Data Set Information
DATA_SET_NAME GO JUP SSD DERIVED ELECTRON FLUX V1.0
DATA_SET_ID GO-J-SSD-5-DDR-STAR-SENSOR-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION This data set contains Galileo Star Scanner data (electron flux, 1.5 to 30 Mev) from Jupiter 0 Orbit through end of mission.
DATA_SET_DESCRIPTION
Data Set Overview
      =================

The Galileo star scanner is providing data on the instantaneous
flux of 1.5 to 30 MeV electrons in the Jovian environment. It is
able to measure fluxes of ~1 x 105 electrons cm-2 sec-1 or greater
which generally means the data are usable inside of about 12 and
rarely as far out as 16.5 Jovian Radii (RJ). Typically, the data
points are spaced about 400 or 80 seconds apart with infrequent
periods of more rapid data depending upon the operational mode.
It should be noted that data are generally accurate in time to
only within 20 seconds without special processing. Pitch angle
information generally cannot be extracted from this data set.
Separate files exist for the Jovian insertion event (J0) and
all subsequent perijove passes except J5 which occurred during
a period of solar conjunction.

      Data
      ====

Time: GMT-UTC time of the measurement in PDS
      format: yyyy-mm-ddThh:mm:ss.sss.

      (Note: This accurately reflects when the data was telemetered,
       not the actual time the data was taken which could be up to
       20 seconds earlier. All data is referenced to the time it
       occurred on the spacecraft time and not ground receipt time.
       Occasional periods of much higher rate telemetry do occur
       (e.g. parts of orbit C21) where data is telemetered every
       2/3 second.)

Sclk: A spacecraft counter from which time information is derived. The
      left hand integers are termed RIMs and increment 1 unit per
      60.66666 seconds. The center two integers are termed
      'minor frames' and increment from 0 to 90 at a rate of 1 unit
      per 2/3 second.  When this cycle is complete one digit is added
      to the RIM count. The final integer is termed an 'RTI' and
      increment from 0 to 9 at a rate of 1 unit per 0.0666666 seconds.
      When this cycle is complete, one unit is added to the minor
      frame count.

Star Code: This is a hexadecimal representation of the star
           scanner health and status. It is collected at the same
           instant as Raw Star Intensity and the reading of Raw
           Background count.

    Position 1 - always should be '0'. Any other number indicates
                 data is suspect.
    Position 2 - always should be 'x'. Any other letter is a flag
                 for suspect data.
    Position 3 - 'f' indicates normal operation
                '1', '2', '5', '6' or '7' indicates anomalous star
                 scanner operation. Suspect data.
                '3' or '4' star scanner is having difficulty
                 recognizing stars. All data is fine unless
               otherwise noted in notes column.
    Position 4 and 5 - Two letters that convert to an 8 bit binary
                       word (hexadecimal). For example C7 = 11000111.
                      First two bits should always be 11. Other
                      numbers mean that the star scanner is
                      re-starting and data is suspect.

                       The final six numbers are a binary
                       representation of recognized stars. In the C7
                       example, three stars are recognized, most
                       likely because only three stars have been
                       loaded into the star scanner memory.

Day of Year (DOY): A fractional representation of the time at which
                   the data was telemetered in GMT-UTC. All data is
                   in spacecraft time and not ground receipt time.
                   January 1 is DOY 001.

                   For example, 6 pm on March 1, 1996 (a leap year)
                   is DOY 61.7500000.

Twist: Spacecraft rotor twist angle in degrees. It is an inertially
       based angle using the EME-50 coordinate system. Twist is the
       angle between the projection of the 1950 North Celestial Pole
       onto the spacecraft X-Y plane and the -X axis of the rotor
       (spinning portion of the spacecraft). This represents the angle
       at which the raw background  and star intensity data was
       telemetered, but not necessarily the angle at which the data
       was taken. It is used to subtract out the effects of
       'star corruption' (see Fieseler [2000]) in the creation of the
       filtered and compensated data sets. It is a real number which
       varies from 0 to 360 degrees.

Raw Star Intensity: The intensity of the most recently recognized
                    star in counts. An integer which can scale from
                    0 to 16,383. Sirius is about 4200 counts and the
                    star scanner is linear for spectrally similar
                    stars. The instrument, however, has a sharp
                    spectral response in the blue and so reddish
                    stars are much dimmer than might otherwise be
                    expected.  Star intensity is put into a buffer
                    for downlink only when a star is recognized. After
                    this, the stale data remains in the buffer until
                    the next star is seen. This buffer is generally
                    only checked and relayed to the ground once per
                    several minutes in most telemetry modes. Star
                    intensity information is primarily used to
                    subtract out the effects of  'star corruption'
                    [Fieseler, 2000] in the creation of the
                    compensated data set.

Raw Background: Far from Jupiter, this is just average brightness of
                the sky, including stars, nebulae, zodiacal light
                taken over the previous 25.6 milliseconds. This is
                termed 'star corruption' Near Jupiter, electron
                bombardment adds signal and eventually overwhelms
                the light from background sources. An integer which
                can scale from 1 to 16,383. It is placed into at the
                same time as star intensity.  This buffer is generally
                only checked and read-out once per several minutes in
                most telemetry modes.

Filtered: This is the filtered data which is derived from the Raw
          background, Star Intensity and Twist data. It represents the
          measured background light with the star corruption
          (deterministic effects of background light) subtracted out.
          A value of -50 means that this data had to be thrown out of
          the processing because the star light could not be
          subtracted out in this instance. Although this data
          frequently appears to be an integer, it is actually real as
          fractional values are do occur in some orbits.

Compensated: This is the compensated data set which is derived from
             the filtered data. It linearizes the star scanner data
             (detector saturation becomes a factor in some cases) and
             corrects for gain changes in the photomultiplier tube.
             A real number. A value of -50 means that this data had
             to be thrown out of the processing because the star light
             could not be subtracted out of the filtered data in this
             instance.

Error low: This is the estimated error in the compensated data applied
           on the low side. It is comprised of an RSS'ed series of
           independent or nearly independent worst case instrument
           errors, biases and computational errors. It accounts for
           aging and radiation damage to the star scanner equipment,
           noise in the background radiation data after being averaged,
           noise in the star light subtracted out of the filtered data,
           attitude errors, calculational errors and biases caused by
           magnetic and temperature effects.

Error high: This is the estimated error in the compensated data
            applied on the high side. It is comprised of an RSS'ed
            series of independent or nearly independent worst case
            instrument errors, biases and computational errors. It
            accounts for aging and radiation damage to the star
            scanner equipment, noise in the background radiation data
            after being averaged, noise in the star light subtracted
            out of the filtered data, attitude errors, calculational
            errors and biases caused by magnetic and temperature
            effects.

Flux: This is the omnidirectional flux of electrons in particles/cm-2
      sec-1 between ~1.5 and 30 MeV external to the spacecraft. Due to
      the steep decrease of electron flux with energy, it can also be
      thought of as simply integral flux above 1.5 MeV. It is thought
      to be no more accurate than within a factor of five. It is an
      integer which would built from knowledge of the jovicentric
      distance and the Compensated data.  The equation used was

         Flux = 1755 * Compensated Counts  * RJ^1.1208

      Where RJ is the most recently Estimated RJ rather than the
      actual RJ at the instant the data was taken. This does not
      cause an error of more than a few percent. The user is
      cautioned that this is equation is preliminary - the star scanner
      data are self-consistent but the attempt to calculate a flux is
      less certain and was based primarily upon comparison with EPD
      data. This flux parameter was forced to a value of zero for all
      cases where the jovicentric distance was outside 20 RJ or when
      it, due to slightly negative values in the compensated counts,
      would have given a negative flux.

Range: Distance from Jupiter center of mass in Jupiter Radii.

Latitude: Planetographic latitude of the spacecraft in degrees.

West Longtitude: Planetographic (West) longitude of the spacecraft in
                 degrees.

L: Distance at which a dipole field line crosses the dipole equator.
   L is given by L = R sin*2(Magnetic Latitude) where R is the distance
   from the center of Jupiter.

Magnetic Latitude: Angle with respect to the dipole equator where the
                   dipole axis tilts 9.6 degrees towards
                   system III (1965.0) West Longitude.

Magnetic Longtitude: Angle around the dipole axis with respect to the
                     prime meridian.  The prime meridian can be
                     considered to intersect with 202 degrees west
                     longitude of System III (1965.0).

Notes:  Text notes describing the transition to different star scanner
        operation modes, suspected problems with the data not captured
        under Star Code and other points of interest.


The files of this data set are in the following structure:

NAME                 TYPE    Description
----------------------------------------------------------------------
PDS Time             char    UTC time
Spacecraft Clock     char    Spacecraft clock time
Star Code            char    Star Scanner status code
Day of Year          float   Decimal day of year
Twist                float   Spacecraft rotor angle (degrees)
Raw Star Intensity   Int     Star intensity (counts)
Raw Background       Int     Background intensity (counts)
Filtered Data        float   Raw intensity minus background
Compensated Data     float   calibrated star intensity
Error, Low           float   Bottom limit from error estimate
Error, High          float   Top limit from error estimate
Flux                 Int     Electron flux
R                    float   Distance from Jupiter to spacecraft (Rj)
Latitude             float   Planetographic latitude (degrees)
West Longitude       float   Planetographic west longitude (degrees)
L                    float   Distance at which a dipole field line
                                crosses the dipole equator
Magnetic Latitude    float   angle to dipole equator (degrees)
Magnetic Longitude   float   angle to dipole equator (degrees)
Notes                char    note on changes in data

      Coordinate System
      =================

    Satellite-Centered Planetographic (Right Handed) Coordinates (SPRH)
    -------------------------------------------------------------------
      SPRH is a spherical 'planetocentric' coordinate system, centered
      at the satellite. The magnetic field components are the standard
      right-handed spherical triad: R, Theta, and Phi. R is radial
      (along the line from the center of the satellite to the center of
      the spacecraft), and positive away from the satellite. Phi, the
      azimuthal component, is parallel to the satellite's
      planetographic equator (Omega x R) and positive in a right-handed
      sense. Theta, the 'southward' component, completes the
      right-handed set. Trajectory components are also right-handed.
      Since all of the satellites studied are nearly phase locked to
      Jupiter, the SPRH prime meridian is effectively the sub-Jupiter
      meridian. More precise definitions are provided by the IAU [1994]
      (see Table 4). Longitude is measured from the prime meridian and
      is positive in a right-handed sense (see figure below). R is the
      radial distance (satellite's center to spacecraft center).
      Latitude is planetocentric.

    System III [1965] Coordinates (SYS3)
    ------------------------------------
      System III [1965] (SYS3) magnetic field vector components form
      the standard right-handed spherical triad (R, Theta, Phi) for a
      Jupiter centered system. Namely, R is radial (along the line from
      the center of Jupiter to the center of the spacecraft), and
      positive away from Jupiter. Phi, the azimuthal component, is
      parallel to the Jovigraphic equator (Omega x R) and positive in
      the direction of corotation. Theta, the 'southward' component,
      completes the right-handed set.

      For SYS3 trajectory both east and west longitudes are provided.
      West longitudes are related to east longitudes by to the
      algorithm:

        west longitude = 360. - east longitude 

      West longitude is defined such that it appears to increase with
      time for a stationary observer [DESSLER1983]. Note, however, that
      R, latitude, and west longitude constitute a left handed set. The
      SYS3 1965 prime meridian is the sub-Earth longitude of
      1965-01-01 00:00 UT. The spin rate (which was determined from the
      rotation rate of the magnetic field) is 9 hrs 55 min 29.719 sec.
      (See [DESSLER1983] for a discussion on Jovian longitude). R is the
      radial (Jupiter's center to spacecraft center) distance. Latitude
      is planetocentric.
DATA_SET_RELEASE_DATE 2000-10-01T00:00:00.000Z
START_TIME 1995-12-07T12:01:00.000Z
STOP_TIME 2000-12-31T11:53:00.000Z
MISSION_NAME GALILEO
MISSION_START_DATE 1977-10-01T12:00:00.000Z
MISSION_STOP_DATE 2003-09-21T12:00:00.000Z
TARGET_NAME IO PLASMA TORUS
IO
JUPITER
TARGET_TYPE PLASMA CLOUD
SATELLITE
PLANET
INSTRUMENT_HOST_ID GO
INSTRUMENT_NAME GALILEO ORBITER STAR SCANNER
INSTRUMENT_ID SSD
INSTRUMENT_TYPE STAR SCANNER
NODE_NAME Planetary Plasma Interactions
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE
There are currently
(as of November, 2000) 28 separate data files reflecting
the 28 orbits Galileo has made of Jupiter and the J0 orbit insertion
event. One orbit, J5, is not included as the spacecraft was behind the
sun in that instance.  In general, the star scanner is insensitive to
electrons outside of about 12 RJ although the files often go out
beyond 35 RJ.
CITATION_DESCRIPTION Fieseler,P.D., GO JUP SSD DERIVED ELECTRON FLUX V1.0, GO-J-SSD-5-DDR-STAR-SENSOR-V1.0, NASA Planetary Data System, 2000
ABSTRACT_TEXT The Galileo star scanner is providing data on the instantaneous flux of 1.5 to 30 MeV electrons in the Jovian environment. It is able to measure fluxes of ~1 x 105 electrons cm-2 sec-1 or greater which generally means the data are usable inside of about 12 and rarely as far out as 16.5 Jovian Radii (RJ). Typically, the data points are spaced about 400 or 80 seconds apart with infrequent periods of more rapid data depending upon the operational mode. It should be noted that data are generally accurate in time to only within 20 seconds without special processing. Pitch angle information generally cannot be extracted from this data set. Separate files exist for the Jovian insertion event (J0) and all subsequent perijove passes except J5 which occurred during a period of solar conjunction.
PRODUCER_FULL_NAME MR. PAUL FIESELER
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