GNSS MK files
===========================================================================

   This ``aareadme.txt'' file describes the contents of the kernels/mk
   directory of the GNSS SPICE Kernel Dataset.

   It was last modified on November 23, 2022 by Ricardo Valles Blanco ESAC/ESA.


Brief Summary
------------------------------------------------------------------------

   This directory contains the SPICE Meta-Kernel files for the GNSS
   spacecrafts. Meta-kernels (also known as ``FURNSH kernel'') are used
   to name a collection of kernels that are to be loaded into a user's
   application at run-time. Meta-kernels are appropriate to group kernels
   that correspond to a certain study group, phase or kernel state of the
   mission.


File naming conventions
------------------------------------------------------------------------

   Naming Scheme for GNSS spacecrafts MKs:

     The naming scheme for the GNSS spacecrafts MKs is:

          gnss[_DESC][_vXXX][_TAG][_NNN].tm

     where

           DESC      a brief description of the scope of study of the
                     scenario (optional);

           vXXX      version number that corresponds to the version of the
                     meta-kernel or the SPICE Kernel Dataset release number
                     (optional; e.g. v121 for Release 1.2.1)

           TAG       a time tag of the MK generation time (optional;
                     e.g. 20160928);

           NNN       a count of the MK version generated for a given TAG
                     (mandatory if TAG is included; e.g 001)



Other directory contents
------------------------------------------------------------------------

     aareadme.txt         This file.

     former_versions      Directory where versions no longer valid are
                          stored for archive purposes.


Particulars
------------------------------------------------------------------------

   Meta-Kernel file management is a critical element of any SPICE dataset.
   For ESA Planetary Missions the Meta-Kernels of the operational SPICE
   repositories are also used to control the version of the SPICE dataset.

   In general missions in operations will have an "operational" Meta-Kernel.
   This MK will contain the latest SPICE kernels available for the mission
   including those kernels generated by the operational pipeline in a
   periodical basis (namely SPK files).

   Since the periodicity of this updates ranges from hours to weeks, the MK
   in the Meta-Kernel directory does not have a version number and is
   regularly overwritten. Nevertheless in order to keep traceability and
   backwards compatibility with former MKs, a duplicate of every generated
   operational MK is stored. This duplicated MK filename is appended with a
   time tag and a version; if the original MK looks like:

     ftp/data/SPICE/GNSS/kernels/mk/gnss_ops.tm

   the following duplicate is generated:

     ftp/data/SPICE/GNSS/kernels/mk/gnss_ops_v111_20220928_001.tm

   For what concerns dataset version kernels, they are generated when a new
   version of the kernel dataset is released. In parallel a new operational
   version is made available.

   New kernel datasets are typically released when new text kernels are
   added, updated or modified, when there is a change in the directory
   structure, etc. Superseded version kernels are moved to the
   'former_versions' directory.


Kernel File Details
------------------------------------------------------------------------

    Name                         Comments
    ---------------------------------------------------------------------

    gnss_ops.tm                  Contains the latest available historic data
                                 kernels generated by the ESA SPICE Service.

    gnss_ops_vXXX_YYYYMMDD_NNN.tm

                                 Is a duplicate of the study MK that
                                 derived from release vXXX. If multiple
                                 study MK files are generated on the
                                 same date the version NNN is increased
                                 starting from 001. Read the
                                 ``Particulars'' section for more
                                 information.


Contact Information
------------------------------------------------------------------------

   If you have any questions regarding this file contact the
   ESA SPICE Service (ESS) at ESAC:

           Alfredo Escalante Lopez
           (+34) 91-8131-429
           spice@sciops.esa.int


References and required readings
------------------------------------------------------------------------

     1. ``Kernel Required Reading'', NAIF Document


End of aareadme file.