 
 
MGS HGA Gimbals CK File for Extended Mission
===========================================================================
 
     Created by Boris Semenov, NAIF/JPL, Thu Jan 11 11:13:32 PST 2007
 
 
Orientation Data in the File
--------------------------------------------------------
 
     This file contains orientation and angular rate data for the Mars
     Global Surveyor (MGS) High Gain Antenna (HGA) Elevation and Azimuth
     gimbal frames. The orientation of the 'MGS_HGA_EL_GIMBAL' is given
     with respect to the 'MGS_HGA_HINGE' frame; orientation of the
     'MGS_HGA_AZ_GIMBAL' is given with respect to the 'MGS_HGA_EL_GIMBAL'
     frame.
 
 
Status
--------------------------------------------------------
 
     This file was created by merging daily HGA Gimbal CK files produced by
     the NAIF, JPL. No timing or any other correction was applied to the
     original data during merge process.
 
 
Pedigree
--------------------------------------------------------
 
     The original CK files used to create this file were officially
     delivered to the MGS SPICE Server by NAIF, JPL. These files contained
     orientation of the HGA gimbal frames. The orientation was computed on
     the ground from the HGA gimbal angles extracted from the spacecraft
     engineering telemetry. HGA gimbal angle data sampling rate was once
     every 32 seconds. The individual daily files were merged together to
     provide complete coverage on a mission phase basis.
 
     A table containing the complete list of original CK files from which
     data were included in this file is provided at the end of these
     comments.
 
 
Approximate Time Coverage
--------------------------------------------------------
 
     This file covers the following period of the Extended phase
     of the mission:
 
        COVERAGE BEGIN TIME (UTC):   2006-OCT-11 00:00:59.027
        COVERAGE END TIME (UTC):     2006-NOV-02 23:24:42.660
 
     This file is a type 3 CK file which provides linear interpolation
     between orientation data points extracted from telemetry. Such
     interpolation is not applied to the whole coverage of the file but
     only inside intervals where enough gimbal telemetry data was available
     and data points were close to each other in time for such
     interpolation to make sense.
 
     Given that nominal gimbal telemetry rate was once every 32 seconds the
     duration of the longest interval over which the data may be
     interpolated was set to 300 seconds, i.e. interpolation was enabled
     only over an eight point drop-out. For all requests for the data
     falling between two adjacent data points separated by more than 300
     seconds the SPICELIB CK readers will return a logical flag stating
     "POINTING NOT FOUND".
 
     Tables containing the complete list of valid interpolation intervals
     for the AZ and EL frame data in the file are provided at the end of
     these comments. Since AZ and EL gimbal values were extracted from
     telemetry by two subsequent Telemetry Data System queries, returned
     sets of points for them, and thus resulting coverage intervals, may be
     different.
 
 
Note Regarding Orientation
--------------------------------------------------------
 
     The orientation of the 'MGS_HGA_EL_GIMBAL' is given with respect to
     the 'MGS_HGA_HINGE' frame and was computed from the gimbal geometry
     and telemetered gimbal angles as follows:
 
         --   the ``MGS_HGA_HINGE'' (-94070) frame was rotated by -85
              degrees about +Z axis to align its axes of the with axes of
              the ``MGS_HGA_EL_GIMBAL'' (-94071) frame in EL=0 position
 
         --   then rotation by the EL angle about +Z axis was applied.
 
     The orientation of the 'MGS_HGA_AZ_GIMBAL' is given with respect to
     the 'MGS_HGA_EL_GIMBAL' frame and was computed from the gimbal
     geometry and telemetered gimbal angles as follows:
 
         --   the ``MGS_HGA_EL_GIMBAL'' (-94071) frame was rotated first by
              +90 degrees about +Y and then by +180 degrees about +Z axis
              to align its axes with the axes of the ``MGS_HGA_AZ_GIMBAL''
              (-94072) frame in AZ=0 positions;
 
         --   then rotation by AZ angle about +Z axis was applied.
 
 
Note Regarding Angular Rates
--------------------------------------------------------
 
     Since MGS s/c engineering telemetry doesn't contain angular rate data
     for the gimbals, the angular rates stored in this file were computed
     from the orientation information. The angular rate for each
     orientation point was computed as average of two rates -- constant
     angular rate that would rotate from previous point to that point and
     constant angular rate that would rotate from that point to the next
     point.
 
     Because angular rates stored in two adjacent points in most cases are
     not the same, and CK readers lineraly interpolate between them, the
     output angular rates in general are almost never constant between any
     two adjacent data points stored in the file.
 
 
Usage Note
--------------------------------------------------------
 
     In order to use this file an MGS SCLK file containing coefficients
     mapping MGS on-board time to ET and frame definitions for the MGS
     spacecraft and HGA hinge and gimbal frames must be loaded into a
     user's program.
 
 
Related Kernels
--------------------------------------------------------
 
     This file was created with LSK file naif0008.tls and MGS SCLK file
     MGS_SCLKSCET.00061.tsc.
 
 
Contacts
--------------------------------------------------------
 
     If you have any question regarding this data contact NAIF at JPL:
 
        Charles H. Acton, Jr
        (818)-354-3869
        chuck.acton@jpl.nasa.gov
 
        Boris V. Semenov
        (818)-354-8136
        boris.semenov@jpl.nasa.gov
 
 
Appendix 1: List of the original CK files
--------------------------------------------------------
 
        mgs_hga_ck_2006-10-11.bc
        mgs_hga_ck_2006-10-12.bc
        mgs_hga_ck_2006-10-13.bc
        mgs_hga_ck_2006-10-14.bc
        mgs_hga_ck_2006-10-15.bc
        mgs_hga_ck_2006-10-16.bc
        mgs_hga_ck_2006-10-17.bc
        mgs_hga_ck_2006-10-18.bc
        mgs_hga_ck_2006-10-19.bc
        mgs_hga_ck_2006-10-20.bc
        mgs_hga_ck_2006-10-21.bc
        mgs_hga_ck_2006-10-23.bc
        mgs_hga_ck_2006-10-25.bc
        mgs_hga_ck_2006-10-26.bc
        mgs_hga_ck_2006-10-27.bc
        mgs_hga_ck_2006-10-28.bc
        mgs_hga_ck_2006-10-29.bc
        mgs_hga_ck_2006-10-30.bc
        mgs_hga_ck_2006-10-31.bc
        mgs_hga_ck_2006-11-01.bc
        mgs_hga_ck_2006-11-02.bc
 
 
Appendix 2: Interpolation Intervals for HGA EL and AZ gimbals
--------------------------------------------------------
 
     Table contains start and stop UTC time for each interval as displayed
     by CKBRIEF utility ran with "-dump -utc" options:
 
 
        CKBRIEF Version: 3.2.0, 2006-11-02. SPICE Toolkit Version: N0061.
 
 
        Summary for: mgs_hga_ext26.bc
 
        Segment No.: 1
 
        Object:  -94071
          Interval Begin UTC       Interval End UTC         AV
          ------------------------ ------------------------ ---
          2006-OCT-11 00:00:59.027 2006-OCT-17 15:17:14.921 Y
          2006-OCT-17 15:23:06.921 2006-OCT-18 00:04:10.915 Y

          (many lines were skipped here to reduce the example size)

          2006-NOV-02 21:16:10.661 2006-NOV-02 22:25:30.660 Y
          2006-NOV-02 23:14:02.660 2006-NOV-02 23:24:42.660 Y
 
 
