Data Set Overview
      =================
   
      This data set includes the complete set of Mars Global Surveyor
      SPICE data files (``kernel files''), which can be accessed using
      SPICE software. The SPICE data contains geometric and other
      ancillary information needed to recover the full value of science
      instrument data. In particular SPICE kernels provide spacecraft
      and planetary ephemerides, instrument mounting alignments,
      spacecraft orientation, spacecraft sequences of events, and data
      needed for relevant time conversions.
      
      This data set is contained on a single virtual volume, MGSP_1000,
      including data from all mission phases and covering from 
      launch, 1996-11-06T08:00:00, through the end time of the latest 
      spacecraft trajectory file supplied in the data set. Until the 
      end of the spacecraft lifespan this data set is accumulating with 
      new data added approximately every three to six months.
      
      Initially this data set was released on multiple volumes,
      each containing the complete set of SPICE kernels for two
      or more mission phases, a single mission phase or a portion
      of a mission phase.  During the transition to the PDS on-line
      distribution system at the end of 2002 the data from all volumes
      were segregated on a single volume, MGSP_1000. The coverages
      of the original volumes are summarized in the table:

      
              VOLUME ID      START TIME           STOP TIME
              ---------  -------------------  -------------------
              MGSP_0001  1996-11-06T08:00:00  1998-05-28T00:00:00
              MGSP_0002  1998-05-28T00:00:00  1999-03-09T00:00:00
              MGSP_0003  1999-03-09T01:00:00  1999-06-02T00:00:00
              MGSP_0004  1999-06-02T00:00:00  1999-08-25T00:00:00
              MGSP_0005  1999-08-25T00:00:00  1999-11-17T00:00:00
              MGSP_0006  1999-11-17T00:00:00  2000-02-09T00:00:00
              MGSP_0007  2000-02-09T00:00:00  2000-05-03T00:00:00
              MGSP_0008  2000-05-03T00:00:00  2000-07-26T00:00:00
              MGSP_0009  2000-07-26T00:00:00  2000-10-18T00:00:00
              MGSP_0010  2000-10-18T00:00:00  2001-02-01T00:00:00


      Data Types (SPICE kernel types)
      ===============================
   
      SPK kernels contain ephemerides for spacecraft, planets,
      satellites, comets and asteroids as well as for moving or
      fixed spacecraft and instrument structures. They provide
      position and velocity, given in a Cartesian reference frame.
      SPK files are located under the ``data/spk'' directory of this
      data set.
      
      PCK kernels contain certain physical, dynamical and
      cartographic constants for target bodies, such as size and shape
      specifications, and orientation of the spin axis and prime
      meridian. PCK files are located under the ``data/pck'' directory
      of this data set.

      IK kernels (Instrument description kernels) give descriptive and
      operational data peculiar to a particular scientific instrument,
      such as internal timing relative to the spacecraft clock and
      field-of-view model parameters. IK files are located under the
      ``data/ik'' directory of this data set.

      CK kernels describe pointing, containing a transformation
      traditionally called the C-matrix which is used to determine
      time-tagged pointing (orientation) angles for a spacecraft
      structure upon which science instruments are mounted. CK files
      are located under the ``data/ck'' directory of this data set.

      EK (Events) kernels are derived from the integrated sequence of
      events used to produce actual spacecraft commands. EK files are
      located under the ``data/ek'' directory of this data set.

      LSK (Leapseconds) kernels contain the leapseconds and the values
      of other constants required to perform a transformation between
      Universal Time Coordinated (UTC) and Ephemeris time (ET). LSK
      files are located under the ``data/lsk'' directory of this data set.

      SCLK (Spacecraft Clock) kernels contain on-board clock
      calibration data required to perform a mapping between Ephemeris
      time (ET) and spacecraft on-board time (SCLK.) SCLK files are
      located under the ``data/sclk'' directory of this data set.

      FK (Frame Definitions) kernels contain information required to
      define reference frames, sources of frame orientation data and
      inter-connections between these frames and other frames supported
      within the SPICE system. This includes mounting alignment
      information for each instrument. FK files are located under
      the ``data/fk'' directory of this data set.

            
      Kernel File Details
      ===================
      
      A brief overview of the different types of MGS kernels included
      in this data set is provided in the CONFIDENCE_LEVEL_NOTE section
      of this file while details specific to individual files are found
      in the ``*info.txt'' files in the corresponding data directory.
      The most detailed description of the data in each file is
      provided in metadata included inside the file -- in the
      description area of text kernels or in the comment area of binary
      kernels.
   
   
      Software
      ========
   
      The SPICE Toolkit contains software modules needed to read
      SPICE kernel files. SPICELIB software is highly documented
      via internal headers. Additional documentation is available
      in separate ASCII text files called Required Reading files.
      For example, the S- and P- Kernel (SPK) Required Reading File,
      named SPK.REQ, describes use of the SPK kernel file readers
      and contains sample programs.
      
      The latest SPICE Toolkit for a variety of computer platforms such
      as PC, Mac, SUN, etc. is available at the NAIF Node of PDS
      electronically (via anonymous FTP and WWW servers). Refer to
      information in ``software/softinfo.txt'' for details regarding
      obtaining this software. Each version of the Toolkit is also
      archived at the NASA National Space Science Data Center.
   

      Loading Kernel Files into a SPICE-based Application
      ===================================================
 
      The easiest way to make data from a collection of SPICE kernels
      available to a SPICE-based application is to list these kernels
      in a meta-kernel and load it into the program using the high
      level SPICE data loader routine FURNSH. This data set provides
      such meta-kernel(s) under the ``extras/mk'' directory. For more
      information about the MGS meta-kernel(s), see the file
      ``extras/mk/mkinfo.txt''.

This data set contains SPICE kernel files created during mission
      operations and after mission data reconstruction and analysis.
      Some general information about this collection follows here, but
      the prospective user is also referred to extensive descriptions
      about each file that are stored inside each kernel file. These
      metadata provide detailed information regarding the information
      source from which the data were derived, the type of processing
      applied to the source data, applicability of the data, etc.
      Metadata are located in the ``comment area'' for binary kernel
      types (SPK, CK, ESQ), accessible using either the COMMNT or
      SPACIT utility program found in the NAIF Toolkit. Metadata are
      located after ``\begintext'' markers within the text kernel types
      (PCK, IK, FK, LSK, SCLK, MK), accessible by using any available
      text file display tool such as a word processor, text editor, or
      the unix ``more'' or ``cat'' commands.
      
      Where there are questions about data accuracy or ``confidence''
      not addressed herein the reader is invited to contact the NAIF
      node of the Planetary Data System for possible further
      information.
      
      
      SPK Files
      =========
      
      Three kinds of SPK files are provided in this archive: SPK files
      for the spacecraft orbit (reconstructed and nominal post-mission
      trajectory), SPK files for Phobos, Deimos, Mars, Earth and Sun,
      and SPK files for the solar array and high gain antenna
      structures and the locations of the MAG/ER instrument components
      on the solar arrays. Each of these kinds is briefly described
      below; more information is available in the file
      ``data/spk/spkinfo.txt''.
      
      Spacecraft Orbit SPK Files
      --------------------------
      
      Most of the included SPK files provide the orbit of the MGS
      spacecraft. Most missions had a single source for this kind of
      data, but for MGS there were three sources: the Mars Surveyor
      Operations Project (MSOP) Navigation Team (NAV), the Mars Orbiter
      Laser Altimeter (MOLA) Team based at the Goddard Space Flight
      Center (GSFC), and the Inner Planet Navigation and Gravity Group
      (IPNG) based at JPL. The MOLA and IPNG groups produced multiple
      solutions for some of the mission phases, presumably yielding
      ever more accurate results as the gravity model used and other
      data handling improvements come into play. It is possible that
      any or all of these three groups will produce yet more--and
      presumably further improved--solutions in the future; these
      should eventually be available from NAIF.
      
      For all three solution sets, each archival SPK file covering
      a particular mission phase was made by merging together numerous
      shorter duration individual files. The component files used
      to make a merged product can be discerned by reading the
      descriptive information (metadata) found in the comment area
      of each file.
            
      The subset of SPKs to be used in a particular application should
      be picked from the archived set considering these factors:
      
         1) Completeness of coverage:  are there gaps in the orbit  
            data, or missing mission phases?
            
         2) Discontinuities:  are position and velocity data continuous 
            across individual orbit data fits comprising the merged 
            product? More particularly, how large are these 
            discontinuities?
            
         3) What kinds of data were used in producing the orbit 
            solutions?  (In all cases, doppler and range data were 
            used. For the MOLA/GSFC solutions, laser range points were 
            also used.)
            
         4) What models were used (particularly what Mars gravity 
            model) and how might this affect the orbit solution?

      Based on these factors NAIF recommends that, unless there are
      special circumstances, the MGS NAV SPKs providing the most
      complete coverage and the latest SPKs produced by IPNG (version
      MGS95J) providing the most accurate solution are used together.
      The two sets of files should be loaded in such way that the IPNG
      MGS95J SPKs have higher priority (loaded last) and provide data
      for all interval that they cover while the MGS NAV SPKs have
      lower priority (loaded first) and provide coverage during the
      gaps in the IPNG MGS95J set.
      
      This data set also includes the orbit number files generated
      during the mission using the NAIF's ORBNUM utility program for
      each of the NAV spacecraft trajectory SPK files for the orbital
      phases of the mission. These files are not SPICE kernels; for
      this reason they are provided in the ``extras/orbnum'' directory.
      For more information about the MGS orbit number files, see the
      file ``extras/orbnum/orbinfo.txt''.

      Post-mission Nominal Spacecraft Orbit SPK
      -----------------------------------------
 
      This data set also includes the post-mission nominal trajectory
      SPK file provided by the MGS NAV team and covering 50 years into
      the future starting at the end of the mission. Since this file
      provides an extremely long term prediction it should only be used
      to get a rough idea where the MGS orbit plane might be years
      after the end of the mission.
      
      Solar System Body SPK Files
      ---------------------------
      
      The MAR033 Martian satellite ephemeris SPK files provided in this
      data set were used by the project up to the fall of 2006. They
      contain ephemeris data for Phobos, Deimos, Earth and the sun.
      Formal one-sigma accuracy information for Phobos and Deimos are
      reported as follows:

         Body         Downtrack      Crosstrack      Radial
                     Uncertainty     Uncertainty   Uncertainty
         ------      -----------     -----------   -----------
         Phobos         15 km           7 km          3 km
         Deimos         30 km          16 km          3 km

      The MAR063 Martian satellite ephemeris SPK file provided in this
      data set superseded the MAR033 files and was used by the project
      starting in the fall of 2006. As the MAR033 files the MAR063 SPK
      contain ephemeris data for Phobos, Deimos, Earth and the sun.
      Formal one-sigma accuracy information for Phobos and Deimos are
      reported as follows:

         Body         Downtrack      Crosstrack      Radial
                     Uncertainty     Uncertainty   Uncertainty
         ------      -----------     -----------   -----------
         Phobos          5 km           2 km          2 km
         Deimos         10 km           3 km          3 km

      Accuracies for Mars-Sun and Mars-Earth directions (positions
      obtained from SPK files) are at the level of 0.001 arc-sec (1
      sigma).
      
      Spacecraft Solar Array, High Gain Antenna and MAG/ER SPK Files
      --------------------------------------------------------------
      
      Included in the SPK archive are two files containing location
      information (fixed offsets) for spacecraft structures--the
      high gain antenna and the Magnetometer instrument components
      mounted on solar arrays. See the metadata for each of these
      files--found in the comment area--for detailed descriptions
      of how the files were produced.
      
      
      CK Files
      ========
      
      Three kinds of C-kernel files are provided in this archive: the
      spacecraft bus orientation CKs (reconstructed and nominal
      orientation for ROTO observations), the solar arrays orientation
      CKs (reconstructed only) and the high gain antenna orientation CKs
      (reconstructed only). Each of these kinds is briefly described
      below; more information is available in the file
      ``data/ck/ckinfo.txt''.

      All three kinds of reconstructed CK files are produced from
      engineering telemetry downlinked from the spacecraft while the
      ROTO CK file was produced from the commanded attitude for each of
      the ROTO observations. As is often the case with spacecraft
      engineering telemetry-based measurements, considerable
      uncertainty exists as to the accuracy of such measurements, and,
      data quality (accuracy and completeness) can vary significantly.
      
      Spacecraft Bus CK Files
      -----------------------
      
      CK files providing the orientation of the spacecraft bus (``the
      spacecraft'') can be used to support interpretation of data
      obtained by all science experiments. The stated requirement on
      spacecraft orientation knowledge is better than three mrad per
      axis, 3-sigma. It has been informally reported that the achieved
      orientation knowledge is significantly better than this, but at
      the time of this archive production there are no known reports
      substantiating this or providing further details.
      
      Processing of the Mars Orbiter Laser Altimeter (MOLA) data by the
      MOLA Team at GSFC led to a determination that the spacecraft
      clock time tags assigned to the downlinked spacecraft orientation
      quaternions that comprise these CK files had a time bias. This
      assessment was verified by the Lockheed Martin Astronautics (LMA)
      spacecraft control team, although firm determination of the
      magnitude has been illusive. The situation was further
      complicated by knowledge that on-board AACS software filter
      settings that resulted in this timing bias varied during the
      mission. The magnitude of this bias has been estimated in the
      range of 1 to nearly 2.5 seconds. 

      Based on this analysis a constant timing correction was applied
      to the time tags of the attitude data points stored in
      the CK files. The correction value used in creating the
      spacecraft bus CK files was set to -1.15 seconds for the data before
      1999-02-26T11:45, switched between -1.15 and -2.3 seconds for the
      data between 1999-02-26 and 1999-03-31, and was set to -2.3
      seconds for the data after 1999-03-31. The internal comments in
      each of the CK files specifically state which value(s) was(were)
      used for the data in the file.

      Unfortunately the MOLA team later concluded that applying the
      larger offset (-2.3 seconds) to the Mapping, Extended and
      Extended-Extended mission attitude time tags might have been a
      mistake and that the smaller value (-1.15 seconds) should have
      been used instead. They suggested that to compensate for the
      ``over-corrected'' timing of the CK data a half of the -2.3
      second offset should be ``taken back'' during reading of the CK
      files by subtracting -1.15 seconds from the CK pointing request
      time. This small diagram illustrates how the MOLA team
      compensated this in their instrument processing software:
 
          CK request time at          ``true''
           which correct s/c         observation
         orientation is stored         time
               |                         |
               | <...................... |
               |    1.15 seconds must    |
               |   be subtracted to get  |
               |    correct orientation  |
               |                         |
               |                         V
               V   ............................................
                 .        2.3 seconds were subtracted           .
                .       by the ground s/w making CK files        .
               V                                                  .
               @                         @ ......................> @
               ^                         ^    1.15 seconds were    ^
               |                         |   added by AACS filter  |
               |                         |                         |
               |                         |                         |
            time tag            ``true'' time for              time tag
           in CK file           which s/c orientation         in s/c TLM
                                 was determined

      Other than computing the spacecraft attitude at the observation
      time minus 1.15 seconds as the diagram suggests, the offset can
      be also ``taken out'' by processing each of the Mapping, Extended
      and Extended-Extended mission spacecraft CK files through the
      CKSMRG program with the ``-C'' argument set to +1.15 seconds.
      
      Nominal ROTO Orientation Spacecraft Bus CK Files
      ------------------------------------------------

      This data set also includes CK files providing predict
      orientation for the spacecraft bus for ``ROTO'' observations
      during Extended and Extended-Extended phases of the mission.
      These files should be used only for the times when reconstructed
      orientation is not available.

      Solar Array CK Files
      --------------------
      
      CK files providing orientation of the solar arrays relative
      to the spacecraft bus are included to support interpretation
      of data collected by the MAG/ER instruments mounted on these
      arrays. The situation is complicated somewhat due to the
      non-complete deployment of one of the two arrays. There is no
      currently known mechanism for estimating the accuracy of the
      solar array CK files; however it is assumed that they nevertheless
      satisfy the requirements of the MAG/ER experiment.

      The first version of the solar array CKs for Cruise, Aerobraking
      1, Science Phasing 1, and Science Phasing 2 mission phases,
      released in 1998, contained incorrect angular rate data resulted
      from the bug in the process that generated daily solar array CKs
      during operations. This was discovered in 2005 and version 2 of
      these files with corrected angular rate data was added to the
      data set. Pointing data was correct and is the same in both
      versions.
      
      High Gain Antenna CK Files
      --------------------------
      
      CK files providing orientation of the high gain antenna (HGA)
      relative to the spacecraft bus are included to support the
      Radio Science experiment. They may also be used to help with
      calibration or data processing for the MAG/ER experiment.
      There is no currently known mechanism for estimating the
      accuracy of the HGA CK files. (It may be possible that the
      Radio Science experiment will later yield some assessment of
      this accuracy.)
      
      Caution on Using CK Files
      -------------------------
      
      While not a data accuracy issue, the CK user is nevertheless
      cautioned to understand and properly use the data found and
      tolerance arguments that are inputs to the CK reader provided
      in the SPICE Toolkit. Descriptions about how to read CK files
      are found in the CK reader routine headers (top of the source
      code files) and in the ``CK Required Reading'' document; these
      are contained in each SPICE Toolkit package.
      
      
      PCK Files
      =========
      
      PCK files provide size, shape and orientation data for ``target''
      bodies such as Mars, Phobos and Deimos. A description of these
      data items and reference to their source is provided inside
      the PCK file, which is a simple text file that can be viewed
      using any word processor, text editor or text display utility.
      
      Of the three PCK files provided in this data set, the first PCK
      file ``pck00006.tpc'' is based on the official IAU/IAG/COSPAR
      values accepted in 1994. This file has been distributed and used
      during pre-mapping and mapping phases of the mission. The data in
      the file is generally rather old and in any case certainly do
      not reflect any new parameter determinations achieved as a result
      of science instrument data processing for the MGS mission.

      The second PCK file ``mars_iau2000_v0.tpc'' is based on the
      IAU/IAG/COSPAR values accepted in 2000. It contains constants only
      for Mars and Martian satellites. Many of these constants have
      been determined as the result of the MGS science data processing.

      The third PCK file ``pck00009.tpc'' is based on the
      IAU/IAG/COSPAR values accepted in 2006. It contains constants for
      for Mars and Martian satellites as well as for other Solar System
      planets and satellites. The Mars and Martian satellites constants
      provided in the PCK file are the same those in the second PCK
      file ``mars_iau2000_v0.tpc''.

      More information about the PCK files included in this data set is
      available in the file ``data/pck/pckinfo.txt''.
      

      FK Files
      ========
      
      Frames kernel files provide specifications for how one reference
      frame is defined relative to another frame. In one case--that
      of fixed offset frames such as used for defining the mounting
      alignment of each antenna relative to the spacecraft--the FK
      file contains the actual parameter values. Metadata describing
      these mounting alignment estimates are provided in the one FK
      file included in this archive. There are no (known) accuracy
      estimates for these data at the time of this archive preparation.

      Historically the frame definitions for MGS were not provided in a
      single FK file as they were for many other missions. Instead some
      of the frames were defined in the SCLK files, others -- in the IK
      files, and yet more frames were defined in the HGA FK file. At
      the end of of the mission all of the frame definitions were
      collected in a single FK file included in this data set along
      with the older HGA FK file. More information about the MGS FK
      files is available in the file ``data/fk/fkinfo.txt''.
      
      
      IK Files
      ========
      
      Instrument kernel files provide specifications for the mounting
      alignment and--where applicable--field-of-view size, shape
      and orientation for the named instrument. Metadata describing
      these estimates are provided in each IK file included in this
      archive. Parameter values were determined from pre-launch
      measurements or from manufacturing blueprints. (An update for
      the MOLA alignment using in-flight measurements is expected
      later in the mission.) There are no (known) accuracy estimates
      for these data at the time of this archive preparation.

      Although this data set includes an IK file(s) for each of the MGS
      instruments -- MAG/ER, MHSA, MOC, MOLA, and TES, -- not all of
      them are equally well developed. On one side of the ``spectrum''
      are the latest MOC and MOLA IK files containing the most up to
      date geometric calibration data, FOV definitions, etc. while on
      the other side is the TES IK still providing bare minimum of
      information based on the pre-launch measurements (a better TES IK
      may be added to the data set at a later date.) Because of that
      users are encouraged to carefully examine the IKs before using
      them. More information about MGS FK files is available in the
      file ``data/ik/ikinfo.txt''.
      
      
      SCLK Files
      ==========
      
      Spacecraft Clock kernel files provide a tabulation of data
      needed for converting time measurements between ephemeris time
      (ET) and spacecraft clock time (SCLK). A SPICE SCLK file is
      made from a similar file--SCLK/SCET file, or SCLKvSCET
      file--produced by another mission entity. Each newly made SCLK
      file fully replaces the previous SCLK file.
      
      For MGS the time correlation accuracy provided in SCLK/SCET
      files is informally reported by the Lockheed Martin spacecraft
      team to be better than 100 milliseconds during cruise and
      better than 10 milliseconds during orbital phases. (NAIF has
      not attempted to obtain or produce an independent corroboration
      of these LMA estimates.) The SPICE SCLK file has essentially
      the same accuracy as the SCLK/SCET file.
      
      SPICE software does not prohibit an SCLK file from being used
      for time conversions occurring for ``future times'' (or more
      accurately, for epochs that occur later than the epoch of the
      last telemetry data used in producing the last correlation
      coefficients found in the SCLK file). Such ``predict'' time
      conversions are likely to be inaccurate (changed somewhat)
      once the epoch of interest has been passed.
      
      More information about the MGS SCLK files is available in the file
      ``data/sclk/sclkinfo.txt''.

      
      LSK Files
      =========
      
      Leapseconds kernel files provide a tabulation of ``leapseconds''
      and some other terms used in converting time measurements
      between ephemeris time (ET) and Universal Time (UTC). ``Spacecraft
      Event Time'' (SCET) is the commonly used name for UTC events
      measured at the spacecraft.
      
      Metadata describing how the LSK data are obtained or computed
      is contained inside the LSK text file. The time conversion
      provided by SPICE LSK files is accurate to approximately
      0.000030 seconds.

      More information about the LSK files is available in the file
      ``data/lsk/lskinfo.txt''.
      
      
      EK Files
      ========
      
      Two kinds of Events kernel (EK) files are included in this
      archive: Experimenter's Notebook EKs and Sequence EKs.  Each of
      these kinds is briefly described below; more information is
      available in the file ``data/ek/ekinfo.txt''.
      
      Experimenter's Notebook EKs kernels are a digital analog to
      the traditional paper laboratory notebook. Hence Experimenter's
      Notebook entries represent truth only as seen by the author
      of the notes--there is no attempt made to independently validate
      any aspect of Experimenter's Notebook information.
      
      Sequence EKs comprise a summary of all commands sent to the
      spacecraft as well as some ground system events and instrument
      state (status) summaries. All Sequence EK entries are time
      tagged. In this archive includes Sequence EKs created the
      automated process for providing ``as run'' inputs reflecting
      what was actually sent to the spacecraft, and what execution
      times were used, was not yet implemented for the in-orbit
      mission phases. The cruise ESQ was produced from a cruise
      phase Predicted Events File (PEF) that was hand edited to
      reflect ``as run'' status. Consequently the validity of this
      ESQ is uncertain, but there is some reason to imagine that
      the handwork was well done.