This description was assembled from various Stardust project
      documents (with permission from the Stardust project) and
      direct contributions from the instrument science lead, Dr.
      Anthony J. Tuzzolino.
 
      SDN:  This document has been updated for the Stardust-NExT (SDN)
      mission, but mostly left intact from the prime mission data sets.
      The prefix 'SDN:' typically precedes updated material.
 
 
      Instrument Overview
      ===================
      The Dust Flux Monitor Instrument (DFMI) was part of the STARDUST
      instrument payload. It provided data on the particle flux and
      mass distribution in the coma of the comet.
 
 
      Scientific Objectives
      =====================
      The prime goal of the DFMI was to measure the particle flux and
      mass distribution during passage through the coma of Comet Wild-2
      in 2004. This information is valuable for assessment of
      spacecraft risk and health, and also for interpretation of the
      laboratory analysis of dust captured by the Aerogel dust
      collectors and returned to Earth.
 
      A secondary science goal was to measure the particle flux and mass
      distribution during the ~7 year interplanetary portions of the
      mission, where, in addition to measurements of the background
      interplanetary dust over the radial range 0.98 AU to 2.7 AU,
      multiple opportunities existed for possible detection by the DFMI
      of interplanetary particles, meteor-stream particles, and
      interstellar dust. This part of the investigation was not achieved
      due to problems with the instrument's power supply.
 
      SDN:  For SDN the primary goal was to measure the particle flux and
      mass distribution during passage through the coma of Comet 9P/Tempel
      1 in 2011.
 
 
      Calibration
      ===========
      A description of the calibration of the DFMI sensors is provided
      in the calibration report document provided with the DFMI data
      set(s).
 
      SDN:  The calibration did not change for Stardust-NExt other than
      adjusting for the Tempel 1 flyby speed of 10.9 km/s.  Calibration
      comprises converting the electrical threshold levels to the
      corresponding particle masses, deriving new thresholds for shield
      penetration and effective area for the acoustic sensors, and
      converting from the raw counts generated by the electronics vs time
      to fluence or flux.
 
 
      Operational Considerations
      ==========================
      A problem with the power supply detected during post-launch
      checkout precluded operation of the instrument for more than
      thirty minutes. Fear of complete failure of the instrument led to
      its use being restricted to about thirty minutes at each of the
      Annefrank and Wild 2 encounters.
 
      SDN:  With the exception of calibration events during CRUISE
      phase, the same was true for the Stardust-NExT mission.
 
 
      Detectors
      =========
      The DFMI consisted of two different dust detector systems --  a
      polyvinylidene fluoride (PVDF) DUST SENSOR UNIT (DSU), which
      measures particles with mass > ~10^-11 g, and a DUAL ACOUSTIC
      SENSOR SYSTEM (DASS), which utilized two quartz piezoelectric
      accelerometers mounted on the first two layers of the spacecraft
      Whipple dust shield to measure the flux of particles with mass >
      3 x 10^-8 g. The Whipple shield structures provided the large
      effective sensitive area required for detection of the expected
      low flux of high-mass particles. At the encounter speed of 6.1
      km/s, the DFMI measurements extended over the particle mass
      range of 8 decades, from 10^-11 to >10^-3 g.  More detailed
      description of the detectors is provided in Economou et al., 2011,
      in Tuzzolino et al., 2003, in Green et al., 2004, and in Tuzzolino,
      1994 ([ECONOMOUETAL2011], [TUZZOLINOETAL2003], [GREENETAL2004],
      [TUZZOLINO1994]).
 
      SDN:  DFMI comprised four sensor subsystems and associated
      electronics:  Two PVDF sensors with sensitive areas of 0.002 and 0.02
      m^2 and thicknesses of 6 and 28 um; the Dual Acoustic Sensor
      Subsystem (DASS) with two piezoelectric sensor, one attached to each
      of the first two layers of the Whipple Shield on the front of the
      spacecraft.
 
      Each sensor was designed to generate an electrical signal in the
      event of being impacted by a dust particle.
 
      See the Measured Parameters section below for the range of particle
      masses detectable by the DFMI detectors at the 9P/Tempel 1 flyby
      parameters.
 
 
      Electronics
      ===========
      A detailed description of instrument electronics and internal
      data processing is provided in Tuzzolino et al., 2003
      [TUZZOLINOETAL2003].
 
      SDN:  The electronics for each PVDF sensor comprised four channels
      for each sensor.  Each channel corresponded to a particle mass range
      dependent on spacecraft/particle relative velocity and the
      composition of the particle.  The raw data in each PVDF channel
      comprised a cumulative count of the number of events as a function
      of time as the spacecraft passed through the coma.  The Acoustic
      sensor operation was more complicated due to the limited bandwidth
      available to the subsystem, so some interpretation is required to
      derive the number of impacts.
 
 
      Location
      ========
      The DSU sensor was mounted on the first layer of the central
      Whipple shield, as is one of the DASS sensors. The second DASS
      sensor was mounted on the second layer of the central Whipple
      shield.
 
 
      Operational Modes
      =================
      During the Wild 2 encounter DFMI operated in ENCOUNTER mode. In
      this mode the instrument provided measurements at least once per
      second, and up to 10 times per second, depending on the dust
      particle flux on the PVDF sensors.  In this mode the counters were
      not reset upon readout, providing accurate cumulative particle
      fluences.
 
      SDN:  During the Tempel 1 encounter DFMI operated in ENCOUNTER
      mode.  For calibrations during non-encounter phases DFMI operated
      in CRUISE mode.  In CRUISE mode the instrument provided measurements
      up to ten times per second down to one measurement per twenty
      seconds.
 
 
      Subsystems
      ==========
      A detailed description of the DFMI subsystems is provided in Economou
      et al., 2011, Green et al., 2004, and Tuzzolino et al., 2003
      ([ECONOMOUETAL2011], [GREENETAL2004], TUZZOLINOETAL2003]).
 
 
      Measured Parameters
      ===================
 
      The DFMI PDVF sensors measure differential and cumulative particle
      fluxes over the particle mass range 10^-11 to 10^-4 g and cumulative
      particle fluxes for masses > 10^-4 g. The acoustic sensors measure
      particle fluxes for particles having mass greater than 3 x 10^-4 g.
 
      SDN:  At the Stardust(SDU)/Tempel 1 relative velocity of 10.9 km/s,
      the mass ranges for differential fluxes were slightly lower but
      similar to those for the Wild 2 prime mission.