Instrument Information
INSTRUMENT_ID SDC
INSTRUMENT_NAME STUDENT DUST COUNTER
INSTRUMENT_TYPE DUST IMPACT DETECTOR
INSTRUMENT_HOST_ID NH
INSTRUMENT_DESC
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REQUIRED READING:                                                             
- Horanyi et al.  (2008) [HORANYIETAL2008]                                    
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      The SDC description was adapted from                                    
                                                                              
        http://lasp.colorado.edu/sdc/                                         
                                                                              
      Horanyi et al. (2008) [HORANYIETAL2008], and                            
      Weaver et al. (2008) [WEAVERETAL2008]                                   
                                                                              
                                                                              
  INSTRUMENT OVERVIEW                                                         
  ===================                                                         
                                                                              
    INTRODUCTION                                                              
    ------------                                                              
      As the name implies, a dust counter is an instrument that counts        
      particles of dust.  There are various ways of making one work, but      
      in the end, the instrument usually collects information on mass,        
      velocity, density, size, or some combination of those four.             
                                                                              
      The Student Dust Counter has 3 main goals.  The first is to map the     
      dust density distribution in the solar system.  Dust is not spread      
      evenly throughout space; instead, it varies in density throughout       
      the Solar System.  The first goal would be to get an accurate map of    
      how this dust density varies.                                           
                                                                              
      The second goal of the Student Dust Counter is to understand the        
      dust particle size distribution and how it varies throughout the        
      Solar System.                                                           
                                                                              
      The third main goal is to determine how fast the Kuiper Belt            
      produces dust.  The small, icy bodies in the Kuiper Belt are            
      constantly colliding and causing little bits of each other to chip      
      off.  These little bits in turn hit each other and slowly grind into    
      dust, in a somewhat similar fashion to how sand on a beach is           
      created.  The SDC team hopes to be able to find out how fast this is    
      happening.                                                              
                                                                              
                                                                              
    SPECIFICATIONS                                                            
    --------------                                                            
      NAME:                    SDC (Student Dust Counter)                     
      DESCRIPTION:             Dust Counter                                   
      PRINCIPAL INVESTIGATOR:  Mihaly Horanyi, U. Colorado                    
      MASS RANGE:              ~4 picogram - 4 nanogram (Note 1)              
      FIELD OF VIEW:           ~ 180 deg                                      
      ANGULAR RESOLUTION:      N/A                                            
      MASS RESOLUTION:         approx factor of 2 in mass                     
                                                                              
      Note 1:  actual mass range dependent on time (spacecraft and particle   
               velocities) during mission                                     
                                                                              
                                                                              
    Final Name                                                                
    ----------                                                                
      After 6 months of successful operations in space the SDC instrument     
      was renamed, and the dedication reads:                                  
                                                                              
      New Horizons, the first mission to Pluto and the Kuiper Belt, is        
      proud to announce that the student instrument (SDC) aboard our          
      spacecraft is hereby named 'The Venetia Burney Student Dust Counter'    
      in honor of Ms. Venetia Burney Phair, who at age of eleven nominated    
      the name Pluto for our solar system's ninth planet.  May 'Venetia'      
      inspire a new generation of students to explore our solar system, to    
      make discoveries which challenge the imagination, and to pursue         
      learning all through their lives.                                       
                                                                              
      In this archive, the name Student Dust Counter and the acronym SDC      
      will continue to be used.                                               
                                                                              
                                                                              
  Scientific Objectives                                                       
  =====================                                                       
    The Student Dust Counter (SDC) will count and measure the sizes of        
    dust particles along New Horizons' entire trajectory, which covers        
    regions of interplanetary space never before sampled.  Such dust          
    particles are created by comets shedding material and Kuiper Belt         
    Objects colliding with one another.  The SDC is managed and was built     
    primarily by students at the University of Colorado in Boulder            
    Laboratory of Atmospheric and Space Physics (LASP), with supervision      
    from a professional space scientist and mentoring from a number of        
    professional engineers at LASP.                                           
                                                                              
                                                                              
  Calibration                                                                 
  ===========                                                                 
    See Horanyi et al. (2008) [HORANYIETAL2008], especially sections 3.4.3    
    and 3.5.                                                                  
                                                                              
                                                                              
  Operational Considerations                                                  
  ==========================                                                  
    1) Autonomy and on/off events                                             
                                                                              
    SDC was designed to take advantage of the quiet state of the              
    spacecraft during non-encounter mission phases, especially                
    hibernation.  Various active spacecraft operations cause mechanical       
    shocks that are picked up by the polyvinylidene fluoride (PVDF)           
    sensors and registered by SDC as science events.  These shocks are        
    particularly evident during three-axis pointing and active spin mode      
    when the spacecraft frequently fires short bursts of the attitude         
    thrusters.  Level four data reduction (section 4 of Horanyi et al.        
    (2008) [HORANYIETAL2008]) is used to filter out any hits that appear      
    within a second of any thruster firing, thereby allowing science          
    recovery between firings.  However because the thruster induced-events    
    are often frequent enough to violate the autonomy rule B (section         
    3.4.2 of Horanyi et al. (2008) [HORANYIETAL2008]), during spacecraft      
    maneuvers many SDC detector channels are switched off, by autonomy        
    processing, for prolonged periods. In addition, in order to minimize      
    autonomy related switching off of the channels, the channels are          
    commanded off and on around DSN tracks when the spacecraft transitions    
    from Passive Spin to Active Spin, called a tweakup. The channels are      
    turned off for normally around 90 minutes each tweakup.                   
                                                                              
    N.B. The duration of the off, as well as the on, periods must be          
    considered in making any calculation of average dust detection event      
    rates.                                                                    
                                                                              
    During spacecraft checkout activities in first six months of the          
    Post-Launch mission phase, spacecraft activity was high and these         
    autonomous off/on events occurred quite frequently.  There were           
    several periods, some weeks or months long, where SDC was either          
    completely off, or on for only hours or minutes at a time.  Later on,     
    the autonomy levels for turning off channels were relaxed, plus the       
    transition to more frequent hibernation operations meant that             
    autonomous off/on events occurred less frequently.                        
                                                                              
    All per-channel off and on events, whether initiated by autonomy or by    
    spacecraft on/off commands to the entire instrument, are recorded for     
    the entire mission to-date in a PDS TABLE sequence file that is           
    provided with all SDC data sets; updated versions will be provided as     
    the mission progresses.                                                   
                                                                              
    Note that event threshold instrument settings are used to trade off       
    maximizing instrument sensitivity against minimizing the number of        
    spurious, non-particle events (noise) detected; see the Threshold         
    section under Measured Parameters below for more detail.                  
                                                                              
                                                                              
    2) Stimulus calibrations generate false positives                         
                                                                              
    The stimulus calibration activity is known to generate false positive     
    events in the science data; data taken during such activities exhibits    
    cross-talk and should be excluded from science analysis.  This data       
    set includes a PDS TABLE, DOCUMENT/SDC_STIM_Vnnnn.TAB, that lists time    
    periods when stimulus calibrations were active (sporadically during       
    Launch and Jupiter mission phases, and about half an hour per year        
    during Annual CheckOuts (ACO) in the Pluto Cruise mission phase).         
    Eventually, the Science Operations Center (SOC) operational pipeline      
    may be enhanced to filter individual events that occur near stimulus      
    events.                                                                   
                                                                              
                                                                              
    3) Channel 11 failed                                                      
                                                                              
    Channel 11 failed before launch; all data from channel 11 should be       
    ignored.                                                                  
                                                                              
                                                                              
    4) No particle events over 2.8E-10 g, as of 2016.                         
                                                                              
    As of late 2016, events from particles larger than 2.8E-10 grams          
    (approximately 3 microns radius*) have not been observed in these data    
    sets; this has been noted as exceptional by peer reviewers of SDC data    
    sets.  The reason for this is an active discussion within the science     
    team and will eventually be addressed in a future delivery of SDC data    
    sets.                                                                     
                                                                              
    The SDC instrument team is currently working on new calibrations of       
    the PVDF sensors in response to both oblique impacts and particles        
    with densities lower than what was used in previous calibrations          
    (i.e. iron).                                                              
                                                                              
    * Assumes a 2500 kg m**-3 density for particles, which is what is         
    generally used by the SDC instrument team.                                
                                                                              
                                                                              
  Detector                                                                    
  ========                                                                    
    The SDC's sensors are thin, permanently polarized PVDF plastic films      
    that generate an electrical signal when dust particles penetrate their    
    surface.  The SDC has a total sensitive surface area of ~0.1 m^2,         
    comprising 12 separate film patches, each 14.2 cm x 6.5 cm, mounted       
    onto the top surface of a support panel.  In addition, there are two      
    reference sensor patches mounted on the backside of the detector          
    support panel, protected from any dust impacts.  These reference          
    sensors, identical to the top surface sensors, are used to monitor the    
    various background noise levels, from mechanical vibrations or cosmic     
    ray hits.                                                                 
                                                                              
    See note about channel 11 in Operational Considerations section above.    
                                                                              
                                                                              
  Electronics & Construction                                                  
  ==========================                                                  
    The Student Dust Counter comprises three major pieces:                    
                                                                              
    The Detector Assembly is 18 inches x 12 inches (46cm x 30cm).  This is    
    the piece of equipment that is mounted on the outside of the              
    spacecraft and is exposed to the dust particles.  The detector is         
    thermally isolated from the New Horizons Spacecraft and lies outside      
    its Thermal Blanket.                                                      
                                                                              
    The Electronics Box is approximately 5.4 inches x 8.25 inches x 1.825     
    inches (13.7cm x 20.96cm x 4.64cm).  This is the brains of the Dust       
    Counter; when a hit occurs on the detector the electronics box will       
    decipher the data and determine the mass and speed of the dust            
    particle.  The electronics box is actually located within the             
    spacecraft and is thermally and electronically bonded to the New          
    Horizons Spacecraft.                                                      
                                                                              
    The Intra-Harness is the 'bridge' between the detector assembly and       
    the electronics box.  It serves a similar purpose as the cable which      
    allows your home computer to communicate with your printer.               
                                                                              
    The space environment through which the New Horizons Mission will be      
    traveling contains a large variety of conditions which can negatively     
    affect spacecraft materials.  The dust collector must be made of a        
    substance which is not affected by changes in the temperature,            
    radiation environment, or quantity of high-energy particles               
    surrounding it.                                                           
                                                                              
    To meet these challenges, a simple, reliable substance called             
    PolyVinyliDene Fluoride (PVDF) has been chosen.  When PVDF is             
    manufactured, it is polarized.  This means all of the molecules in the    
    material are aligned so that they are pointing in the same direction.     
                                                                              
    When a dust particle impacts on the detector, it randomly re-aligns       
    some of these previously organized molecules, resulting in the            
    destruction of dipoles.  This depolarization generates an electric        
    signal; signals beyond a preset noise threshold (see Measured             
    Parameters below) are recorded.                                           
                                                                              
                                                                              
  Operating Modes                                                             
  ===============                                                             
    Data taking and Autonomy.  See Horanyi et al. (2008) [HORANYIETAL2008]    
    for details.                                                              
                                                                              
                                                                              
  Measured Parameters                                                         
  ===================                                                         
    Along with various instrument configuration settings, the SDC records     
    four main parameters for each detected Interplanetary Dust Particle       
    (IDP) impact event: measured charge (generated by each event);            
    timestamp; count; channel (sensor number).                                
                                                                              
    The measured charge of an event in its raw form is a 16-bit unsigned      
    integer value in the range 65535-0; note that this SDC raw integer        
    value decreases with increasing event charge in physical units            
    (equivalent electrons).                                                   
                                                                              
                                                                              
    Calibration                                                               
    -----------                                                               
      Based on ground and in-flight calibrations, the actual charge, in       
      equivalent electrons, of an event can be inferred from its raw          
      integer value measurement.                                              
                                                                              
      Assuming a stable keplerian orbit at the location of the spacecraft     
      at the time of the event for an assumed impact particle defines a       
      spacecraft-relative velocity for the particle.                          
                                                                              
      The mass of an assumed impact particle may be estimated from the        
      combination of its spacecraft-relative velocity and the inferred        
      charge of the event.                                                    
                                                                              
      See Horanyi et al. (2008) [HORANYIETAL2008] and James et al. (2010)     
      [JAMESETAL2010] for more details about SDC calibration.                 
                                                                              
                                                                              
    Thresholds                                                                
    ----------                                                                
      The SDC channels have threshold integer values set by uplinked          
      commands and/or by autonomy rules; thresholds limit the effective       
      sensitivity of the instrument.  Threshold values are recorded along     
      with each detected event.  Note that the scale of the threshold         
      integer values are reversed with respect to charge, like the raw        
      integer measurements described above, so the threshold integer          
      values are maxima.                                                      
                                                                              
      Setting the threshold levels is a tradeoff between                      
                                                                              
      1) the desire for maximum instrument sensitivity, and                   
                                                                              
      2) the desire to exclude non-particle events (noise) such as other      
      spacecraft events.                                                      
                                                                              
      Events that do not extend below the threshold integer value (smaller    
      charges) will not be detected or recorded.  When the minimum integer    
      value (charge peak) of an event goes below the threshold integer        
      value it will be detected, which triggers the measuring and             
      recording of the event.  There is a delay between this detection        
      trigger of an event and the time when its recored value measured;       
      because of that delay, the event charge will decay and it is            
      possible that the measured integer value will be slightly above the     
      threshold value (the event will have slightly less measured charge      
      in equivalent electrons than the equivalent threshold charge).          
                                                                              
      See Horanyi et al. (2008) [HORANYIETAL2008] for more details about      
      SDC thresholds.
REFERENCE_DESCRIPTION