Data Set Overview
 =================
 
    The SP-2 experiment on Vega spacecraft was intended
    for studying the spatial and mass distributions of
    dust particles in the cometary coma over the mass
    range 1.e-16 to 1.e-6 g.  Covering such a broad mass
    range was made possible by using sensors of two
    types, namely, impact plasma and acoustic.
 
     The threshold sensitivity of the dust particle
    acoustic detector in terms of the transferred
    momentum is given by Pmin ~ 2x10**-5 gcm/s.  Taking
    into account that the recoil momentum may exceed the
    particle momentum mV by 5 to 10 times, the minimum
    mass of recorded particles is < 3x10**-13 g.  The
    measurement range n (> m)x3x10**-13 to ~ 2x10**-6 g
    is divided into 16 channels.  With the relative width
    delta/m ~ 2.82, sensitive area S = 500 cm**2,
    accumulation time for one spectrum is 1 s, which
    corresponds to the spatial resolution ~ 80 km over
    the flyby trajectory.  The counting rate of small
    mass particles is about 4095 1/s.
 
     The ionization detector is capable of recording
    particles with mass 3x10**-16 to 3x10**-11g.  The
    number of channels is 6, with relative width delta/m
    = 10, sensitive area - 40 cm**2.  The limit counting
    rate of small mass particles is ~ 65,500 1/s.  The
    accumulation time for one spectrum is 1 s.
 
     The flyby trajectories of the Vega spacecraft in the
    cometocentric frame can be specified by the
    coordinates of the closest approach to the nucleus
    R0(R0x,R0y,R0z) and the components of the relative
    velocity V(Vx,Vy,Vz).  The corresponding values for
    Vega1 and Vega2 were as follows:
 
 
    Vega 1:
    R0x = 7830 km;      R0y = 2480 km;      R0z = 3400 km;
    Vx = 28.64 km/s;    Vy = -72.73 km/s;   Vz =-12.95km/s;
 
    Vega 2:
    R0x = 7100 km;      R0y = 2680 km;      R0z = 2630 km;
    Vx = 30.53 km/s;    Vy = -69.44 km/s;   Vz =-11.88km/s;
 
 
    If the results of the dust flux measurements are
    referred to the time reckoned from the instant of
    closest approach, the corresponding distances to the
    cometary nucleus can be found as R=R0*sqrt(1 +
    (t/t0)^2), where the parameter t0 = R0/V.  In the
    course of measurements the numbers of particle
    impacts with masses exceeding the channel threshold
    is counted in each pulse height channel at 1 second
    intervals along the trajectory:
 
	 N(>m) = F(>m)*S*T = n(>m)*V*S*T,
 
    where n(>m) is the number density, F(>m)=n(>m)*V the
    cumulative flux, S the effective sensor area (500 cm2
    for the acoustic sensor and 28.57 cm2 for the impact
    plasma one), T=63/64s the accumulation time in each
    measurement.
 
     For the acoustic sensors, dead time corrections were
    introduced at channel count rate N(>m) > 50/s.  For
    the fast impact plasma sensors such corrections were
    not needed.
 
     The SP-2 data from IKI (Dyachkov) are formatted into
    table containing 2092 records.  Each record consists
    of 18 columns and contains time of measurement
    referred to one of closest approach, 5 columns of
    impact plasma sensor data, and 12 columns of acoustic
    sensor data.

Confidence Level Overview
=========================
    N/A