INSTRUMENT: FLUXGATE MAGNETOMETER
  SPACECRAFT: VOYAGER 1
 
  Instrument Information
  ======================
    Instrument Id                  : MAG
    Instrument Host Id             : VG1
    Pi Pds User Id                 : NNESS
    Principal Investigator         : NORMAN F. NESS
    Instrument Name                : FLUXGATE MAGNETOMETER
    Instrument Type                : MAGNETOMETER
    Build Date                     : 1977-09-05
    Instrument Mass                : 5.600000
    Instrument Length              : 13.000000
    Instrument Width               : UNK
    Instrument Height              : UNK
    Instrument Serial Number       : UNK
 
 
  Instrument Description
  ======================
    The magnetic field experiment carried out on the Voyager 1
    mission consists of dual low field (LFM) and high field
    magnetometer (HFM) systems.  The dual systems provide greater
    reliability and, in the case of the LFM's, permit the
    separation of the spacecraft magnetic fields from the ambient
    fields.  Additional reliability is achieved through electronics
    redundancy.  The wide dynamic ranges of +/- 0.002 G for the
    LFM's and +/- 20 G for the HFM's, low quantization uncertainty
    (+/- 12.4, 488 nanoTesla respectively), low sensor RMS noise
    level (0.006 nanoTesla), and the use of data compaction schemes
    to optimize the experiment information rate all combine to
    permit the study of a broad spectrum of phenomena during the
    mission.
 
 
  Science Objectives
  ==================
    The investigations of the magnetic fields and magnetospheres of
    the major planetary systems in the outer Solar System and their
    interactions with the solar wind are primary objectives of the
    space exploration program to be conducted during the Voyager 1
    mission.  In addition, the investigation of the interplanetary
    magnetic field phenomena during the flights is of fundamental
    importance both to the understanding of the magnetospheric
    observations and to a number of outstanding questions in basic
    plasma physics and in the general dynamics of the solar wind.
    If the Heliospheric boundary is penetrated, accurate
    measurement of the interstellar magnetic field is also an
    important objective.
 
 
  Operational Considerations
  ==========================
    There are no special operational considerations for the
    magnetometer described in [BEHANNONETAL1977].  All magnetometer
    data are calibrated.  Three types of in-flight calibrations are
    performed: 1) sensitivity calibrations, 2) zero-level
    calibrations, based on rolls of the spacecraft, and 3) boom-
    alignment calibrations based on the activation of on-board
    coils and resulting data (especially important when dual
    magnetometers are used and in strong fields for any
    magnetometer).  Sensitivity calibrations (for 8 ranges) are
    done approximately once every two months (early in the mission
    they were done more frequently).  The magnetometer team
    generally use one or two axis rolls (cruise maneuvers, CRSMR's)
    of the spacecraft for zero level calibrations as often as they
    are provided which is variable this is about three times per
    year for the so-called mini-CRSMR's, which are two axis rolls.
    Full CRSMR's and z-axis (only) roll-maneuvers have not occurred
    within the last few years (full CRSMR's and mini's differ only
    in the number of rolls in each).  The magnetometer team usually
    succeeds in arguing for a series of rolls near each planetary
    encounter.  Boom-alignment calibrations were done once after
    launch and around the time of the Jupiter encounter.  Others
    have been executed, but it has been determined that the inter-
    sensor misalignment is small and constant.
 
 
  Measured Parameters
  ===================
    The following LFM and HFM values are derived from Table 1 in
    [BEHANNONETAL1977].
 
    LFM Dynamic ranges and quantization uncertainty:
 
    Range (nT)               Quantization (nT)
    ----------------------------------------------
    1.  +/- 8.8                    +/- .0022
    2.  +/- 26                     +/- .0063
    3.  +/- 79                     +/- .019
    4.  +/- 240                    +/- .059
    5.  +/- 710                    +/- .173
    6.  +/- 2100                   +/- .513
    7.  +/- 6400                   +/- 1.56
    8.  +/- 50,000                 +/- 12.2
 
    HFM Dynamic ranges and quantization uncertainty:
 
    Range (nT)               Quantization (nT)
    ----------------------------------------------
    1.  +/- 5E+4                   +/- 12.3
    2.  +/- 2E+6                   +/- 488
 
 
  Calibration Description
  =======================
    The 13 meter Astromast booms have proved in extensive
    pre-flight testing to be highly rigid with respect to bending
    motions but soft to torsional or twisting motion.  Deployment
    repeatability test have shown as much as +/- 7 degrees
    uncertainty in the knowledge of the boom twist angle (about the
    boom axis) at the magnetometer sensor positions, compared with
    +/- 0.5 uncertainty in bend angles (rotation about axes
    orthogonal to the boom axis).  In order to minimize sensor
    alignment uncertainties, a method to estimate an angular
    correction matrix was developed that eliminates most of the
    twist uncertainty and some of the bend uncertainty.  A special
    calibration coil has been wound around the periphery of the
    spacecraft's high gain antenna to generate, upon command, a
    known magnetic field at both LFM magnetometer sensors.  The
    difference between measurements taken when the coil is turned
    on and off is the coil field, independent of all external
    fields.  Using a 20 turn coil of 1/2 amp yields nominal field
    intensities 0f 33.4 and 6.1 nanoTesla at the inboard and
    outboard sensors, respectively.  All magnetometer data are
    calibrated.  Three types of in-flight calibrations are
    performed: 1) sensitivity calibrations, 2) zero-level
    calibrations, based on rolls of the spacecraft, and 3)
    boom-alignment calibrations based on the activation of on-board
    coils and resulting data (especially important when dual
    magnetometers are used and in strong fields for any
    magnetometer).  Sensitivity calibrations (for 8 ranges) are
    done approximately once every two months (early in the mission
    they were done more frequently).  The magnetometer team
    generally use one or two axis rolls (cruise maneuvers, CRSMR's)
    of the spacecraft for zero level calibrations as often as they
    are provided which is variable this is about three times per
    year for the so-called mini-CRSMR's, which are two axis rolls.
    Full CRSMR's and z-axis (only) roll-maneuvers have not occurred
    within the last few years (full CRSMR's and mini's differ only
    in the number of rolls in each).  The magnetometer team usually
    succeeds in arguing for a series of rolls near each planetary
    encounter.  Boom-alignment calibrations were done once after
    launch and around the time of the Jupiter encounter.  Others
    have been executed, but it has been determined that the
    inter-sensor misalignment is small and constant.  For more
    information, consult [BEHANNONETAL1977].
 
 
  LFM and HFM Detectors
  =====================
    Detector Type                  : RING CORE
    Detector Aspect Ratio          : 0.000000
    Nominal Operating Temperature  : 273.000000
 
    Total Fovs                     : 1
    Data Rate                      : UNK
    Sample Bits                    : 12
 
    The magnetometer consists of 6 ring core detectors.  These are
    designated as low field magnetometers (LFM) 1-3 and high field
    magnetometers (HFM) 1-3.  The basic sampling rate is .06 +/-
    .006 seconds.  Sampling rate for the high field system is .6
    seconds.  The detectors measure in the interval of +/- 2.0E+6
    nT for HFM, and +/- 5.0E+4 for LFM.  Nominal operating
    temperature for all detectors is 273 K, though the sensors were
    tested over a range of +/- 60 degrees about the nominal
    temperature.
 
    Both high and low field magnetometer sensors utilize a ring
    core geometry and thus have lower drive power requirements and
    better zero level stability than other types of fluxgates and
    are smaller in size [ACUNA1974].  The cores consist of an
    advanced molybdenum alloy, especially developed in cooperation
    with the Naval Surface Weapons Center, White Oak, Maryland,
    which exhibits extremely low noise and high stability
    characteristics.  The use of this alloy and the ring core
    sensor geometry thus allows the realization of compact, low
    power, ultrastable fluxgate sensors with a noise performance
    that is improved almost an order of magnitude over the best
    previously flown fluxgate sensors.  The HFM's use specially
    processed miniature ring cores (1 cm diameter) which minimize
    the power required to measure large fields.  This description
    is taken directly from [BEHANNONETAL1977].
 
 
    Vector Components
    -----------------
      The LFM1 detector and the HFM1 detector are designated as the
      detectors which measure the i component of the vector
      (i,j,k).  The LFM2 detector and the HFM2 detector are
      designated as the detectors which measure the j component of
      the vector (i,j,k).  The LFM3 detector and the HFM3 detector
      are designated as the detectors which measure the k component
      of the vector (i,j,k).
 
 
      'HFM' Section Parameter 'MAGNETIC FIELD COMPONENT'
      --------------------------------------------------
      Instrument Parameter Name      : MAGNETIC FIELD COMPONENT
      Sampling Parameter Name        : TIME
      Instrument Parameter Unit      : NANOTESLA
      Minimum Instrument Parameter   : -2000000.000000
      Maximum Instrument Parameter   : 2000000.000000
      Minimum Sampling Parameter     : 0.600000
      Maximum Sampling Parameter     : 0.600000
      Noise Level                    : 0.006000
      Sampling Parameter Interval    : 0.600000
      Sampling Parameter Resolution  : 0.600000
      Sampling Parameter Unit        : SECOND
 
      A measured parameter equaling the magnetic field strength
      (e.g.  in nanoTeslas) along a particular axis direction.
      Usually the three orthogonal axis components are measured by
      three different sensors.
 
 
      'LFM' Section Parameter 'MAGNETIC FIELD COMPONENT'
      --------------------------------------------------
      Instrument Parameter Name      : MAGNETIC FIELD COMPONENT
      Sampling Parameter Name        : TIME
      Instrument Parameter Unit      : NANOTESLA
      Minimum Instrument Parameter   : -50000.000000
      Maximum Instrument Parameter   : 50000.000000
      Minimum Sampling Parameter     : 0.060000
      Maximum Sampling Parameter     : 0.060000
      Noise Level                    : 0.006000
      Sampling Parameter Interval    : 0.060000
      Sampling Parameter Resolution  : 0.060000
      Sampling Parameter Unit        : SECOND
 
      A measured parameter equaling the magnetic field strength
      (e.g.  in nanoTeslas) along a particular axis direction.
      Usually the three orthogonal axis components are measured by
      three different sensors.
 
 
  Electronics
  ===========
    The instrument is composed of two completely redundant systems:
    the 'P' or primary system and the 'S' or secondary system.
 
    The experiment electronics instrumentation consists of the
    flux-gate magnetometer electronics and associated controls, and
    the calibration and data processing electronics.  Complete
    redundancy is provided for the analog to digital converters,
    data and status readout buffers, command decoders and power
    converters.  Thus not only can the two magnetometers of a
    system be interchanged, but considerable cross-strapping within
    the electronics permits interchange of critical internal
    functions as well.  This significantly reduces the impact of
    single-component failure on the ability of the experiment to
    continue successful operation during the mission duration of >
    4 years.  This description is directly transposed from
    [BEHANNONETAL1977] page 249.
 
 
  Operational Modes
  =================
    Data Path Type                 : REALTIME
    Instrument Power Consumption   : 2.200000
 
    In the CRUISE mode, only the LFM subsystem is operating.  The
    basic sample rate in this mode is 50/3 vectors/second.
 
    In the ENCOUNTER mode, both LFM and HFM subsystems are
    operating.  The basic sample rate in this mode is 50/3
    vectors/second for the LFM system and 5/3 vectors/second for
    the HFM system.
 
 
  Instrument Mounting
  ===================
    The LFM is located near the tip of the magnetometer boom and
    the HFM is located near the spacecraft body.  See
    [BEHANNONETAL1977] for a picture of the actual magnetometer
    mounting positions and a complete description.