Galileo Magnetometer Pre-Jupiter Calibrated Bundle
    Galileo Solar System Magnetometer Averaged Cruise RTN Coordinates
    Calibrated Data Collection

    PDS3 DATA_SET_ID               = GO-SS-MAG-4-SUMM-CRUISE-RTN-V1.0
    PDS3 DATA_SET_NAME             =
                   GALILEO MAGNETOMETER CRUISE DATA (RTN COORDINATES)
    START_TIME                     = 1989-12-31T00:14:12.369
    STOP_TIME                      = 1994-12-31T03:58:41.145
    PDS3 DATA_SET_RELEASE_DATE     = 1996-06-01
    PRODUCER_FULL_NAME             = MARGARET G. KIVELSON
    
    References: 
                 
    Kivelson, M.G., Khurana, K.K.,
    Russell, C.T., Walker, R.J., Joy, S.P.,Green, J., Aiken, W.C.
    GALILEO MAGNETOMETER CRUISE DATA (RTN COORDINATES),
    GO-SS-MAG-4-SUMM-CRUISE-RTN-V1.0, NASA Planetary Data
    System, 1996"

    Collection Data Overview
    ================
    This collection contains data acquired by the Galileo Magnetometer
    during the Interplanetary Cruise to Jupiter. The data are at varying
    resolution depending on the averaging constant applied by the
    instrument. These data have been fully processed to remove instrument
    response function characteristics. The data are provided in physical
    units (nanoTesla) and in 2 coordinate systems. This set of data files
    contains data in Inertial Rotor Coordinates (IRC= despun spacecraft).
    These files contain some of the data processing parameters from the
    AACS system as well as the sensor zero level for the spin aligned
    sensor. The data are also being archived in RTN coordinates which are
    provided on a separate collection. Trajectory have been
    provided in heliographic coordinates as a separate collection.

    In order to provide a more complete solar wind collection the high
    resolution magnetometer data from the Earth1 encounter, Earth2
    encounter and Ida encounter was averaged down to 16 minute resolution
    and included with this interplanetary cruise data. The 16 minute
    averages are derived from the following collections:

    urn:nasa:pds:galileo-mag-prejup-calibrated:data-earth1-rdr-high-res
    urn:nasa:pds:galileo-mag-prejup-calibrated:data-earth2-rdr-high-res

    Data inside the earth's bowshock was excluded from the 16 min
    averages.


    Data Columns (IRC):

    sc_clk   S/C clock counter given in the form rim:mod91:mod10:mod8
    time     S/C event time (UT) given in the form yyymmddT<time>Z
    Br       Magnetic field Radial component in RTN coordinates <nT>
    Bt       Magnetic field tangential component in RTN coordinates <nT>
    Bn       Magnetic field normal component in RTN coordinates <nT>
    Bmag     |B| Magnitude of B <nT>
    R        Radial distance from the Sun[AU]
    LAT      Solar Latitude (deg)
    LON      Solar Longitude (deg)
    avg_con  averaging interval (Rims)
    delta    Delta
    lambda   Lambda


  Data Acquisition
  ================
    The data for this collection were acquired as part of the normal
    instrument calibration activities associated with the cruise to
    Jupiter. As such, the instrument was commonly configured in modes
    which required calibration even though they may not have been the
    optimal mode for science data acquisition. The Galileo magnetometer
    has 8 possible acquisition configurations (modes). There are two
    sensor triads mounted 7 and 11 meters from the rotor spin axis
    (inboard and outboard) along the boom. Each of the sensor triads has
    two gain states (high and low). In addition, the sensor triads can be
    'flipped' to move the spacecraft spin-axis aligned sensor into the
    spin plane and visa versa. Please see the instrument description for
    full details on the instrument, sensors, and geometries. The
    combinations of sensor, gain state, and flip direction form modes.

   _____________________________________________________________________
                             Mode Characteristics
   _____________________________________________________________________
            Mode Name            Acronym         range      quantization
   _____________________________________________________________________
   Inboard,  left,  high range*    ILHR      +/- 16384 nT       8.0   nT
   Inboard,  right, high range*    IRHR      +/- 16384 nT       8.0   nT
   Inboard,  left,  low  range*    ILLR      +/-   512 nT       0.25  nT
   Inboard,  right, low  range*    IRLR      +/-   512 nT       0.25  nT
   Outboard, left,  high range*    ULHR      +/-   512 nT       0.25  nT
   Outboard, right, high range*    URHR      +/-   512 nT       0.25  nT
   Outboard, left,  low  range*    ULLR      +/-    32 nT       0.008 nT
   Outboard, right, low  range*    URLR      +/-    32 nT       0.008 nT


                 __________________________________________
                   s/c clock         date/time          mode
                  __________________________________________
                   00104651:00:0    89-353/20:53        ULLR
                   00120107:00:0    89-364/17:21        URHR
                   00120117:00:0    89-364/17:31        IRHR
                   00120150:00:0    89-364/18:04        IRLR
                   00120178:00:0    89-364/18:33        ILLR
                   00120199:00:0    89-364/18:54        ILHR
                   00120209:00:0    89-364/19:04        URHR
                   00120231:00:0    89-364/19:26        URLR
                   00120283:00:0    89-364/20:19        ULLR
                   00120313:00:0    89-364/20:49        ULHR

                   00120492:00:0    89-363/23:50        ULHR

                   00572976:00:0    90-040/03:00        ULHR
                   00572976:00:0    90-316/17:00        ULLR
                   00578673:00:0    90-320/17:00        URLR
                   00586204:00:0    90-325/23:55        URHR
                   00592915:00:0    90-330/17:01        ILLR
                   00597439:00:0    90-333/21:15        IRLR
                   00610156:00:0    90-342/19:33        IRHR
                   00610509:00:0    90-343/01:30        IRLR
                   00615701:00:0    90-346/17:00        URLR
                   00618550:00:0    90-348/17:00        URHR
                   00624261:00:0    90-352/17:15        ULHR

                   01003052:72:8    90-253/16:36        ULLR
                   01600269:00:0    92-308/00:48        ULLR
                   01605562:00:0    92-311/18:10        ILLR
                   01629549:00:0    92-328/14:14        IRLR
                   01632087:00:0    92-330/09:00        ULLR
                   01635479:00:0    92-332/18:23        URHR
                   01638675:00:0    92-335/00:01        URLR
                   01639786:00:0    92-335/18:45        IRLR
                   01639974:00:0    92-335/21:55        URLR
                   01640958:00:0    92-336/14:30        IRLR
                   01641285:00:0    92-336/20:40        URHR
                   01641351:00:0    92-336/21:07        IRHR
                   01641407:00:0    92-336/22:15        ILHR
                   01641465:00:0    92-336/23:02        URLR
                   01642481:00:0    92-337/16:22        ULHR
                   01644143:00:0    92-338/20:10        IRLR
                   01646048:00:0    92-340/04:16        ILLR
                   01649533:00:0    92-342/15:00        ULLR
                   01650524:00:0    92-343/07:42        ULHR
                   01650907:00:0    92-343/14:09        ILHR
                   01651026:00:0    92-343/16:10        ULHR
                   01656418:00:0    92-347/11:01        ILLR
                   01659057:00:0    92-349/07:30        ULLR

                   02271339:18:2    94-048/05:34        URLR
                   02378309:54:6    94-123/08:13        ULLR
                   02618987:18:2    94-292/08:04        URLR
                   02702827:18:2    94-351/04:56        ULLR


    * Range is the opposite of gain - high range equals low gain


  Coordinate Systems
  ==================
    The data are being archived in two coordinate systems. The first
    coordinate system is referred to as inertial rotor coordinates (IRC).
    This coordinate system has the Z axis along the rotor spin axis,
    positive away from the antenna and the X and Y axes lies in the rotor
    spin plane. In a crude sense, when the spacecraft is far from Earth,
    +X points south, normal to the ecliptic plane, positive Y lies in the
    ecliptic plane in the sense of Jupiter's orbital motion and positive Z
    is in the anti-earth direction. The spacecraft antenna (negative Z
    direction) is kept earthward pointing to about +/- 10 deg accuracy.

    The second coordinate system is RTN coordinates. This system places
    Br along the Sun-spacecraft line with the positive direction away
    from the sun. Bnormal is along the direction of the Sun spin axis
    crossed with the radial axis. Btangential is in the direction of
    Bnormal crossed with the radial axis.


  Onboard Spacecraft Processing
  =============================
    The majority of the processing of the interplanetary cruise data is
    done onboard the spacecraft. The following procedures take place
    onboard.

    1) Data is recursively filtered and decimated to 4.5 vectors/second
    2) Sensor zero levels are subtracted and gains are applied
    3) Data is transformed from a sensor coordinate system to a spacecraft
       coordinate system using an orthogonality matrix
    4) Data are decimated again to 2/3 second resolution
    5) Data are despun into inertial rotor coordinates
    6) A recursive filter is applied and data are decimated to a variable
       resolution

    These steps are explained in further detail below.

    1) Recursive filter and decimation

       The Galileo magnetometer samples the magnetic field 30 times per
       second. These highest rate samples are recursively filtered and
       then resampled by the instrument at 4.5 vectors per second using a
       7,7,6 decimation pattern.

           Recursive Filter

           B(t) = 1/4 Bs(t) + 3/4 B(t-1)

           B  = output field
           Bs = input field measured by the sensor
           t  = sample time

       The pattern is generated by doubling the spacecraft clock modulo 10
       counter and then applying the decimation scheme. This gives 3
       vectors every spacecraft minor frame (about 2/3 second) which are
       sampled unevenly. The first vector in a minor frame is sampled
       approximately 0.200 seconds after the last vector in the preceding
       minor frame. The other two samples are taken approximately 0.233
       seconds apart.

    2) The data was processed onboard the spacecraft using a fixed zero
       level which was provided at the start of each data acquisition
       interval. These zero levels were determined using various methods
       and were periodically updated as significant changes in level were
       noted. Knowledge of the two spin plane sensor zero levels is not
       critical. The data is generally averaged over a long enough
       interval that any error in the zero levels is removed. Knowledge of
       the spin aligned sensor zero level is critical. However, this can
       be corrected for once the data has been received on the ground
       and is discussed below under Ground Data Processing.

    3) Orthogonality matrix applied: The determination of a calibration
       matrix is too complex to describe here. The method employed has
       been well described in [KHURANAETAL1996].

    4) The data is decimated to 2/3 second resolution by keeping
       only the first minor frame of data.

    5) Despinning data to inertial rotor coordinates: The  nominal
       transformation to IRC from SRC is

          (Bx)   ( cos(theta)   -sin(theta)  0 ) (Bxs)
          (By) = ( sin(theta)    cos(theta)  0 ) (Bys)
          (Bz)   (   0               0       1 ) (Bzs)

       Where s denotes spinning coordinates and theta is the rotor spin
       angle.

    6) Recursive filter and decimation: A recursive filter is applied in
       in the following manner.

       Recursive Filter

           B(t) = 1/C Bs(t) + (1-1/C) B(t-1)

           B  = output field
           Bs = input field measured by the sensor
           t  = sample time
           C  = averaging constant

       The averaging constant is variable and is given at the start of
       each data acquisition period. The data is then decimated. There
       is a one to one correspondence between the averaging constant
       used and the decimation factor as outlined below.

   Time per sample(Rims)       Averaging constant    Decimation Factor
   -------------------------------------------------------------------
          1                        1024                   1
          2                         512                   2
          4                         256                   4
          8                         128                   8
         16                          64                  16
         32                          32                  32
         64                          16                  64
        128                           8                 128
        256                           4                 256
        512                           2                 512
       1024                           1                1024


  Ground Data Processing
  ======================
      Once the data is on the ground there is very little that can be done
      to improve the onboard processing because of the heavy filtering
      and decimation. The following procedure is done on the ground

    1) Data is converted to nanoTesla
    2) The zero level of the spin aligned sensor is corrected for.
    3) Timing is set to account for a phase delay
    4) Rotation is performed to account for phase delay
    5) Data are transformed to RTN coordinates to
       produce the RTN collection.

    These steps are outlined in greater detail below.

    1) Conversion to nanoTesla simply requires dividing the instrument
       data numbers by a constant scale factor. For the inboard high range
       (low gain) mode the scale factor is 2. For the inboard low range
       and outboard high range, the scale factor is 64. The outboard low
       range data has a scale factor of 1024.

    2) The zero level of the spin axis aligned sensor was determined by
       several means. One method is to take 25 day averages of the data
       from the spin aligned sensor. The basis of this method is that if
       the spacecraft is relatively close to the ecliptic plane, over one
       solar rotation the average of the suns magnetic field in the
       spacecraft z-direction is zero. Therefore whatever remains after
       averaging is taken to be an offset. The second method is dependent
       on the four quadrant structure of the solar wind. For this method
       we look only at points where By(IRC coordinates) crosses from
       positive to negative values. Here we assume that based on the
       four quadrant structure, as we pass from quadrant to quadrant
       By(IRC) will change signs and Bz(IRC) will go to zero. The values
       of Bz(IRC) where By(IRC) crosses zero are then averaged over a
       fifty day period. For the majority of the cruise data the
       instrument was configured in the ULLR mode. This mode puts sensor 3
       along the spin axis. After looking at the results of these two
       method it became apparent that the spin aligned sensor 3 offset had
       a substantial drift that was correlated to the change in
       temperature. The offset determinations  for sensor 3 were fit to
       temperature. It was found that two different fits were necessary.
       For temperatures greater than 272K a straight line fit was used.

         zoff = -17.60926 + .02608*(Temp)

         zoff = Offset for sensor three [nT]
         Temp = Temperature at the outboard sensor [K]


       For temperatures less than 272K a second fit was determined.
         zoff = 22.9016799 + (2511.27490/Temp) - (3176088.25)/(Temp*Temp)

         zoff = Offset for sensor three [nT]
         Temp = Temperature at the outboard sensor [K]

       A second instrument configuration commonly used during the
       cruise to Jupiter was the URLR mode. This mode places sensor2
       along the spin aligned axis. For unknown reasons this sensor
       was not as susceptible to changes in temperature and showed
       no strong zero level drifts over time. A fixed offset of
       2.75574nT was removed from sensor 2.

    3) In order to account for the long recursive filters applied
       the timing of the data is corrected to be:

       rim=rim + (avg_con - (rim % avg_con)) +1/e*avg_con

       rim     = starting rim of the averaging interval
       avg_con = length of the averaging interval(rims)

    4) There is a phase delay associated with the Analog to Digital
       converter of the instrument. This means that when the data is
       despun onboard the spacecraft, the data and the angle used to
       despin it are slightly out of phase. In order to correct this
       delay the data are rotated by a phase angle. The delay is
       equivalent to the rotation outlined below.

       Bx'= cos(delay) * Bx - sin(delay) * By
       By'= sin(delay) * Bx - cos(delay) * By

       delay = -0.045163

    To transform the data to RTN coordinates the following step is taken

    5) The data are transformed first into Earth Mean Equatorial(equinox
       1950) coordinates. This system is directly supported by the SPICE
       software provided by the Navigation and Ancillary Information
       Facility (NAIF) at JPL as inertial coordinate system 'FK4'. The
       angles required for this transformation come directly from the
       Galileo Attitude and Articulation Control System (AACS) data. The
       transformation matrix for this rotation is:


   --                                                               --
   | (cosTsinDcosR - sinTsinR)  (-sinDsinTcosR - cosTsinR)  cosDcosR |
   |                                                                 |
   | (cosTsinDsinR + sinTcosR)  (-sinDsinTsinR + cosTcosR)  cosDsinR |
   |                                                                 |
   | -cosDcosT                  sinTcosD                    sinD     |
   --                                                               --

       where

       R = Rotor-Right Ascension
       D = Rotor-Declination
       T = Rotor-Twist - Rotor-Spin-angle  (despun data)

       Once in an inertial coordinate system, SPICE software provides
       subroutines which return the transformation matrices to GSE
       (G_GSETRN), GSM (G_GSMTRN), or RTN (G_RTNTRN) coordinate systems
       for any ephemeris time. These matrices have been used to perform
       the coordinate system transformations. The spacecraft/planet (SPK),
       leap second (TS), and planetary constants (PCK) kernels required
       for these transformations have been archived in the PDS by NAIF.
       The SPICE toolkit (software) can be obtained
       from the NAIF node of the PDS for many different platforms and
       operating systems. At the time of this archive, the SPICE toolkit
       was available via an anonymous-ftp site at naif.jpl.nasa.gov"

         CONFIDENCE_LEVEL_NOTE              = "

  Data Quality
  ============
    Data quality assessment is a rather vague concept which we will try to
    address in a somewhat qualitative manner. Each aspect of the data
    processing sequence can be analyzed to determine its maximum possible
    error contribution. In theory, these errors could be summed to provide
    estimates of the maximum error for each data point. We have not taken
    our error analysis to that level. We believe that our calibrations
    (sensor geometry and gains) are good enough that they produce a
    negligible source of data error. In addition, we believe that the
    coordinate system transformations which are derived from the SPICE
    kernels and Toolkit are negligible sources of error in the magnetic
    field vectors. The sources of error which we feel are the most
    significant are those associated with magnetic sources aboard the
    spacecraft, especially those with temporal or spacecraft orientation
    variations. The next greatest contributor of error is the data from
    the AACS which affects our knowledge of the spacecraft orientation and
    hence rotates the magnetic field vector. Lastly, telemetry or software
    errors which produce 'spikes' or bit errors in the data are error
    sources.

    Magnetic sources associated with the spacecraft have been identified.
    Over the long averaging intervals of all the interplanetary cruise
    data this source of noise is eliminated. There are some time intervals
    when the zero levels of the spin plane sensors show large variations
    (1-5 nT) on short time scales (minutes to hours). After a while
    (hours to days) the offsets return to their nominal levels. The source
    of these magnetic fields has not yet been identified. The method of
    removing offsets does not remove these rapidly varying effects.

    Errors associated with AACS angles have various effects on the data.
    The rotor right ascension and declination are crucial to the
    understanding of the spacecraft orientation. Fortunately, these angles
    are slowly varying and can be interpolated to better than 1 degree of
    accuracy for long (many hour) time periods except near major
    spacecraft maneuvers.

    During some time intervals no AACS data is available. As a result,
    these intervals can not be transformed from spacecraft coordinates RTN
    coordinates.

    During several intervals of the interplanetary cruise the spacecraft
    lost it's sector data. Sector data gives the magnetometer the
    neccessary information to despin the magnetic field data spin plane
    components (Bx_sc  and By_sc in spacecraft coordinates). If the
    magnetic field spin plane  components are not despun they will appear
    as a sin wave. The next step in the processing done onboard the
    spacecraft is averaging. The data that is not despun will be averaged
    to zero as you would expect a sin wave to be averaged over many
    periods. The intervals where sector data was lost have not been
    removed from the processed IRC collection. The reason for this is that
    these intervals can be valuable in helping to determine sensor zero
    levels. These intervals have been cut from the processed data in RTN
    coordinates. Below is a list of time where sector data was lost.

    1990-Jan-26 19:35:48   to   1990-Jan-31 05:17:29
    1991-Jan-16 20:24:58   to   1991-Jan-21 17:36:00
    1991-Feb-12 18:47:00   to   1991-Feb-25 18:08:00
    1993-Jan-27 09:00:40   to   1993-Jan-30 12:30:27"