURNSH. Using these meta-kernels
   makes it easy to load with one call a comprehensive SPICE data
   collection for a given period. Like the text kernels archived in
   this data set, these meta-kernels are UNIX text files that have
   lines terminated with a line feed character, LF (ASCII 10).

   The names of the meta-kernels provided in this directory follow this
   pattern:

      msgr_YYYY_vVV.tm

   when ``YYYY'' is the year covered by the kernels listed in the file
   and ``VV'' is the file version.

   Multiple versions of a meta-kernel for the same year may exist if
   new kernels were added to the archive in a later release and the
   meta-kernel for that year had to be updated to incorporate them. The
   reasons for adding new kernels include (but are not limited to)
   adding new kinds of kernels, adding new versions of existing kernels
   containing more complete or more accurate data, and adding new
   versions of existing kernels superseding the existing kernels that
   had errors. If more than one meta-kernel file for the same year is
   present, then the file with the latest version number supersedes all
   earlier versions. The latest meta-kernels can be loaded together in
   any order to provide coverage for more than one year. (Note that on
   some environments loading too many kernels at once may slow down
   data access.)

   Although the meta-kernels were created such that on a UNIX
   workstation they can be loaded into a SPICE-based application
   directly from the root directory of the data set -- because the
   PATH_VALUES keyword is set to './data' and '/' is used as the path
   delimiter -- it is recommended that users make local copies of these
   files and update the PATH_VALUES keyword in each of them to point to
   the actual location of the data set's 'data' directory on their
   system. Additional changes including replacing '/' and '\' in all
   path specifications and converting UNIX line terminators to
   terminators native to the user's system may be required to use these
   meta-kernels on non-UNIX workstation.

   The following guidelines were followed to pick and set priority --
   determined by the order in which the kernel files are listed, with
   the latest one taking precedence -- for the kernel files included in
   these meta-kernels:

      -  the latest archived versions of SPK, LSK, PCK, SCLK, IK, and
         FK were included

      -  both the monthly reconstructed and MDIS-exposure spacecraft
         orientation CKs were included with the reconstructed CKs
         taking precedence (listed last) and MDIS-exposure spacecraft
         CKs having lower priority and used when the monthly
         reconstructed CKs do not provide coverage. 

   This directory also includes the MDIS specific meta-kernel,
   mdis_cklist_v02.tm, listing supplemental spacecraft attitude CKs
   covering just MDIS exposures. This meta-kernel, added to the archive
   in Release 4 (April 2009), is obsolete because the CKs listed in it
   were superseded by newer versions and these newer versions are
   listed in the yearly meta-kernels.