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Instrument Information

INSTRUMENT_ID MAG
INSTRUMENT_NAME TRIAXIAL FLUXGATE MAGNETOMETER
INSTRUMENT_TYPE MAGNETOMETER
INSTRUMENT_HOST_ID VG2
INSTRUMENT_DESC
 
    INSTRUMENT: TRIAXIAL FLUXGATE MAGNETOMETER
    SPACECRAFT: VOYAGER 2
 
    Instrument Information
    ======================
      Instrument Id                  : MAG
      Instrument Host Id             : VG2
      Pi Pds User Id                 : NNESS
      Principal Investigator         : NORMAN F. NESS
      Instrument Name                : TRIAXIAL FLUXGATE MAGNETOMETER
      Instrument Type                : MAGNETOMETER
      Build Date                     : 1977-08-20
      Instrument Mass                : 5.600000
      Instrument Length              : 13.000000
      Instrument Width               : UNK
      Instrument Height              : UNK
      Instrument Serial Number       : UNK
      Instrument Manufacturer Name   : UNK
 
    Instrument Description
    ======================
      The magnetic field experiment carried out on the Voyager 2
      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 2
      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].
 
    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.
REFERENCE_DESCRIPTION Acuna, M.H., L.F. Burlaga, R.P. Lepping, and N.F. Ness, Initial Resultsfrom the Voyager 1 and 2 Magnetic Field Experiments, Proceedings of theSolar Wind IV Conference, Burghausen, 1978, H. Rosenbauer (Ed.), MaxPlanck Institut, Rept. No. MPAE-W-100-81-31, 1981.

Behannon, K.W., M.H. Acuna, L.F. Burlaga, R.P. Lepping, N.F. Ness, and F.M.Neubauer, Magnetic Field Experiment for Voyagers 1 and 2, Space Sci. Rev., Vol.21, p. 235, 1977.

Ness, N.F., K.W. Behannon, R.P. Lepping, and K.H. Schatten, Use of TwoMagnetometers for Magnetic Field Measurements on a Spacecraft, J. Geophys.Res., Vol. 76, p. 3564, 1971.

Ness, N.F., M.H. Acuna, R.P. Lepping, L.F. Burlaga, K.W. Behannon, andF.M. Neubauer, Magnetic Field Studies at Jupiter by Voyager 2: PreliminaryResults, Science, Vol. 206, p. 966, 1979.