PDS_VERSION_ID                = PDS3
RECORD_TYPE                   = STREAM
OBJECT                        = TEXT
  NOTE                        = "Comments on the Viking Orbiter 
                                 SPICE Archive"
  PUBLICATION_DATE            = 2008-12-03
END_OBJECT                    = TEXT
END


COMMENTS ON THE VIKING ORBITER SPICE DATA ARCHIVE
=================================================

   This document contains comments and errata concerning the Viking 
   Orbiter SPICE Data Archive.


1. Text Kernel File Format
--------------------------

   All SPICE text kernel files (LSK, PCK, SCLK, IK, FK) provided in
   this data set have lines terminated by only <LF> (UNIX convention.)
   This is dictated by NAIF's archiving approach to include a
   consistent set of UNIX binary (IEEE architecture) and text (<LF>
   only for end of line marker) kernels on the archive volumes.

   However, the format of the text kernels is specified in their
   associated labels as ASCII (INTERCHANGE_FORMAT = ASCII.) This is a
   violation of the PDS standard stating that lines in ASCII files must
   be delimited by the combination of <CR><LF>. This line termination
   treatment is standard practice for SPICE data sets in the PDS.


2. Use of SPACECRAFT_NAME in the Labels
---------------------------------------

   PDS labels for SPICE kernels provided in this data set contain the
   deprecated keyword SPACECRAFT_NAME instead of the keyword
   INSTRUMENT_HOST_NAME. This is standard practice for SPICE data sets
   in the PDS and is dictated by NAIF's archiving approach to make
   SPICE archives for more recent missions consistent with SPICE
   archives for older missions, for which use of SPACECRAFT_NAME was
   legitimate.


3. Values of INSTRUMENT_NAME in the Labels
------------------------------------------

   PDS labels for SPICE kernels provided in this data do not set the
   keyword INSTRUMENT_NAME to "SPICE KERNELS", that is the name of the
   instrument described by the instrument catalog file SPICE_INST.CAT
   provided in the data set. Instead this keyword is set to either
   "N/A" or the name(s) of the instrument(s) or structure(s), the
   geometric parameters of which a particular kernel file provides.
   While this error does prevent the individual data products from
   being associated with the "SPICE KERNELS" instrument, it does not
   affect usability of the SPICE data provided in this data set in any
   way because the SPICE Toolkit does not use any information from the
   PDS label to access the data.

   The other side of this error is that the data set does not include
   instrument catalog files for the following instruments named in
   the INSTRUMENT_NAME keyword in the PDS labels:

      "SCAN PLATFORM"
      "VISUAL IMAGING SUBSYSTEM - CAMERA A"
      "VISUAL IMAGING SUBSYSTEM - CAMERA B"



4. Missing FILE_RECORDS Keyword in the Binary Kernel Labels
-----------------------------------------------------------

   All labels for binary SPICE kernels provided in this data set are
   missing the FILE_RECORDS keyword, which is required because these
   labels have the RECORD_TYPE keyword set to FIXED_LENGTH. While this
   error violates the PDS standards, it does not affect usability of
   the SPICE data provided in this data set in any way because the
   SPICE Toolkit does not use any information from the PDS labels to
   access the data.


5. Unrecognized MISSION_PHASE Name Values
-----------------------------------------

   The MISSION_PHASE_NAME value "PRE ORBITAL SCIENCE" used in some
   labels is not defined in the ``mission.cat''. Despite that
   this value is kept in the labels because it is used in the 
   MISSION_PHASE_NAME field in the VO image catalog.


6. Limited Applicability of This Data Set
-----------------------------------------

   Because much of the data included in this data set -- spacecraft
   orientation CKs, some SPKs and EKs -- was derived from the geometry
   information associated with the imaging experiment this data set
   does not provide sufficient data to compute geometry for other VO
   experiments (IRTM and MAWD). Kernels needed to support geometry
   computations for other experiments may be created and added to the
   data set in a later release if time and resources permit.


7. Absence of Kernels for Approach Phase
----------------------------------------

   This data set does not include kernels for the approach phase.
   Such kernels may be created and added to the data set in a later
   release if time and resources permit.


8. Incomplete FK Files
-----------------------

   The FKs provided in the data set lack most of the descriptive
   information expected in FK files as well as actual alignment data in
   the frame definitions for the non-imaging experiments. New versions
   of FKs including this information may be created and added to the
   data set in a later release if time and resources permit.