Data Set Overview
    =================
    Mass spectrometric measurements of ions in the coma of comet
    Giacobini- Zinner were made during the encounter of the
    International Cometary Explorer (ICE) on 11 September 1985, when the
    spacecraft passed within 7800 km of the nucleus on its antisunward
    side. For mass-to-charge (M/Q) ratios from 14 to 33 amu/e-, H20+ was
    the dominant ion; several other species were also detected.
 
    The ICI was designed for solar wind measurements and was used to
    study the composition of the solar wind and the velocity
    distributions of and velocity differences among solar wind ions.
    The ions in the solar wind are highly charged since they retain the
    charge states acquired in the corona; the appropriate range of
    values of M/Q normally covered by the ICI was 1.4 to 5.8 amu/e-
    measured over a solar wind velocitv (V) range of 300 to 620 km per
    sec. The ranges of M/Q and V in which observations were made were
    set by parameters read into the instrument microprocessor through
    the spacecraft command system.  To cover values of M/Q and V
    appropriate to the comet (where singly charged ions are expected), a
    set of parameters was found that selected 14 M/Q values between 14
    and 33 amu/e- for V between 80 to 224 km per sec and 14 M/Q values
    between 1.4 and 3 amu/e- for V between 237 and 463 km per sec. The
    M/Q resolution was in the range 20 to 30 for solar wind observations
    but depended on the parameter MV/Q and was 11 at M/Q of 33 amu/e-
    and V of 230 km per sec.   During the encounter the spacecraft was
    moving at a speed relative to the comet of 21 km per sec and crossed
    its tail almost perpendicularly. The distances travelled by the
    spacecraft during each measurement were several times the ionic
    gyroradius in most conditions along the trajectory.  Detections were
    recorded on September 11 from 10:26 through 11:35 UT; closest
    approach is recorded as 11:02 UT.
 
 
    Data
    ====
    Ion Composition Instrument during the International Cometary
    Explorer encounter:
 
    Arrays are composed of scans in velocity as the M/Q values is held
    constant. For low mode, there are 14 scans beginning at 1.38 amu/e-
    and there are 12 velocity steps (unequal) for each M/Q scan.  The
    steps are listed as follows: 237.71 km/s, 252.61 km/s, 268.31 km/s,
    285.11 km/s, 302.91 km/s, 321.71 km/s, 341.81 km/s, 363.11 km/s,
    385.81 km/s, 409.91 km/s, 435.41 km/s, 462.61 km/s. The process is
    repeated for 13 additional scans (total of 14) in the following
    order: 1.38 amu/e-, 1.48 amu/e-, 1.58 amu/e-, 1.67 amu/e-, 1.76
    amu/e-, 1.88 amu/e-, 2.00 amu/e-, 2.21 amu/e-, 2.26 amu/e-, 2.40
    amu/e-, 2.54 amu/e-, 2.70 amu/e-, 2.87 amu/e-, 3.05 amu/e-.  Counts
    for a 'M/Q vs V' bin are collected every 2.97 seconds, which is one
    spacecraft spin; there are 420 spins in a complete cycle which spans
    21.13 min.   The time spent on each scan is 35.72 seconds.  The
    sequence of scans is not continuous but interleaved with the other
    mode of sampling (M/Q 14-32 amu/e- for V=80-224 km/s); a scan begins
    every 89.3 seconds in each mode.
 
    For the high mode, there are 14 scans beginning at 14.4amu/e- and
    there are 18 velocity steps (unequal) for each M/Q scan. The
    velocity steps are as follows: 80.01 km/s, 85.01 km/s, 90.31 km/s,
    95.91 km/s, 101.91 km/s, 108.31 km/s, 115.01 km/s, 122.21 km/s,
    129.81 km/s, 137.91 km/s, 146.51 km/s, 155.71 km/s, 165.41 km/s,
    175.71 km/s, 186.61 km/s, 198.31 km/s, 210.61 km/s, 223.81 km/s. The
    process is repeated for 13 additional scans (total of 14) in the
    following order: 14.4 amu/e-, 15.3 amu/e-, 16.3 amu/e-, 17.3 amu/e-,
    18.4 amu/e-, 19.5 amu/e-, 20.8 amu/e-, 22.1 amu/e-, 23.4 amu/e-,
    24.9 amu/e-, 26.5 amu/e-, 28.1 amu/e-, 29.9 amu/e-, 31.7 amu/e-.
    Counts per each M/Q-vs-V bin are collected every 2.97 seconds which
    is one complete spacecraft spin; there are 420 spins in a complete
    cycle that takes 21.13 min.  The time spent on each scan is 53.58
    seconds.  The sequence of scans is not continuous but interleaved
    with the other mode of sampling (M/Q 1.38-3.05 amu/e- for V=237-463
    km/s).   In each array, a value of -1 indicates no data value.

Review
    ======
       PDS Peer review was held in Fall 1998.
 
    Data gaps
    =========
       The original data was submitted as hard copy.   The individual
       arrays were scanned by Image-Right under contract with NSSDC. The
       period of the hard copy covered from Sept 9 through Sept 13 but
       it was determined after discussions with the PI (Coplan) that the
       scans from Sept 11 19:56 through Sept 13 5:41 were suspect
       (Coplan et al. 1987) so they were not digitized.   Only encounter
       tables are included here.